Prostate-specific antigen dynamics after neoadjuvant androgen-deprivation therapy and carbon ion radiotherapy for prostate cancer.

BACKGROUND: This study aimed to explain the dynamics of prostate-specific antigen (PSA) levels in patients with prostate cancer who were treated with carbon ion radiotherapy (CIRT) and neoadjuvant androgen-deprivation therapy (ADT).
METHODS: Eighty-five patients with intermediate-risk prostate cancer who received CIRT and neoadjuvant ADT from December 2015 to December 2017 were analyzed in the present study. The total dose of CIRT was set at 51.6 Gy (relative biological effectiveness) delivered in 12 fractions over 3 weeks. The PSA bounce was defined as a ≥0.4 ng/ml increase of PSA levels from the nadir, followed by any decrease. PSA failure was defined using the Phoenix criteria.
RESULTS: The median patient age was 68 (range, 48-81) years. The median follow-up duration was 33 (range, 20-48) months. The clinical T stage was T1c, T2a, and T2b in 27, 44, and 14 patients, respectively. The Gleason score was 6 in 3 patients and 7 in 82 patients. The median pretreatment PSA level was 7.37 (range, 3.33-19.0) ng/ml. All patients received neoadjuvant ADT for a median of 6 (range, 2-117) months. PSA bounces were observed in 39 patients (45.9%), occurring a median of 12 (range, 6-30) months after CIRT. PSA failure was observed in eight patients (9.4%), occurring a median of 21 (range, 15-33) months after CIRT. The 3-year PSA failure-free survival rate was 88.5%. No clinical recurrence was observed during the follow-up period. Younger age and lower T stage were significant predictors of PSA bounce. Younger age was a significant predictor of PSA failure.
CONCLUSIONS: In this study, we identified the significant predictors of the occurrence of PSA bounce and failure. Further follow-up is needed to reveal the clinical significance of PSA dynamics.

Background

Among cancers, prostate cancer ranks second globally in morbidity and fifth in mortality [1]. Radiotherapy is one of the definitive treatments for localized or locally advanced prostate cancer. The number of patients treated with radiotherapy for prostate cancer has been increasing in Japan according to a structural survey conducted by the Japanese Society for Therapeutic Radiology and Oncology [2]. Brachytherapy, intensity-modulated radiotherapy (IMRT), and particle beam radiotherapy are the radiotherapy modalities used for patients with prostate cancer [3-6].

The first carbon ion radiotherapy (CIRT) clinical trial for prostate cancer was initiated in 1995 at the National Institute of Radiological Sciences (Chiba, Japan) [7]. CIRT offers biological and physical advantages over conventional photon radiotherapy with X-rays. Regarding the biological aspect, carbon ion beams have an estimated 2–3-fold higher relative biological effectiveness (RBE) than X-rays [8, 9]. In terms of the physical aspect, a more conformal dose distribution can be delivered via CIRT based on the ability of accelerated carbon ions to release a maximal amount of energy at the end of their track, resulting in a Bragg peak [10]. These features have led to favorable clinical outcomes for CIRT in prostate cancer [6, 11]. In the ion-beam Radiation Oncology Center in Kanagawa (i-ROCK), similar to previous studies of CIRT for prostate cancer, favorable clinical outcomes were achieved for prostate cancers treated with CIRT [12].

Serum prostate-specific antigen (PSA) is a sensitive marker of treatment outcomes for prostate cancer [13]. Fluctuation of PSA levels is often observed after radiotherapy without any clinical recurrence [14-16]. Such benign PSA fluctuation, which was first reported in 1997, is known as the PSA bounce [17]. PSA bounces can be disconcerting for patients and physicians [18], and they may lead to unnecessary salvage treatment for cases that meet the definition of PSA failure. Therefore, accurate clinical interpretation of PSA dynamics after radiotherapy for prostate cancer is necessary to avoid patient anxiety or a false-positive diagnosis of relapse, which can instigate unnecessary treatment [19].

PSA bounces have been observed after various radiotherapy modalities for prostate cancer, such as low-dose-rate brachytherapy (LDR-BT), high-dose-rate brachytherapy (HDR-BT), IMRT, and stereotactic radiotherapy (SRT). However, only one study has reported PSA dynamics after CIRT [20]. In that study, although PSA dynamics after CIRT alone was revealed, that after CIRT using androgen-deprivation therapy (ADT) was not investigated. Thus, the present study aimed to explain the dynamics of PSA in patients with prostate cancer who were treated with CIRT and ADT.

Materials and methods

The study was approved by the institutional review board of Kanagawa Cancer Center (approval number: 2019–171). Written informed consent was obtained from all patients. Clinical data obtained between December 2015 and December 2019 was accessed in this study. The source of medical records used in this work was Kanagawa Cancer Center.

Patients

In total, the cases of 85 consecutive patients with intermediate-risk prostate cancer who received CIRT at i-ROCK between December 2015 and December 2017 were analyzed in the present study. The patients were classified using the D’Amico risk group classification [21]. The clinical stage was determined using computed tomography (CT), magnetic resonance imaging (MRI), bone scintigraphy, and other diagnostic images. The eligibility criteria for this study were as follows: (i) histological diagnosis of prostate adenocarcinoma, (ii) cT1cN0M0 to T2bN0M0 according to the 7th UICC classification, (iii) performance status of 0–2, (iv) age of 20 years or older, (v) no previous treatment for prostate cancer excluding ADT, and (vi) followed up at least 1 year post-CIRT.

CIRT

All patients were treated at i-ROCK in Japan. The first clinical treatment for prostate cancer at the i-ROCK was performed in 2015 [22].

Patients were placed in the supine position on a vacuum mattress (BlueBAG: Elekta AB, Stockholm, Sweden) and immobilized using thermoplastic shells (Shellfitter: Kuraray, Tokyo, Japan). Enema was used before CT for CIRT planning. The rectum was emptied as much as possible using a laxative and an antiflatulent before each session, and enema was performed if the patient did not defecate within 24 h of treatment. The patients urinated and drank water 60 min before CT. A set of CT images with 2-mm-thick slices was taken for treatment planning.

Contouring of the target volumes and normal tissues was performed using MIM maestro software version 5.6 (MIM Software Inc., Cleveland, OH, USA). Dose calculation and optimization were performed using the Monaco version 5.20 system (Elekta AB).

