Trends in Radiation Dose and Technique For Anal Canal Squamous Cell Carcinoma

Anal canal squamous cell carcinoma (SCC) is managed definitively with chemoradiation, reserving surgery for salvage. The dosage of radiation has varied from 30 Gy to in excess of 60 Gy. RTOG 0529 established intensity modulated radiation therapy (IMRT) as standard of care for anal canal SCC with doses of 50.4 to 54 Gy. We sought to use the National Cancer Database to examine trends in dose selection and radiation technique over time.

We queried the National Cancer Database from 2004 to 2015 for cases of anal cancer stage groups 1 to 3, treated with definitive doses of radiation with chemotherapy. Dose escalation was defined as >54 Gy. Univariable and multivariable analyses were performed to identify factors predictive of dose, IMRT, and overall survival. Propensity-adjusted Cox proportional hazard ratios for survival were used to account for indication bias.

We identified 7792 patients meeting the eligibility criteria, with 4269 treated to doses of 45 to 54 Gy and 3163 treated to doses >54 Gy. Patients who were older, had government or private insurance, IMRT treatment, treatment at an academic center, or more recent years were less likely to get dose escalation. The use of dose escalation decreased over time, from 50% in 2005 to 30% in 2015. IMRT use increased over time from 2% to 63%. On multivariable analysis with propensity score included it was found that increased age, higher comorbidity score, lower income, shorter distance to facility, and male sex were predictive of decreased overall survival. In addition, escalated dose was associated with a lower survival (hazard ratio: 1.10, 95% confidence interval: 1.01-1.20, P=0.03).

The results of this analysis show a steady increase in the use of IMRT, with corresponding decrease in dose escalation. These findings correlate with the results of RTOG 0529 establishing IMRT as standard of care for anal SCC, using doses of 50.4 to 54 Gy.