Abstract
Purpose: Investigate Cherenkov light emission in intensity modulated radiation therapy (IMRT) of laryngeal cancer; identify detection configurations for tumour probing using measurements of Cherenkov light at the patient surface.
Methods: Numerical experiments were performed using Monte Carlo simulations and clinical Computed Tomography (CT) and radiotherapy treatment plan data for a two-beam IMRT treatment. CT data indicated the tissue types, and plan data was utilised to simulate radiation delivery. Spectrally dependent values were assigned to the optical parameters (absorption, scattering, refractive index, anisotropy) of each tissue type. Dose calibration (the number of Monte Carlo events corresponding to a 1cGy dose at the isocenter) was obtained by simulating the delivery of a 10 x 10 cm2 radiation field to water. The spatial and spectral characteristics of Cherenkov light within the tissue and at the patient surface were determined, as well as the origin within the tissue of light emerging in various regions on the surface.
Results: Emitted Cherenkov light is localized in the tissue in regions of high-dose delivery. The spectrum of Cherenkov light at the patient surface is consistent with the tissue optical absorption spectrum and presents a peak in the near-infrared region. Cherenkov light emitted within the gross tumour volume (GTV) and immediately surrounding tissue emerges at the patient surface on a well-defined, beam-independent region, called here “GTV spot”. Near-infrared light emerging on the GTV spot has comparable intensity with light emerging on other areas on the surface.
Conclusion: Measurements of near-infrared light on the patient surface can potentially enable probing the GTV and surrounding tissue for monitoring tumour changes during the treatment course. Restricting the light measurements to the reduced-area GTV spot (that can be determined a priori through simulations) could lead to easier implementation of a Cherenkov-light-based functional tomographic imaging technology with the radiotherapy system.