The prostate volume was measured via CT imaging. The gross tumor volume was not defined. The clinical target volume (CTV) included the entire prostate and proximal seminal vesicles. Planning target volume (PTV) 1 was created by adding anterior and lateral margins of 10 mm and a posterior margin of 5 mm to the CTV. Boost therapy was performed using PTV2, in which the posterior edge was set in front of the anterior wall of the rectum to reduce the rectal dose in the ninth course of treatment [23, 24]. The rectum was delineated as the organ at risk from 10 mm above the upper margin of the PTV to 10 mm below the lower margin of the PTV.

The total dose was set at 51.6 Gy (RBE). After the first eight fractions were delivered using PTV1, boost therapy was performed using PTV2 in the latter four fractions. The PTV was covered by ≥95% of the prescribed dose, and the maximum PTV dose was limited to <105% of the prescribed dose. The dose constraint for the rectum aimed at V80% < 10 ml.

CIRT was administered once daily for 4 days a week for 3 weeks. All patients were treated using the spot scanning method. CIRT was performed from both the right and left sides of the patient. One port was used for each treatment session. Verification of the patient position was performed using in-room CT during the first, fifth, and ninth treatment sessions. In each treatment session, a computer-aided online positioning system was employed to verify the positioning accuracy to less than 1 mm.

ADT

Urologists administered ADT. Neoadjuvant ADT was administered for 4–8 months through the end of CIRT [6]. ADT was performed via combined androgen blockade with an antiandrogen plus medical castration in principle. We performed a representative ADT using a combination of bicalutamide and leuprorelin acetate.

Follow-up

A urologist and a radiation oncologist conducted patient follow-up at 3-month intervals for the first 3 years after CIRT and at 6-month intervals thereafter. PSA was measured at each follow-up visit. In the present study, the PSA bounce was defined as a PSA increase of at least 0.4 ng/ml from the nadir PSA level, followed by any decrease [25, 26]. PSA failure was defined using the Phoenix definition, namely, the nadir PSA level plus 2 ng/ml [27]. The follow-up period and the time to the event were calculated from the start of CIRT to the date of the event.

Statistical analysis

Statistical analysis was performed using STATA software (version 13.1, TX, USA). The correlation of clinical variables with PSA dynamics was assessed via the Cox regression analyses. Prognostic factors, for which p value was calculated as <0.10, were evaluated using the multivariate stepwise Cox regression model [28]. Comparative analyses for continuous variables, such as PSA level and age of the two groups, were examined using the Mann–Whitney U test. Non-parametric receiver operating characteristic (ROC) curves were generated and Youden index (J = max [sensitivity + specificity– 1]) was used to determine the optimal cut-off values [29]. Comparative analyses for categorical variables of the two groups were examined using the chi-squared test. A p value of <0.05 was considered significant. The PSA failure-free survival rate was estimated using the Kaplan–Meier method.

Results

Patient characteristics

Patient characteristics are summarized in Table 1. The median patient age was 68 (range, 48–81) years. The median follow-up duration was 33.1 (range, 20.1–48.3) months. All patients completed CIRT on schedule. Neoadjuvant ADT was administered to all patients, and the median duration of ADT was 6.2 (range, 2.3–116.9) months. The patient who received ADT for 116.9 months, which is an outlier, was treated via combined androgen blockade in the first year. PSA elevation was observed 4 years after initial ADT, and the patient was treated by antiandrogen alone irregularly when PSA elevation was observed. Four months of combined androgen blockage was performed in this patient before CIRT. Pre-CIRT PSA levels were measured a median of 15 (range, 0–40) days before the start of CIRT.

Table 1

Patient characteristics (n = 85).

Characteristics	n (%)
Follow-up duration, months, median (range)	33.1 (20.1–48.3)
Age, years, median (range)	68 (48–81)
T stage
1c	27 (31.8%)
2a	44 (51.8%)
2b	14 (16.5%)
Pretreatment PSA, ng/ml, median (range)	7.37 (3.33–19.0)
< 10	62 72.9%)
10 ≤ 20	23 (27.1%)
Gleason score
6	3 (3.5%)
7	82 (96.5%)
D’Amico classification
intermediate	85 (100.0%)
ADT
neoadjuvant	85 (100.0%)
duration, month, median (range)	6.2 (2.3–116.9)
Prostate volume, cc, median (range)	26.9 (11.9–88.2)
pre-CIRT PSA, ng/ml, median (range)	0.31 (0.01–3.28)
Time to nadir PSA, month, median (range)	3 (3–24)

PSA: Prostate specific antigen, ADT: Androgen deprivation therapy.

PSA dynamics

PSA dynamics for all patients is presented in Fig 1(a). The average PSA dynamics based on the presence or absence of the PSA bounce is presented in Fig 1(b). The average PSA level in the PSA bounce group was significantly higher than that in the PSA bounce-free group beyond 3 months after CIRT (p < 0.05). The average PSA dynamics for the presence or absence of PSA failure is presented in Fig 1(c). The average PSA level in the PSA failure group was significantly higher than that in the PSA failure-free group before CIRT and at all time points between 6 and 36 months after CIRT, excluding 30 months (p < 0.05).

Fig 1

(a). Prostate-specific antigen (PSA) dynamics after carbon ion radiotherapy (CIRT) for all patients. The PSA dynamics in patients with biochemical relapse is indicated by the red line. No clinical recurrence was observed. (b). The average PSA dynamics in patients with or without PSA bounces. (c). The average PSA dynamics in patients with or without PSA failure.

PSA bounces were observed in 39 patients (45.9%) a median of 12 (range, 6–30) months after CIRT. Predictive significance of clinical variables for the occurrence of PSA bounces was assessed via Cox regression analysis (Table 2). In the univariate analysis, younger age, lower T stage, and higher PSA nadir were significantly associated with the occurrence of a PSA bounce (p < 0.001, 0.015, and 0.029, respectively). The median ages of patients with and without PSA bounces were 68 (range, 48–79) and 70 (range, 55–81) years, respectively (p = 0.001). The T stage in the PSA bounce group was T1c, T2a, and T2b in 16 (41.0%), 20 (51.3%), and 3 (7.7%) patients, respectively, versus 11 (23.9%), 24 (52.2%), and 11 (23.9%) patients, respectively, in the PSA bounce-free group (p = 0.027). The median PSA nadir of patients with and without PSA bounces were 0.014 ng/ml (range, 0–2.183 ng/ml) and 0 ng/ml (range, 0–0.201 ng/ml), respectively (p = 0.002). ADT duration was not correlated with the occurrence of PSA bounce (p = 0.731). In the multivariate analyses, younger age and lower T stage were significantly associated with the occurrence of a PSA bounce (p < 0.001 and 0.049, respectively). The ROC curve analysis calculated the area under the ROC curve (AUC) as 0.705 and determined a cut-off value of 68 years, at which the sensitivity and specificity were measured to be 76.1 and 61.5%, respectively (Fig 2a).

