Dr Jigar Dubal

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.

Significance Cherenkov light emitted in the tissue during radiation therapy enables unprecedented approaches to tumor functional imaging for early treatment assessment. Cherenkov light-based tomographic imaging requires image reconstruction algorithms based on internal light sources that, in turn, require knowledge about the characteristics of the Cherenkov light within the patient. Aim We aim to investigate the spatial and spectral characteristics of Cherenkov light within the patient and at the patient's surface, and the origin within the tissue of light reaching the surface, to provide insight for the development of image reconstruction algorithms for Cherenkov light-based tomographic imaging. Approach Numerical experiments using clinical patient data and Monte Carlo simulations are performed for the radiation therapy of laryngeal cancer for intensity-modulated radiation therapy and volumetric-modulated arc radiation therapy. Results The emitted Cherenkov light is concentrated in regions of high delivered dose, with the spatial distribution within the patient and at the patient's surface depending on the treatment type and patient anatomy. The Cherenkov light at the patient's surface is dominant in the near-infrared spectral region. Light emitted within the tumor emerges at the patient's surface on a well-defined radiation beam-independent region. The distribution within the patient of the emitted light that emerges on reduced areas on the patient's surface containing this region is similar to that of the light that emerges across the entire patient's surface. Conclusions Detailed information about the spectral and spatial characteristics of Cherenkov light is provided. In addition, these results suggest that surface light measurements restricted to smaller areas containing the region where the light emitted in the tumor emerges (that can be determined through simulations prior to the treatment) could enable probing the tumor while being easier to integrate with the radiotherapy system and while the effect of measurement data incompleteness on image reconstruction may not be too strong.

We perform numerical experiments based on Monte Carlo simulations and clinical CT data to investigate Cherenkov light emission in molecular radiation therapy of hyperthyroidism, and demonstrate that Cherenkov light-based dosimetry could be feasible.

Numerical experiments based on Monte Carlo simulations and clinical CT data are performed to investigate the spatial and spectral characteristics of Cherenkov light emission and the relationship between Cherenkov light intensity and deposited dose in molecular radiotherapy of hyperthyroidism and papillary thyroid carcinoma. It is found that Cherenkov light is emitted mostly in the treatment volume, the spatial distribution of Cherenkov light at the surface of the patient presents high-value regions at locations that depend on the symmetry and location of the treatment volume, and the surface light in the near-infrared spectral region originates from the treatment site. The effect of inter-patient variability in the tissue optical parameters and radioisotope uptake on the linear relationship between the dose absorbed by the treatment volume and Cherenkov light intensity at the surface of the patient is investigated, and measurements of surface light intensity for which this effect is minimal are identified. The use of Cherenkov light measurements at the patient surface for molecular radiation therapy dosimetry is also addressed.