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

Abstract

Purpose: To investigate correlates and predictors of outcomes of stereotactic body radiation therapy (SBRT) for patients with abdominal and pelvic oligometastases from different primary tumors.

Methods and materials: 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.

Results: 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).

Conclusions: 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.