Table 2

Predictive significance of clinical factors for the occurrence of PSA bounce.

	Univariate			Multivariate
	HR	(95% CI)	p-value	HR	(95% CI)	p-value
Age	0.92	(0.88–0.96)	< 0.001	0.92	(0.88–0.96)	< 0.001
T stage	0.55	(0.34–0.89)	0.015	0.60	(0.37–0.99)	0.049
Gleason score	0.69	(0.17–2.86)	0.605	-
initial PSA	0.97	(0.88–1.07)	0.587	-
Prostate volume	1.02	(0.99–1.04)	0.088	1.01	(0.99–1.03)	0.159
ADT duration	1.00	(0.98–1.02)	0.731	-
pre-CIRT PSA	1.28	(0.89–1.84)	0.181	-
PSA nadir	2.55	(1.10–5.88)	0.029	2.00	(0.87–4.64)	0.104
Time to PSA nadir	0.93	(0.81–1.06)	0.284	-

PSA: Prostate specific antigen, ADT: Androgen deprivation therapy, CIRT: Carbon ion radiotherapy, HR: Hazard ratios, CI: Confidence interval.

Prognostic factors, for which p value was calculated as < 0.10, were evaluated by multivariate analysis.

Fig 2

(a). ROC curve for the correlation between PSA bounce and age. The area under the ROC curve was 0.705. The cut-off value was 68 years, at which the sensitivity and specificity were 76.1 and 61.5%, respectively. (b). ROC curve for the correlation between PSA bounce and age. The area under the ROC curve was 0.844. The cut-off value was 65 years, at which the sensitivity and specificity were 77.9 and 87.5%, respectively.

PSA failure was observed in eight patients (9.4%). The characteristics of eight patients with PSA failure are summarized in Table 3. Of these eight patients with PSA failure, the PSA level decreased in seven patients without any treatment such as ADT in a median of 3 (range, 3–15) months after PSA failure. No salvage treatments were performed in these seven patients in the follow-up period. The remaining patient received ADT immediately after the occurrence of PSA failure without radiological confirmation of clinical recurrence. As shown in Fig 3, the 3-year PSA failure-free rate was 88.5%. PSA failure occurred in a median of 21 (range, 15–33) months after CIRT. Clinical recurrence was not detected by CT, MRI, and bone scintigraphy.

Table 3

Characteristics of patients with PSA failure.

Age	T stage	PSA (ng/ml)	Gleason score	Time to failure (month)	PSA dynamics after PSA failure	Time to decreasing PSA after PSA failure (month)
61	T2b	17.09	7	33	decreased spontaneously	3
61	T2a	9.2	7	21	decreased spontaneously	3
64	T1c	11.21	7	21	decreased spontaneously	15
58	T2a	8.43	7	15	decreased spontaneously	3
54	T1c	4.83	7	15	decreased spontaneously	6
63	T2a	14.79	7	30	decreased spontaneously	3
50	T2a	6.27	7	21	decreased spontaneously	3
68	T2a	8.35	7	24	decreased by ADT	3

PSA: Prostate specific antigen, ADT: Androgen deprivation therapy.

Fig 3

Prostate-specific antigen (PSA) failure-free rate.

The 3-year PSA failure-free rate was 88.5%.

The predictive significance of clinical variables for the occurrence of PSA failure was assessed via the Cox regression analyses (Table 4). In the univariate analysis, younger age, higher pre-CIRT PSA levels, and higher PSA nadir were significantly associated with the occurrence of PSA failure (p = 0.002, 0.007, and 0.003, respectively). The median ages of patients with and without PSA failure were 61 (range, 50–68) and 69 (range, 48–81) years, respectively (p = 0.001). The median pre-CIRT PSA levels of patients with and without PSA failure were 1.24 (range, 0.30–3.97) and 0.25 (range, 0.01–3.28) ng/ml, respectively (p = 0.009). The median PSA nadir of patients with and without PSA bounces were 0.014 ng/ml (range, 0–2.183 ng/ml) and 0 ng/ml (range, 0–0.201 ng/ml), respectively (p = 0.002). ADT duration was not correlated with the occurrence of PSA failure (p = 0.614). In the multivariate analysis, only younger age was statistically significantly associated with the occurrence of PSA failure (p = 0.008). The ROC curve analysis calculated the area under the ROC curve (AUC) as 0.844 and determined a cut-off value of 65 years, at which the sensitivity and specificity were calculated as 77.9 and 87.5%, respectively (Fig 2b).

Table 4

Predictive significance of clinical factors for the occurrence of PSA failure.

	Univariate			Multivariate
	HR	(95% CI)	p-value	OR	(95% CI)	p-value
Age	0.86	(0.79–0.95)	0.002	0.85	(0.75–0.96)	0.008
T stage	1.02	(0.37–2.82)	0.962	-
Gleason score	NA	-	-	-
initial PSA	1.12	(0.95–1.31)	0.166	-
Prostate volume	1.03	(0.99–1.07)	0.093	1,04	(0.97–1.09)	0.153
ADT duration	0.93	(0.71–1.22)	0.614	-
pre-CIRT PSA	2.45	(1.28–4.70)	0.007	1.61	(0.72–3.57)	0.244
PSA nadir	6.67	(1.88–23.64)	0.003	3.34	(0.92–12.08)	0.066
Time to PSA nadir	0.84	(0.54–1.31)	0.443	-
PSA bounce	7.84	(0.96–63.85)	0.054	2.52	(0.28–22.93)	0.411

PSA: Prostate specific antigen, ADT: Androgen deprivation therapy, CIRT: Carbon ion radiotherapy, HR: Hazard ratios, CI: Confidence interval, NA: Not available.

Prognostic factors, for which p value was calculated as < 0.10, were evaluated by multivariate analysis.

Discussion

We investigated the dynamics of PSA in patients with prostate cancer who were treated with CIRT and neoadjuvant ADT in the present study. The occurrence of PSA bounce and failure was correlated with younger age. To the best of our knowledge, this is the first report of PSA dynamics after CIRT with neoadjuvant ADT.

