Correlation of Three Different Approaches of Small Bowel Delineation and Acute Lower Gastrointestinal Toxicity in Adjuvant Pelvic Intensity-Modulated Radiation Therapy for Endometrial Cancer

We investigate in this study the approach of small bowel delineation that would best correlate with acute lower GI toxicity during adjuvant intensity-modulated radiation therapy (IMRT) for endometrial cancer in this study. Thirty-two endometrial cancer patients (FIGO IB-IVA) were treated with postoperative pelvic IMRT to 48.2 ± 3.1 Gy. The small bowel was delineated as separate loops, limited bowel space (BS), or an intestinal cavity (IC). The volume of the small bowel (VSB) in absolute volume or as the percentage of the total volume at various dose levels was obtained from the dose volume histograms (DVHs). Each patient's acute lower gastro-intestinal (GI) toxicity was assessed prospectively during the course of IMRT. After a median follow up of 19.6 months, the median survival, loco-regional control, progression-free-survival (PFS), and distant metastasis-free survival (DMFS) were 40.9 months, 81.2%, 62.5%, and 68.8%, respectively. Acute lower GI toxicity observed were of grade 0, 1, and 2 only: 34.4%, 31.2%, and 34.4%, respectively. The difference in %VSB with the small bowel delineated as IC at 45 Gy (%VSB_IC45) between grade 2 and grade 0 acute lower GI toxicity reached statistical significance upon linear regression analysis (p = 0.0347). Thus, the proportion of small bowel contoured as IC in the high dose region can potentially be an important predictor for acute lower GI toxicity during and after postoperative pelvic IMRT.