Dosimetric analysis of daily use of IGRT in prostate treatment with intensity modulated

The main application of image-guided radiotherapy (IGRT) in the cancer prostate treatment is to ensure the delivery of the prescribed dose to the tumor. With the modality cone beam computed tomography (CBCT) prostate, seminal vesicles, bladder and rectum can be previewed before each treatment and the actual dose delivered to these organs can be controlled, through the alignment of patient isocenter. The aim of this study was to analyze the tumor coverage and dose to organs at risk effectively obtained during the patient's treatment. Three patients with prostate cancer were treated with intensity modulated radiotherapy (IMRT) or volumetric modulated arc radiotherapy (VMAT) techniques with 74 Gy and 2 Gy per fraction. It was performed daily isocenter location of the prostate with CBCT. A radioncologist drew the clinical target volume (CTV), rectum and bladder in CBCT's and treatment fields were applied retrospectively in each CBCT for dose calculation. For the CTV it was considered the D95 (dose that covers 95% of the volume), for the rectum V50 (volume receiving 50 Gy), V60, V65 and V70 and for bladder V65 and V70. The average D95 of the prostate after the offset was 202 cGy, the V50, V60 and V65 of the rectum for one patient was reduced by 9.6%, 16.6% and 31%, respectively, and V65 of the bladder to another patient was also reduced by 3.5% in IGRT. The results showed that the use of IGRT provided a reduction in the irradiated volume of healthy organs. Thus it is concluded that the use of daily CBCT allows reproducibility of treatment, reducing delayed toxicities and increasing the probability of tumor control. (author)