IMRT plans that were adapted to perfused but not ventilated lung on 4D-V/Q PET/CT allowed for reduced dose to the functional lung while maintaining consistent plan quality.
David Ball, MD; Peter MacCallum Cancer Centre
PURPOSE: To assess the utility of functional lung avoidance using intensity-modulated radiation therapy (IMRT) informed by four-dimensional ventilation/perfusion positron emission tomography/computed tompgraphy (4D-V/Q PET/CT) in patients with non–small-cell lung cancer (NSCLC).
MATERIALS AND METHODS: In a prospective clinical trial, patients underwent 4D-V/Q PET/CT scanning before 60 Gy of definitive chemoradiation. Both “highly perfused” (HPLung) and “highly ventilated” (HVLung) lung volumes were delineated using a visually adapted 70th percentile standardized uptake value (SUV) threshold method. The HVLung was universally smaller than HPLung; so, a “ventilated lung volume” (VLung) was created to approximate the HPLung using a 50th percentile SUV threshold. For each patient, four IMRT plans were created, optimized to the anatomical lung, HPLung, VLung, and HPLung volumes. IMRT that was optimized to the anatomical lung was compared with functionally adapted IMRT using functional lung volumetrics, including mean lung dose (MLD), V5, V10, V20, V30, V40, V50, and V60 parameters. Plan quality was assessed by dose to 95% and 5% of planning target volume (PTV) (D95 and D5), conformity index (CI), and heterogeneity index (HI).
RESULTS: The study cohort consisted of 20 patients with 80 IMRT plans. The mean (+/– SD) lung volume for the HPLung and VLung was similar at 1,876 cc (+/– 677 cc) and 1,904 cc (+/– 505 cc), respectively, while HVLung was smaller at 932 cc (+/– 258 cc). Plans that were optimized to HPLung resulted in a significant reduction of functional MLD by a mean of 13.0% (1.7 Gy; P = .02). Functional V5, V10, and V20 were improved by 13.2%, 7.3%, and 3.8%, respectively (P < .04). There was no sparing of dose to functional lung when adapting to VLung or HVLung. Plan quality was highly consistent with a mean PTV D95 and D5, ranging from 60.8–61.0 Gy and 63.4–64.5 Gy, respectively, and with mean CI and HI ranging from 1.11–1.17 and 0.94–0.95, respectively.
CONCLUSIONS: IMRT plans that were adapted to perfused but not ventilated lung on 4D-V/Q PET/CT allowed for reduced dose to the functional lung while maintaining consistent plan quality.
Proceedings of the 97th Annual Meeting of the American Radium Society - americanradiumsociety.org