Intensity-modulated radiotherapy vs. conventional radiotherapy in the treatment of anal squamous cell carcinoma: A propensity score analysis

Background and purpose Definitive chemoradiation is the standard management for anal squamous cell carcinoma (ASCC); more conformal pelvic radiotherapy using intensity modulated radiotherapy (IMRT) minimizes toxicity but may increase locoregional recurrences (LRR). We compared IMRT and conventional radiotherapy (CRT) outcomes in ASCC patients. Material and methods We retrospectively reviewed records of 223 ASCC patients treated at Memorial Sloan-Kettering Cancer Center from 1991 to 2010. Forty-five patients received IMRT and 178 CRT. We determined locoregional recurrence-free survival (LRFS), distant metastases-free survival (DMFS), and overall survival (OS) for each radiation modality. A propensity score analysis was performed using potentially confounding variables. Locoregional and distant patterns of failure for CRT and IMRT were compared. Results Patients treated with IMRT had significantly higher N stage (P <.01), and were less likely to be treated with induction chemotherapy (P =.01). The 2-year LRFS, DMFS, and OS were 87%, 86%, and 93%, respectively, for IMRT; and 82%, 88%, 90%, respectively, for CRT; with no significant difference in outcomes by univariate analysis or in a propensity score analysis adjusted for disparity between the groups. Conclusions This large, single-institution experience of definitive chemoradiation for ASCC using CRT vs. IMRT demonstrates that outcomes are not compromised by more conformal radiotherapy. In the absence of prospective, multi-institutional, randomized trials of IMRT in ASCC, these retrospective data, using methods to minimize bias, can help to establish the role of IMRT in the definitive therapy of ASCC.