Suitability of microDiamond detectors for the determination of absorbed dose to water around high‐dose‐rate <sup>192</sup>Ir brachytherapy sources

Kaveckyte, Vaiva; Benmakhlouf, Hamza; Carlsson, Gudrun Alm; Tedgren, Åsa Carlsson

doi:10.1002/mp.12694

Cited by 11 publications

(15 citation statements)

References 49 publications

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“…Our results hence do not contradict findings in high‐energy photon and electron beams reporting negligible beam quality dependence . Furthermore, no significant relative intrinsic energy dependence was observed in our previous study of microDiamond detectors in 192 Ir beam which had an effective photon energy close to 300 keV.…”

Section: Discussionsupporting

confidence: 61%

“…Figure shows ratios of SiD2 and mD1 detector readings in 125 I beam at 5 mm and 10 mm distance from the source and in calibration beams. For comparison, the corresponding detector reading ratios in the 192 Ir beam for three SDDs (15, 25, and 55 mm) are included from a previous study . If the detectors’ response would be affected only by their absorbed‐dose energy response (Section 3.B), the change in detector reading ratio per absorbed dose to water or air‐kerma (depending on measurement setup) would be approximately equal to MC‐calculated ratios

{\bar{D}}_{SiD} / {\bar{D}}_{mD}

or a given beam quality (see insert in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…For comparison, the corresponding detector reading ratios in the 192 Ir beam for three SDDs (15,25, and 55 mm) are included from a previous study. 9 If the detectors' response would be affected only by their absorbeddose energy response (Section 3.B), the change in detector reading ratio per absorbed dose to water or air-kerma FIG. 7.…”

Section: C Measurements With An 125 I Seedmentioning

confidence: 99%

“…These characteristics shown in high‐energy beams combined with the closeness of the effective atomic numbers of water and carbon prompted a question about diamond detector’s applicability in low‐energy photon beams, such as BT and diagnostic x‐ray fields. It has been shown that the microDiamond detector is suitable for the determination of absorbed dose to water and for relative measurements in HDR 192 Ir beams, and percentage depth‐dose curve determination in kilovoltage (kV) x‐ray beams …”

Section: Introductionmentioning

confidence: 99%

“…These characteristics shown in high-energy beams combined with the closeness of the effective atomic numbers of water and carbon prompted a question about diamond detector's applicability in low-energy photon beams, such as BT and diagnostic x-ray fields. It has been shown that the microDiamond detector is suitable for the determination of absorbed dose to water 9 and for relative measurements in HDR 192 Ir beams, 10 and percentage depth-dose curve determination in kilovoltage (kV) x-ray beams. 11 Having in mind the possible application of microDiamond detectors for experimental nonrelative dosimetry of, for example, electronic BT treatments (40-100 kV) or treatments using 125 I seeds, the purpose of this study was to further investigate the response of microDiamond detectors at low photon energies (from 25 to 250 kV x-ray beams) and compare it with that in a 60 Co beam.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of a synthetic diamond detector response in kilovoltage photon beams

et al. 2020

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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...

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Section: Discussionsupporting

confidence: 61%

{\bar{D}}_{SiD} / {\bar{D}}_{mD}

or a given beam quality (see insert in Fig.…”

Section: Discussionmentioning

confidence: 99%

Section: C Measurements With An 125 I Seedmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigation of a synthetic diamond detector response in kilovoltage photon beams

et al. 2020

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

et al. 2020

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Purpose To investigate the suitability of the microDiamond detector (mDD) type 60019 (PTW‐Freiburg, Germany) to measure the anisotropy function F(r,θ) of High Dose Rate (HDR) 192Ir brachytherapy sources. Methods The HDR 192Ir brachytherapy source, model mHDR‐v2r (Elekta AB, Sweden), was placed inside a water tank within a 4F plastic needle. Four mDDs (mDD1, mDD2, mDD3, and mDD4) were investigated. Each mDD was placed laterally with respect to the source, and measurements were performed at radial distances r = 1 cm, 3 and 5 cm, and polar angles θ from 0° to 168°. The Monte Carlo (MC) system EGSnrc was used to simulate the measurements and to calculate phantom effect, energy dependence and volume‐averaging correction factors. F(r,θ) was determined according to TG‐43 formalism from the detector reading corrected with the MC‐based factors and compared to the consensus anisotropy function CONF(r,θ). Results At 1 cm, the differences between measurements and MC simulations ranged from −0.8% to +0.8% for θ = 0° and from −2.1% to + 2.3% for θ ≠ 0°. At 3 and 5 cm, the differences ranged from +1.4% to +3.9% for θ = 0°, and from −0.4% to +2.9% for θ ≠ 0°. All differences were within the uncertainties (k = 2). At small angles, the phantom effect correction was up to −1.9%. This effect was mainly caused by the air between source and needle tip. The energy correction was angle‐independent everywhere. For small angles at 1 cm, the volume‐averaging correction was up to −2.9% and became less important for larger angles and distances. The differences of the measured F(r,θ) corrected with the MC‐based factors to CONF(r,θ) ranged from –1.0% to +3.4% for mDD1, –2.2% to +4.2% for mDD2, –2.5% to +4.0% for mDD3, and −2.6% to +3.4% for mDD4. All differences were within the uncertainties (k = 2) except one at (3 cm, 0°). For all the mDDs, F(r,0°) was always higher than CONF(r,0°), with average differences of +3.1% (1 cm), +3.6% (3 cm), and +1.9% (5 cm). The inter‐detector variability was within 2.9% (1 cm), 1.8% (3 cm), and 3.4% (5 cm). Conclusions A reproducible method and experimental setup were presented for measuring and validating F(r,θ) of an HDR 192Ir brachytherapy source in a water phantom using the mDD. The phantom effect and the volume‐averaging need to be taken into account, especially for the smaller distances and angles. Good agreement to CONF(r,θ) was obtained. The discrepancies at (1 cm, 0°), accurately predicted by the MC results, may suggest a reconsideration of CONF(r,θ), at least for this position. The slight overestimations at (3 cm,0°) and (5 cm,0°), both in comparison to CONF(r,θ) and MC results, may be due to an underestimation of the air volume between source and needle tip, dark current, intrinsic over‐response of the mDDs, or radiation‐induced charge imbalance in the detector’s components. The results indicate that the mDD is a valuable tool for measurements with HDR 192Ir brachytherapy sources and support its employment for the determination and validation of TG‐43 parameters of such sources.

