Investigation of a synthetic diamond detector response in kilovoltage photon beams

Abstract

Purpose An important characteristic of radiation dosimetry detectors is their energy response which consists of absorbed‐dose 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 low‐energy brachytherapy (BT) beams, we determined their intrinsic and absorbed‐dose energy responses in 25–250 kV beams relative to a 60Co 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 air‐kerma free in air in six x‐ray beam qualities (from 25 to 250 kV) and in terms of absorbed dose to water in a 60Co beam at the national metrology laboratory in Sweden. The PENELOPE/penEasy MC radiation transport code was used to calculate the absorbed‐dose 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 125I 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 extra‐cameral components on the absorbed‐dose 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 60Co 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 TG‐43 formalism‐based calculations for the 125I seed. MC study of microDiamond detector design features provided a possible explanation for inter‐detector response variation at low‐energy photon beams by differences in the effective thickness of the active volume. Conclusions MicroDiamond detectors had a non‐negligible variation in the relative intrinsic energy response (factor of 2) which was comparable to that in the absorbed‐dose energy response relative to water at low‐energy photon beams. Silicon diodes, in contrast, had an absorbed‐dose energy dependence on photon energy that varied by a factor of 6, whe...

Suitability of the microDiamond detector for experimental determination of the anisotropy function of High Dose Rate 192Ir brachytherapy sources

“…Its impact would be higher where the signal is comparatively smaller, which in our case would be at larger distances and smaller angles. (c) Angular dependence of the factor k bq : Kaveckyte et al 45 have shown that mDDs have a non‐negligible variation of the relative intrinsic energy dependence for effective photon energies <140 keV, which can lead to an over‐response by a factor 2. Although the effective photon energies in our investigated range are considerably higher than 140 keV, it is possible that low energy components of the spectrum, which are expected to have a comparatively larger impact at (3 cm, 0°) and (5 cm, 0°), could cause an over‐response of the mDD, so that the approximation of treating k bq as a constant in Eq.…”

Monte Carlo calculation of the relative TG-43 dosimetry parameters for the INTRABEAM electronic brachytherapy source

“…This implies that non-intrinsic beam quality dependence was accounted for in the calculations. Our study did not take into account the intrinsic beam quality dependence of the response, which was shown to increase substantially with reducing effective photon energy from 375 keV to below 13 keV (Kaveckyte et al 2020). Below 50 keV, however, the response variation shows more variability depending on the assumed sensitive volume thickness.…”

Monte Carlo characterization of high atomic number inorganic scintillators for in vivo dosimetry in 192Ir brachytherapy

“…On the other hand, the intrinsic energy dependence R Q 0 ,Q is determined by combining MC and measurements. [33][34][35] It is thus clear that the accuracy of the determined absorbed dose to water relies on complete characterization of detector response using both MC and experimental methods, and on the knowledge under what measurement conditions the detector response changes regardless of the magnitude of the change itself.…”

“…The quantity $$f_{Q,Q_{0}}$$ is referred to as a ratio of the absorbed‐dose energy dependence of detector cavity relative to water in beam qualities Q and Q 0 , and can be calculated using MC methods alone. On the other hand, the intrinsic energy dependence $$R_{Q_{0},Q}$$ is determined by combining MC and measurements 33–35 . It is thus clear that the accuracy of the determined absorbed dose to water relies on complete characterization of detector response using both MC and experimental methods, and on the knowledge under what measurement conditions the detector response changes regardless of the magnitude of the change itself.…”