Main Session
Sep
28
SS 02 - GI 1: The OPERATIC Side of Rectal Cancer - Organ Preservation, Evaluating Recurrences, and the Immune Checkpoints
110 - IMPARC: A Prospective Trial of Stereotactic Proton Reirradiation for Locoregionally Recurrent Rectal Cancer
Presenter(s)
Poonam Dalwadi, MD, BS - Washington University/B-JH/SLCH Consortium, St. Louis, MO
P. Dalwadi1, A. Mo2, R. I. Chin3, C. Hatscher4, K. Stavroulaki5, P. Mata5, L. E. Henke6, T. Zhao4, H. Kim2, and S. N. Badiyan7; 1Washington University/B-JH/SLCH Consortium, St. Louis, MO, 2WashU Medicine, Department of Radiation Oncology, St. Louis, MO, 3Washington University School of Medicine, Department of Radiation Oncology, St. Louis, MO, 4Washington University School of Medicine in St. Louis, Department of Radiation Oncology, St. Louis, MO, 5Washington University in St. Louis, St. Louis, MO, 6Department of Radiation Oncology, University Hospitals Seidman Cancer Center, Case Western Reserve University, Cleveland, OH, 7Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX
Purpose/Objective(s):
Hyperfractionated reirradiation has become a standard option for locoregionally recurrent rectal cancer (LRRA) previously treated with definitive radiation. Hyperfractionated treatment schedules are protracted and logistically challenging to administer, with modest long-term control rates possibly due to an insufficient biological effective dose. We prospectively evaluated the maximum tolerated dose (MTD), safety and efficacy of 5 fraction (fx) stereotactic intensity-modulated proton therapy (IMPT) in patients with previously irradiated LRRA.Materials/Methods:
Patients with histologically confirmed previously irradiated LRRA were enrolled on a prospective trial (NCT04827732). Dose escalation from 30 Gy in 5 fxs [relative biological effectiveness 1.1] to 40 Gy in 5 fxs was performed following the TITE-CRM method. Primary objective was to determine MTD which was defined as the dose associated with 35% probability of dose-limiting toxicity. Secondary endpoints include local control (LC), locoregional control (LRC) progression-free survival (PFS), and overall survival (OS). Toxicity was graded using CTCAE v5.0, while EORTC QLQ-C30 and QLQ-CR29 questionnaires evaluated quality of life (QOL) and bowel symptoms, respectively.Results:
From 2021-2024, 16 patients were screened and 14 met eligibility requirements. Median age at enrollment was 59 years (yr) (range 27-29). Initially, most patients had at least Stage IIIB disease with 57% treated with short course radiation (RT) 25-35 Gy in 5 fx while the rest were treated with long course from 45-54 Gy. Ten (71.4%) patients had a total mesorectal excision after the first course of RT. Median interval between initial RT and trial enrollment was 39.2 months (mo) (range 11.7-195.7). At time of reirradiation, 5 (35.7%) patients had distant metastases. Six patients received 30 Gy, 3 received 35 Gy, and 4 received 40 Gy. Median reirradiation target volume was 74.5cc (range = 1.9-516) and MTD was 40 Gy/5 fxs. Cumulative dose to composite bowel D0.5cm3 was 81.3 Gy EQD2 (range = 40-141). One patient experienced a grade 4 rectal perforation. Two patients experienced grade 3 acute GI toxicity. No patient-reported significant decline in QOL or bowel function was detected up to 1-yr post-treatment. With median follow-up of 23 mo, 2-yr LC was 78.6%, median PFS was 5.4 mo with distant sites as most common first failure. Median overall survival was 23.3 mo with 1-yr OS of 64.3%. Two (14.3%) patients underwent resection of their reirradiated tumor after stereotactic IMPT.Conclusion:
This prospective clinical trial evaluating stereotactic IMPT for LRRA demonstrated excellent local control with reasonable grade 3+ GI toxicity. However, caution should be exercised in re-irradiating the entire circumference of the bowel with full dose. Reirradiation with stereotactic IMPT to 40 Gy may be a viable alternative to accelerated hyperfractionated reirradiation. Further follow-up and studies are needed to assess late toxicity and long-term efficacy.