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A high‐Z inorganic scintillator–based detector for time‐resolved in vivo dosimetry during brachytherapy

et al. 2021

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Purpose High‐dose rate (HDR) and pulsed‐dose rate (PDR) brachytherapy would benefit from an independent treatment verification system to monitor treatment delivery and to detect errors in real time. This paper characterizes and provides an uncertainty budget for a detector based on a fiber‐coupled high‐Z inorganic scintillator capable of performing time‐resolved in vivo dosimetry during HDR and PDR brachytherapy. Method The detector was composed of a detector probe and an optical reader. The detector probe consisted of either a 0.5 × 0.4 × 0.4 mm3 (HDR) or a 1.0 × 0.4 × 0.4 mm3 (PDR) cuboid ZnSe:O crystal glued onto an optical‐fiber cable. The outer diameter of the detector probes was 1 mm, and fit inside standard brachytherapy catheters. The signal from the detector probe was read out at 20 Hz by a photodiode and a data acquisition device inside the optical reader. In order to construct an uncertainty budget for the detector, six characteristics were determined: (1) temperature dependence of the detector probe, (2) energy dependence as a function of the probe‐to‐source position in 2D (determined with 2 mm resolution using a robotic arm), (3) the signal‐to‐noise ratio (SNR), (4) short‐term stability over 8 h, and (5) long‐term stability of three optical readers and four probes used for in vivo monitoring in HDR and PDR treatments over 21 months (196 treatments and 189 detector calibrations, and (6) dose‐rate dependence. Results The total uncertainty of the detector at a 20 mm probe‐to‐source distance was < 5.1% and < 5.8% for the HDR and PDR versions, respectively. Regarding the above characteristics, (1) the sensitivity of the detector decreased by an average of 1.4%/°C for detector probe temperatures varying from 22 to 37°C; (2) the energy dependence of the detector was nonlinear and depended on both probe‐to‐source distance and the angle between the probe and the brachytherapy source; (3) the median SNRs were 187 and 34 at a 20 mm probe‐to‐source distance for the HDR and PDR versions, respectively (corresponding median source activities of 4.8 and 0.56 Ci, respectively); (4) the detector response varied by 0.6% in 11 identical irradiations over 8 h; (5) the sensitivity of the four detector probes decreased systematically by 0–1.2%/100 Gy of dose delivered to the probes, and random fluctuations of 4.8% in the sensitivity were observed for the three probes used in PDR and 1.9% for the probe used in HDR; and (6) the detector response was linear with dose rate. Conclusion ZnSe:O detectors can be used effectively for in vivo dosimetry and with high accuracy for HDR and PDR brachytherapy applications.

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Suitability of microDiamond detectors for the determination of absorbed dose to water around high‐dose‐rate ¹⁹²Ir brachytherapy sources

Cited by 11 publications

References 49 publications

Investigation of a synthetic diamond detector response in kilovoltage photon beams

Investigation of a synthetic diamond detector response in kilovoltage photon beams

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

A high‐Z inorganic scintillator–based detector for time‐resolved in vivo dosimetry during brachytherapy

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Suitability of microDiamond detectors for the determination of absorbed dose to water around high‐dose‐rate 192Ir brachytherapy sources

Cited by 11 publications

References 49 publications

Investigation of a synthetic diamond detector response in kilovoltage photon beams

Investigation of a synthetic diamond detector response in kilovoltage photon beams

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

A high‐Z inorganic scintillator–based detector for time‐resolved in vivo dosimetry during brachytherapy

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Suitability of microDiamond detectors for the determination of absorbed dose to water around high‐dose‐rate ¹⁹²Ir brachytherapy sources

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