Incorporating 4DCT-Based Elasticity Information As a Regional Physiological Representation for Function Preserving Lung SBRT Treatment Planning

Abstract

Recent advancements in radiotherapy treatment delivery techniques have led to the ability to develop treatment plans that can intelligently spare the most functional normal tissue. Specifically, for lungs, such a treatment plan can greatly improve patient’s quality of life. There is a need for a CT-based lung functional biomarker that can be used for function-preserving treatment planning to reduce lung toxicity after radiation therapy. Lung tissue elasticity has been shown to correlate with overall lung tissue function. The purpose of this study is to investigate the feasibility of avoiding functional lung regions characterized by 4DCT-derived lung tissue elasticity to minimize functional lung dose during stereotactic body radiotherapy (SBRT) treatment planning. 4DCT-based lung elastography was used to retrospectively derive elasticity information for 7 lung cancer patients treated with SBRT. All patients had early and late stage COPD as classified by GOLD 2017. Functional lung tissue was empirically determined to be the lung parenchymal tissue with elastic moduli between 4 and 8 kPa. Clinical and functional avoidance SBRT plans were developed, with the latter having additional constraints in order to preferentially spare the functional lung tissue. Plans were accepted once they met all TG-101 normal tissue constraints. The plan quality was evaluated for both clinical and functional plans by comparing target coverage and max OAR dose. Dose-volume and dose-function metrics were also investigated. Functional-avoidance plans were able to evade functional lung regions while maintaining target coverage and strict normal tissue constraints. While the plan quality was similar between functional and clinical plans, dose volume and dose function metrics illustrated a decrease in dose to functional and total lung volumes. More improvements in the planned dose distributions were seen in patients with mild stage COPD as compared to late stage COPD patients. With lung tissue elasticity providing patient-specific maps of spatial function and physiology, clinically relevant function-preserving SBRT plans were developed for 7 patients. This study has shown that is feasible to develop functional-tissue sparing SBRT plans that preferentially spare the functional lung tissue while maintaining clinically acceptable plan quality. The avoidance of elasticity-defined functional lung tissue in radiotherapy has the potential to lead to less radiation-induced toxicity after radiotherapy treatment, and better patient quality of life.