Acute gastrointestinal toxicity and bowel bag dose-volume parameters for preoperative radiation therapy for retroperitoneal sarcoma

Purpose: Acute gastrointestinal (GI) toxicity has been studied in GI and gynecological (GYN) cancers, with volume receiving 15 Gy (V15) <830 mL, V25 <650 mL, and V45 <195 mL identified as dose constraints for the peritoneal space (bowel bag [BB]). There are no reported constraints derived from retroperitoneal sarcoma (RPS), and prospective trials for RPS have adopted some of the GI and GYN constraints. This study quantified GI toxicity during preoperative radiation therapy (RT) for RPS, assessed toxicity using published constraints, and evaluated predictors for toxicity.

Methods and materials: From 2003 to 2013, 56 patients with RPS underwent preoperative RT at 2 institutions. Toxicity was scored using Radiation Therapy Oncology Group criteria for upper and lower acute GI toxicity. BB was contoured on planning computed tomography scans per Radiation Therapy Oncology Group atlas guidelines with review by a radiologist. Relationships among toxicity, clinical factors, and BB dose were analyzed.

Results: Three patients (5%) developed grade ≥3 acute GI toxicity: 2 grade 3 toxicities (anorexia and nausea) and 1 grade 5 toxicity (tumor-bowel fistula). Thirty-six patients (64%) had grade 2 toxicity (nausea, 55%; diarrhea, 23%; pain, 20%). Tumor size was the only significant clinical predictor of grade ≥2 acute GI toxicity. Larger mean BB volumes predicted for grade ≥2 toxicity (P = .001). On receiver operating characteristics analysis, V30 was the best discriminator for toxicity (P = .0001). Median BB V15 was 1375 mL; 75% of patients had V15 ≥830 mL. Median V25 was 1083 mL; 68% had V25 ≥650 mL. Median V45 was 575 mL; 82% had V45 ≥195 mL. V25 ≥650 mL was significantly associated with grade ≥2 toxicity (P = .01).

Conclusions: Among patients treated with preoperative RT for RPS, significant acute GI toxicity was very low despite BB dose exceeding established constraints for most cases. Acceptable dose constraints for RPS may be higher than those for GI or GYN cancers. Further assessment of dose-volume constraints for RPS is needed.