Temporal Change in Tumor Volume Following Stereotactic Radiosurgery to a Single Brain Metastasis

Stereotactic radiosurgery (SRS) can be used to achieve local control of metastatic brain lesions. However, the temporal response of these lesions to SRS is incompletely understood and quantified. We aimed to examine the temporal response to SRS of single brain metastases from 4 different primary cancers.

A retrospective chart review was performed of patients who underwent SRS at our institution from 2009 to 2012. Clinical, treatment, and volumetric data were collected. All patients were treated according to Radiation Therapy Oncology Group 90-05 schema.

This study included 204 patients (116 men and 88 women) with a median age of 61 years (range, 27-86 years). Of patients, 20 (10%) had breast cancer, 79 (39%) had non-small cell lung cancer, 69 (34%) had melanoma, and 36 (17%) had renal cell carcinoma. Initial overall median tumor volume was 0.8 cm³ (range, 0.02-16.9 cm³). Median tumor volume was 0.5 cm³ (range, 0.02-20.4 cm³) at 1 month after SRS, 0.3 cm³ (range, 0.02-10.8 cm³) at 3 months after SRS, and 0.4 cm³ (range, 0.02-18.6 cm³) at 6 months after SRS. Based on the joint model constructed from our results, we demonstrate a median 16% (95% confidence interval, 11%-20%) reduction in tumor volume every 30 days.

The results of this study demonstrate a consistent reduction in tumor volume following SRS over a 6-month period. Responses were modest over the first 30 days but accelerated at 3 months and varied by tumor type.