Multiple definitions of the PSA bounce have been reported, and no consensus has been established. Several studies used the definition of an increase of >0.2 ng/ml in PSA levels followed by a spontaneous decrease to the pre-bounce level or lower [13, 16, 20, 30, 31]. In the present study, no patient met this definition, as the nadir PSA level was extremely low because of the use of neoadjuvant ADT. Thus, we defined the PSA bounce as an increase of at least 0.4 ng/ml followed by any decrease, in line with previous studies [25, 26]. In a study of PSA bounces in patients treated with conventional external radiotherapy, the bounce was defined as an increase of 0.5 ng/ml [32]. Conversely, the PSA bounce was defined as an increase of 0.1 ng/ml followed by two consecutive decreases after IMRT [33].

PSA bounces have been mainly reported after brachytherapy. PSA bounces were observed in 28%–49% of patients after LDR-BT [14]. In two other studies, PSA bounces were observed in 43 and 48% of patients treated with HDR-BT, respectively [34, 35]. In a study of PSA dynamics after HDR-BT combined with conventional external beam radiotherapy, PSA bounces were detected in 31% patients [36].

PSA bounces have also been observed in patients treated with external beam radiotherapy alone. After IMRT, the occurrence rate of PSA bounces ranged 11%–32% [25, 33, 37, 38]. Recently, SRT has been performed for the definitive treatment of prostate cancer, and PSA bounces were also observed after SRT. In a multi-institutional analysis of PSA dynamics, PSA bounces were noted in 26% of patients [18]. Only one study of PSA dynamics after particle beam radiotherapy has been reported [20]. In that study, PSA bounces were observed in 55.7% of patients treated with CIRT alone for prostate cancer.

Age was one of the first and most frequently described predictive factors for PSA bounces after brachytherapy [14]. Age was a significant consistent predictor of PSA bounces after IMRT [25, 33]. Regarding other treatment modalities, namely, SRT or HDR-BT combined with external beam radiotherapy, younger age was a significant predictor for PSA bounces [18, 36]. In addition, age was detected as a predictive factor for PSA bounces after CIRT [20]. Similar results were observed in the present study, as younger age was a predictive factor for PSA bounces and PSA failure. Therefore, it is suggested that age is a predictor for PSA bounce regardless of the radiotherapy modality.

In the present study, lower T stage was significantly correlated with PSA bounce. In a study of the PSA bounce after LDR-BT, lower T stage was one of the predictive factors for PSA bounce [39]. Sengoz et al. reported that PSA bounce was more frequent in patients with T1–2 stage cancers after external body radiation therapy [40]. The mechanism by which lower T stage tended to correlate with PSA bounces was unclear. Several previous studies have suggested that T stage has no correlation with PSA bounces [14, 19, 36]. Further investigation is warranted to reveal the correlation between T stage and PSA bounces.

Despite the accumulation of data on post-radiotherapy PSA dynamics, its relevance to clinical outcomes remains unclear. One study suggested that PSA bounces did not predict biochemical recurrence or clinical disease recurrence [33]. Another study reported that PSA bounces after external beam radiotherapy were correlated with PSA failure [26]. By contrast, some reports stated that the PSA bounce was a good predictive factor for PSA failure [19]. Hinnen et al. found that PSA bounces after LDR-BT were predictive of better outcomes [41]. A long-term analysis suggested that the PSA bounce was a significant factor for better overall survival [42]. In CIRT, PSA bounce positivity was a significant predictor of favorable 5-year PSA failure-free survival [20]. In the present study, a significant correlation between PSA bounces and PSA failure was not observed; however, PSA bounces tended to correlate with PSA failure. Longer follow-up is warranted to further explain this issue.

Some patients who exhibited PSA bounces experienced increases in PSA levels of 2 ng/ml or more, which met the Phoenix criteria. The PSA bounce exceeds the 2 ng/ml limit in approximately 10% of patients after brachytherapy [13]. Approximately 1% of patients treated with SRT experienced a PSA increase of >2 ng/ml above the nadir [18]. However, PSA levels spontaneously decreased without any treatment in those patients. A similar clinical course was observed in the present study, as most patients experienced spontaneous decreases of PSA levels. Therefore, even among patients with PSA increases exceeding 2 ng/ml, which met the PSA failure criteria, continuous close PSA surveillance should be considered to confirm the PSA bounce without immediate treatment such as ADT. These findings may provide important information for both patients and physicians to understand PSA dynamics after CIRT.

The present study had several limitations, such as its single-institutional nature, small number of patients, short observation period, and lack of cases of clinical recurrence. In particular, the small number of PSA failure cases could reduce the power of the statistical analysis. Although the correlation between PSA bounces and androgen production in younger age patients was suggested [43], serum androgen levels were not measured in the present study.

Conclusions

We observed the dynamics of PSA in patients with prostate cancer who were treated with CIRT and neoadjuvant ADT in the present study. PSA levels should be examined after treatment to survey for clinical recurrence. Further follow-up is needed to reveal the clinical significance of PSA dynamics.

14 Jul 2020

PONE-D-20-18791

Prostate-Specific Antigen Dynamics After Carbon Ion Radiotherapy for Prostate Cancer

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Reviewer #1: Dear authors, thank you for submitting this manuscript, which I read with great interest. Please find my comments below, which I hope will be a positive contribution.

Summary:

This manuscript reviews the retrospective analysis of PSA failure and bounce for the patients with intermediate-risk prostate cancer treated with CIRT combined with neoadjuvant hormonal therapy at a single institution. There is limited information about PSA kinetics about CIRT combined with hormonal therapy.

This reviewer has some significant concerns that need to be addressed by the authors:

Comments:

Abstraction

Line 53, 54:

It would be helpful to have a more specific conclusion based on the findings of the data reported in the paper. Statements with "investigated" are not conclusions.

Background

Line 74-77:The facility's description is considered to be not directly relevant in the background. I recommend that you consider moving it to the methods paragraph.

Materials and Methods

Line 134-135: Describe the details of dose constraints other than the rectum.

Line 156: Statistical Analysis Paragraph

"The correlation of clinical variables with PSA dynamics was assessed via logistic regression." In Table 2 and 4, was logistic regression analysis performed for both univariate and multivariate analyses? If not, please add a different test method used for univariate analysis.

PSA failure and PSA bounce are both time series data and it is not appropriate to use logistic regression in the test method

In the multivariable analysis, the number of independent variables greatly exceeds the number of occurrence events, which lead to inappropriate results. Describe the process of selecting explanatory variables.

Clarify the detail about the statistical methods for differences between groups in the PSA time series used in Figures 1b and 1c.

Results

Tables:

Remove unnecessary gray lines in each table.

