An experimental and Monte Carlo investigation of the energy dependence of alanine/EPR dosimetry: I. Clinical x-ray beams

Abstract

The energy dependence of alanine/EPR dosimetry, in terms of absorbed dose-to-water for clinical 6, 10, 25 MV x-rays and 60Co gamma-rays was investigated by measurements and Monte Carlo (MC) calculations. The dose rates were traceable to the NRC primary standard for absorbed dose, a sealed water calorimetry. The electron paramagnetic resonance (EPR) spectra of irradiated pellets were measured using a Bruker EMX 081 EPR spectrometer. The DOSRZnrc Monte Carlo code of the EGSnrc system was used to simulate the experimental conditions with BEAM code calculated input spectra of x-rays and gamma-rays. Within the experimental uncertainty of 0.5%, the alanine EPR response to absorbed dose-to-water for x-rays was not dependent on beam quality from 6 MV to 25 MV, but on average, it was about 0.6% lower than its response to 60Co gamma-rays. Combining experimental data with Monte Carlo calculations, it is found that the alanine/EPR response per unit absorbed dose-to-alanine is the same for clinical x-rays and 60Co gamma-rays within the uncertainty of 0.6%. Monte Carlo simulations showed that neither the presence of PMMA holder nor varying the dosimeter thickness between 1 mm and 5 mm has significant effect of the energy dependence of alanine/EPR dosimetry within the calculation uncertainty of 0.3%.

Energy dependence of different materials in ESR dosimetry for clinical X-ray 10MV beam

“…Taking in to account experimental uncertainties, DLalanine results agree with others in literature (0.9920 ± 0.0065, Zeng et al, 2004;0.9870 ± 0.005, Bergstrand et al, 2003). Zeng et al (2004) expressed the parameters that influence the energy dependence of a chemical dosimeter to ESR dosimetry, using 60 Co as reference, by the following formula:…”

“…However, there are few papers that focused on the alanine response to doseto-water for different high-energy photons (Zeng et al, 2004). The same consideration applies to 2-methylalanine, a potential substitute of DL-alanine for radiotherapy dosimetry (Olsson et al, 2002), due to its dose sensitivity.…”

Response of l-alanine and 2-methylalanine minidosimeters for K-Band (24GHz) EPR dosimetry

“…The correlation coefficients (r) after fitting the doseresponse data were 0.9998 and 0.9997 for L-alanine and 2MA, respectively. Since the slope of the straight line represents the sensitivity of the material for a specific radiation energy [45], it can seen that 2MA shows a better radiation sensitivity with respect to L-alanine of approximately 60% in good agreement with the literature for X-Band measurements [32]. The error bars indicated for each dose value (Figs.…”

The response of alanine to a 150keV X-ray beam

“…The response of the alanine/EPR system to MeV photon beams has been well documented in many studies (Zeng et al, 2004;Sharpe, 2003;Bergstrand et al, 2003;Nagy, 2000;Olsen et al, 1990). However, we found very few detailed studies of its response to lowerenergy keV X-ray beams, with one exception by Olko (2002).…”

“…The procedures for the EPR measurements of the irradiated alanine pellets and the corrections to the acquired data are described in detail in a previous paper (Zeng et al, 2004). The typical standard uncertainty for EPR measurement was about 0.2% (1s) in this study.…”