Clinical outcomes and dosimetric considerations using stereotactic body radiotherapy for abdominopelvic tumors

PURPOSE/OBJECTIVES: To present clinical outcomes, early toxicity, and dosimetric constraints for patients undergoing stereotactic body radiation therapy (SBRT) for abdominal or pelvic tumors. MATERIALS AND METHODS: From May 2008 to February 2010, 47 patients with 50 lesions in proximity to hollow viscous organs at risk, including stomach, duodenum, small bowel, and colon, underwent SBRT at Mayo Clinic. Treated sites included liver (21), lymph node (14), adrenal gland (6), intramuscular (4), pancreas (3), and spleen (2). Treatment planning was performed with full body immobilization and 4-dimensional computed tomography (CT)-based planning with daily cone-beam CT or stereoscopic kV imaging for pretreatment image guidance. SBRT was delivered in 1 to 5 consecutive daily fractions in a single week. The most commonly prescribed dose was 50 Gy in 5 fractions (median 45 Gy, range: 20 to 60 Gy). Toxicities were scored by CTCAE v.3. Local failure was defined as per the Response Evaluation Criteria in Solid Tumors. RESULTS: Median follow-up was 12 months (range: 2 to 28 mo). Tumor responses of the 48 target lesions evaluable by Response Evaluation Criteria in Solid Tumor were complete response in 18 lesions (36%), partial response in 12 lesions (24%), stable disease in 12 lesions (24%), and progressive disease in 6 lesions (12%). Kaplan-Meier estimates of local control, overall survival, and freedom from metastasis at 6 and 12 months were 98%, 90%, and 63%, and 87%, 62%, 37%, respectively. Treatment was well-tolerated acutely without reported grade ≥3 toxicity. Five grade 3 late toxicities were reported, and 1 patient died of complications from duodenal perforation 11 months after SBRT. No dose correlation with toxicity could be established. CONCLUSIONS: SBRT is a practical treatment option for patients with abdominopelvic tumors. Relapse typically occurs outside treatment fields, and most patients achieve a favorable response. The dose constraints used in this cohort of patients was associated with acceptable early treatment-related toxicity.