Determination of In-Vivo 2D Correction Factors to Convert Cherenkov Imaging to Dose for TSE Patients
T Zhu1*, W Zhong1, H Sun1, Y Zhu1, T Miao2, A Dimofte1, I Paydar1, A Maity1, L Dong1, J Plastaras1, (1) University of Pennsylvania, Philadelphia, PA, (2) Yale University, New Haven, CT
Presentations
PO-GePV-M-187 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Cherenkov imaging has been used to quantify the surface dose in total skin electron therapy (TSET) patients. However, current method has yield large differences between Cherenkov imaging converted doses and doses determined by in-vivo dosimetry (IVD). Determination of 2D correction factors is necessary to correctly convert Cherenkov imaging intensity to dose on patient specific geometries.
Methods: Large PVC board was used to determine the ratio between measured dose using IVD and Cherenkov intensity on the flat 2-D plane for dual-field from nominal 6MeV electron beams at the treatment distance (SSD-500 cm). This 2D correction factor is then applied to Cherenkov intensity to obtain Cherenkov converted dose normalized to dose on the central axis of the beam. Then, patient specific Cherenkov intensity converted dose are compared to dose determined by IVD at 5 locations to determine the magnitude of additional dose correction factors, all are normalized to the umbilicus point. Topas Monte-Carlo simulations were performed on the same patient geometries to determine the ratio of the normalized Cherenkov intensity map and the normalized surface dose map, both normalized to the central-axis, as 2D dose dose correction factor.
Results: On PVC board, the 2D correction factor was found to be less than 15%. For the 18 patients evaluated, the in-vivo correction factor (std) was found to be 1.07 ± 0.07, 1.10 ± 0.09, 1.32 ± 0.02, 1.8 ± 0.3, 1.4 ± 0.3 for Chest, right hand, perineum, right shin, and vertex, respectively. 2D correction factors determined from MC simulation were consistent with the measured point ratios and the major cause of the 2D correction factors was the spoiler plate.
Conclusion: Monte Carlo simulations in patient specific geometries provide a mean to determine the in-vivo 2D correction factors to convert Cherenkov intensity to dose that agrees with IVD.
Funding Support, Disclosures, and Conflict of Interest: NIH R21CA239127-01A1
Keywords
Optical Dosimetry, Optical Imaging, Monte Carlo
Taxonomy
IM- Optical : Quantitative imaging
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