| dc.description.abstract | Purpose: Currently, in radiation treatment planning for locally advanced non-small cell lung cancer (LA-NSCLC), the heart is typically contoured as a whole organ at risk. Both photon and proton beam techniques are used for this purpose in research. The dose delivered to the heart has emerged as a significant consideration in predicting patients’ survival outcomes. Therefore, the purpose of this thesis was to investigate the feasibility of delineating specific substructures within the heart, assess the robustness of treatment plans for these structures, and analyze the variation in dose distribution among them. This analysis involved comparing the dose received by substructures with that of the whole heart, as well as comparing the dose distributions between photon beam and proton beam planning. Methods: Contouring was done on fifteen patients, nine with both rapid contrast computer tomography (CT) scans in planning state of treatment, and for all fifteen average intensity projection four-dimensional (AVE-4D) CT scans in both planning state of treatment and week 1. In-house and new Python scripts were used to quantify the geometric differences of the structures. Existing in-house intensity-modulated radiation therapy (IMRT) and intensity-modulated proton therapy (IMPT) plans were utilized, with prescribed doses of 60-66 Gy. The substructures and the dose metrics utilized for analysis were based on existing literature that links radiation dose to radiation-induced heart disease or survival outcomes. Results: Nineteen substructures of the heart and the cardiovascular system were found from literature and contoured. The volume of the substructures was found to have significant change for ten of the structures in the planning state of treatment between the different CT scans, while only one of the structures had significant change between the AVE-4D-CT scans. The overlap of the structures were generally higher for large structures (> 10 cc), with some exceptions. Dmean, D45%, V15Gy and V30Gy were used as dose metrics for analysis. Five of the substructures, mostly situated at the base of the heart, was found to not be robust over time in IMRT planning, with significant change between planned dose and actual dose. Only one, the superior vena cava, was found to not be robust for IMPT planning. All of the substructures were found to get significantly less dose with IMPT than IMRT. Many of the substructures had significant different dose than to the heart with both IMRT and IMPT. Conclusion: IMPT demonstrates the potential to significantly reduce the radiation dose to all substructures considered in this project, thereby potentially improving the overall survival of LA-NSCLC patients undergoing radiation treatment. The base of the heart is of particular interest, as certain parts were found to be less robust in IMRT planning and some parts received higher doses compared to the heart as a whole. Additionally, larger structures show promise for feasible and beneficial contouring using AVE-4D-CT. Further studies, including a larger patient cohort, focusing on the base of the heart, especially the left atrium, and the great vessels superior to the heart, would be valuable. | |
