Cherenkov light emission in external beam radiation therapy of the larynx

Numerical experiments for the radiation therapy of laryngeal cancer are performed using clinical data to investigate the characteristics of Cherenkov light emitted during treatment delivery, and the origin of light within the patient emerging on certain regions on the patient surface. Intensity-Modulated Radiation Therapy (IMRT) and Volumetric-Modulated Arc Radiation Therapy (VMAT), the two main treatment modalities used clinically, are considered. It is confirmed that the emitted Cherenkov light is dominant in the ultraviolet spectral region and is concentrated in tissue in regions of high-dose delivery, with the spatial distribution depending on the treatment type. The Cherenkov light at the patient surface is dominant in the near-infrared spectral region. Light emitted within the tumour and immediately surrounding tissue emerges at the patient surface on a well-defined radiation-beam-independent region that is also the region of high surface light intensity. This suggest that surface light measurements restricted to this smaller region on the patient surface (that can be determined through simulations prior to the treatment) could enable probing the tumour, while being easier to integrate with the radiotherapy system. The spectral and spatial characteristics of the emitted light that contributes to surface light (the internal light sources) are also investigated, and the unveiled characteristics can provide guidance for the development of image reconstruction algorithms for Cherenkov light-based tomographic imaging for tumour monitoring during radiation therapy.