Dosimetric Parameters Predictive of Acute Gastrointestinal Toxicity in Patients with Anal Carcinoma Treated with Concurrent Chemotherapy and Intensity-Modulated Radiation Therapy

Abstract

Objective: To determine the dosimetric parameters predictive of acute gastrointestinal (GI) toxicity in anal cancer patients treated with intensity-modulated radiotherapy (IMRT) and concurrent chemotherapy. Methods: Fifty-eight anal cancer patients were treated with concurrent chemotherapy and IMRT. The bowel was delineated on the planning CT and included the intestinal cavity. Regression models with multiple independent predictors were used to test associations of clinical factors and dosimetric parameters with clinically significant GI toxicity (grade ≥3). Significant dosimetric factors were fitted to a normal tissue complication probability curve using a logit function and subsequently analyzed at multiple bowel volumes to determine the threshold for clinically significant GI toxicity. Results: Two patients (3.4%) experienced no acute GI toxicity, whereas 20 (34.5%) experienced grade 1 toxicity, 20 (34.5%) experienced grade 2, 16 (27.6%) experienced grade 3 and none experienced grade 4. Analysis showed that the volumes of bowel receiving 30 Gy (V30) and 40 Gy (V40) both correlated with clinically significant acute GI toxicity. In patients whose V30 was >310 cm³, the rate of clinically significant acute GI toxicity was 38.9%, compared to 9.1% if V30 was ≤310 cm³ (p = 0.016). If V40 was ≤70 cm³, the rate of acute grade ≥3 toxicity was 6.3%, versus 35.7% if V40 was >70 cm³ (p = 0.045). Conclusion: This analysis demonstrates that the bowel dosimetric parameters are associated with clinically significant acute GI toxicity when IMRT is used in the management of anal cancer patients.