Tumor Response After Stereotactic Body Radiation Therapy to Nonspine Bone Metastases: An Evaluation of Response Criteria

Abstract

To evaluate the applicability of the Response Evaluation Criteria in Solid Tumors (RECIST 1.1) and University of Texas MD Anderson (MDA) Cancer Center criteria in the setting of stereotactic body radiation therapy (SBRT) to nonspine bone metastases. Patients who were treated with SBRT to nonspine bone metastases were identified by retrospective chart review. An independent musculoskeletal radiologist evaluated response to treatment using computed tomography (CT) scans. Thirty-three patients were treated to 42 nonspine bone metastases. The most common primary cancer cites were renal cell carcinoma (RCC) (33.3%), lung (24.2%), and prostate (18.2%). Bone metastases were either mainly lytic (57.1%), mainly sclerotic (28.6%), or mixed (14.3%). When lytic and sclerotic lesions were evaluated according to RECIST 1.1, local control (LC) was 83%, 85%, 88%, and 80% for those with CT imaging between months 1 to 3, 4 to 6, 7 to 9, and 10 to 12, respectively. When evaluated by the MDA criteria by density, LC within each time period was slightly greater. Overall LC decreased considerably when evaluated by MDA in terms of size. Consensus definitions of response are required as they have implications on clinical trials and disease management. Without consistent response criteria, outcomes from clinical trials cannot be compared and treatment efficacy remains undetermined.