A pilot feasibility study of definitive concurrent chemoradiation with pencil beam scanning proton beam in combination with 5-fluorouracil and mitomycin-c for carcinoma of the anal canal.

Abstract

733 Background: Definitive chemoradiation (CRT) with concurrent 5-fluorouracil (5-FU)/mitomycin C (MMC) for anal cancer yields high rates of long term survival. However, CRT has significant acute and long term toxicity. Pencil beam scanning proton beam (PBS-PT) may potentially reduce this toxicity. This is a pilot study evaluating the feasibility of definitive concurrent CRT with PBS-PT with 5-FU/MMC for anal cancer. Methods: Pts were enrolled on an NCI sponsored, prospective, multi-institutional, pilot study (NCT 01858025). Key eligibility were ECOG 0-2, age 18+, invasive SCC of the anal canal, clinically staged T1-4, N0-3. Pts were treated per RTOG 0529 RT schema; for T1-2, N0: 50.4 Gy to primary CTV, 42 Gy to elective LNs; for T3+ or N+: 54 Gy to primary CTV, 50.4-54 Gy to involved LN, and 45 Gy to elective LNs. Pts received 5-FU/MMC on day 1 and 29. The primary objective of this study was to determine feasibility of PBS-PT with 5-FU/MMC, determined if grade 3+ dermatologic toxicity is < 48% (grade 3+ dermatologic toxicity from RTOG 98-11). The secondary endpoint was rates of overall grade 3+ toxicities, clinical complete response (cCR) rate and patterns of local regional tumor recurrence. Results: Between February 2014 to April 2017, we enrolled 25 patients into our study, all of whom were analyzed. 23 pts (92%) completed treatment per protocol, 2 pts died on treatment due to underlying comorbidities. Median time to completion of treatment was 42 days (range 38-49). The Grade 3+ radiation dermatitis was 24% (Table 1). With a median follow-up of 17.6 months (range 7.7-42.0) among the 21 patients still alive, the 1 year local control, progression-free survival, and overall survival are 100%, 83% and 87%, respectively. Conclusions: In our prospective, pilot study of PBS-PT with concurrent 5-FU/MMC, PBS-PT was found to be feasible. While felt to be unrelated to the study, the two Grade 5 adverse events on this small study highlights potentially treatment related risks of this effective yet toxic regimen. Clinical trial information: NCT01858025. [Table: see text]