1098 - Quantification of Local-Regional Deformation Based on Cherenkov Imaged Vasculature for Breast Radiotherapy Patients

Y. Chen¹, S. M. Decker¹, P. Bruza¹, L. A. Jarvis^2,3, D. J. Gladstone^1,4, B. W. Pogue⁵, K. S. Samkoe^1,4, and R. Zhang^1,4; ¹Thayer School of Engineering, Dartmouth College, Hanover, NH, ²Geisel School of Medicine, Dartmouth College, Hanover, NH, ³Department of Radiation Oncology and Applied Sciences, Dartmouth Cancer Center, Dartmouth Health, Lebanon, NH, ⁴Dartmouth Cancer Center, Dartmouth Health, Lebanon, NH, ⁵University of Wisconsin-Madison, Madison, WI

Purpose/Objective(s): Variations in patient positioning can profoundly influence treatment outcomes, so accurate positioning is crucial for precise radiotherapy dose delivery. This study introduces a novel application of Cherenkov imaging and hypothesizes that it allows for the precise quantification of local-regional tissue deformations to improve the accuracy of patient positioning in breast cancer radiotherapy. For the first time, local-regional deformation is quantified based on Cherenkov imaged vasculature, opening a new avenue to improve the precision of patient positioning. Materials/

Methods: Optical attenuation by blood provides sufficient contrast between vasculature and surrounding tissues. After segmenting blood vessels within Cherenkov images as patient-specific biological fiducial markers, a rigid and non-rigid combined registration was deployed to quantify both inter- and intra-fraction positioning accuracy. The submillimeter accuracy was validated by imaging an anthropomorphic chest phantom with similar human vasculature during a simulated breast radiotherapy treatment, whereas the inter- and intra-fraction variations were simulated by couch shifts and respiratory motion. For 10 patients, 2D maps of local-regional tissue deformations based on non-rigid registration followed by a global shift based on a rigid registration has been quantified in the treatment region for the first time.
Results: The accuracy was validated to be within 0.83 ± 0.49 mm for the simulated inter- and intra-fraction variations. A paired t-test revealed no significant difference between the simulated and quantified variations. (P value = 0.2883 > 0.05). A retrospective Cherenkov imaging dataset including 10 breast cancer patients was analyzed for patient positioning variations within their treatment course, revealing an inter-fraction setup uncertainty of 3.71 ± 2.36 mm. Quantitative 2D deformation maps per fraction indicated local-regional deformation in addition to conventional global shifts. Much fewer deformations of 0.0487 ± 0.0385 mm quantified by the non-rigid registration performed after the rigid registration was observed compared to the rigid shift of 3.66 ± 2.35 mm in a paired t-test (P value < 0.0001), which indicates rigid registration captured the majority of global variations, with non-rigid registration addressing the residual local deformations.
Conclusion: This study reports the first directly observed local-regional deformation and a method to precisely quantify the global and local variations in patient positioning based on rigid and non-rigid registrations using Cherenkov imaged vasculature. This novel approach demonstrates the feasibility of providing real-time quantitative imaging guidance to inform inter- and intra-fraction positioning, enhancing the precision of breast cancer radiotherapy.