Investigation of a synthetic diamond detector response in kilovoltage photon beams
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2019-12-27 |
| Journal | Medical Physics |
| Authors | Vaiva Kaveckyte, Linda Persson, Alexandr MaluĆĄek, Hamza Benmakhlouf, Gudrun Alm Carlsson |
| Institutions | Linköping University, Swedish Radiation Safety Authority |
| Citations | 12 |
Abstract
Section titled âAbstractâPurpose An important characteristic of radiation dosimetry detectors is their energy response which consists of absorbedâdose and intrinsic energy responses. The former can be characterized using Monte Carlo (MC) simulations, whereas the latter (i.e., detector signal per absorbed dose to detector) is extracted from experimental data. Such a characterization is especially relevant when detectors are used in nonrelative measurements at a beam quality that differs from the calibration beam quality. Having in mind the possible application of synthetic diamond detectors (microDiamond PTW 60019, Freiburg, Germany) for nonrelative dosimetry of lowâenergy brachytherapy (BT) beams, we determined their intrinsic and absorbedâdose energy responses in 25-250 kV beams relative to a 60 Co beam, which is usually the reference beam quality for detector calibration in radiotherapy. Material and Methods Three microDiamond detectors and, for comparison, two silicon diodes (PTW 60017) were calibrated in terms of airâkerma free in air in six xâray beam qualities (from 25 to 250 kV) and in terms of absorbed dose to water in a 60 Co beam at the national metrology laboratory in Sweden. The PENELOPE/penEasy MC radiation transport code was used to calculate the absorbedâdose energy response of the detectors (modeled based on blueprints) relative to air and water depending on calibration conditions. The MC results were used to extract the relative intrinsic energy response of the detectors from the overall energy response. Measurements using an independent setup with a single ophthalmic BEBIG I25.S16 125 I BT seed (effective photon energy of 28 keV) were used as a qualitative check of the extracted intrinsic energy response correction factors. Additionally, the impact of the thickness of the active volume as well as the presence of extraâcameral components on the absorbedâdose energy response of a microDiamond detector was studied using MC simulations. Results The relative intrinsic energy response of the microDiamond detectors was higher by a factor of 2 in 25 and 50 kV beams compared to the 60 Co beam. The variation in the relative intrinsic energy response of silicon diodes was within 10% over the investigated photon energy range. The use of relative intrinsic energy response correction factors improved the agreement among the absorbed dose to water values determined using microDiamond detectors and silicon diodes, as well as with the TGâ43 formalismâbased calculations for the 125 I seed. MC study of microDiamond detector design features provided a possible explanation for interâdetector response variation at lowâenergy photon beams by differences in the effective thickness of the active volume. Conclusions MicroDiamond detectors had a nonânegligible variation in the relative intrinsic energy response (factor of 2) which was comparable to that in the absorbedâdose energy response relative to water at lowâenergy photon beams. Silicon diodes, in contrast, had an absorbedâdose energy dependence on photon energy that varied by a factor of 6, whereas the intrinsic energy dependence on beam quality was within 10%. It is important to decouple these two responses for a full characterization of detector energy response especially when the user and reference beam qualities differ significantly, and MC alone is not enough.