Room: Stars at Night Ballroom 2-3
Purpose: During functional avoidance treatment planning, there is a risk that functional sparing may negatively impact target coverage and sparing of other critical structures. It is unknown to what level tradeoffs made in prospective vs. retrospective studies will differ. Here, we have evaluated clinical tradeoffs made in an ongoing functional avoidance trial and developed a semi-automated workflow for performing controlled tradeoffs between functional sparing and other goals.
Methods: Twenty-one locally advanced lung cancer patients enrolled on an IRB-approved pilot study of response-driven adaptive radiotherapy underwent perfusion SPECT guided functional avoidance planning and delivery. The sparing region was defined as the volume of lungs-GTV above the mean perfusion intensity and sparing was prioritized below target coverage and standard OAR limits. The clinical plan was retrospectively replanned with increasing levels of functional sparing using a semi-automated method to produce controlled tradeoffs with the competing objectives
Results: The average mean dose reduction in the functional sparing region was 3.6 +/- 4.7% (range 0-20.2%) in 21 clinical plans. After retrospective replanning allowing the maximum tradeoff in target coverage (D95% reduction by 1.5%) and allowing other OARs to approach, but not exceed standard limits, the functional sparing increased to 11.9 +/- 7.5% (range 0-27.6%). The most common required tradeoffs to improve functional sparing were target coverage, and heart maximum and mean dose.
Conclusion: Functional avoidance treatment planning for lung patients on a clinical trial resulted in a reduction in mean dose to the high perfusion regions of 3.6 +/- 4.7%. Increased reductions of 11.9 +/-7.5% were possible when allowing PTV D95% reductions of up to 1.5% and increases in heart mean and maximum doses. Allowable tradeoffs in coverage and heart dose should be considered in future studies to automate and standardize functional avoidance planning.
Funding Support, Disclosures, and Conflict of Interest: Supported by NIH P01-CA059872; M. Matuszak Disclosure: Research Grant, Consulting with Varian Medical Systems, outside of the current work.