Characterisation of Cherenkov Light Emission In High Dose-Rate (HDR) Brachytherapy and Its Potential Applications to In-Vivo Dosimetry.
Abstract
Purpose
To quantify the spatial and spectral characteristics of Cherenkov light generated during interstitial HDR brachytherapy and determine its relationship with the deposited dose, enabling the development of a real-time Cherenkov light-based dosimetry technique. Real-time dose monitoring has potential to enhance treatment outcomes by detecting deviations from the planned treatment.
Methods
Monte Carlo simulations were performed to model dose deposition and Cherenkov light emission from an Ir-192 source in a clinical HDR afterloader. The Ir-192 pellet, capsule, and source cable, was modelled within an interstitial PEEK needle positioned at the centre of a 10x10x10 cm3 tissue-equivalent phantom. Optical properties of source components were obtained from literature; phantom properties were experimentally measured and incorporated to simulate Cherenkov light production and transport to the phantom surface. Clinically relevant dose delivery was simulated and the magnitude, spatial distribution and spectral dependence of Cherenkov light emission in the phantom and fluence at the surface were quantified.
Results
Cherenkov light emission demonstrated strong spatial agreement with the deposited dose, particularly in high-dose regions representative of clinical target volumes. This relationship remained robust despite attenuation and scattering introduced by high-density source encapsulation components. With a source-to-surface distance of 5 cm, the Cherenkov light fluence at the surface was up to 1.5x106 photons mm-2, indicating practical detectability under clinically-realistic conditions. Spectral analysis identified maximum surface fluence in the 700-800 nm range, presenting a localised hotspot consistent with the source position. A linear calibration relationship was established between the surface fluence and the deposited dose enabling dose estimations from measurements of Cherenkov light.
Conclusion
In a clinical interstitial geometry, Cherenkov light provides a surrogate for the deposited dose and can support accurate source localisation. Identification of an optimal near-infrared spectral window and dose-fluence calibration establishes a practical foundation for the development of real-time, non-invasive HDR brachytherapy dosimetry.