SpaceOAR Hydrogel Placement in Patients Undergoing Proton Therapy and Low-Dose-Rate Brachytherapy

Abstract

Dose escalation in prostate cancer has been shown to improve biochemical control in patients treated with definitive radiotherapy. Despite advances in radiation therapy techniques including intensity-modulated radiotherapy, volumetric arc therapy and proton therapy, rectal toxicity continues to be a concern. One method of reducing rectal dose and limiting subsequent toxicity is insertion of a biodegradeable hydrogel (SpaceOAR) to increase the distance between the rectum and prostate, thus decreasing the radiation dose received by the rectal wall. This device has been used in a variety of clinical scenarios in the treatment of prostate cancer, including external beam radiation therapy (EBRT), stereotactic body radiation therapy (SBRT) and brachytherapy. However, there have been no reported cases of a SpaceOAR hydrogel being placed prior to proton therapy that is later followed by a low dose-rate (LDR) prostate brachytherapy boost. We present a case report of SpaceOAR placement in a man who presented with intermediate risk prostate cancer who received combined modality therapy using androgen deprivation therapy (ADT) and proton therapy followed by an LDR brachytherapy boost. We report that SpaceOAR hydrogel was stable with no signs of radiation degradation post-EBRT. Additionally, placement of LDR seeds was feasible several months after rectal spacer implant and following a 5-week course of proton therapy with no dosimetric consequences. In conclusion, placement of an absorbable hydrogel spacer material can increase separation between the rectum and prostate and appears stable throughout proton therapy. The absorbable hydrogel is clearly visualized after proton therapy and appears safe for administration of LDR brachytherapy as a boost.