Room: Stars at Night Ballroom 4
Purpose: Imaging the Cherenkov light emitted during radiotherapy has provided clinicians with the ability to monitor beam shape as it is delivered to the patient, however the extraction of quantitative dose information is difficult in patients and other non-homogeneous media. Therefore, the aim of this study is to utilize reflected light from an integrated patient alignment system to correct for large-scale Cherenkov light absorption.
Methods: Cherenkov images were acquired using an intensified CMOS camera (DoseOptics LLC, Lebanon, NH), throughout six, fixed beam radiotherapy treatments to body sites including breast and thigh. Reflectance images were taken using optical source lighting from alignment camera pods (Align-RT, Vision-RT, London, United Kingdom). Seven gelatin phantoms were mixed (blood, intralipid) and layered with synthetic skin tones varying from light to dark pigment to generate a calibration between alignment light reflectance and Cherenkov light. This calibration was then used to apply a linear, tissue attenuation correction factor to the median Cherenkov intensity of the treatment field.
Results: The phantom calibration yielded the linear fit parameter RÂ² = 0.97 between reflectance and emission values. Half the patient data sets also fit this trend, but it was found that sites with -100 HU or higher in density did not. Corrections were applied to both the calibration, and the primarily-adipose patient datasets, such that the standard deviation over mean for the uncorrected sets were reduced from 21.5% to 8.0% standard error.
Conclusion: A relationship was established between alignment-light-based reflectance and dose-normalized Cherenkov emission, making corrections possible for treatment sites consisting of primarily adipose tissue. Two major benefits include (1) providing an additional use for a previously integrated, FDA-approved patient alignment system, and (2) negating image registration by requiring only one camera. In future work, anatomical correction factors will be applied to treatment sites containing denser soft and fibroglandular tissues.
Funding Support, Disclosures, and Conflict of Interest: Dr. Brian Pogue (PI) is the president and co-founder of DoseOptics, a company manufacturing Cherenkov imaging systems. This work was not financially supported by DoseOptics.