Impact of hydrogel peri-rectal spacer insertion on seminal vesicles intrafraction motion during 1.5 T-MRI-guided adaptive stereotactic body radiotherapy for localized prostate cancer.

MR-guided daily adaptive radiotherapy may represent a game changer for prostate stereotactic body radiotherapy, given the possibility to better visualize soft-tissues anatomy and to daily recalculate the treatment plan based on real-time conditions. The use of devices like rectal ballon or rectal gel spacers has gained interest in the last years for the possibility to better spare the rectum during prostate radiotherapy. This is one of the first experiences exploring the role of rectal spacer on seminal vesicles intrafraction motion during MR-guided SBRT for prostate cancer.