Table1: The sum of pretreatment PSA is not 85. Correct the number of patient numbers in each category.

Table2: The results of PSA nadir is not correctly displayed.

Reviewer #2: Given the fact that the clinical significance of PSA bounce is unclear and its definition is various, I think such a prospective observational study is valuable. This manuscript is very important as the first report of PSA dynamics after CIRT with neoadjuvant ADT.

I have one question that there were 8 patients with PSA failure, 7 were followed up, and only 1 was treated immediately. What is the reason for this difference?

Reviewer #3: General comments

Carbon ion radiotherapy requires advanced technique and the patient number is limited compared with those who receive photon radiotherapy. The current study analyzed intermediate risk prostate cancer patients who received CIRT and ADT to illustrate the dynamics of PSA after treatment.

It is essential to further describe the intention to investigate PSA dynamics for prostate cancer after CIRT and ADT and potential clinical impact to emphasize the value of this study.

Specific comments

Materials and methods section

1. How many patients were in the favorable intermediate risk group among the 85 patients? If any, please describe the indication of neoadjuvant ADT use.

2. Please describe the ADT regimen (drug name and dosage) specifically and clarify the last dose of ADT and its active duration.

3. Please explain why patients received neoadjuvant ADT of various duration (4 to 8 months) in this study. Did the authors investigate whether the duration of ADT administration was associated with the time interval of subsequent incidents of PSA bounce/PSA failure?

Statistical analysis section

4. Please describe the starting date to calculate the follow-up time.

5. The current study investigated the correlation between different continuous variables and PSA bounce/PSA failure. ROC curve analysis should be adopted to survey the potential cutoff value of these continuous variables.

6. Cox regression should be considered in multivariate analysis to investigate the effect of these variables on the time it takes for PSA bounce or PSA failure to happen.

Results section

7. The median follow-up time was 33.1 (range, 20.1–48.3) months, which is relatively short for intermediate risk group prostate cancer patients.

8. Compared with conventional fractionated RT for prostate (about 7 to 8 weeks), the treatment course of 3 weeks using CIRT was relatively short. Usually, the decline of PSA after RT is gradual and it usually take several months to reach the PSA nadir. Most patients in the current study reached nadir rapidly within 3 to 4 months after CIRT. How can the authors confirm that the nadir is due to the effect of CIRT (unique RBE?) rather than effect of ADT?

9. Only eight patients developed biochemical failure during follow-up of this cohort. The small number could reduce the power of statistical analysis.

10. Seven of eight patients developed PSA failure and five of them had PSA level decrease spontaneously. Please explain the findings.

11. Only one out of eight patients with PSA failure received salvage ADT. What about the other patients? Did those patients receive any other salvage therapy? Otherwise, the authors should provide the subsequent management and clinical course of those patients.

Discussion section

12. The authors could try to review the published literature to compare the PSA dynamics of intermediate risk prostate cancer patients receiving CIRT, CIRT with ADT, IMRT, and IMRT with ADT.

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

10 Aug 2020

Reviewer #1:

Thank you for your review and precise suggestions. We have revised our manuscript according to your suggestions as follows:

“Dear authors, thank you for submitting this manuscript, which I read with great interest. Please find my comments below, which I hope will be a positive contribution.

Summary:

This manuscript reviews the retrospective analysis of PSA failure and bounce for the patients with intermediate-risk prostate cancer treated with CIRT combined with neoadjuvant hormonal therapy at a single institution. There is limited information about PSA kinetics about CIRT combined with hormonal therapy.

This reviewer has some significant concerns that need to be addressed by the authors:”

Comments:

Abstraction

“Line 53, 54:

It would be helpful to have a more specific conclusion based on the findings of the data reported in the paper. Statements with "investigated" are not conclusions.”

We have revised the Conclusion of the Abstract. A new sentence has been added to explain our study in the Conclusion. (Page 4, lines 54 to 55).

“This study revealed the significant predictors of PSA bounce and PSA failure.”

“Background

Line 74-77:The facility's description is considered to be not directly relevant in the background. I recommend that you consider moving it to the methods paragraph.”

The sentence describing our facility has been moved to the Materials and Methods section. (pages 7–8, lines 112–113).

“Materials and Methods

Line 134-135: Describe the details of dose constraints other than the rectum.”

V80% < 10ml for the rectum was the only dose constraint in this study. Other DVH parameters for the rectum were not used for dose constraints. We did not use dose constraints for other normal tissues, such as bladder, urethra, penile bulb, and femoral head.

“Line 156: Statistical Analysis Paragraph

"The correlation of clinical variables with PSA dynamics was assessed via logistic regression." In Table 2 and 4, was logistic regression analysis performed for both univariate and multivariate analyses? If not, please add a different test method used for univariate analysis.

PSA failure and PSA bounce are both time series data and it is not appropriate to use logistic regression in the test method

In the multivariable analysis, the number of independent variables greatly exceeds the number of occurrence events, which lead to inappropriate results. Describe the process of selecting explanatory variables.”

We have revised the statistical analysis according to the comments. The Cox regression model was newly adopted for both univariate and multivariate analyses. Another reviewer suggested that we analyze the ROC curve. We have revised the manuscript to explain the statistical methods in the Materials and Methods section. (Page 10, lines 161–167).

“The correlation of clinical variables with PSA dynamics was assessed via Cox regression model. Prognostic factors of which p value was calculated as < 0.10 were evaluated by multivariate stepwise Cox regression model [28]. Comparative analyses for continuous variables such as PSA level and age of the two groups were examined using the Mann–Whitney U test. Receiver operating characteristic (ROC) curves were generated and used to determine the optimal cut-off value.”

The results were modified using the Cox regression model. We have revised Tables 2 and 4 to reflect these changes and have revised the text to explain the new results. (Page 15, lines 203–205; page 16, lines 210–214; page 19, lines 238–240; and pages 19–20, lines 244–246).

“In the univariate analysis, younger age, lower T stage and higher PSA nadir were statistically significantly associated with the occurrence of a PSA bounce (p = 0.000, 0.015 and 0.029, respectively).”

“The median PSA nadir of patients with and without PSA bounces were 0.014 (range, 0-2.183) and 0 (range, 0-0.201) ng/ml, respectively (p = 0.002). In the multivariate analysis, younger age and lower T stage were significantly associated with the occurrence of a PSA bounce (p = 0.000 and 0.049, respectively).”

“In the univariate analysis, younger age, higher pre-CIRT PSA levels, and higher PSA nadir were significantly associated with the occurrence of PSA failure (p = 0.002, 0.007, and 0.003, respectively).”

