4D Treatment Dose Reconstruction for Scanned Ion Beam Therapy

Purpose/Objective(s): To report the initial outcomes and toxicity of SABR for oligometastases. Materials/Methods: Fifty-three patients with a minimum potential followup of 1 year were treated with SABR directed to a total of 99 metastatic sites (lung n Z 65, liver n Z 14, bone n Z 10, lymph node n Z 9, soft tissue n Z 1). The most commonly used SABR regimen was 50 Gy in 5 consecutive daily fractions using conformal arc technique with daily image guidance using CBCT. The most common primary sites were colorectal cancer (CRC; 28%), non-small cell lung carcinoma (NSCLC; 19%), soft tissue sarcoma (STS; 15%), and renal cell carcinoma (RCC; 8%). Median time to metastatic progression from initial diagnosis was 1.2 years (range, 0-13.1 years). The majority of patients were treated for solitary metastases (59%). Prior to SABR, 45% were treated for metastatic disease with surgery, chemotherapy or both. Fourteen patients received additional SABR for limited progression. Results: Median follow-up was 1.3 years (1.4 years for living patients). Local control (LC), distant-progression free survival (DPFS), causespecific survival (CSS), and overall survival (OS) at 1 and 2 years were 92%, 56%, 87%, 85%, and 74%, 40%, 70%, 69%, respectively, after the initial course of SABR. After a second course of SABR for limited progression the 1-year DPFS was only 22%. On univariate analysis there was no significant predictor for LC, although liver metastases and CRC primaries showed a trend toward decreased LC. Two-year DFPS, CSS, and OS were worse for patients with multiple metastatic sites, multiple organ involvement, increased cumulative GTV at initial SABR course, and when all measurable disease was not treated with SABR. Grade 3+ toxicity was observed in only 3 patients. Conclusions: In selected patients with limited metastatic disease, SABR resulted in durable disease control in a significant percentage of patients with minimal toxicity. Author Disclosure: R. Dagan: None. A.R. Yeung: None. R.A. Zlotecki: None. C.G. Morris: None. P. Okunieff: None.