Room: Karl Dean Ballroom C
Purpose: The effect of functional lung avoidance planning on radiation dose-dependent changes in regional lung perfusion is unknown. We characterized patient-specific dose-response on longitudinal perfusion SPECT/CT in two cohorts of lung cancer patients treated with and without functional lung avoidance techniques.
Methods: MAA-SPECT/CT treatment position scans at baseline and three months post-treatment were acquired in 14 stage IIB-IIIB NSCLC patients from an interventional study (FLARE-RT) and 8 lung cancer patients from an observational study (LUNG-RT). Incidence of baseline COPD trended lower in FLARE-RT patients (3/14 [21%]) compared to LUNG-RT patients (5/8 [63%], Fisherâ€™s Exact p=0.08). FLARE-RT plans included perfused lung dose constraints while LUNG-RT plans adhered to clinical standards. Pre/post-treatment SPECT/CT scans were rigidly co-registered to planning 4DCT scans. Tumor-subtracted lung dose was converted to EQD2 and discretized into 5 GyEQD2 increments. Mean dose and percent change between pre- and post-RT MAA-SPECT uptake (%Î”PERF), normalized to total tumor-subtracted lung uptake, were calculated in each binned dose region. Dose-response data were parameterized by sigmoid logistic functions to estimate minimum reduction (%Î”PERFáµ?â?±â?¿), maximum reduction (%Î”PERFáµ?áµƒË£), dose midpoint (Dáµ?â?±áµˆ), and dose-response slope (b).
Results: Dose-response goodness-of-fit was higher in FLARE-RT (RÂ²=0.97) compared to LUNG-RT (RÂ²=0.84). FLARE-RT response was characterized by >10% increase in perfusion at low doses for 5/14 patients (|%Î”PERFáµ?â?±â?¿|=16-42%), which was not observed in any LUNG-RT patients. Median Dáµ?â?±áµˆ trended higher for FLARE-RT compared to LUNG-RT (28 GyEQD2 vs. 21 GyEQD2, Mann-Whitney p=0.09). Slope b had narrower inter-patient range in FLARE-RT (0-7.1) than LUNG-RT (1.0-15.8), while %Î”PERFáµ?áµƒË£ had broader range in FLARE-RT (3-136%) than LUNG-RT (1-110%).
Conclusion: Functional lung avoidance planning may promote increased post-treatment perfusion in low-dose regions for select patients, though inter-patient variability in dose-response parameters remains high. Individualized estimation of regional lung perfusion response can further refine risk-adaptive strategies to minimize lung function deficits and toxicity incidence.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by NIH/NCI R01CA204301.