SU‐F‐T‐507: Modeling Cerenkov Emissions From Medical Linear Accelerators: A Monte Carlo Study

Abstract

Purpose: Cerenkov emissions are a natural byproduct of MV radiotherapy but are typically ignored as inconsequential. However, Cerenkov photons may be useful for activation of drugs such as psoralen. Here, we investigate Cerenkov radiation from common radiotherapy beams using Monte Carlo simulations. Methods: GAMOS, a GEANT4‐based framework for Monte Carlo simulations, was used to model 6 and 18MV photon beams from a Varian medical linac. Simulations were run to track Cerenkov production from these beams when irradiating a 50cm radius sphere of water. Electron contamination was neglected. 2 million primary photon histories were run for each energy, and values scored included integral dose and total track length of Cerenkov photons between 100 and 400 nm wavelength. By lowering process energy thresholds, simulations included low energy Bremsstrahlung photons to ensure comprehensive evaluation of UV production in the medium. Results: For the same number of primary photons, UV Cerenkov production for 18MV was greater than 6MV by a factor of 3.72 as determined by total track length. The total integral dose was a factor of 2.31 greater for the 18MV beam. Bremsstrahlung photons were a negligibly small component of photons in the wavelength range of interest, comprising 0.02% of such photons. Conclusion: Cerenkov emissions in water are 1.6x greater for 18MV than 6MV for the same integral dose. Future work will expand the analysis to include optical properties of tissues, and to investigate strategies to maximize Cerenkov emission per unit dose for MV radiotherapy.

Enhancing Radiation Therapy Through Cherenkov Light-Activated Phototherapy

“…The results described above indicate that RECA treatment can increase both cell kill and MHC I expression. This result is interesting because prior calculations based on superficial psoralen treatments suggest that the combined dose (defined as the product of CL intensity and psoralen concentration) from 2- to 12-Gy MV radiation treatments at 100 μM may be 1-2 orders of magnitude weaker than that used in superficial applications that use photo-activation from a standard UV lamp (18). Monte Carlo simulation studies estimate CL dose of 4-8 μJ/cm 2 per 1 Gy delivered within the wavelength range of 250 to 850 nm in tissue (simulated without absorption) from a Varian proprietary phase space file for 6-MV radiation treatment beam (12).…”

“…Figure 6A shows the spectrum of the psoralen absorption band, a psoralen–ultraviolet A (PUVA) light source (1), and the CL spectrum in water, obtained from GEANT4/GAMOS Monte Carlo simulations (18). An excellent match is observed in the overlap between the psoralen absorbance peaks and the CL emission wavelengths.…”