CT-Guided Interstitial Low Dose-RATE Brachytherapy for Recurrent Colorectal Cancer.

Abstract

PURPOSE/OBJECTIVE(S)\nPatients with pelvic or retroperitoneal recurrences of colorectal cancer (CRC) have poor overall survival, with retrospective studies suggesting a possible survival benefit with local therapy. However, many patients present with disease that is either unresectable, or in which resection will result in significant morbidity or margin positivity. We sought to examine the local control, overall survival (OS), and toxicity of minimally invasive CT-guided low dose-rate (LDR) brachytherapy in this setting, for which there is limited published data.\n\n\nMATERIALS/METHODS\nThis study was a retrospective analysis of all patients at our institution who have undergone CT-guided LDR brachytherapy for recurrent CRC. Patient, tumor, and treatment characteristics were collected, along with physician-reported symptoms in the medical record. Patients underwent dose calculation based on pre-implantation CT imaging and contouring of gross tumor volume (GTV), followed by CT-guided percutaneous interstitial needle placement of either Iodine-125 or Palladium-103 permanent seed implants prescribed to the GTV. Response Evaluation Criteria in Solid Tumors (RECIST) criteria were used to interpret treatment response, and the Kaplan-Meier method was used to estimate rates of overall survival (OS) and in-field control (IFC). IFC was defined as a lack of progression of disease within the pre-implantation defined target volume.\n\n\nRESULTS\nBetween December 2016 and August 2020, 13 patients underwent 18 CT-guided LDR seed implantations (6 I-125, 12 Pd-103) for pelvic or retroperitoneal recurrences of CRC at our institution, with a median follow-up of 17 months. 17 treatments were for pelvic recurrences, while one treatment was for a retrocaval nodal recurrence. The median prescribed dose to the target volume was 80 Gy (range 40-110 Gy), with a median target volume of 5.0 cc (range 0.6-25.5 cc). The 1-year estimated rates of OS and IFC were 94.4% (CI 84.4-100%) and 82.4% (CI 66.1-100%), respectively. All in-field failures occurred in targets above the median target volume of 5 cc. All patients previously received definitive treatment for either initially locally advanced (8 patients) or limited metastatic disease (5 patients). Of the 18 implantations, four were performed for isolated pelvic recurrences and 13 for either oligo-progressive or oligo-recurrent metastatic disease, with a median of two active sites of disease at the time of seed implantation. One patient received palliative brachytherapy after a poly-metastatic recurrence. No patients experienced grade 2 or higher toxicities. Three patients experienced a grade 1 toxicity (proctitis, pain, and fatigue), and one patient developed an asymptomatic recto-vaginal fistula detected on imaging, which was outside of the brachytherapy field.\n\n\nCONCLUSION\nCT-guided interstitial LDR brachytherapy achieved high rates of control and overall survival with minimal long-term toxicity in patients with pelvic and retroperitoneal recurrences of CRC.