Impact of lung density on the lung dose estimation for radiotherapy of breast cancer

Background and purpose: To investigate the impact of the clinical implementation of a deterministic particle transport method on the lung dose evaluation for radiotherapy of breast cancer focusing on dosimetric effects of the lung density. Material and methods: Fourteen patients with left sided breast cancer having both deep inspiration breath hold (DIBH) and free breathing CT scans were studied. Lung density variations for 157 patients treated under DIBH were quantified and the cases with the lowest lung densities for breast and for loco regional treatment added to the study. Dose calculations were performed with the class-b type algorithm AAA and the deterministic algorithm Acuros XB. Monte Carlo method was utilized as reference. Differences in the dose distributions were evaluated by comparing DVH parameters. Results: Lung density variations between 0.08 and 0.3 g/cm(3) and between 0.02 and 0.25 g/cm(3) were found for loco-regional and tangential breast treatments under DIBH, respectively. Lung DVH parameters for patients with medium and high lung density obtained by the different algorithms agreed within 3%. Larger differences were observed for low lung density cases where the correction based algorithm under-estimated V-10Gy and overestimated V-40Gy by up to 5%. The least affected parameter, V-20Gy, deviated by less than 2% for all cases and densities. Conclusions: Dosimetric constrains for lung based on V-20Gy required minimum changes due to implementation of the new algorithm regardless of breathing technique or type of treatment. Evaluation criteria utilizing V-10Gy or V-40Gy needed reconsideration, especially for treatments under DIBH involving low lung density. (C) 2017 The Authors. Published by Elsevier Ireland Ltd on behalf of European Society of Radiotherapy & Oncology. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).