“The median PSA nadir of patients with and without PSA bounces were 0.014 (range, 0-2.183) and 0 (range, 0-0.201) ng/ml, respectively (p = 0.002).”

The Cox regression model revealed that T stage was also correlated with PSA bounces, so we have added explanations of these results to the Results section. (Page 20, lines 212 to 214) We have also added a discussion about the relationship between T stage and PSA bounces to the Discussion section. (Page 24, lines 294 to 301).

“In the multivariate analysis, younger age and lower T stage were significantly associated with the occurrence of a PSA bounce (p = 0.000 and 0.049, respectively).”

“In the present study, lower T stage was significantly correlated with PSA bounce. In a study of the PSA bounce after LDR-BT, lower T stage was one of the predictive factors for PSA bounce [38]. Sengoz et al. reported that PSA bounce was more frequent in patients with T1-2 stage after external body radiation therapy [39]. The mechanism which lower T stage tended to correlate with PSA bounces was unclear. On the other hand, there were several studies suggested that T stage had no correlation with PSA bounces [14, 19, 35]. Further investigation is warranted to reveal the correlation between T stage and PSA bounces.”

We have added a new figure to show the ROC curves (Fig. 2a and 2b).

“Clarify the detail about the statistical methods for differences between groups in the PSA time series used in Figures 1b and 1c.”

We have revised the manuscript to clarify the statistical methods for PSA in each of the two groups. (Page 11, lines 164 to 166).

“Comparative analyses for continuous variables such as PSA level and age of the two groups were examined using the Mann–Whitney U test.”

“Results

Tables:

Remove unnecessary gray lines in each table.”

The gray lines are not shown in the PDF file. We have attached the PDF file for the tables.

“Table1: The sum of pretreatment PSA is not 85. Correct the number of patient numbers in each category.

Table2: The results of PSA nadir is not correctly displayed.”

We have revised Tables 1 and 2 accordingly.

Reviewer #2:

Thank you for your review and precise suggestions. We have revised our manuscript according to your suggestions as follows:

“Given the fact that the clinical significance of PSA bounce is unclear and its definition is various, I think such a prospective observational study is valuable. This manuscript is very important as the first report of PSA dynamics after CIRT with neoadjuvant ADT.

I have one question that there were 8 patients with PSA failure, 7 were followed up, and only 1 was treated immediately. What is the reason for this difference?”

We had not decided the treatment protocol after PSA failure, and each urologist determined the treatment policy for each case. We have to consider the treatment policy for the patient with PSA failure. As the results of the present study showed that PSA level decreased without treatment in many PSA failure cases, we believe that careful follow-up is important.

Reviewer #3:

Thank you for your review and precise suggestions. We have revised our manuscript according to your suggestions.

“General comments

Carbon ion radiotherapy requires advanced technique and the patient number is limited compared with those who receive photon radiotherapy. The current study analyzed intermediate risk prostate cancer patients who received CIRT and ADT to illustrate the dynamics of PSA after treatment.”

“It is essential to further describe the intention to investigate PSA dynamics for prostate cancer after CIRT and ADT and potential clinical impact to emphasize the value of this study.”

Specific comments

Materials and methods section

“1. How many patients were in the favorable intermediate risk group among the 85 patients? If any, please describe the indication of neoadjuvant ADT use.”

Thirty patients were found to be in the favorable intermediate risk group after NCCN classification. Because we used the D’Amico classification in this study, intermediate risk was not divided into favorable and unfavorable groups. It is still unclear whether ADT is necessary for patients with favorable intermediate risk of prostate cancer treated by CIRT. This is a subject for future analysis.

“2. Please describe the ADT regimen (drug name and dosage) specifically and clarify the last dose of ADT and its active duration.”

We have explained the ADT regimen in the Materials and Methods section. (Page 10, lines 148–149).

“We performed a representative ADT using a combination of bicaltamide and leuprorelin acetate.”

“3. Please explain why patients received neoadjuvant ADT of various duration (4 to 8 months) in this study. Did the authors investigate whether the duration of ADT administration was associated with the time interval of subsequent incidents of PSA bounce/PSA failure?”

The ADT duration was determined by the results of previous research. We have added a reference to clarify the previous research. (Page 10, line 147).

The ADT duration was not associated with either PSA bounce or PSA failure (Tables 2 and 4).

Statistical analysis section

“4. Please describe the starting date to calculate the follow-up time.”

We have modified the Materials and Methods section to clarify the starting date in order to calculate the follow-up time. (Page 10, lines 157 to 158).

“5. The current study investigated the correlation between different continuous variables and PSA bounce/PSA failure. ROC curve analysis should be adopted to survey the potential cutoff value of these continuous variables.”

We performed a ROC curve analysis. We have added new sentences to the Materials and Methods section to explain the statistical analysis. (Page 11, lines 166–167).

“Receiver operating characteristic (ROC) curves were generated and used to determine the optimal cut-off value.”

We have added new figures (Fig. 2a and 2b) and sentences to explain the results of the ROC analyses. (Page 16, lines 214–217 and page 20, lines 247–250).

“The ROC curve analysis calculated the area under the ROC curve (AUC) as 0.705 and determined a cut-off value of 68 years, at which the sensitivity and specificity were measured to be 76.1 and 61.5 %, respectively. (Fig 2(a))”

“The ROC curve analysis calculated the area under the ROC curve (AUC) as 0.844 and determined a cut-off value of 65 years, at which the sensitivity and specificity were calculated as 77.9 and 87.5 %, respectively. (Fig 2(b))”

“6. Cox regression should be considered in multivariate analysis to investigate the effect of these variables on the time it takes for PSA bounce or PSA failure to happen.”

We have revised the statistical analysis section. Cox regression model was newly adopted for both univariate and multivariate analyses. We have revised the Materials and Methods section to explain the statistical methods. (Page 10, lines 161–167).

“The correlation of clinical variables with PSA dynamics was assessed via the Cox regression analyses. Prognostic factors, for which p value was calculated as <0.10, were evaluated using the multivariate stepwise Cox regression model [28]. Comparative analyses for continuous variables, such as PSA level and age of the two groups, were examined using the Mann–Whitney U test. Receiver operating characteristic (ROC) curves were generated and used to determine the optimal cut-off values.”

The results were changed by the Cox regression model. We have revised Tables 2 and 4 and have added sentences to explain these results. (Page 15, lines 203 to 205; page 16, lines 210–214; page 19, lines 238–240; pages 19–20, lines 244–246).

