VMAT-Based Planning Allows Sparing of a Spatial Dose Pattern Associated with Radiation Pneumonitis in Patients Treated with Radiotherapy for a Locally Advanced Lung Cancer

Abstract

<h3>Purpose/Objective(s)</h3> In patients treated with radiotherapy for a locally advanced lung cancer, respect of dose constraints to organs at risks (OARs) insufficiently protects patients from acute pulmonary toxicity (APT), such toxicities being associated with a potential impact on treatment's completion and the patients' quality of life. Dosimetric planning doesn't take into account regional lung functionality. An APT prediction model combining usual dosimetry features with the mean dose (DMean_Pmap) received by a voxel-based volume (Pmap) localized in the posterior right lung has been previously developed. A DMean_Pmap ≥ 30.3Gy was associated with a higher risk of APT. In the present study, the authors aim to demonstrate the possibility of decreasing the DMean_Pmap via a volumetric arc therapy (VMAT)-based adapted planning and evaluate the impact on the risk of APT. <h3>Materials/Methods</h3> Among the 207 patients included in the initial study, only patients who presented with an APT ≥ grade 2 and with a probability of APT (Prob_APT) ≥ 8% based on the prediction model were included. Dosimetry planning was optimized with a new constraint (DMean_Pmap < 30.3Gy) added to the usual constraints. Initial and optimized treatment plans were compared using the T-test for independent variables and the non-parametric Mann-Whitney U test otherwise, regarding both doses to OARs and PTV (Planning Target Volume) coverage. Conformity and heterogeneity indexes were also compared. Risk of APT was recalculated using the new dosimetric features and the APT prediction model. <h3>Results</h3> Dosimetric optimization was considered successful for 27 out of the 44 included patients (61.4%), meaning the dosimetric constraint on the Pmap region was achieved without compromising the PTV coverage (p = 0.61). Optimization significantly decreased median DMean_Pmap from 28.8Gy (IC95% 24.2-33.4) to 22.1Gy (IC95% 18.3-26.0). When recomputing the risk of APT using the new dosimetric features, optimization significantly reduced the risk of APT (p < 0.0001) by reclassifying 43.2% (19/44) of the patients. <h3>Conclusion</h3> Our approach appears as both easily implementable on a daily basis and efficient at reducing the risk of APT. Regional radiosensitivity should be considered in usual lung dose constraints, opening the possibility of an easily implementable adaptive dosimetry planning.