SU‐E‐T‐406: Dosimetric Impact of the Air‐Filled Rectal Balloon for Prostate Proton Treatment

Purpose: To investigate the dosimetric impact of the air‐filled rectal balloon for prostate treatment with proton beams. Methods: Proton beam is used for prostate treatment because it can provide a conformal dose coverage to the target. Prostate localization accuracy is crucial to guarantee the treatment targeting. The use of rectal balloon has been shown to be effective in reducing the prostate motion during the treatment. Air‐filled rectal balloon has been used most commonly, but could create dose perturbation at the air‐tissue interface. In this work, intensity modulated proton treatment (IMPT) plans were generated for ten patients with air‐filled rectal balloon for prostate localization. Monte Carlo dose calculations were performed for each patient and the dose distribution were compared with those when the rectal balloons filling material is changed to water. The doses to the prostate and the rectal wall were compared for these two situations. The dosimetric impacts from the air‐filled balloon are then summarized. Results: It was found that the dosimetric impact to the prostate by the air‐filled balloon is minimum. The changes in the minimum dose, the maximum dose and the mean dose to the prostate caused by the air‐filled balloon are within 1%. The maximum dose to the rectal wall was reduced by 3.4% (from −0.4% to 5.3%) on average. However, the mean dose to rectal wall was increased by 13.3% (from 10.2% to 17%) on average. The DVH comparison show that the volume of the rectal wall receiving dose less than 50% of the prescription dose increased significantly. Conclusion: The air‐filled rectal balloon has no significant impact on the target dose coverage. It reduces the maximum dose of the rectum wall but increase its mean dose significantly. Overall, the air‐filled rectal balloon is feasible for prostate proton treatment.