1 Endorectal balloon for prostate SBRT: Influence on internal pudendal arteries dose sparing?

Abstract

Introduction One of the most common side effects from radiotherapy treatment of localized prostate cancer remains erectile dysfunction. Vessel-sparing radiotherapy has shown promising results on preserving erectile function when compared to historical series. In this dosimetric study, we aim to evaluate the influence of an endorectal balloon (ERB) on the dose sparing of internal pudendal arteries (IPA) in treatment planning of prostate stereotactic RT (SBRT). Methods Twelve localized prostate cancer patients, simulated with and without ERB, were planned to receive 36.25 Gy (7.25Gyx5) to the planning treatment volume (PTV). IPA were delineated on each scanners using registration with MRI. Plans with and without ERB were optimized using Rapidplan™ (Varian), a knowledge based software, with standard sparing of regionally involved organs at risk (rectal and bladder wall, and femoral heads) and no dose constraints on IPA. A total of 24 volumetric arc therapy plans were optimized using a 10MV FFF beam with 2 full arcs. SBRT doses to IPA ( D 2 % and D mean ) were compared between groups using non-parametric tests. Results The IPA volumes were similar in the two CT datasets, with a median volume of 4.75 cc (range, 3.8–7.2) vs. 4.95 cc (range, 3.8–7, p = 0.721) in patients with and without ERB, respectively. The median mean IPA dose was significantly lower using ERB (10.5 vs. 12.8 Gy, p = 0.023). Median IPA D 2 % was also lower with ERB (17.6 vs. 20.8 Gy without ERB), but the difference was not significant. No clinically significant differences in target coverage, rectal, and bladder walls doses were observed between the two groups. Conclusions The use of ERB for prostate SBRT showed a significant sparing of IPA compared to plans generated with an empty rectum. As no specific dose constraints are yet available for vessel-sparing SBRT, optimal reduction of IPA doses should be attempted for maximal EF preservation.