Predicting Indirect Radiation-Induced Damage Using Parametric Response Mapping and Dosimetric Analysis
A Wuschner1*, E Wallat2, M Flakus3, G Christensen4, J Reinhardt5, J Bayouth6, (1) University of Wisconsin, Madison, WI, (2) University of Wisconsin, Madison, WI, (3) University of Wisconsin, Madison, WI, (4) University of Iowa, Iowa City, IA, (5) University of Iowa, Iowa City, IA, (6) University of Wisconsin, Madison, WI
Presentations
PO-GePV-M-73 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To identify correlations between pre-RT comorbidities and/or irradiation of feeding vasculature/airways with post-RT indirect damage in SBRT-treated lung cancer patients.
Methods: Two 4DCTs were acquired pre-RT and 12 months post-RT in 17 subjects enrolled in an IRB approved clinical trial. Full inspiratory and expiratory phases were deformably registered to the expiratory phase for both scans. Parametric response maps (PRM) were created to classify voxels as normal, parenchymal disease (PD), functional small airway disease (fSAD), or Emphysema using established Hounsfield Unit(HU) thresholds [PD: >-810 on inspiration; fSAD: -950 to -810 on inspiration, <-856 on expiration; normal: >-856 on expiration; emphysema: <-950 on inspiration, <-856 on expiration]. The post-RT PRM map was deformably registered to the pre-RT frame of reference for voxel-wise comparisons. Dose distributions were analyzed to determine if a main bronchial airway or pulmonary vessel or artery was irradiated >5 Gy. Subjects were compared for instances of indirect damage, defined as any voxel receiving <5 Gy but increasing >12% in HU (variance in HU for repeat scans taken 5 minutes apart).
Results: Eight subjects were airway-irradiated and 7/8 showed indirect damage. All but one subject analyzed showed a pre-RT comorbidity. All airway-irradiated subjects with pre-existing PD, 3/4 airway-irradiated with pre-RT COPD, and all subjects with both pre-RT PD and COPD showed indirect damage post-RT along with one airway-irradiated subject without pre-RT comorbidities. Neither of the patients with PD pre-RT but without airway-irradiation showed indirect damage. Having just COPD pre-RT did not strongly correlate with outcomes (2/4 patients experienced indirect damage).
Conclusion: The combined knowledge of PRM map derived pre-RT comorbidities and irradiation of major airway/vessel potentially has predictive power in determining if patients will present with indirect radiation-induced damage post-RT.
Funding Support, Disclosures, and Conflict of Interest: Joseph M. Reinhardt is a shareholder in VIDA Diagnostics, Inc John E. Bayouth has ownership interest in MR Guidance, LLC, which has business activity with technology used in this study ViewRay, Inc.
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