Program Information
Maximizing Cherenkov Emissions From Medical Linear Accelerators Using Custom Filtration: A Monte Carlo Study
Z Shrock*, S Yoon , M Oldham , J Adamson , Duke University Medical Center, Durham, NC
Presentations
TH-CD-708-5 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 708
Purpose: Cherenkov light is a natural byproduct of MV radiotherapy; recent results demonstrate that it can activate the drug psoralen sufficiently to induce cytotoxicity and increase MHC1 signal in vitro. Here, we investigate methods to maximize Cherenkov production per unit dose, using filters placed in the beam path of common radiotherapy photon beams.
Methods: GAMOS, a GEANT4-based framework for Monte Carlo simulations, was used to model primary photon beams using spectra from a Varian linear accelerator. The primary beam chosen was 10MV Flattening Filter Free photons, with 10MV, 15MV, and 18MV beams for comparison. Simulations tracked Cherenkov production and dose from the beams irradiating a 17.8cm³ cubic water phantom at 1mm³ detectors with depths of 8 to 9cm; SSD was set to 94cm. Filters of varying material and thickness were placed 15cm below the 10MV FFF beam source. Primary photon histories varied with thickness of the filter, from 100 million histories for no filter to 2 billion histories with a 10cm filter.
Results: An Aluminum filter boosted Cherenkov/dose by factors ranging from 1.08 for 2cm thickness to 1.63 for 20cm. Copper boosted Cherenkov/dose by factors ranging from 1.23 for 2cm to 1.58 for 10cm. Iron boosted Cherenkov/dose by factors from 1.17 for 2cm to 1.66 for 10cm. For comparison, 15MV and 18MV beam had 1.69 and 1.99 higher Cherenkov/dose relative to 10MV FFF, respectively. An Aluminum filter produced the greatest increase in Cherenkov emission for the same reduction in dose rate.
Conclusion: Aluminum shows the most promise to boost Cherenkov per dose without overly compromising dose rate, while Copper offers a compromise between Cherenkov production and filter thickness. The greatest effect is achieved by increasing photon energy to 15MV or 18MV. Future work will expand analysis to include further materials, higher photon energies, and to include optical properties of tissues.
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