Why diamond dimensions and electrode geometry are crucial for small photon beam dosimetry

Marsolat, Fanny; Tromson, D.; Tranchant, Nicolas; Pomorski, M.; Bassinet, C.; Huet, C.; Derreumaux, S.; Chea, M.; Cristina, Karen; Boisserie, G.; Buchheit, I.; Marchesi, V.; Gaudaire-Josset, S.; Lisbona, A.; Lazaro, D.; Hugon, R.; Bergonzo, P.

doi:10.1063/1.4937994

Cited by 16 publications

(21 citation statements)

References 43 publications

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“…The diamond front surface was 1.0 mm × 1.0 mm and the active volume thickness (e AV ) was chosen in accordance with three aspects: the numerical results presented in this paper, the Bragg peak dose perturbation less than 2% required by the Proton therapy Center of the Curie Institute and the technical constraint of the electrode design. 10  Electrodes: The electrodes on the two faces of the diamond crystal were made by depositing a 100 nm conductive material on the entire front and back surfaces of the crystal in order to reduce the dose rate dependence (Marsolat et al 2015), potentially allowing the use of the SCDD-Pro in high dose rate proton pencil beams.…”

Section: Detector Designmentioning

confidence: 99%

Development of a synthetic single crystal diamond dosimeter for dose measurement of clinical proton beams

et al. 2017

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The scope of this work was to develop a synthetic single crystal diamond dosimeter (SCDD-Pro) for accurate relative dose measurements of clinical proton beams in water. Monte Carlo simulations were carried out based on the MCNPX code in order to investigate and reduce the dose curve perturbation caused by the SCDD-Pro. In particular, various diamond thicknesses were simulated to evaluate the influence of the active volume thickness (e ) as well as the influence of the addition of a front silver resin (250 µm in thickness in front of the diamond crystal) on depth-dose curves. The simulations indicated that the diamond crystal alone, with a small e of just 5 µm, already affects the dose at Bragg peak position (Bragg peak dose) by more than 2% with respect to the Bragg peak dose deposited in water. The optimal design that resulted from the Monte Carlo simulations consists of a diamond crystal of 1 mm in width and 150 µm in thickness with the front silver resin, enclosed by a water-equivalent packaging. This design leads to a deviation between the Bragg peak dose from the full detector modeling and the Bragg peak dose deposited in water of less than 1.2%. Based on those optimizations, an SCDD-Pro prototype was built and evaluated in broad passive scattering proton beams. The experimental evaluation led to probed SCDD-Pro repeatability, dose rate dependence and linearity, that were better than 0.2%, 0.4% (in the 1.0-5.5 Gy min range) and 0.4% (for dose higher than 0.05 Gy), respectively. The depth-dose curves in the 90-160 MeV energy range, measured with the SCDD-Pro without applying any correction, were in good agreement with those measured using a commercial IBA PPC05 plane-parallel ionization chamber, differing by less than 1.6%. The experimental results confirmed that this SCDD-Pro is suitable for measurements with standard electrometers and that the depth-dose curve perturbation is negligible, with no energy dependence and no significant dose rate dependence.

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Section: Detector Designmentioning

confidence: 99%

Development of a synthetic single crystal diamond dosimeter for dose measurement of clinical proton beams

et al. 2017

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“…The electric field outside the volume under the electrode is therefore not uniform and is too weak to fully collect the generated charge. The full coverage electrodes also improve the dose rate linearity and the charge collection efficiency [68]. However, electrical contacts that are too large (too close to the plate lateral faces) may induce unexpected leakage conduction at high fields through a large density of defects situated on the lateral sides of the diamond substrate.…”

Section: Diamond Dimensions and Electrodes Geometrymentioning

confidence: 99%

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

et al. 2021

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Many new X-Ray treatment machines using small and/or non-standard radiation fields, e.g., Tomotherapy, Cyber-knife, and linear accelerators equipped with high-resolution multi-leaf collimators and on-board imaging system, have been introduced in the radiotherapy clinical routine within the last few years. The introduction of these new treatment modalities has led to the development of high conformal radiotherapy treatment techniques like Intensity Modulated photon Radiation Therapy, Volumetric Modulated Arc Therapy, and stereotactic radiotherapy. When using these treatment techniques, patients are exposed to non-uniform radiation fields, high dose gradients, time and space variation of dose rates, and beam energy spectrum. This makes reaching the required degree of accuracy in clinical dosimetry even more demanding. Continuing to use standard field procedures and detectors in fields smaller than 3 × 3 cm2, will generate a reduced accuracy of clinical dosimetry, running the risk to overshadowing the progress made so far in radiotherapy applications. These dosimetric issues represent a new challenge for medical physicists. To choose the most appropriate detector for small field dosimetry, different features must be considered. Short- and long-term stability, linear response to the absorbed dose and dose rate, no energy and angular dependence, are all needed but not sufficient. The two most sought-after attributes for small field dosimetry are water equivalence and small highly sensitive (high sensitivity) volumes. Both these requirements aim at minimizing perturbations of charged particle fluence approaching the Charged Particle Equilibrium condition as much as possible, while maintaining high spatial resolution by reducing the averaging effect for non-uniform radiation fields. A compromise between different features is necessary because no dosimeter currently fulfills all requirements, but diamond properties seem promising and could lead to a marked improvement. Diamonds have long been used as materials for dosimeters, but natural diamonds were only first used for medical applications in the 80 s. The availability of reproducible synthetic diamonds at a lower cost compared to natural ones made the diffusion of diamonds in dosimetry possible. This paper aims to review the use of synthetic poly and single-crystal diamond dosimeters in radiotherapy, focusing on their performance under MegaVoltage photon beams. Both commercial and prototype diamond dosimeters behaviour are described and analyzed. Moreover, this paper will report the main related results in literature, considering diamond development issues like growth modalities, electrical contacts, packaging, readout electronics, and how do they affect all the dosimetric parameters of interest such as signal linearity, energy dependence, dose-rate dependence, reproducibility, rise and decay times.

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“…However, as shown in several studies on synthetic diamond detectors the response may also depend on other factors. For instance, changes in charge collection due to nonconformity of electric field in the detector, 33 the presence of impurities, 34 higher responsivity to low-energy x rays, 35 and field-size dependent charge imbalance in the structural components of the detector. 36 The latter effect explained discrepancies between measurements and MC simulations in 6 MV small fields, but it cannot explain the inter-detector variability reported in this article.…”

Section: D Measurements With An 125 I Bt Seedmentioning

confidence: 99%

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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Why diamond dimensions and electrode geometry are crucial for small photon beam dosimetry

Cited by 16 publications

References 43 publications

Development of a synthetic single crystal diamond dosimeter for dose measurement of clinical proton beams

Development of a synthetic single crystal diamond dosimeter for dose measurement of clinical proton beams

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

Investigation of a synthetic diamond detector response in kilovoltage photon beams

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