Stereotactic body radiation therapy for abdominal and pelvic oligometastases: Dosimetric targets for safe and effective local control.

Abstract

To investigate correlates and predictors of outcomes of stereotactic body radiation therapy (SBRT) for patients with abdominal and pelvic oligometastases from different primary tumors. We evaluated outcomes of 38 consecutive patients with 44 unresectable nodal and soft-tissue oligometastases in the abdominal pelvic region who were treated with SBRT between November 2008 and April 2014. Thirty-two patients had solitary lesions and 6 patients had 2 lesions. The median prescription dose was 40 Gy (24-50 Gy) delivered in 4-5 fractions. The median gross tumor volume was 18.7 mL (0.7-194.1 mL). We evaluated tumor response, local control (LC), and overall survival (OS) rates as well as acute and chronic toxicities. At a median follow-up of 19 months (0.9-53.4 months), tumor responses were: complete response 31.8%, partial response 38.6%, standard deviation 20.5%, and progressive disease 9.1%. The overall 1- to 2-year LC and OS rates were 100%/75.1% (95% confidence interval [CI], 54.4%-88.4%) and 95.2% (95% CI, 82.8%-98.8%)/88.9% (95% CI, 68.1%-95.1%), respectively. On univariate analysis, increasing SBRT dose, smaller gross tumor volume, and asymptomatic lesions were associated with improved LC (P = .01, P<.001, and P = .01, respectively). On multivariate analysis, advanced original primary disease stage predicted for worse OS (P = .001). One patient developed a colovesicular fistula at 20.9 months in the setting of local tumor progression with a volume of bowel receiving 20 Gy (V(20Gy)) = 26.9 mL. The overall mean bowel V(20Gy) achieved was 16 ± 22.9 mL. Another patient had grade 2 proctitis at 13 months after SBRT. Pain relief was achieved in 81.8% of patients with symptomatic lesions (N = 11). Our results suggest that SBRT doses 40-50 Gy in 5 fractions (biological effective dose 72-100 Gy10) with bowel V(20Gy) ≤20 mL are efficacious and associated with minimal toxicity for abdominal pelvic nodal and soft-tissue oligometastases. Palliation of symptoms is achievable in most patients with symptomatic lesions. SBRT for oligometastases may be a good alternative to systemic therapy in selected patients.