Chest wall dose assessment in stereotactic ablative radiotherapy delivered with volumetric modulated arc therapy for peripheral lung tumors

BackgroundNo consensus on how to best predict for chest wall injury following SABR exists. We report our experience in chest wall dose assessment when treating peri-pleural lung lesions with stereotactic ablative radiotherapy (SABR) delivered with volumetric modulated arc therapy (VMAT).Methods40 patients with peri-pleural peripheral lung tumors underwent SABR between July, 2012 and February, 2015. Chest wall toxicity, dose distribution, and the influence of chest wall delineation method were investigated.ResultsAfter a median follow up of 16 months, no rib fracture or skin toxicity was observed. 4 patients (10%) reported persistent chest wall pain (grade 1-2). High dose rate's association with chest wall pain trended toward statistical significance (p=0.06). PTV exclusion and reducing chest wall expansion to 1 cm led to significant dose reduction in the chest wall dose volume parameters (p<0.05). Only three local failures were observed among 44 lesions treated.ConclusionsThe risk of chest wall pain following SABR delivered with VMAT is low. High dose rate, which is 1400 MU/min with flattening filter free (FFF) beams vs. 500-600 MU/min with non-flattening filter free (non-FFF) beams, may contribute to it. Chest wall dose volume parameters may vary with PTV exclusion; while chest wall expansion of 1 cm may fail to account for some high dose regions in the chest wall.