IMG-55. Characteristics of large metastases to the brain treated with stereotactic radiosurgery at a single institution: a survey of 1355 lesions and their sites of origin

In recent years, stereotactic radiosurgery (SRS) has had a growing role in the non-surgical management of brain metastases. New evidence in SRS treatment strategies have expanded indications for treatment beyond the traditional limitations regarding size and number. Despite these advances, data regarding the characteristics of large metastatic lesions (>2 cm) is scarce. In this article, we sought to characterize the distribution of clinical demographics and sites of origin in patients with large metastatic lesions (>2 cm) treated with SRS. A retrospective review was conducted of a large imaging database of patients undergoing SRS at a single institution (University of Minnesota Medical Center) between August 2005 to December 2022. Included were metastases that underwent single fraction or fractionated SRS. T1 weighted post-contrast images and lesion segmentations were used to calculate tumor volumetrics and imaging characteristics. Metastatic lesions measuring at least 2 cm in one or more axes were included. 1355/8453 (16.0%) metastatic lesions were >2 cm in at least one dimension. 638 unique patients (278 males, 360 females) were identified. The most common primary sites of origin were: non-small cell lung (206 patients, 361 lesions), breast (130 patients, 314 lesions), melanoma (100 patients, 320 lesions), renal (61 patients, 109 lesions), small cell lung cancer (44 patients, 85 lesions). The largest average lesion volume was from metastases from sarcoma lesions (24 patients, 43 lesions, average volume: 9340 mm^3). Large metastases (>2cm) represent a sizable minority of lesions treated with SRS. Non-small cell lung, breast, melanoma, renal, and small cell lung cancer were the top five most common primary sites of origin. Metastatic bladder and sarcomas had the largest average lesion volume.