Prospective evaluation of small bowel dose and acute gastrointestinal toxicity during pelvic radiotherapy for gynaecologic malignancies.

Introduction: Acute gastrointestinal (GI) toxicity is common in patients receiving pelvic radiotherapy (RT) and the small bowel (SB) is a dose-limiting organ at risk. There is a quandary in the dose constraints for SB while using intensity-modulated radiotherapy (IMRT) for gynecological malignancies.

Objectives: To investigate the correlation between the radiation dose received by SB and the incidence of acute lower GI toxicities, and to identify dose parameters that may reduce toxicity risk.

Materials and methods: Fifty-eight patients diagnosed with gynecological cancers and received RT with IMRT technique were analyzed in this prospective observational study. Oral contrast was administered during the simulation scan as per institution protocol. The individual SB loops were delineated as per Radiation Therapy Oncology Group (RTOG) consensus guidelines. The volume of SB (cc) receiving 10, 15, 20, 30, and 40 Gy were analyzed. Grades of acute GI toxicities were assessed weekly according to RTOG scoring criteria. The odds of developing GI toxicities were analyzed using a logistic regression test.

Results: Out of the study population, 26 patients (45%) were diagnosed with carcinoma of the cervix, and 32 patients (55%) were diagnosed with carcinoma of the endometrium. 33 patients (57%) also received concurrent chemotherapy. Overall, Grade I, II, and III GI toxicities were observed in 32%, 62%, and 5% of patients, respectively. None of the patients developed GI toxicity during weeks 1 and 2 of RT. A significantly higher incidence of ≥grade 2 GI toxicity was observed with a mean SB-V30 Gy >210 cc (P = 0.001) and SB-V40 Gy >103 cc (P = 0.001). Patients with SB-V30 Gy ≥210 cc had 2.2 times higher odds of developing ≥ grade 2 enteritis compared to those with SB-V30 Gy <210 cc (OR = 2.2; 95% CI, 1.5-6.3; P = 0.003). Likewise, the odds of developing ≥grade 2 enteritis were 2.9 times higher in patients with SB-V40 Gy ≥103 cc compared to those with SB-V40 Gy <103 cc (OR = 2.90; 95% CI, 2.1-5.1; P = 0.002).

Conclusions: Higher radiation doses to individual SB loops lead to a decrease in cellular reserves of intestinal mucosa resulting in ≥grade 2 acute GI toxicity in patients receiving IMRT for gynecological malignancies.