MOSFET Dosimetry on Modern Radiation Oncology Modalities

Rosenfeld, Anatoly

doi:10.1093/oxfordjournals.rpd.a006009

Cited by 90 publications

(46 citation statements)

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“…In general, it is of extreme importance to calculate the PD down to the level of 0.1% of the central axis maximum dose (dmax) [8] and its determination has been the subject of extensive investigation [2,[9][10][11][12][13][14][15][16][17][18][19][20] . Metal oxide semiconductor field effect transistor (MOSFET) is used as a clinical dosimeter for radiotherapy beams, and mobileMOSFET seems to be the appropriate dose verification system [21][22][23][24][25][26][27][28][29][30] , since due to its small size it can be positioned very easily on the patient's skin, and can evaluate the delivered dose both at the target and at organs at risk [21] . This paper aims to assess the PD in high-energy photon beam radiotherapy as a function of the distance from the edge of the field, the depth, the field size and the energy of the photon beam, while the overall accuracy has been investigated by comparing the derived experimental results to corresponding ones obtained with an ionization chamber.…”

Section: Introductionmentioning

confidence: 99%

Peripheral dose measurement in high-energy photon radiotherapy with the implementation of MOSFET

Vlachopoulou

Malatara²,

Delis³

et al. 2010

WJR

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AIM:To study the peripheral dose (PD) from highenergy photon beams in radiotherapy using the metal oxide semiconductor field effect transistor (MOSFET) dose verification system. METHODS:The radiation dose absorbed by the MOS-FET detector was calculated taking into account the manufacturer's Correction Factor, the Calibration Factor and the threshold voltage shift. PD measurements were carried out for three different field sizes (5 cm × 5 cm, 10 cm × 10 cm and 15 cm × 15 cm) and for various depths with the source to surface distance set at 100 cm. Dose measurements were realized on the central axis and then at distances (1 to 18 cm) parallel to the edge of the field, and were expressed as the percentage PD (% PD) with respect to the maximum dose (dmax).The accuracy of the results was evaluated with respect to a calibrated 0.3 cm 3 ionization chamber. The reproducibility was expressed in terms of standard deviation (s) and coefficient of variation.RESULTS: % PD is higher near the phantom surface and drops to a minimum at the depth of dmax, and then tends to become constant with depth. Internal scatter radiation is the predominant source of PD and the depth dependence is determined by the attenuation of the primary photons. Closer to the field edge, where internal scatter from the phantom dominates, the % PD increases with depth because the ratio of the scatter to primary increases with depth. A few centimeters away from the field, where collimator scatter and leakage dominate, the % PD decreases with depth, due to attenuation by the water. The % PD decreases almost exponentially with the increase of distance from the field edge. The decrease of the % PD is more than 60% and can reach up to 90% as the measurement point departs from the edge of the field. For a given distance, the % PD is significantly higher for larger field sizes, due to the increase of the scattering volume. Finally, the measured PD obtained with MOSFET is higher than that obtained with an ionization chamber with percentage differences being from 0.6% to 34.0%. However, when normalized to the central dmax this difference is less than 1%. The MOSFET system, in the early stage of its life, has a dose measurement reproducibility of within 1.8%, 2.7%, 8.9% and 13.6% for 22.8, 11.3, 3.5 and 1.3 cGy dose assessments, respectively. In the late stage of MOSFET life the corresponding values change to 1.5%, 4.8%, 11.1% and 29.9% for 21.8, 2.9, 1.6 and 1.0 cGy, respectively. CONCLUSION:Comparative results acquired with the MOSFET and with an ionization chamber show fair agreement, supporting the suitability of this measurement for clinical in vivo dosimetry.

