Trends in radiation dose and technique for anal canal squamous cell carcinoma.

Abstract

621 Background: Anal canal squamous cell carcinoma (SCC) is managed definitively with chemo and XRT, reserving surgery for salvage. Many different radiation dose schemes have been used, varying from 30 Gy to doses exceeding 60 Gy. RTOG 0529 established IMRT as a standard of care for anal canal SCC, using doses of 50.4-54 Gy. We used the National Cancer Database(NCDB) to examine trends in dose selection and radiation technique over time, as well as any potential effect on outcome. Methods: We queried the NCDB from 2004-2015 for cases of anal canal SCC stage 1-3, treated with definitive doses of XRT to the pelvis with chemo. Dose escalation was defined as > 54 Gy. Univariable and multivariable analyses were performed to identify factors predictive of increased dose and overall survival (OS). Propensity-adjusted Cox proportional hazard ratios for survival were used to account for indication bias. Results: We identified 7,792 patients meeting the eligibility criteria, with 4,269 treated to conventional doses and 3,163 treated to > 54 Gy. Patients that were older, had government or private insurance, were treated with IMRT, or at an academic center in a more recent year were less likely to get dose escalation. Increasing T and N stage were predictive of escalated dose. The use of dose escalation decreased over time, from 50% in 2005 to 30% in 2015. In contrast, IMRT use increased over that time from 2% to 63%. On multivariable analysis increasing age, higher comorbidity score, treatment at an academic center, and increasing stage corresponded to worse OS. Increased income, private insurance, IMRT use, increased distance to facility, and female gender all predicted improved OS. Multivariable analysis with propensity score included confirmed increased age, higher comorbidity score, income, distance, and gender as predictive of OS. In addition, escalated dose was found to have inferior outcome (OR: 1.10 95%CI: 1.01-1.20, p = 0.03). Conclusions: The results of this NCDB analysis show a steady increase in the use of IMRT over time, with a corresponding decrease in dose escalation. In this study, dose escalation was shown to have inferior outcomes, although that result is likely influenced by the increasing age, stage, and comorbidity scores in that group of patients.