The influence of detector size relative to field size in small-field photon-beam dosimetry using synthetic diamond crystals as sensors

Ade, Nicholas; Nam, T.L.

doi:10.1016/j.radphyschem.2015.04.005

Cited by 7 publications

(5 citation statements)

References 41 publications

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“…It is possible, for example, to understand if the crystal structure is pure (peak at 1,332.8 cm -1 ) or if there are other contributions due to vacancies that could act as a trapping center for charges (other peaks). For the pcCVD substrate, the level of defects could also depend on the large concentration of grain boundaries [46][47][48][49]. This analysis is sometimes complemented by optical spectrophotometry or FTIR methods to detect substitutional defects in the diamond lattice.…”

Section: Characterization Techniquesmentioning

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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Section: Characterization Techniquesmentioning

confidence: 99%

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

et al. 2021

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“…In these conditions lateral charged particle equilibrium is lost because the size of the field becomes small compared to the range of the dose depositing electrons. Small fields have also a very large percentage of the field made up by penumbra; if the detector is larger than 1/4th of the lateral field dimension, the detector size is large compared to the beam dimensions making volume averaging within the detector problematic [8]. Due to these physical conditions small field dosimetry requires different correction factors related to different characteristics of the detector like the density of the sensitive volume, the presence of extra components like metal electrodes and the volume averaging [27][28][29].…”

Section: Small Field Dosimetrymentioning

confidence: 99%

“…In diamond material, defects and impurities are present and they strongly influence the lifetime of charge carriers, generating a slow dynamic response and affecting the reproducibility and time stability [7]. In the last decade most of these limitations have been overcome but the dimensions of the detector's sensitive volume and the electrode geometry are still crucial to the solution of the dosimetric issues observed in small photon beams with diamond detectors [8,9]. Recently a new technology to create graphitic paths in the diamond bulk has emerged [10][11][12][13] allowing to create 3-dimensional structures like the 3-D silicon detectors [14].…”

Section: Introductionmentioning

confidence: 99%

Evaluation of a 3D diamond detector for medical radiation dosimetry

Kanxheri

Servoli

et al. 2017

J. Inst.

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Synthetic diamond has several properties that are particularly suited to applications in medical radiation dosimetry. It is tissue equivalent, not toxic and shows a high resistance to radiation damage, low leakage current and stability of response. It is an electrical insulator, robust and realizable in small size; due to these features there are several examples of diamond devices, mainly planar single-crystalline chemical vapor depositation (sCVD) diamond, used for relative dose measurement in photon beams. Thanks to a new emerging technology, diamond devices with 3-dimensional structures are produced by using laser pulses to create graphitic paths in the diamond bulk. The necessary bias voltage to operate such detector decreases considerably while the signal response and radiation resistance increase. In order to evaluate the suitability of this new technology for measuring the dose delivered by radiotherapy beams in oncology a 3D polycrystalline (pCVD) diamond detector designed for single charged particle detection has been tested and the photon beam profile has been studied. The good linearity and high sensitivity to the dose observed in the 3D diamond, opens the way to the possibility of realizing a finely segmented device with the potential for dose distribution measurement in a single exposure for small field dosimetry that nowadays is still extremely challenging.

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“…Water phantom and commercial ionization chambers were used for calibration and comparison with commercial dosimeters [155][156][157][158]. Other than x-ray and electron beams [159] such Schottky diode detectors have also been tested for small field [160] photon beams in clinical radiation therapy ( Figure 8IV) [161]. Moreover the same PIM structure had been irradiated with 20nm to 100nm UV and EUV radiation with very good photoconductivity, without undesirable memory effect, good response time and high signal to noise ratios [162].…”

Section: Scd Detectors (Figure 9)mentioning

confidence: 99%

Microwave Plasma CVD Grown Single Crystal Diamonds - A Review

Mallik

2016

J. Coat. Sci. Technol.

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Diamond offers a range of unique properties, including wide band of optical transmission, highest thermal conductivity, stiffness, wear resistance and superior electronic properties. Such high-end properties are not found in any other material, so theoretically it can be used in many technological applications. But the shortcoming has been the synthesis of the diamond material in the laboratory for any meaningful use. Although microwave plasma chemical vapour deposited (MPCVD) has been in practice since 1980s for the diamond growth but it is in the past 7-8 years that its potential has been realised by the industry due to capability of MPCVD to deposit diamond, pure and fast, for commercial uses. There are many CVD techniques for growing diamond but among them MPCVD can only make single crystal diamond (SCD) effectively. SCD grown by MPCVD is also superior to other forms of diamond produced in the laboratory. For example, SCD is necessary for the best electronic properties-often outperforming the polycrystalline diamond (PCD), the high pressure high temperature (HPHT) diamond and the natural diamond. In many applications the short lateral dimensions of the lab-grown diamond available is a substantial limitation. Polycrystalline CVD diamond layers grown by hot filament CVD solved this problem of large area growth, but the presence of grain boundaries are not appropriate for many uses. On the other hand, there is still limitation in the area over which SCDs are grown by MPCVD, only upto 10-15 mm lateral sizes could have been achieved so far, while there are recipes which rapidly grow several mm thick bulk SCDs. This lateral size limitation of SCDs is primarily because of the small seed substrate dimension. Although natural and HPHT diamonds may not be suitable for the intended application, still they are routinely used as substrates on which SCD is deposited. But the problem lies in the availability of large area natural SCD seeds which are extremely rare and expensive. Moreover, large diamond substrate plates suitable for CVD diamond growth have not been demonstrated by HPHT because of the associated high economic risk in their fabrication and use. Other than lateral dimension, purity of SCD is also very important for technological use. Natural diamond is often strained and defective, and this causes twins and other problems in the CVD overgrowth or fracture during synthesis. In addition, dislocations which are prevalent in the natural diamond substrate are replicated in the CVD layer, also degrading its electronic properties. HPHT synthetic diamond is also limited in size, and generally is of poorer quality in the larger stones, with inclusions being a major problem. There will be much research interest in the next 10 years for the MPCVD growth of SCD. Purer and bigger SCDs will be tried to grow with faster and reproducible MPCVD recipes. Here the MPCVD growth of SCD is being reviewed keeping in mind its huge technological significance in the next decades or so. Discoveries of the commercial productions of silico...

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The influence of detector size relative to field size in small-field photon-beam dosimetry using synthetic diamond crystals as sensors

Cited by 7 publications

References 41 publications

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

Diamond Detectors for Radiotherapy X-Ray Small Beam Dosimetry

Evaluation of a 3D diamond detector for medical radiation dosimetry

Microwave Plasma CVD Grown Single Crystal Diamonds - A Review

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