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Section: Introductionmentioning

confidence: 99%

Peripheral dose measurement in high-energy photon radiotherapy with the implementation of MOSFET

Vlachopoulou

Malatara²,

Delis³

et al. 2010

WJR

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“…MOSFET dosimeters have the added benefit of a micronscale sensitive volume, allowing them to measure the absorbed dose in steep dose gradient conditions. 5,6) Larger detectors can only measure a volume average dose, which lacks precision and results in a large uncertainty in the measurement like ionization chamber and TLD detectors in a build up region of MV X-ray from LINAC . In an X-ray field delivered by a medical LINAC, the thin sensitive volume of the MOSFET proves invaluable in the build-up region of the depth dose curve, where the dose gradient is very steep.…”

Section: Introductionmentioning

confidence: 99%

“…They can provide accurate integrated dose readings, but their reading becomes less accurate when the mean energy spectrum of the beam is less than 250 keV. Below 200 keV, the MOSFET begins to over respond and demand calibration in the same field 6,10) This paper aims to investigate the performance of the new MOSkin™ dosimeter and a fiber optic dosimetry system when irradiated on a LINAC. The MOSkin™ was designed at the Centre for Medical Radiation Physics (CMRP), University of Wollongong, Australia, while the fiber optic dosimetry (FOD) system utilizes a BCF-20 scintillating crystal from Saint-Gobain Crystals (Bicron).…”

Section: Introductionmentioning

confidence: 99%

Comparison of the New MOSkin Detector and Fiber Optic Dosimetry System for Radiotherapy

Kwan

Lee

Yoo

et al. 2008

Journal of Nuclear Science and Technology

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In radiotherapy, interest in real-time dosimetry stems from the desire to monitor the dose delivered to the target volume and the surrounding normal tissue to enable clinicians to track the progress of the treatment, and prevent surrounding tissue from receiving too much radiation dose. In this study, the dosimetric performance of the new MOSkin dosimeter and a Bicron BCF-20 scintillating fiber was compared to depth dose measurements taken with a Farmer-type ionization chamber. The performance of the MOSkin and BCF-20 detectors in the build-up region of the depth dose curve, where the dose gradient is steep, is also compared to readings taken with an Attix chamber. At depths greater than 15 mm, the MOSkin readings deviated from the ion chamber readings by up to 4%, while the fiber optic dosimeter always remained within 3% of the ionization chamber reading. In the build-up region, the MOSkin proved quite capable of measuring the dose at build up when compared to the Attix chamber results, while the fiber optic dosimeter was not able to measure the dose in this region with a high level of precision due to the thick sensitive volume of the scintillating crystal.

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“…Usually, a pMOS dosimeter, sometimes referred to as RADFET, has a gate oxide thickness of about 1 m, and has been grown using a special process. During the last decade, technology in the field of dosimetry for radiation therapy has matured and several instruments with pMOS as radiation detectors have become commercially available [12,13]. These systems perform well but at a relatively high cost for the main frame and head sensors.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of a low-cost commercial mosfet as radiation dosimeter

Asensio¹,

Carvajal²,

López‐Villanueva³

et al. 2006

Sensors and Actuators A: Physical

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In this work, a low-power commercial MOS transistor was tested as a gamma radiation dosimeter. Due to the small size of its detector, low cost, reproducibility, minimal power requirements, signal conditioning and data processing, it offers excellent possibilities as a dose monitor in radiotherapy. Sensor irradiation in the unbiased mode was aimed at improving patient comfort and facilitating use. Uncertainties in the results were obtained from an exhaustive dosimetric study, following a full statistical study using Monte Carlo analysis techniques. A procedure to compensate for temperature effects was introduced in order to correct the dosimetric parameter extracted. Excellent linearity and good reproducibility were found in the accumulated threshold voltage shift as a function of the accumulated dose, up to 58 Gy (air equivalent). The uncertainty regarding sensor sensitivity was found to be less than 1% for individual device calibration. When collective calibration was carried out, the uncertainty was around 5%, accounting for a set of 31 devices. In this case, a mean value of 29.2 mV/Gy was obtained. In addition, the angular and dose rate dependencies showed good behaviour. These results suggest that the transistor studied would be an excellent candidate for use as the sensing device of a low-cost measurement system capable of in vivo dosimetry.

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MOSFET Dosimetry on Modern Radiation Oncology Modalities

Cited by 90 publications

References 0 publications

Peripheral dose measurement in high-energy photon radiotherapy with the implementation of MOSFET

Peripheral dose measurement in high-energy photon radiotherapy with the implementation of MOSFET

Comparison of the New MOSkin Detector and Fiber Optic Dosimetry System for Radiotherapy

Evaluation of a low-cost commercial mosfet as radiation dosimeter

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