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Dose Rearrangement in High Dose Locally Advanced Lung Patients Based On Perfusion Imaging
C Matrosic*, D Jarema , F Kong , D McShan , M Stenmark , D Owen , R Ten Haken , M Matuszak , University of Michigan, Ann Arbor, MI
Presentations
SU-F-BRF-11 Sunday 4:00PM - 6:00PM Room: Ballroom FPurpose: The use of mean lung dose (MLD) limits allows individualization of lung patient tumor doses at safe levels. However, MLD does not account for local lung function differences between patients, leading to toxicity variability at the same MLD. We investigated dose rearrangement to minimize dose to functional lung, as measured by perfusion SPECT, while maintaining target coverage and conventional MLD limits.
Methods: Retrospective plans were optimized for 15 locally advanced NSCLC patients enrolled in a prospective imaging trial. A priority-based optimization system was used. The baseline priorities were (1) meet OAR dose constraints, (2) maximize target gEUD, and (3) minimize physical MLD. As a final step, normal tissue doses were minimized. To determine the benefit of rearranging dose using perfusion SPECT, plans were reoptimized to minimize functional lung gEUD as the 4th priority.
Results: When only minimizing physical MLD, the functional lung gEUD was 10.8+/-5.0 Gy (4.3–19.8 Gy). Only 3/15 cases showed a decrease in functional lung gEUD of >4% when rearranging dose to minimize functional gEUD in the cost function (10.5+/-5.0 Gy range 4.3-19.7). Although OAR constraints were respected, the dose rearrangement resulted in >10% increases in gEUD to an OAR in 4/15 cases. Only slight reductions in functional lung gEUD were noted when omitting the minimization of physical MLD, suggesting that constraining the target gEUD minimizes the potential to redistribute dose.
Conclusion: Priority-driven optimization permits the generation of plans that respect traditional OAR limits and target coverage, but with the ability to rearrange dose based on functional imaging. The latter appears to be limited due to the decreased solution space when constraining target coverage. Since dose rearrangement may increase dose to other OARs, it is also worthwhile to investigate global biomarkers of lung toxicity to further individualize treatment in this population.
Funding Support, Disclosures, and Conflict of Interest: Partially supported by R01-CA142840 and P01-CA59827
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