Proton Reirradiation of Recurrent Rectal Cancer: Dosimetric Comparison, Toxicities, and Preliminary Outcomes

Abstract Purpose: Locally advanced rectal adenocarcinoma is effectively treated with chemoradiation and surgery; however, 10 to 25% of patients locally recur within or near a previously irradiated field. Proton radiation therapy (PRT) is ideally suited to the problem of reirradiation for locally recurrent rectal cancer (LRRC). Patients and Methods: Seven patients with LRRC in or near prior radiation fields were enrolled on this prospective study from March 2010 to February 2011. All patients underwent positron emission tomography (PET)/computed tomography (CT) simulation and were stratified by low volume (clinical target volume 250 cm3, n=3). Primary endpoints were feasibility and acute toxicity (within 90 days from PRT initiation). Dosimetry was compared using the Wilcoxon signed-rank test. Tumor response was defined according to PERCIST criteria. Results: Median follow-up was 14 months (4.9–22.6). Median dose of prior RT was 5040 cGy. Mean PRT dose was 6120 cGy (RBE) (rang...