Poster abstracts

Poster number 33 submitted by Sara Lim

Enhanced radiotherapy with heavy element radiosensitization using low energy X-rays

Sara N Lim (Biophysics Graduate Program, the Ohio State University), Anil K. Pradhan, Sultana N. Naha (Depratment of Astronomy, the Ohio State University), Rolf F. Barth, Weilan Yang, Robin J. Nakkula (Department of Pathology, Ohio State University Medical Center), Erica H. Bell (Department of Radiation Oncology, Ohio State University Medical Center), Claudia Turro, Alycia M Palmer (Department of Chemistry, the Ohio State University)

Abstract:
Purpose: Current X-ray radiotherapy involves subjecting patients to extremely large amounts of high energy radiation resulting in unnecessary, damaging radiation exposure. Combining radiotherapy with heavy-element (HZ) radiosensitizers like platinum-based chemotherapeutics and gold nanoparticles could be highly effective at increasing the dose to cancerous tumors relative to normal tissue. This is achieved by stimulating the release of highly damaging electrons from the HZ upon irradiation. Since this sensitization is highly energy dependent, we have performed both numerical simulations and in vitro studies to determine the most suitable energy range.

Methods: Theoretical calculations and Monte Carlo simulations using the Geant4 code package for X-ray dose deposition in HZ-sensitized tissues and cells were carried out using broadband X-ray sources at energies of 100, 160, 250 kilovolts (kV) and 6 megavolts (MV). In vitro experiments were performed to compare the survival rate of radiosensitized cells after irradiation using either a 160 kV or a 6 MV broadband source with carboplatin as the radiosensitizer.

Results: The simulations and computations show that dose enhancement using platinum are significant only in low energy region < 200 keV. More damage occurs at 160 kV relative to other energy ranges. This is likely to be the result of the increased flux in the energy range preferentially absorbed by the HZ for 160 kV X-rays. Significantly, in vitro results has shown more cell death using 160 kV X-rays relative to 6 MV in cells treated with carboplatin, a Pt drug. At the same drug concentration, irradiation with the 6 MV linac showed no additional cell death relative to unirradiated controls, while irradiation with the 160 kV showed a decrease in cell viability.

Significance: These results show that the high energy, MV X-rays used in radiotherapy is less effective as a therapeutic agent compared to low energy, kV X-rays used with a radiosensitizer. kV X-rays results in more damage to cancer cells, particularly if they are radiosensitized. based on our calculations, treatment of cancerous lesions with in 10 cm of the skin maybe be more effective with the use of HZ radiosensitizers and low energy, kV X-rays.

References:
Lim, SN, Pradhan, AK, Nahar, SNN, et al. Superiority of low energy 160 kV X-rays compared to high energy 6 MV photons for platinum sensitized treatment of the F98 glioma. International Journal of Radiation Biology. (Submitted)

Lim, S, Montenegro, M, Pradhan, AK, et al. Broadband and monochromatic X-ray irradiation of platinum: Monte Carlo simulations for dose enhancement factors and resonant theranostics. 2012 World Congress Medical Physics and Biomedical Engineering, May 26-31, 2012 (conference location)

Keywords: radiosensitization, radiotherapy