Does image-guided radiotherapy improve toxicity profile in whole pelvic-treated high-risk prostate cancer? Comparison between IG-IMRT and IMRT.

PURPOSE: To evaluate the impact of adding image-guided (IG) technique to intensity-modulated radiotherapy (IMRT) on dosimetric avoidance of organs at risk (OAR) and acute toxicities. METHODS AND MATERIALS: A total of 25 consecutively treated patients (10 from National University Hospital and 15 from University of California San Francisco) with high-risk prostate cancer formed the study cohort. All received definitive IMRT with prophylactic nodal RT. Similar IMRT contouring and planning techniques were used at both centers. At the University of California, San Francisco, intraprostatic fiducial markers were used for daily pretreatment on-line corrections (IG-IMRT). In contrast, at the National University Hospital, no fiducial markers were used (IMRT). At the University of California, San Francisco, the planning target volume margins to the prostate were 2-3 mm. At the National University Hospital, they were 1 cm circumferentially, except for 0.5 cm posteriorly. The acute rectal and bladder toxicities and dosimetric endpoints to the planning target volume and organs at risk were compared.
RESULTS: The planning target volume dose coverage was not significantly different between IMRT and IG-IMRT for the prostate, seminal vesicles, and lymph nodes. The volume of rectum and bladder receiving >/=40, >/=60, and >/=70 Gy were all significantly less using IG-IMRT (p <0.001). IG-IMRT yielded lower acute Radiation Therapy Oncology Group Grade 2 rectal (80% vs. 13%, p = 0.004) and bladder (60% vs. 13%, p = 0.014) toxicities.
CONCLUSIONS: IG-IMRT, using daily target localization with fiducial markers, permits the use of smaller margins and correspondingly lower doses to the organs at risk, such as the rectum and bladder. These tangible gains appear to translate into lower clinically significant toxicities.