Analysis of daily changes in volume and predicted doses for critical organs and the prostate during radiotherapy

Abstract Introduction The analysis of the differences in the daily volumes and the predicted dose to the actual dose in the bladder, rectum, and targets in prostate radiotherapy is presented. Material and methods The analysis was performed for 30 patients treated with prostate cancer. Precision treatment planning system was used to calculate the dose distribution. Patients were set up on the treatment table in the treatment position every day. kVCT images were acquired. kVCT images were imported into the PreciseART module. Organs at Risk and the prostate (PTV) volumes were copied onto these daily actual CT images and then automatically deformed to their current shapes. They were used to recalculate the updated therapeutic treatment plan. 726 CT examinations were analyzed. The volumes and dose values from clinical treatment plan have been used as reference values for the PTV, bladder, and rectum. Changes in volumes and doses for reference values and daily CT images were analyzed. Results The average daily changes in PTV, bladder and rectum volumes ranged from -0.3% to 14.4%, -21.7% to 32.5% and -10.5% to 32.5%, respectively. Corresponding standard deviations ranged from 1.0% to 5.5%, 4.9% to 35.5% and 5.8% to 25.2%, respectively. Corresponding median values ranged from -0.2% to 14.1%, -22.0% to 37.8% and -10.9 to 32.8, respectively. The average daily changes in PTV, bladder and rectum projected doses ranged from -1.4% to 2.9%, -9.0% to 24.8% and -25.4% to 15.9%, respectively. Corresponding standard deviations ranged from -1.4% to 2.6%, 0.0% to 14.8% and 0,0% to 17,2%, respectively. Corresponding median values ranged from -1.5% to 2.7%, -8.8% to 28.7% and -25.9% to 17.2%, respectively. Conclusions Qualitative data analysis showed that the greatest differences in volumes and doses occurred for these structures. For the prostate, these changes were lower than for other organs.