Room: Osceola Ballroom C
Purpose: To characterize the optical emission from imaging both Cherenkov and scintillation signals underneath thermoplastic masks and bolus materials to assess feasibility of real-time in vivo surface dosimetry during head and neck radiotherapy at the level of the mask, bolus or tissue.
Methods: Radioluminescence emissions were imaged using a time-gated intensified CMOS camera during head and neck radiotherapy treatment of a tissue equivalent body phantom. Emission spectra and relative emission intensity of different colored radiotherapy masks were measured to infer contribution to captured optical signals. Emission from small plastic scintillator targets was characterized underneath transparent bolus and thermoplastic mask material, and parameters such as air gap thickness were analyzed. Lastly, Cherenkov emission from a patient undergoing VMAT treatment for head and neck cancer was imaged through the mask.
Results: Cherenkov and scintillation intensity from underneath transparent bolus material can be quantified to estimate delivered surface dose. The transparent bolus material is found to transmit >80% of optical light at wavelengths of interest. Luminescence emission intensity and spectrum varies from different colored mask materials, and therefore the choice of mask color could impact measured signal. Imaging of plastic scintillators indicates that scintillation dose response linearity is maintained when imaged through transparent bolus material. Additionally, scintillator intensity is shown to drop up to a maximum of 6% in the presence of airgaps between the bolus and surface of up to 2 cm. Finally, Cherenkov images from patient treatment show potential for beam verification underneath mask material in head and neck cancer patients.
Conclusion: This work illustrates the potential for using time-gated intensified imaging of optical emission during head and neck radiotherapy to measure local delivered surface doses. Tracking emission intensity across fractions could inform changes or abnormalities in dose delivery during treatment, and across treatments could help interpret or reduce skin reactions.
Funding Support, Disclosures, and Conflict of Interest: This work has been sponsored by NIH research grant R01EB023909. B Pogue is the president ad co-founder of DoseOptics LLC, manufacturing the C-Dose camera provided for this research. This work was not financially supported by DoseOptics.