Comparison of outcomes of intensity-modulated radiotherapy and 3-D conformal radiotherapy for anal squamous cell carcinoma using a propensity score analysis.

Abstract

3555 Background: IMRT has been shown to reduce acute dermatologic and gastrointestinal toxicities when compared to 3DCRT in the treatment of ASCC; however, there has been concern that focal IMRT fields may lead to elevated rates of locoregional recurrence. We examined the efficacy of definitive chemoradiation (CRT) using intensity modulated radiotherapy (IMRT) as compared with 3D conformal radiotherapy (3DCRT) for patients (pts) with anal squamous cell carcinoma (ASCC). Methods: We retrospectively assessed 221 pts with ASCC treated with definitive CRT at MSKCC from 05/1991 to 01/2010. Of these pts, 44 received IMRT between 07/2005-01/2010, and 177 received 3DCRT between 05/1991-04/2007. Local recurrence-free survival (LRFS), distant metastasis-free survival (DMFS), colostomy-free survival (CFS), and overall survival (OS) were estimated by Kaplan-Meier methods and compared using a log-rank test. To account for biases arising from nonrandom allocation of pts to treatment groups, a propensity score analysis was performed using the potential confounding variables of age, gender, chemotherapy regimens, histology, T-stage and N-stage, to balance the covariates and allow for a more accurate estimate of the treatment effects. Results: Median follow-up time for survivors was 24.5 and 74.1 months for the IMRT and 3DCRT groups, respectively. The patients in the IMRT group received a median dose of 5,600cGy (mean 5,260cGy) to the primary tumor, compared to 4,500cGy (mean 4,739cGy) in the 3DCRT group. The IMRT and 3DCRT groups had similar durations of RT treatment with means of 41.5 and 41.4 days, respectively. The IMRT group had significantly (p<0.01) higher N-stage. The 2-year LRFS, DMFS, CFS, and OS was 88%, 83%, 96%, and 92%, respectively for the IMRT group and 81%, 88%, 91%, and 89%, respectively for the 3DCRT group with no significant difference between the groups. Longer treatment duration was associated with worse tumor control with every 10 days of delay resulting in a 31% increase in LR rate. Conclusions: In this large cohort of pts with ASCC treated with definitive CRT, use of IMRT, when compared to 3DCRT, does not appear to adversely affect outcomes.