A Case of Hydrogel Spacer Intravasation of the Internal Iliac Vein and Associated Thrombus Formation During Preparation for Prostate Cancer External Beam Radiotherapy.

Use of rectal spacer gel has been associated with decreased risk of radiation therapy (RT)-related rectal toxicity in clinical trials and has been increasingly adopted. Optimal management of spacer-related toxicities, such as rectal wall and vascular infiltration, remains poorly defined. To address this gap, we present a case of extensive hydrogel intravasation of the periprostatic venous plexus with development of associated bland thrombus extending to the level of the common iliac vein. The patient was evaluated for placement of an inferior vena cava (IVC) filter and anticoagulation by a multidisciplinary team. After undergoing 6 months of anticoagulation without IVC filter placement, both the hydrogel and the associated thrombus resolved asymptomatically. We review the timeline of these events, their associated symptomatology, our rationale in management of this clinical scenario, and propose a treatment paradigm.