Proton Beam Therapy for Abdominopelvic Reirradiation: Outcomes from the Proton Collaborative Group REG001-09 Trial

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International Journal of Radiation Oncology • Biology • Physics


Purpose/Objective(s): Reirradiation (reRT) is associated with increased risk of potentially severe or fatal toxicity. Proton beam therapy (PBT) is uniquely suited for reRT due to superior sparing of normal tissue compared to x-ray therapy. While the dosimetric advantage of PBT is well described, published clinical outcomes of abdominopelvic reRT are lacking. Materials/Methods: Clinical outcomes of patients who received proton reRT to the abdomen or pelvis enrolled on the Proton Collaborative Group REG001-09 trial (NCT01255748) were evaluated. Acute and late toxicities were assessed per the Common Terminology for Adverse Events (CTCAE) version 4.0. Results: Fifty-two patients were evaluated with median age 66 years (range: 34-86 years), most with ECOG performance status 0-1 (77%). The majority had a primary cancer of the colon, rectum, or anal canal (79%) and received reRT most commonly to the pelvis (90%), typically the sacrum/presacral region or rectum/anal canal. Most received only 1 course of prior overlapping RT (92%) and the median interval from prior RT completion to reRT start was 36 months (range: 8-156 months). The median total prior RT dose was 50.4 Gy (range: 18-95 Gy) in a median 28 fractions (range: 3-50 fractions) while the median reRT dose was 50.4 GyE (range: 30-66 GyE) in a median 28 fractions (range: 10-56 fractions). Uniform scanning and pencil beam scanning utilization was similar. Concurrent chemotherapy was received by 61%. With median follow-up of 11 months (range: 3-63), overall survival was 81% and median progression free survival was 8.4 months (range: 0.2-37). Acute or late grade 2 toxicity occurred in 42% and 15%, respectively. Acute or late grade 3+ toxicity occurred in 8% and 2%, respectively. There was no grade 5 toxicity. Overall, toxicity outcomes were not significantly different based on PBT delivery technique. Cumulative initial plus reRT dose was not able to be assessed. Median maximum reRT dose to small bowel, large bowel, and rectum were 23 Gy, 0 Gy, and 47 Gy, respectively. Median mean dose to bladder and genitalia were 5 Gy and 0.1 Gy, respectively. Conclusion: PBT resulted in favorably low dose to organs at risk, which likely contributed to our finding of minimal severe toxicity from reRT although longer follow up is needed to better assess late toxicity and tumor control. Future studies should evaluate whether PBT may facilitate safe dose escalation in patients who receive reRT. Table 1. Acute and late toxicities (%) among patients receiving proton reirradiation.




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