Radiation-Associated Aortocolonic Fistula in Urothelial Carcinoma: Multidisciplinary Management and Case Report.

Upper tract urothelial carcinoma (UTUC) is an uncommon and aggressive malignancy that often presents as an invasive disease. After receiving systemic therapy, stereotactic body radiation therapy (SBRT) offers a non-surgical option for consolidative local tumor control by delivering radiation doses in limited fractions. While SBRT is generally well tolerated in the treatment of UTUC, there is a small but serious risk of radiation-associated complications. We present a case of a 67-year-old male with metastatic UTUC of the renal pelvis treated with chemotherapy and immunotherapy. Due to persistent disease at the primary site, he underwent consolidative SBRT using a PULSAR (Personalized Ultra-fractionated Stereotactic Adaptive Radiotherapy) approach to his left kidney mass. Weeks later, he developed a renocolic fistula that was complicated by sepsis. Despite a diverting colostomy and antibiotics, he re-presented with hemorrhagic shock due to an aortocolonic fistula that required emergent endovascular aortic repair (EVAR). This case illustrates a rare but serious complication of consolidative SBRT in a patient with extensive retroperitoneal malignancy. Multidisciplinary planning and close surveillance are critical to ensuring the safe integration of SBRT in the management of metastatic UTUC.