Author: Vikas Aragam, Edward Castillo, Richard Castillo, Yingxuan Chen, Yevgeniy Vinogradskiy, Lydia J. Wilson ๐จโ๐ฌ
Affiliation: Thomas Jefferson University, Emory University, University of Texas at Austin ๐
Purpose: 4DCT-based ventilation imaging (4DCT-ventilation) has been innovatively applied in radiotherapy treatment planning to minimize doses to functional portions of the lung, known as functional avoidance (FA). FA aims to reduce pulmonary toxicity. Methods are needed to identify which patients will gain a dosimetric benefit from FA. The purpose of this work was to evaluate which factors were associated with significant dosimetric benefit from 4DCT-ventilation FA.
Methods: The study analyzed 67 advanced-stage lung cancer patients enrolled in a 4DCT-ventilation FA phase 2 clinical trial. We evaluated the associations of patient, clinical, and imaging factors with dosimetric benefit from FA, defined as the differences in mean dose (ฮMean) and functional V20Gy (ฮfV20Gy) between the functional and clinical plan. Patient factors included age and performance status; clinical factors included histology and presence of emphysema. 4DCT-ventilation-based imaging factors were calculated to characterize the degree of functional heterogeneity and included the mean ventilation and volume with less than 20% maximum ventilation (V20vent) in lung subregions. We developed a novel method to calculate the mean percent overlap between the target and functional lung regions along external beam paths. We analyzed continuous data via regression and categorical data via the Studentโs t-test or ANOVA (ฮฑ=0.05), as appropriate.
Results: Of the patient and clinical factors analyzed, only presence of emphysema was significantly (p=0.05) associated with ฮfV20Gy. Within lung subregions, high mean ventilation and low V20vent were indicative of larger ฮfV20Gy (p=0.04, 0.01, respectively). Quadratic regression identified a statistically significant peak (p=0.05) in target-functional-lung overlap data, with 75% overlap having the largest ฮfV20Gy.
Conclusion: Our work identified metrics that are associated with a dosimetric benefit from FA including emphysema status, imaging-based parameters, and structure overlap measures. Our work demonstrates that a variety of factors must be examined to determine which patients can maximally benefit from FA radiotherapy.