Purpose: To quantitatively determine the effects of dose build-up and tissue optical properties on the reemitted Cherenkov signal during radiation therapy.
Methods: Diffuse liquid tissue phantoms were created with several different scattering and absorption properties to simulate the optical range of various human tissue types. A linear accelerator irradiated the phantoms with 200 MU using 6, 10, and 18 MV x-rays at 100 cm SSD and a field-size of 10x10 cm². The phantom was irradiated at the entrance surface with the gantry positioned top-down at 180°, and at the exit surface at a depth of D_max, determined by previously measured PDD curves, with the gantry positioned at 0°. An intensified camera fixed to the ceiling was used to capture all images. For each phantom, the reemitted Cherenkov signal was measured as the mean pixel intensity of a rectangular ROI.
Results: Comparing the reemitted Cherenkov intensity at the phantom’s entrance and exit surfaces demonstrated the competing effects of both increased Cherenkov photon generation and greater attenuation of Cherenkov photons as the build-up region increases with higher energy x-rays. The competing effects, of order ~44% and ~46% respectively, resulted in a nearly constant reemitted Cherenkov signal out of the entrance surface at various energies. Additionally, the reemitted Cherenkov signal increased ~10% and decreased ~20% with varying scattering and absorption tissue optical properties, respectively, between phantoms.
Conclusion: This study provides a progressive step towards verifying dose delivery during radiation therapy treatments by exploring the reemitted Cherenkov signal in real-time. The results demonstrate how the reemitted Cherenkov signal varies with dose build-up and tissue optical properties. Further studies should investigate how other factors, such as field-size and optical property heterogeneities, affect the reemitted Cherenkov signal.
Funding Support, Disclosures, and Conflict of Interest: B. Pogue and P. Bruza are employed part time by DoseOptics LLC, manufacturing the C-Dose cameras provided for this research. D. Alexander is a paid consultant for DoseOptics LLC outside of this work.
Not Applicable / None Entered.