| Summary: | An important modality for the treatment of prostate cancer is teletherapy. The use of image-guided radiotherapy (IGRT) is a valuable tool in this treatment. This study retrospectively compared how repositioning the patient based on bone structure (B-ISO) and the prostate itself (P-ISO) affected the volumetric dose in the rectum, bladder, and clinical treatment volume (CTV). Additionally, the probability of normal tissue complication (NTCP) for the rectum was computed. We evaluated 155 cone-beam computed tomography (CBCT) from 8 patients. The treatment plans used beam modulation techniques. The planning target volume (PTV) margin adopted in both scenarios was 1 cm. The organs of interest were outlined over each CBCT and then treatment plans were applied so that the absorbed dose could be computed. NTCP values were calculated for the rectum. Analyzing dose-volume metrics published by the Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC), there was no significant difference between the two repositioning strategies for the rectum and bladder. There was a slight degradation in CTV coverage for the B-ISO strategy, but still with adequate coverage. Analysis of the uniform equivalent dose (EUD) and NTCP for the rectum showed little sensitivity to the strategy used. The present study showed that the use of CBCT in radiotherapy for prostate cancer treatment did not significantly improve volumetric doses for the rectum, bladder, and CTV, as well as NTCP for the rectum.
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