Determination of the active volumes of solid‐state photon‐beam dosimetry detectors using the <scp>PTB</scp> proton microbeam

Poppinga, Daniela; Delfs, Björn; Meyners, Jutta; Langner, Frank; Giesen, U.; Harder, Dietrich; Poppe, B; Looe, Hui Khee

doi:10.1002/mp.12948

Cited by 11 publications

(20 citation statements)

References 16 publications

(38 reference statements)

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“…The thickness t of the active volume of the microSilicon detector was measured using the method developed in the previous study, based on the following equation:

t = \frac{I \cdot W}{n \cdot S \cdot e}

where I represents the detector current, W the energy expenditure per electron released in the silicon material (W = (3.6 ± 0.1) eV), n the proton rate, S the energy‐dependent proton stopping power in the active detector volume, and e represents the elementary charge.…”

Section: Methodsmentioning

confidence: 99%

Three‐dimensional characterization of the active volumes of PTW microDiamond, microSilicon, and Diode E dosimetry detectors using a proton microbeam

Poppinga¹,

Kranzer²,

Ulrichs

et al. 2019

Medical Physics

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Purpose The purpose of this work is the three‐dimensional characterization of the active volumes of commercial solid‐state dosimetry detectors. Detailed knowledge of the dimensions of the detector’s active volume as well as the detector housing is of particular interest for small‐field photon dosimetry. As shown in previous publications from different groups, the design of the detector housing influences the detector signal for small photon fields. Therefore, detailed knowledge of the active volume dimension and the surrounding materials form the basis for accurate Monte Carlo simulations of the detector. Methods A 10 MeV proton beam focused by the microbeam system of the Physikalisch‐Technische Bundesanstalt was used to measure two‐dimensional response maps of a synthetic diamond detector (microDiamond, type 60019, PTW Freiburg) and two silicon detectors (microSilicon, type 60023, PTW Freiburg and Diode E, type 60017, PTW Freiburg). In addition, the thickness of the active volume of the new microSilicon was measured using the method developed in a previous study. Results The analysis of the response maps leads to active area of 1.18 mm2 for the Diode E, 1.75 mm2 for the microSilicon, and 3.91 mm2 for the microDiamond detector. The thickness of the active volume of the microSilicon detector was determined to be (17.8 ± 2) µm. Conclusions This study provides detailed geometrical data of the dosimetric active volume of three different solid‐state detector types.

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“…The thickness t of the active volume of the microSilicon detector was measured using the method developed in the previous study, based on the following equation:

t = \frac{I \cdot W}{n \cdot S \cdot e}

Section: Methodsmentioning

confidence: 99%

Three‐dimensional characterization of the active volumes of PTW microDiamond, microSilicon, and Diode E dosimetry detectors using a proton microbeam

Poppinga¹,

Kranzer²,

Ulrichs

et al. 2019

Medical Physics

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“…The same correction can be applied to the mD detector by considering that its polarity, that is, the type of charge carriers being collected, can be changed by reversing the contact connected to the electrometer. Figure (left insert) shows an x‐ray image of the mD detector (adopted from Poppinga et al …”

Section: Methodsmentioning

confidence: 99%

“…). The diamond chip with the sensitive diamond layer (1–2 μm thick) defined by the Schottky contact is shown as a green line. The type of charge carriers, that is, positive or negative, collected depends on which detector's contact (blue or red) is connected to the electrometer.…”

Section: Methodsmentioning

confidence: 99%

“…They have shown that by reducing the sensitive area in the simulations and hence the associated volume‐averaging effect, better agreement between Monte Carlo and experimental results can be achieved. This proposition has since been disproved by three working groups . All studies used miniature beams to measure the sensitive area of the mD detector and have demonstrated that the sensitive area of the mD detector coincides with the manufacturer's specification within the experimental uncertainty.…”

Section: Introductionmentioning

confidence: 99%

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The role of radiation‐induced charge imbalance on the dose‐response of a commercial synthetic diamond detector in small field dosimetry

Looe

Poppinga²,

Kranzer³

et al. 2019

Medical Physics

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Purpose Discrepancy between experimental and Monte Carlo simulated dose–response of the microDiamond (mD) detector (type 60019, PTW Freiburg, Germany) at small field sizes has been reported. In this work, the radiation‐induced charge imbalance in the structural components of the detector has been investigated as the possible cause of this discrepancy. Materials and methods Output ratio (OR) measurements have been performed using standard and modified versions of the mD detector at nominal field sizes from 6 mm × 6 mm to 40 mm × 40 mm. In the first modified mD detector (mD_reversed), the type of charge carriers collected is reversed by connecting the opposite contact to the electrometer. In the second modified mD detector (mD_shortened), the detector's contacts have been shortened. The third modified mD detector (mD_noChip) is the same as the standard version but the diamond chip with the sensitive volume has been removed. Output correction factors were calculated from the measured OR and simulated using the EGSnrc package. An adapted Monte Carlo user‐code has been used to study the underlying mechanisms of the field size‐dependent charge imbalance and to identify the detector's structural components contributing to this effect. Results At the smallest field size investigated, the OR measured using the standard mD detector is >3% higher than the OR obtained using the modified mD detector with reversed contact (mD_reversed). Combining the results obtained with the different versions of the detector, the OR have been corrected for the effect of radiation imbalance. The OR obtained using the modified mD detector with shortened contacts (mD_shortened) agree with the corrected OR, all showing an over‐response of less than 2% at the field sizes investigated. The discrepancy between the experimental and simulated output correction factors has been eliminated after accounting for the effect of charge imbalance. Discussions and conclusions The role of radiation‐induced charge imbalance on the dose–response of mD detector in small field dosimetry has been studied and quantified. It has been demonstrated that the effect is significant at small field sizes. Multiple methods were used to quantify the effect of charge imbalance with good agreement between Monte Carlo simulations and experimental results obtained with modified detectors. When this correction is applied to the Monte Carlo data, the discrepancy from experimental data is eliminated. Based on the detailed component analysis using an adapted Monte Carlo user‐code, it has been demonstrated that the effect of charge imbalance can be minimized by modifying the design of the detector's contacts.

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“…obtained by assuming a smaller effective collecting volume of the detector than the manufacturer‐specified physical volume. In the meantime, it has been demonstrated experimentally, however, that the manufacturer‐specified physical volume of the detector is correct, but recent work has also shown that photon scatter induced by the large metallic contacts in the vicinity of the diamond chip yields a substantial detector signal . It is plausible that the photon scatter by these metallic contacts has a similar perturbation effect as a reduction in the effective collecting volume.…”

mentioning

confidence: 99%

Reply to “Comments on the TRS‐483 Protocol on Small field Dosimetry” [Med. Phys. 45(12), 5666–5668 (2018)]

et al. 2018

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Determination of the active volumes of solid‐state photon‐beam dosimetry detectors using the PTB proton microbeam

Cited by 11 publications

References 16 publications

Three‐dimensional characterization of the active volumes of PTW microDiamond, microSilicon, and Diode E dosimetry detectors using a proton microbeam

Three‐dimensional characterization of the active volumes of PTW microDiamond, microSilicon, and Diode E dosimetry detectors using a proton microbeam

The role of radiation‐induced charge imbalance on the dose‐response of a commercial synthetic diamond detector in small field dosimetry

Reply to “Comments on the TRS‐483 Protocol on Small field Dosimetry” [Med. Phys. 45(12), 5666–5668 (2018)]

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