“In the univariate analysis, younger age, lower T stage and higher PSA nadir were statistically significantly associated with the occurrence of a PSA bounce (p = 0.000, 0.015 and 0.029, respectively).”

“The median PSA nadir of patients with and without PSA bounces were 0.014 (range, 0-2.183) and 0 (range, 0-0.201) ng/ml, respectively (p = 0.002). In the multivariate analysis, younger age and lower T stage were significantly associated with the occurrence of a PSA bounce (p = 0.000 and 0.049, respectively).”

“In the univariate analysis, younger age, higher pre-CIRT PSA levels, and higher PSA nadir were significantly associated with the occurrence of PSA failure (p = 0.002, 0.007, and 0.003, respectively).”

“The median PSA nadir of patients with and without PSA bounces were 0.014 (range, 0-2.183) and 0 (range, 0-0.201) ng/ml, respectively (p = 0.002).”

The Cox regression model revealed that T stage was also correlated with PSA bounces, so we have added sentences to explain these results in Results section. (Page 20, lines 212 to 213) and have added a discussion regarding the relationship between T stage and PSA bounces in the Discussion section. (Page 24, lines 293 to 300).

“In the multivariate analysis, younger age and lower T stage were significantly associated with the occurrence of a PSA bounce (p = 0.000 and 0.049, respectively).”

“In the present study, lower T stage was significantly correlated with PSA bounce. In a study of the PSA bounce after LDR-BT, lower T stage was one of the predictive factor for PSA bounce [38]. Sengoz et al. reported that PSA bounce was more frequent in patients with T1-2 stage after external body radiation therapy [39]. The mechanism which lower T stage tended to correlate with PSA bounces was unclear. On the other hand, there were several studies suggested that T stage had no correlation with PSA bounces [14, 19, 35]. Further investigation is warranted to reveal the correlation between T stage and PSA bounces.”

Results section

“7. The median follow-up time was 33.1 (range, 20.1–48.3) months, which is relatively short for intermediate risk group prostate cancer patients.”

We also believe that the short follow-up duration is a limitation in this study. A longer follow-up is warranted to reveal the clinical significance of PSA dynamics.

“8. Compared with conventional fractionated RT for prostate (about 7 to 8 weeks), the treatment course of 3 weeks using CIRT was relatively short. Usually, the decline of PSA after RT is gradual and it usually take several months to reach the PSA nadir. Most patients in the current study reached nadir rapidly within 3 to 4 months after CIRT. How can the authors confirm that the nadir is due to the effect of CIRT (unique RBE?) rather than effect of ADT?”

Darivis et al. reported the relationship between ADT and CIRT alone (ref 20). They did not mention the duration for PSA nadir, but a figure in that study demonstrated that it takes several months or more to reach PSA nadir by CIRT alone. Therefore, it is suggested that the short time to PSA nadir in the present study may be affected ADT.

9. Only eight patients developed biochemical failure during follow-up of this cohort. The small number could reduce the power of statistical analysis.

We also believe that the small number of patients with PSA failure is a limitation of the present study. Further investigation is warranted in the future.

10. Seven of eight patients developed PSA failure and five of them had PSA level decrease spontaneously. Please explain the findings.

Because clinical recurrence was not observed in any of the seven patients, careful surveillance of PSA was selected and PSA level was decreased without any salvage treatment. Several cases that met the PSA failure criteria among patients with PSA bounce have been reported in previous studies (13, 18). A similar clinical course was observed in these seven patients in this study.

11. Only one out of eight patients with PSA failure received salvage ADT. What about the other patients? Did those patients receive any other salvage therapy? Otherwise, the authors should provide the subsequent management and clinical course of those patients.

The seven patients with PSA failure did not receive any salvage therapy. We have added the following sentence to clarify this point:

“No salvage treatments were performed in these seven patients in the follow-up period.” (Page 18, line 226 to 227).

Discussion section

12. The authors could try to review the published literature to compare the PSA dynamics of intermediate risk prostate cancer patients receiving CIRT, CIRT with ADT, IMRT, and IMRT with ADT.

We could not find any previous literature that investigated PSA dynamics limited to intermediate risk groups. Especially for CIRT, there has been only one study into PSA dynamics (Darwis et al.) (20). Therefore, we believe that the present study has novelty and may provide important information for both patients and physicians to understand PSA dynamics after CIRT.

Submitted filename: Responce to Reviewers.docx

Click here for additional data file.

26 Aug 2020

PONE-D-20-18791R1

Prostate-Specific Antigen Dynamics After Carbon Ion Radiotherapy for Prostate Cancer

PLOS ONE

Dear Dr. Takakusagi,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: All comments have been addressed

Reviewer #2: All comments have been addressed

Reviewer #3: (No Response)

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: Partly

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

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PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

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Reviewer #2: Yes

Reviewer #3: No

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The revised version is well re-written replying the comments of the reviewers. I feel that the revised manuscript is suitable for publication.

Reviewer #2: Given the fact that the clinical significance of PSA bounce is unclear and its definition is various, I think such a prospective observational study is valuable. This manuscript is very important as the first report of PSA dynamics after CIRT with neoadjuvant ADT. I think this paper is worthy for publication.

Reviewer #3: Thank the authors for revising the manuscript; however, some problems remain in the revised manuscript.

1. The topic of the manuscript is “Prostate-Specific Antigen Dynamics After Carbon Ion Radiotherapy for Prostate Cancer.” If the authors were not able to confirm whether the PSA dynamics was due to the effect of CIRT, ADT or both, the issue of this investigation should be “Prostate-Specific Antigen Dynamics After Neoadjuvant ADT and CIRT for Prostate Cancer.” Precisely, the study demonstrated the prostate-specific antigen dynamics after neoadjuvant androgen-deprivation therapy combined with carbon ion radiotherapy for intermediate risk prostate cancer patients.

2. Table 1 demonstrated that the duration of ADT were enormously diverse with median of 6.2 months (ranging from 2.3 to 116.9 months). Essentially, this arises the concern of its potential effects on the time period for PSA bounce or PSA failure. This issue stayed unexplained in the revised manuscript.

3. Only eight patients developed biochemical failure during follow-up of this cohort. The small number could reduce the power of statistical analysis, which should be estimated in the manuscript.

4. Importantly, the statistical analyses have some fundamental problems even after revision. The results of the univariate analysis and Cox regression model of multivariate analysis provided in Table 2 and Table 3 were insufficient to demonstrate how those parameters were correlated with the time period for PSA bounce or PSA failure to happen. For example, if younger age and lower T stage were not clearly defined in the investigation, how did authors conclude that younger age and lower T stage were associated with the time period for PSA bounce or PSA failure to occur after CIRT?

