Cherenkov light–based dosimetry for molecular radiation therapy of thyroid cancer: an in-silico study

OBJECTIVE: There is a need for patient-specific dose quantification (dosimetry) in Molecular Radiation Therapy (MRT). Cherenkov light generated in the tissue by charged particles produced by the radioactive decay of radio-pharmaceuticals offers an unprecedented opportunity for MRT dosimetry. While the intensity of the emitted Cherenkov light is proportional to the dose, the intensity of light emerging and measured at the patient surface depends on patient anatomy and tissue optical characteristics. This results in an inter-patient variability of the linear relationship between Cherenkov light intensity at the patient surface and the dose delivered to the tumour that hinders the implementation of Cherenkov light-based dosimetry. A multi-patient study of Cherenkov light emission in MRT of thyroid cancer is performed and a correction technique for the surface light intensity is introduced to reduce this inter-patient variability. APPROACH: Numerical experiments using clinical patient Computed Tomography data and Monte Carlo simulations are performed for a set of patient anatomies and a range of values of tissue optical parameters and tumour radioisotope uptakes, resulting in 135 treatment realisations. The impact of anatomy and tissue optical characteristics on the characteristics of Cherenkov light is investigated. A patient-specific factor defined as the product between the fraction of the light emitted in the tumour that emerges on the patient surface and tumour volume and mass density is introduced to correct the intensity of light emerging at the patient surface for the dependence on patient anatomy and tissue optical characteristics. MAIN RESULTS: There is a large inter-patient variability in the relationship between the surface light intensity and dose delivered to the tumour. The correction technique greatly reduces this variability and enables the derivation of a dosimetry calibration curve. SIGNIFICANCE: This study provides an important step towards quantitative MRT dosimetry based on Cherenkov light emitted during treatment.