SU-F-T-663: Cerenkov Radiation Enhanced Radiotherapy with Titanium Dioxide Nanoparticle: A Monte Carlo Study
Purpose:
A recent publication has shown that by delivering titanium dioxide nanoparticles (titania) as a photosensitizer into tumors, Cerenkov radiation (CR) produced by radionuclides could be used for substantially boosting damage to cancer cells. The present work compares CR production by various clinically relevant radiation sources including internal radionuclides and external beam radiotherapy (EBRT), and provides preliminarily computational results of CR absorption by titania.

Methods:
1) Geant4.10.1 was used to simulate ionizing radiation-induced CR production in a 1cm diameter spherical volume using external radiotherapy sources: Varian Clinac IX 6MV and Eldorado 60Co, both with 10*10 cm2 field size. In each case the volume was placed at the maximum dose depth (1.5cm for 6MV source and 0.5cm for 60Co). In addition, 18F, 192Ir and 60Co were simulated using Geant4 radioactive decay models as internal sources. Dose deposition and CR production spectra in 200nm-400nm range were calculated as it is the excitation range of titania. 2) Using 6MV external source, the absorption by titania was calculated via the track length of CR in the spherical volume. The nanoparticle concentration was varied from 0.25 to 5µg/g.

Results:
Among different radioactive sources, results showed that 18F induced the highest amount of CR per disintegration, but 60Co had the highest yield per unit dose. When compared with external sources, 6MV source was shown to be the most efficient for the the same delivered dose. Simulations indicated increased absorption for increasing concentrations, with up to 68% absorption of generated CR for 5µg/g titania concentration.

Conclusion:
The results demonstrate that 6MV beam is favored with a higher CR yield, compared to radionuclides, and that the use of higher concentrations of titania may increase photosensitization. From the findings, we propose that if sufficiently potent concentrations of titania are delivered to tumors this could substantially boost EBRT.