Because CIRT requires advanced techniques and the patient number is limited compared with those who receive photon radiotherapy, this requires careful statistical analysis to investigate PSA dynamics to confirm its clinical impact.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #2: No

Reviewer #3: No

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

9 Sep 2020

Reviewer #1: The revised version is well re-written replying the comments of the reviewers. I feel that the revised manuscript is suitable for publication.

We thank the reviewer for evaluating our manuscript and for their encouraging comments.

Reviewer #2: Given the fact that the clinical significance of PSA bounce is unclear and its definition is various, I think such a prospective observational study is valuable. This manuscript is very important as the first report of PSA dynamics after CIRT with neoadjuvant ADT. I think this paper is worthy for publication.

We appreciate the reviewer’s feedback and are elated to hear this news.

Reviewer #3: Thank the authors for revising the manuscript; however, some problems remain in the revised manuscript.

We thank the reviewer for evaluating our manuscript. According to the suggestions, we have revised the manuscript as follows.

1. The topic of the manuscript is “Prostate-Specific Antigen Dynamics After Carbon Ion Radiotherapy for Prostate Cancer.” If the authors were not able to confirm whether the PSA dynamics was due to the effect of CIRT, ADT or both, the issue of this investigation should be “Prostate-Specific Antigen Dynamics After Neoadjuvant ADT and CIRT for Prostate Cancer.” Precisely, the study demonstrated the prostate-specific antigen dynamics after neoadjuvant androgen-deprivation therapy combined with carbon ion radiotherapy for intermediate risk prostate cancer patients.

We have revised the title to “Prostate-Specific Antigen Dynamics After Neoadjuvant Androgen-Deprivation Therapy and Carbon Ion Radiotherapy for Prostate Cancer,” as per their insight (page 1, lines 2–3).

2. Table 1 demonstrated that the duration of ADT were enormously diverse with median of 6.2 months (ranging from 2.3 to 116.9 months). Essentially, this arises the concern of its potential effects on the time period for PSA bounce or PSA failure. This issue stayed unexplained in the revised manuscript.

Tables 2 and 3 demonstrate that the ADT duration was not associated with the occurrence of PSA bounce and failure. This has been delineated in the Results section as follows:

ADT duration was not correlated with the occurrence of PSA bounce (p = 0.731) (page 16, lines 219–220).

ADT duration was not correlated with the occurrence of PSA failure (p = 0.614) (page 20, lines 258–259).

3. Only eight patients developed biochemical failure during follow-up of this cohort. The small number could reduce the power of statistical analysis, which should be estimated in the manuscript.

We agree with the reviewer’s comment that this small number of patients has contributed to a reduction of statistical power. We have acknowledged this as a limitation of our study, which is as follows:

In particular, the small number of PSA failure cases could reduce the power of the statistical analysis (page 26, lines 341–342).

4. Importantly, the statistical analyses have some fundamental problems even after revision. The results of the univariate analysis and Cox regression model of multivariate analysis provided in Table 2 and Table 3 were insufficient to demonstrate how those parameters were correlated with the time period for PSA bounce or PSA failure to happen. For example, if younger age and lower T stage were not clearly defined in the investigation, how did authors conclude that younger age and lower T stage were associated with the time period for PSA bounce or PSA failure to occur after CIRT?

Because CIRT requires advanced techniques and the patient number is limited compared with those who receive photon radiotherapy, this requires careful statistical analysis to investigate PSA dynamics to confirm its clinical impact.

In the present study, we solely aimed to determine the occurrence of PSA bounce, PSA failure, and related clinical factors; elucidation of the time period for PSA bounce or failure to occur was beyond the scope of this study. This has been stated in the manuscript as follows:

In this study, we identified the significant predictors of the occurrence of PSA bounce and failure. (page 4, lines 55–56).

The occurrence of PSA bounce and failure was correlated with younger age. (page 22, lines 273–274).

Submitted filename: Responce to reviwers.docx

Click here for additional data file.

12 Oct 2020

PONE-D-20-18791R2

Prostate-Specific Antigen Dynamics After Neoadjuvant Androgen-Deprivation Therapy and Carbon Ion Radiotherapy for Prostate Cancer

PLOS ONE

Dear Dr. Takakusagi,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

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Stephen Chun

Academic Editor

PLOS ONE

Additional Editor Comments (if provided):

After additional statistical review, with minor revisions as suggested by Reviewer #4 to clarify methodology, this manuscript will be acceptable for publication.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

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Reviewer #4: All comments have been addressed

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Reviewer #4: Yes

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Reviewer #4: Yes

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Reviewer #4: In the statistical analysis section, authors should give details on how the ROC curves were used to generate the optimal cutoffs (was it from univariable model? Or multivariable model?) or list any appropriate reference articles.

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Reviewer #4: No

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16 Oct 2020

Reviewer #4:

We thank the reviewer for evaluating our manuscript. According to the suggestions, we have revised the manuscript as follows.

“In the statistical analysis section, authors should give details on how the ROC curves were used to generate the optimal cutoffs (was it from univariable model? Or multivariable model?) or list any appropriate reference articles.”

We used Youden index to determine the optimal cut-off value. We have revised the statistical analysis section to clarify how the cut off value was generated (Page 11, lines 172-174) and a new reference have been added (ref number 29)

“Non-parametric receiver operating characteristic (ROC) curves were generated and Youden index (J = max [sensitivity + specificity – 1]) was used to determine the optimal cut-off values [29].”

“29) Conroy AL, Liles WC, Molyneux ME, Rogerson SJ, Kain KC. Performance characteristics of combinations of host biomarkers to identify women with occult placental malaria: a case-control study from Malawi. PLoS One. 2011;6(12)”

Submitted filename: Responce to reviwer.docx

Click here for additional data file.

19 Oct 2020

Prostate-Specific Antigen Dynamics After Neoadjuvant Androgen-Deprivation Therapy and Carbon Ion Radiotherapy for Prostate Cancer

PONE-D-20-18791R3

Dear Dr. Takakusagi,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Stephen Chun

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

28 Oct 2020

PONE-D-20-18791R3

Prostate-Specific Antigen Dynamics After Neoadjuvant Androgen-Deprivation Therapy and Carbon Ion Radiotherapy for Prostate Cancer

Dear Dr. Takakusagi:

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on behalf of

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Academic Editor

PLOS ONE