The energy dependence and dose response of a commercial optically stimulated luminescent detector for kilovoltage photon, megavoltage photon, and electron, proton, and carbon beams

Abstract

Optically stimulated luminescent detectors, which are widely used in radiation protection, offer a number of potential advantages for application in radiation therapy dosimetry. Their introduction into this field has been somewhat hampered by the lack of information on their radiation response in megavoltage beams. Here the response of a commercially available optically stimulated luminescent detector (OSLD) is determined as a function of energy, absorbed dose to water, and linear energy transfer (LET). The detector response was measured as a function of energy for absorbed doses from 0.5 to 4.0 Gy over the following ranges: 125 kVp to 18 MV for photons, 6-20 MeV for electrons, 50-250 MeV for protons, and 290 MeV/u for the carbon ions. For the low LET beams, the response of the detector was linear up to 2 Gy with supralinearity occurring at higher absorbed doses. For the kilovoltage photons, the detector response relative to 6 MV increased with decreasing energy due to the higher atomic number of aluminum oxide (11.2) relative to water (7.4). For the megavoltage photons and electrons, the response was independent of energy. The response for protons was also independent of energy, but it was about 6% higher than its response to 6 MV photons. For the carbon ions, the dose response was linear for a given LET from 0.5 to 4.0 Gy, and no supralinearity was observed. However, it did exhibit LET dependence on the response relative to 6 MV photons decreasing from 1.02 at 1.3 keV/microm to 0.41 at 78 keV/microm. These results provide additional information on the dosimetric properties for this particular OSL detector and also demonstrate the potential for their use in photon, electron, and proton radiotherapy dosimetry with a more limited use in high LET radiotherapy dosimetry.

Angular dependence of the nanoDot OSL dosimeter

“…Measurements were not converted to absolute dose considering the other correction factors that have inherent uncertainties; e.g., energy dependence, absolute reader sensitivity, etc. [12][13][14][15] Inclusion of this would introduce unnecessary uncertainty that this study did not attempt to address; however, a facility using an OSL system would need to characterize these basic factors to reduce uncertainty in converting the OSLD measurement to an absorbed dose.…”

“…15 Sensitivity of the dosimeter has been shown not to change significantly at cumulative doses below 10 Gy. 11,12,19 Even so, the experiments were performed in such a way as to keep the cumulative dose as even as possible amongst the dosimeters to eliminate such uncertainties. No dosimeter received a cumulative dose over 10 Gy.…”

“…1, [12][13][14][15] While the basic features of OSL dosimetry using aluminum oxide have been investigated, there are still unanswered questions about the performance of commercial OSLDs in a clinical environment. This study is aimed at determining whether there is any angular dependence of the response of the aluminum oxide-based nanoDot.…”

“…An initial drop-off of signal has been observed in the first minutes following irradiation, thus it is recommended to wait at least 10-15 min before read out. 11,12 The use of light for signal read-out allows superior control over the dosimeter reading, with a quick on-off capability. This has made OSLDs an appealing option for treatment field dosimetry for patients receiving radiation therapy.…”

Surface dose measurements with commonly used detectors: a consistent thickness correction method

“…For instance, the EPM for a Landauer OSL was determined by Zhuang and Olch (11) to be ${\mathrm{D}}_{\text{OSL}}=0.8 \text{mm}$, and 0.07 cm 2 /gm by Reft (31) . The thickness of TLD100 was 0.38 mm ($\rho =2.64 \mathrm{normalg}/{\text{cm}}^3$); therefore, with the assumption that the EPM is located at the midpoint of the TLD, then ${\mathrm{D}}_{\text{TLD}}=0.5 \text{mm}$ of water.…”