(S002) Outcomes and Prognostic Factors of Stereotactic Body Radiotherapy for Soft Tissue Sarcoma Metastases

Kenneth Merrell, Samuel Francis, Benjamin Mou, Christopher Hallemeier, Kenneth Olivier; Department of Radiation Oncology, Mayo Clinic; University of Utah School of Medicine

Background: Radiobiology studies suggest that soft tissue sarcoma (STS) is a radioresistant tumor. Primary therapy for localized and oligometastatic STS is surgical resection, often in combination with radiation therapy (RT). Stereotactic body RT (SBRT) allows delivery of large conformal doses of radiation, potentially overcoming radioresistance. We reviewed our institutional outcomes of patients treated with SBRT for metastatic STS.

Materials and Methods: A retrospective chart review was performed on 21 patients with 30 metastatic STS lesions who received SBRT at Mayo Clinic between May 2008 and June 2013. Patients were treated with 3D conformal, static-field, or volumetric arc intensity-modulated radiation therapy. The median dose (cGy) and fractionation of lung, bone, liver, and soft tissue was 5,000/5, 2,400/1, 4,250/5, and 4,000/4, respectively. Tumor response was scored using Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1). Toxicity was scored using National Cancer Institute (NCI) Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v4). Local control (LC) and overall survival (OS) were estimated using the Kaplan-Meier method.

Results: Median age was 49 years (range: 30–85 yr). Median follow-up time was 24 months (range: 3–65 yr). Median tumor size was 24 mm (range: 6–145 mm). The most common histologies included pleomorphic sarcoma (n = 5, 24%), leiomyosarcoma (n = 4, 19%), and synovial cell sarcoma (n = 3, 14%), with 95% (n = 20) being high-grade sarcoma. The sites that were treated included bone (n = 11, 36.6%), lung (n = 15, 50%), liver (n = 2, 6.7%), and soft tissue (n = 2, 6.7%). LC at 12, 24, and 48 months was 94.4%, 82.6%, and 82.6%, respectively. Rates of complete response, partial response, and stable disease were 6% (n = 2), 43% (n = 13), and 47% (n = 14), respectively. There were two local failures: one after a partial response and one in a patient with progressive disease on the first follow-up scan. Univariate analysis demonstrated no association with histologic subtype, tumor size, site treated, or RT dose with regard to LC. Median survival was 24 months, with rates of OS at 12, 24, and 48 months of 74.4%, 57.9%, and 12.5%, respectively. Acute and late toxicities were rare, with none higher than grade II. The most frequent toxicities included acute pain flare (n = 2), acute nausea (n = 3), and late cough (n = 2).

Conclusions: SBRT provides excellent local control for metastatic STS. Treatments were well tolerated, with no side effects greater than grade II. Most patients received SBRT after failing multiple lines of chemotherapy, and thus, survival was poor. This study demonstrates that SBRT is an excellent option for local therapy in metastatic STS and warrants further investigation.

Proceedings of the 96th Annual Meeting of the American Radium Society - americanradiumsociety.org