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Using Modulated and Reflected Light to Correct Clinical Cherenkov Images for Patient-Specific Tissue Variations During Whole Breast Radiotherapy

R Hachadorian1*, P Bruza2 , L Jarvis3 , D Gladstone4 , B Pogue5 , (1) Dartmouth College, Hanover, NH, (2) Thayer School Of Engineering, Dartmouth College, Hanover, NH, (3) Dartmouth-Hitchcock Med. Ctr., Lebanon, NH, (4) Dartmouth-Hitchcock Medical Center, Lebanon, NH, (5) Thayer School Of Engineering, Dartmouth College, Hanover, NH


(Saturday, 3/30/2019)  

Room: Exhibit Hall

Purpose: Imaging Cherenkov emission during radiotherapy has been developed to establish real-time, treatment field verification in vivo. Signal linearity between Cherenkov emission and absorbed dose exists, which yields potential for establishing quantitative dose verification. However, intensities vary as much as 45% between patients due to differences in tissue optical properties, alone. Our goal is to correct Cherenkov images for large scale differences in absorption, including those due to variable melanin concentrations, and subcutaneous vasculature.

Methods: Cherenkov emission was imaged for both calibration data and patient treatment data, using an intensified CMOS camera on a Varian Clinac with online background subtraction. Optical property maps were acquired using spatial frequency domain imaging (SFDI) over five spatial frequencies and four NIR wavelengths, then optimized for correction by spectral weighting. Reflectance images were taken using the iCMOS camera, where an Align RT system integrated into clinical workflow was used as a light source. Corrections to patient data were applied using a previously established calibration.

Results: When using SFDI as a means for subsurface vasculature correction, the percent differences associated with the corrected image lateral, inferior and medial vessels (6%, 4%, and 7% respectively) adhered more closely to the intensity gradient associated with the treatment plan, compared to that of the uncorrected image (22%, 14%, and 10% respectively). Using optimization, corrected image intensity absorbed due to areolar pigment improved almost completely, relative to the treatment plan, as compared to the uncorrected image. Establishing an Align RT reflectance-based calibration for variable skin tones allowed us to normalize patient data.

Conclusion: Using Align RT light as a source for reflectance images allowed us to characterize Patient data for large-scale tissue optical properties and SFDI optical property maps have enabled the development and application of a pixel-by-pixel method to correct Cherenkov images for surface and subsurface attenuation.

Funding Support, Disclosures, and Conflict of Interest: Brian Pogue (PI) is the president and co-founder of DoseOptics LLC, a company which designs and manufactures Cherenkov Cameras. This work was not financially supported by DoseOptics.

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