(Tuesday, 7/31/2018) 4:30 PM - 6:00 PM
Room: Davidson Ballroom A
Purpose: Imaging Cherenkov emission during radiotherapy has been developed to establish real-time field verification in vivo. Potential for signal linearity with absorbed dose exists, however, intensities vary as much as 45% between patients due to differences in tissue optical properties. The purpose of this study was to use controlled tissue phantoms to establish a calibration for the relationship between Cherenkov emission and diffuse optical parameters, to correct images for inherent patient-to-patient variations.
Methods: Cherenkov emission and optical property data were acquired throughout a titration of increasing blood in a 1% Intralipid solution, followed by a separate titration of increasing Intralipid in a 1% blood solution. A PIMAX4 ICCD and DoseOptics CDose were used to image Cherenkov emission during delivery of 200MU at 6MV, with 0.03µs gate delay, 3.25µs gate width and 50 AoC. Optical property data was taken using the Reflect RS (Modulated Imaging Inc.) which custom calibration enabled the acquisition of SFDI data from 42cm, over a 300cm² field. AlignRT was used to measure diffuse reflectance.
Results: Normalized curves indicate that linearly increasing blood concentration and absorption coefficient, resulted in an inverse relationship to Cherenkov intensity C(µ�,µs',…). Increases in highly-absorbing features, such as blood, by only 2% have large influence over observed Cherenkov intensity, illustrating reductions up to 65%. Interestingly, variations in scattering coefficient had a much smaller effect. Sample to sample variation F(µ�) followed a high-correlation inverse relationship, which forms the basis for calibrating Cherenkov images for tissue optical property variation, i.e. C(µ�)/F(µ�)=1.

Conclusion: The inverse relationship between Cherenkov emission and absorption coefficient were readily quantified using wide-field SFDI and a systematic series of tissue phantoms. Applying optical property corrections to the Cherenkov over a range of days and patients will allow us to bring uniformity to the realm of Cherenkov dosimetry for future in vivo dose verification.
Funding Support, Disclosures, and Conflict of Interest: R01 EB023909
Keywords
Taxonomy
TH- External beam- photons: Standard field experimental dosimetry
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