Integration of Functional Imaging to Guide Adaptive Treatment Planning for Lung SBRT
Abstract
Purpose
Hyperpolarized Xenon imaging is a recent FDA-approved MRI technique that can measure physiological changes in ventilation, membrane uptake, and red blood cell transfer of gas throughout the lung. The scope of this work is to demonstrate the feasibility of integrating this functional imaging technique with MRI-guided adaptive radiotherapy (MRIgART) to avoid highly functioning lung during treatment. For the purposes of this work, lung function was discretized into 5-functional tiers using the Xenon imaging, and a planning technique was developed called FA5T (Functional avoidance, 5 tiers) to minimize dose to the highest functioning lung.
Methods
Three lung cancer patients receiving SBRT were retrospectively planned using FA5T in Monaco for the Elekta Unity MRLinac. Optimization objectives were assigned to the discretized functional levels in the FA5T scheme from published predictive dosimetric markers of radiation-induced pneumonitis that used ventilation or perfusion-based functional imaging metrics. Functional loss following treatment was estimated from the dose distributions from a standard, conformity-based SBRT treatment plan and compared to the FA5T optimization schema.
Results
The incorporation of functional imaging within the treatment planning optimization framework provides a method to preserve physiological function that would have otherwise been overlooked with standard treatment planning goals. The volume of high-functioning lung receiving at least 10 Gy was reduced between 40-54% using the proposed FA5T schema while still satisfying the dosimetric goals to their conventional SBRT counterparts. As a result of these dosimetric reductions, it was estimated that FA5T could preserve 1.6 to 2.6 times as much high-functioning lung volume compared to a standard SBRT treatment plan.
Conclusion
A clinical planning framework is presented to enable functionally adaptive MR-guided lung SBRT. The ability to integrate these markers into adaptive workflows represents a major opportunity to improve the efficacy of radiotherapy by adapting treatments based on functional as well as anatomical information.