Intensity Modulated Radiation Therapy Versus Conventional Radiation for Anal Cancer in the Veterans Affairs System.

PURPOSE

Compared with conventional radiation therapy, intensity modulated radiation therapy (IMRT) may reduce acute toxicity from anal cancer treatment, potentially leading to improved long-term outcomes. We analyze the effect of IMRT on short- and long-term outcomes among a large sample of US veterans.

METHODS AND MATERIALS

From a national Veterans Affairs database, we identified 779 patients (n = 403 conventional radiation therapy, n = 376 IMRT) with locally advanced anal squamous cell carcinoma diagnosed between 2000 and 2015 and treated with concurrent chemoradiation therapy. Radiation treatment planning and dosimetric constraints were not standardized across patients. We analyzed the effect of IMRT on short-term outcomes (acute toxicity, treatment breaks, and incomplete chemotherapy) and long-term outcomes (survival and ostomy placement) in multivariable logistic regression, Fine-Gray, and frailty models, adjusting for potential confounders.

RESULTS

IMRT was associated with decreased radiation treatment breaks ≥5 days (odds ratio [OR] 0.58; 95% confidence interval [CI] 0.37-0.91; P = .02), increased rates of receiving 2 cycles of mitomycin C chemotherapy (OR 2.04; 95% CI 1.22-3.45; P = .007), increased rates of receiving 2 cycles of any chemotherapy (OR 3.45; 95% CI 1.82-6.25; P < .001), and decreased risk of ostomy related to tumor recurrence or progression (subdistribution hazard ratio 0.60; 95% CI 0.37-0.99; P = .045). IMRT was not associated with a decrease in grade 3 to 4 hematologic toxicity (P = .79), hospitalization for gastrointestinal toxicity (P = .59), or cancer-specific survival (P = 0.18).

CONCLUSIONS

Among a large sample of US veterans with anal cancer, IMRT was associated with higher rates of receiving 2 chemotherapy cycles, decreased radiation treatment breaks, and decreased rates of ostomy placement. IMRT appears to offer substantial benefits over conventional radiation therapy for patients undergoing concurrent chemoradiation therapy for anal cancer.