Water equivalent PRESAGE for synchrotron radiation therapy dosimetry.

Purpose: Synchrotron Radiation Therapy techniques are currently being trialed and commissioned at synchrotrons around the world. The patient treatment planning systems (TPS) developed for these treatments use simulated data of the synchrotron x-ray beam to produce the dosimetry in the treatment plan. The purpose of this study was to investigate a water equivalent PRESAGE dosimeter capable of 3D dosimetry over an energy range suitable for synchrotron x-ray beams.

Methods: Water equivalent PRESAGE dosimeters were fabricated with a radiological effective atomic number similar to water over an energy range of 10 keV to 10 MeV. The dosimeters were irradiated at various energies, scanned using optical CT (OCT) scanning and compared to ion chamber measurements. Percentage depth dose and beam profiles of the synchrotron beam were compared to Monte Carlo (MC) model simulations.

Results: The PDD profiles of the water equivalent PRESAGE agreed with ion chamber measurements and MC calculations within 2% for all keV energies investigated. The PRESAGE also showed good agreement to the MC model for depths below 5 mm of the synchrotron beam where ion chamber data do not exist. The spatial resolution of the OCT was not sufficient to accurately measure the penumbra of the synchrotron beams compared to MC calculations or EBT3 film; however, the water equivalent PRESAGE was able to verify dose profile characteristics of the MC model.

Conclusions: The radiological response of a water equivalent PRESAGE dosimeter has been validated for synchrotron x-ray beam energies along with the ability to independently verify dose distributions of a MC model.