1. Vertebral Fractures After Stereotactic Ablative Radiotherapy of Lung Tumors Todd A. Aguilera MD PhD 1, Nicholas Trakul MD PhD 2, David B. Shultz MD PhD 1, Peter G Maxim PhD 1, Maximilian Diehn MD PhD 1, and Billy W Loo Jr. MD PhD 1 1 Department of Radiation Oncology, Stanford Cancer Institute, Stanford CA 2 Department of Radiation Oncology, USC, Los Angeles CA; Correspondence toddagu1@stanford.edutoddagu1@stanford.edu Poster #57010 Background Not much is known about risk of vertebral fracture after stereotactic radiation of lung tumors Objective Evaluate Stanford SABR experience for vertebral fractures that developed in the coplanar treatment field Results Six of 236 patients (2.5%) developed fractures to vertebral bodies that received considerable dose Patients were predominantly women and had low bone density

2. Table of 6 patients and pertinent clinical factors Sex (Age) StgTxDose/ fraction # Max dose (Gy) Distance to VB (cm) Prior or multi fx Rib Fx Osteo- penia Time to fx (mo) 1W(87)1ACK30/15.57.2priorY13 2W(66)1ACK25/12.510.5multiY24 3W(64)1ACK50/448<128 4M(77)3BVMAT25/1 x 2, 20/1 5.5/ 26<1, 4multi12/21 5W(89)1BVMAT50/435<1Y9 6W(81)1BVMAT54/312.26Y14 CK= Cyberknife; VMAT= Linac based volume modulated arch therapy; VB= vertebral body

3. 13 mth 25 mth 5 Gy 3 Gy 25 Gy 10 Gy 5 Gy Pretreatment 12 months 21 months This patient had 3 lesions treated and developed fractures at 2 levels. T8 T10

4. Vertebral fracture after lung SABR: Summary Stereotactic radiation may increase vertebral fracture risk in high risk patients. – Doses as low as 5 Gy may increase risk – One patient had prior fracture – Two patients developed fractures concurrently at untreated levels Postmenopausal women with low bone density appear to have the greatest risk. At least 2 of 4 patients with clinical follow up had associated pain