Influence of radiation treatment technique on outcome and toxicity in anal cancer.

Objective: Intensity-modulated radiation therapy (IMRT) has largely supplanted three-dimensional conformal radiation (3D-CRT) for definitive anal cancer treatment due to decreased toxicity and potentially improved outcomes. Convincing data demonstrating its advantages, however, remain limited. We compared outcomes and toxicity with concurrent chemotherapy and IMRT vs 3D-CRT for anal cancer.

Methods: We performed a single-institution retrospective review of patients treated with IMRT or 3D-CRT as part of definitive mitomycin-C/5-fluorouricil-based chemoradiation for anal cancer from January 2003 to December 2012.

Results: One hundred sixty-five patients were included, with 61 and 104 receiving IMRT and 3D-CRT, respectively. Overall, 92.7% had squamous cell carcinoma. The mean initial pelvic dose was 48.3 and 44 Gy for IMRT and 3D-CRT, respectively. Complete response, partial response, and disease progression rates were similar (IMRT 83.6, 8.2, 8.2%; 3D-CRT 85.6, 6.7, 7.7%; p  = 0.608, p  = 0.728, p  = 0.729). There was no significant difference in overall survival ( p  = 0.971), event-free survival ( p  = 0.900), or local or distant recurrence rates ( p  = 0.118, p  = 0.373). IMRT caused significantly less acute grade 1-2 incontinence ( p  = 0.035), grade 3-4 pain ( p  = 0.033), and fatigue ( p  = 0.030). IMRT patients had significantly fewer chronic post-treatment toxicities ( p  = 0.008), outperforming 3D-CRT in six of eight toxicities reviewed. Though total treatment length was comparable (43.6 and 44.5 days), IMRT recipients had fewer (27.9 vs 41.3% of patients, p  = 0.89), shorter treatment breaks (mean 2.9 vs 4.1 days, p  = 0.229).

Conclusion: This report represents the largest series directly comparing concurrent chemotherapy with IMRT vs 3D-CRT for definitive treatment of anal cancer. IMRT significantly reduced acute and post-treatment toxicities and allowed for safe and effective pelvic dose escalation.