A Novel Device for Protecting Rectum During Prostate Cancer Irradiation: In Vivo Data on a Large Mammal Model

Purpose: Hypofractionation schemes and associated higher rectal doses have evoked the need for improved protection of the rectum during prostate cancer irradiation. Materials and Methods: An implantable, biodegradable, inflatable, preshaped triangular balloon of commercially used poly(L-lactide-co-ε-caprolactone) co-polymer material was developed to provide separation between prostate and rectum. Biocompatibility and degradability of the balloon implanted subcutaneously or perineally, and in the context of transperineal implantation and local irradiation were evaluated in several in vivo studies. Results: The device was found to be biocompatible in subcutaneously implanted rabbits up to 42 days, in a transperineally implanted dog up to 12 months and in 8 transperineally implanted pigs up to 6 months. Upon inflation in situ the balloon separated the tissues, remained inflated for several months and subsequently biodegraded. No systemic or local toxicity was noted, as shown by histopathology. Device insertion into the perineal area using a dedicated introductory kit was convenient and feasible. Three-month followup in irradiated pigs that received 15 Gy in 3 fractions 1 week apart showed a stable balloon position with no local or systemic side effects. Conclusions: This novel device was safe and effective for its intended use of separating tissues for a desired duration. A clinical study will commence to evaluate the safety and efficacy of this device during irradiation in patients with prostate cancer.