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Gold Nanoparticle Dose Enhancement of Inverse-Compton Scattered Narrow Band Photon Beams: A Monte Carlo Study

Y Yang

YM Yang1*, I Gadjev2 , J Rosenzweig2 , K Sheng1 (1) UCLA School of Medicine, Los Angeles, CA (2) UCLA Department of Physics and Astronomy, Los Angeles, California


SU-K-205-9 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 205

Purpose: Inverse-Compton Scattering (ICS) light sources produce high energy photons of tunable wavelength in the 100keV range. In comparison with the broad-band spectra produced by ortho- and megavoltage radiotherapy accelerators, the narrow bandwidth photon spectra produced ICS sources are well-suited for gold nanoparticle dose enhancement. Monte Carlo simulations of the ICS source, treatment geometry, and various levels of gold uptake were performed determine the optimal treatment configuration for realistic nanoparticle uptake conditions.

Methods: The ICS source spectrum was obtained using a 3D time and frequency domain simulation, producing a phase-space distribution of the Compton scattered X-rays of energy 91keV and 1milliradian divergence. The Geant4 v10.03 Monte Carlo code was used to simulate a rotational arc treatment of the ICS beam in a head phantom comprising of a 15.3cm sphere of ICRU brain material surrounded by a 7mm thick layer of ICRU compact bone. The central 4cm diameter region of brain was simulated with 0g/g, 10ug/g, 100ug/g, 1mg/g, 10mg/g, and 100mg/g gold uptake. Microdosimetric dose enhancement and dose delocalization were tabulated in kernels allowing for evaluation of the biological effect as a function of nanoparticle location within a cell.

Results: For zero gold uptake, a rotationally symmetric ICS treatment can deliver 95% of the skull maximum dose to the prescription depth. With gold nanoparticle uptake levels of 10ug/g, 100ug/g, 1mg/g, 10mg/g, and 100mg/g, physical dose enhancement of +0%, +<1%, +9.6%, +89.6%, and +363% was observed. These dosimetric results, combined with previous in-vivo studies of gold nanoparticles irradiated by synchrotron and LDR brachytherapy sources, suggest that in addition to physical dose enhancement, there may be a factor of 7-15 fold increase in biological effect.

Conclusion: The ICS photon source produces photon beams that potentially improve upon the dosimetric enhancement offered by gold nanoparticles with existing X-ray sources.

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