Dose response of various radiation detectors to synchrotron radiation

Abstract

Accurate dosimetry is particularly difficult for low- to medium-energy x-rays as various interaction processes with different dependences on material properties determine the dose distribution in tissue and radiation detectors. Monoenergetic x-rays from synchrotron radiation offer the unique opportunity to study the dose response variation with photon energy of radiation detectors without the compounding effect of the spectral distribution of x-rays from conventional sources. The variation of dose response with photon energies between 10 and 99.6 keV was studied for two TLD materials (LiF:Mg,Ti and LiF:Mg,Cu,P), MOSFET semiconductors, radiographic and radiochromic film. The dose response at synchrotron radiation energies was compared with the one for several superficial/orthovoltage radiation qualities (HVL 1.4 mm Al to 4 mm Cu) and megavoltage photons from a medical linear accelerator. A calibrated parallel plate ionization chamber was taken as the reference dosimeter. The variation of response with x-ray energy was modelled using a two-component model that allows determination of the energy for maximum response as well as its magnitude. MOSFET detectors and the radiographic film were found to overrespond to low-energy x-rays by up to a factor of 7 and 12 respectively, while the radiochromic film underestimated the dose by approximately a factor of 2 at 24 keV. The TLDs showed a slight overresponse with LiF:Mg, Cu, P demonstrating better tissue equivalence than LiF:Mg, Ti (maximum deviation from water less than 25%). The results of the present study demonstrate the usefulness of monoenergetic photons for the study of the energy response of radiation detectors. The variations in energy response observed for the MOSFET detectors and GAF chromic film emphasize the need for a correction for individual dosimeters if accurate dosimetry of low- to medium-energy x-rays is attempted.

Investigation of TLD-700 energy response to low energy x-ray encountered in diagnostic radiology

“…By taking the ratio R Q of the measured air kerma response for X-ray quality X to the measured air kerma response for Cs source R Cs , we obtain the relative energy response of TLD chips, S(Q), given by the Equation 6. We have represented S(Q), the relative energy response in Figure 6.…”

“…The knowledge of TLD energy response is necessary to estimate the uncertainty of any personal dosimetry system, and an experimental method is considered as the most reliable option [6].…”

“…Kearfott et al [12] observed an energy response of LiF TL ribbon for low energy x-rays. Kron et al [6], studied energy response of LiF for low energy synchrotron radiation. Muhogora et al [13,14] studied energy response of LiF chips for typical ISO 4037 X-ray beams² and some diagnostic qualities.…”

Evaluation of MOSFETs for entrance dose dosimetry for 6 and 10 MV photons with a custom made build up cap

“…This is slightly more than Dmax for 6 MV (1.50 cm), and slightly less than Dmax for 10 MV (2.50 cm). Aluminium is a good choice of material for a build up cap as MOSFETs have energy dependence for low energy photons, increasing in sensitivity by up to 3 times at around 50 keV 12 , to 4.5 times at 75kV 5 . They are therefore more likely to be affected by characteristic radiation from higher Z materials.…”

Monte Carlo Simulation of TLD Response Function: Scatterd Radiation Application

“…This popularity is due, in part, to approximate tissue equivalence and low signal fading [3]. Knowledge of TL response, especially at commonly used photon energies, is useful to estimate the uncertainty of dosimetry system, and experimental methodology has elsewhere been regarded as the most reliable option [4]. TLDs are relative dosimeters and therefore have to be calibrated against absolute dosimetry systems such as a calibrated ion chamber.…”