Addressing the Impact of Skin Pigmentation on Quantitative Cherenkov Dosimetry in the First Diverse Patient Imaging Study

• Published in: International journal of radiation oncology, biology, physics Vol. 120; no. 2; p. S225
• Main Authors: Decker, S.M., Andreozzi, J., Hernandez, D., Alexander, D.A., Wickramasinghe, V., Hachadorian, R., Oraiqat, I., Chen, E., Washington, I., Zhang, R., Jarvis, L.A., Bruza, P., Gladstone, D.J., Pogue, B.W.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.10.2024
• ISSN: 0360-3016
• DOI: 10.1016/j.ijrobp.2024.07.2313

Many modern biomedical technologies rely on detecting in vivo optical signals as a noninvasive means for diagnosis or treatment of disease. The interaction of light in superficial tissue is highly dependent on an individual's skin pigmentation (i.e. epidermal melanin) and must be considered for accurate, quantitative measurements. Cherenkov imaging, an emerging technology that detects light from patients undergoing radiation treatment, could face similar limitations. We present the first reported in vivo Cherenkov imaging study of a diverse patient population towards mitigating the impact of skin pigmentation on quantitative Cherenkov light-based dosimetry. A multi-institutional collaboration was formed to increase the opportunity for imaging a diverse population. Cherenkov imaging was completed with a time-gated, iCMOS camera, and color background images were taken simultaneously with an RGB camera module under standardized lighting. Under an IRB-approved retrospective protocol, skin pigmentation was assessed per patient by calculating the relative luminance (L = 0.2126*R + 0.7152*G + 0.0722*B) of their treated area from the color images. Additionally, 2D dose maps were generated by projecting the exponentially-weighted dose from the surface to 5mm into the body, representative of Cherenkov emission, and used for reference surface dose estimations. To date, N6MV=23 and N15MV=20 imaged patients, encompassing a wide variety of skin pigmentations, fit our assessment criteria: right-sided breast radiotherapy patients without reconstructive implants or temporary expanders. The initial generated intensity of Cherenkov light is proportional to the radiation dose delivered, providing a unique opportunity for non-contact, real-time surface dosimetry. However, the detected light emission is highly dependent on patients’ skin pigmentation. Our results revealed that, for the same dose, the Cherenkov emission intensity was nearly four times less for dark skin patients compared to their Caucasian counterparts. Additionally, a linear relationship exists between Cherenkov intensity per unit dose and individuals’ relative skin luminance, enabling a linear calibration factor based on skin pigmentation. Application of this calibration factor significantly improved Cherenkov-to-dose linearity amongst the cohort, from R2=0.79 to 0.96 for 6MV and R2=0.19 to 0.91 for 15MV (p<0.05), marking the highest reported linearity for in vivo patient data. This study is the first of its kind dedicated to assessing Cherenkov imaging amongst a diverse patient population, and developed a linear calibration technique based upon measuring the skin luminance for each patient. It demonstrates significant mitigation of the effect of skin pigmentation through the addition of color imaging, representing a critical step towards achieving quantitative Cherenkov dosimetry.