Effects of respiratory and cardiac motion on estimating radiation dose to the left ventricle during radiotherapy for lung cancer

Purpose Establish a workflow to evaluate radiotherapy (RT) dose variation induced by respiratory and cardiac motion on the left ventricle (LV) and left ventricular myocardium (LVM). Methods Eight lung cancer patients underwent 4D‐CT, expiratory T1‐volumetric‐interpolated‐breath‐hold‐examination (VIBE), and cine MRI scans in expiration. Treatment plans were designed on the average intensity projection (AIP) datasets from 4D‐CTs. RT dose from AIP was transferred onto 4D‐CT respiratory phases. About 50% 4D‐CT dose was mapped onto T1‐VIBE (following registration) and from there onto average cine MRI datasets. Dose from average cine MRI was transferred onto all cardiac phases. Cumulative cardiac dose was estimated by transferring dose from each cardiac phase onto a reference cine phase following deformable image registration. The LV was contoured on each 4D‐CT breathing phase and was called clinical LV (cLV); this structure is blurred by cardiac motion. Additionally, LV, LVM, and an American Heart Association (AHA) model were contoured on all cardiac phases. Relative maximum/mean doses for contoured regions were calculated with respect to each patient's maximum/mean AIP dose. Results During respiration, relative maximum and mean doses on the cLV ranged from −4.5% to 5.6% and −14.2% to 16.5%, respectively, with significant differences in relative mean doses between inspiration and expiration (P 0.14). Significant differences were observed in AHA segmental doses depending on tumour proximity compared to global LV doses on expiratory 4D‐CT (P