Room: Track 4
Purpose: We developed a methodology to utilize gas-exchange maps in functional avoidance treatment planning. For a cohort of patients with lung cancer, we created both gas-exchange-guided and ventilation-guided treatment plans on each subject, and evaluated the reductions in gas-exchange-weighted functional dose metrics.
Methods: Eleven patients that received conventional RT for non-small cell lung cancer were studied. Patients underwent a pre-RT hyperpolarized ¹²?Xe gas-exchange MRI, producing images of xenon in gas-phase (ventilation) and transiently bound to red blood cells in the alveolar capillaries (gas-exchange), and an anatomical ¹H image. After deformably registering the MRI images to the CT treatment planning space, functional avoidance treatment plans were generated using both gas-exchange and ventilation maps. Starting with the clinically approved plan, new optimization criteria to reduce dose to highly functioning lung were added. All clinical dose-volume limits and target coverage criteria were adhered to, as in the clinical plans. For all plans, gas-exchange maps were used to calculate function-weighted effective uniform dose (fEUD), function-weighted volume receiving =20Gy (fV20), and mean dose in the highest functioning 33% and 50% volumes of lung (MLD-f33% and MLD-f50%). We compared functional avoidance plans to the corresponding clinical plans, using the Wilcoxon signed rank test for significance (P-values Bonferroni corrected).
Results: Compared to the clinical plans, fEUD decreased by an average of 75±24cGy (P=0.01) and 60±17cGy (P=0.01) for gas-exchange- and ventilation-optimization, respectively. Similarly, fV20 decreased by 1.4±0.8% and 1.1%±0.4%, respectively, but neither were statistically significant (P>0.05). The MLD-f33% decreased by 134±41cGy (P=0.01) and 68±29cGy (P>0.05), respectively; MLD-f50% decreased by 95±29cGy (P=0.01) and 61±20cGy (P=0.05).
Conclusion: Gas-exchange-guided functional avoidance treatment planning may most effectively reduce patient toxicity associated with reduced blood oxygen transport. However, in many patients, ventilation-guided planning may incidentally reduce doses to higher gas-exchange regions. The methodology developed here enables future prospective trials to examine patient outcomes.
Funding Support, Disclosures, and Conflict of Interest: B.Driehuys is CTO for, a board member of, and a shareholder in Polarean, Inc.