Anal cancer outcomes in patients treated with intensity modulated versus 3-dimensional chemoradiotherapy.

Abstract

662 Background: Combined chemoradiotherapy (CRT) has been successful in both tumor eradication and colostomy prevention in patients with squamous-cell carcinoma of the anal canal. Unfortunately, CRT can be toxic with high rates of acute gastrointestinal and skin toxicity. This can necessitate treatment interruptions, prolonging therapy, possibly leading to loss of local control. In RTOG 0529, intensity modulated radiation therapy (IMRT) decreased the rate of treatment interruption compared to historical controls. We aim to compare toxicity and outcomes in patients treated with CRT based on radiation technique. Methods: We retrospectively reviewed 107 consecutive patients, 39 HIV+, 68 HIV-, who underwent definitive CRT for anal cancer at a single institution between 2004 and 2013. Overall survival (OS), colostomy-free survival (CFS), local recurrence-free survival (LRFS) and distant metastasis-free survival (DMFS) were analyzed. Chi-square test was used to compare frequencies and t-test was used to compare means. Kaplan-Meier survival was calculated and differences were evaluated by Log-rank statistic. Results: Median follow-up was 15 months. Radiation technique was IMRT in 60% of patients with the remainder treated with 3-dimensional conformal radiation therapy (3D). Dose to the draining lymph nodes was higher in patients treated with IMRT (mean dose 40 Gy vs. 32 Gy, p < 0.001). Fewer patients had a greater than 10 day treatment break in IMRT cohort than the 3D cohort (21% vs. 43%, p = 0.028). Three-year OS (91% vs. 47%, p < 0.001) and DMFS (88% vs 64%, p= 0.033) were improved in patients treated with IMRT. There was no significant difference in acute GI or skin toxicity. There was no difference in stage, number of chemotherapy cycles and dose reductions, growth factor support, transfusion necessity, hospital admission, LRFS, sphincter function preservation, or CFS. Conclusions: In this cohort, patients treated with IMRT had better OS and DMFS than patients treated with 3D. Higher radiation doses to the draining lymph nodes and fewer prolonged treatment breaks may contribute to improved outcomes in patients treated with IMRT. Further studies are necessary to establish the etiology of this difference in outcomes.