COMPARISON OF ANGULAR FREE-IN-AIR AND TISSUE-EQUIVALENT PHANTOM RESPONSE MEASUREMENTS IN p-MOSFET DOSIMETERS

Pomije, Brian D.; Huh, Chul Haeng; Tressler, Michael A.; Hintenlang, David E.; Bolch, Wesley E.

doi:10.1097/00004032-200105000-00011

Cited by 22 publications

(22 citation statements)

References 6 publications

(37 reference statements)

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“…A standard deviation of 0.5 mV/Gy is obtained from −90 to 90 • of incidence, corresponding with an uncertainty of 5%. This uncertainty is similar to or even below that of other pMOS dosimeters [5][6][7]27,28]. Moreover, no memory effect is observed when irradiating in a different order with different incidence angles.…”

Section: Angular Dependencesupporting

confidence: 73%

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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Section: Angular Dependencesupporting

confidence: 73%

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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“…11 Our methodology ensures the delivery of constant exposure in the sensitivity evaluation. 2,9 All dosimeter models showed a linear response to exposure for the tube potentials and tube currenttime stations evaluated as shown in Figs. 11-14.…”

Section: Resultsmentioning

confidence: 89%

Characterization of metal oxide semiconductor field effect transistor dosimeters for application in clinical mammography

Benevides¹,

Hintenlang

2006

Medical Physics

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Five high-sensitivity metal oxide semiconductor field effect transistor dosimeters in the TN-502 and 1002 series (Thomson Nielsen Electronics Ltd., 25B, Northside Road, Ottawa, ON K2H8S1, Canada) were evaluated for use in the mammography x-ray energy range (22-50 kVp) as a tool to assist in the documentation of patient specific average glandular dose. The dosimeters were interfaced with the Patient Dose Verification System, model No. TN-RD 15, which consisted of a dosimeter reader and up to four dual bias power supplies. Two different dual bias power supplies were evaluated in this study, model No. TN-RD 22 in high-sensitivity mode and a very-high sensitivity prototype. Each bias supply accommodates up to five dosimeters for 20 dosimeters per system. Sensitivity of detectors, defined as the mV/C kg(-1), was measured free in air with the bubble side of the dosimeter facing the x-ray field with a constant exposure. All dosimeter models' angular response showed a marked decrease in response when oriented between 120 degrees and 150 degrees and between at 190 degrees and 220 degrees relative to the incident beam. Sensitivity was evaluated for Mo/Mo, Mo/Rh, and Rh/Rh target-filter combinations. The individual dosimeter model sensitiVity was 4.45 x 10(4) mV/C kg(-1) (11.47 mV R(-1)) for TN-502RDS(micro); 5.93 x 10(4) mV per C kg(-1) (15.31 mV R(-1)) for TN-1002RD; 6.06 x 10(4) mV/C kg(-1) (15.63 mV R(-1)) for TN-1002RDI; 9.49 x 10(4) mV per C kg(-1) (24.49 mV R(-1)) for TN-1002RDM (micro); and 11.20 x 10(4) mV/C kg(-1) (28.82 mV R(-1)) for TN-1002RDS (micro). The energy response is presented and is observed to vary with dosimeter model, generally increasing with tube potential through the mammography energy range. An intercomparison of the high-sensitivity mode of TN-RD-22 was made to the very-high sensitivity bias power supply using a Mo/Mo target-filter. The very-high sensitivity-bias power supply increased dosimeter response by 1.45 +/- 0.04 for dosimeter models TN-1002RD and TN-1002RDM. The responses of all dosimeter models were found to be linear for tube potentials of between 24 and 48 kVp. Dosimeters showed a reproducibility varying from 15.5% to 31.8%. depending on the model of dosimeter. Micro MOSFETS model Nos. TN-1002RDS and TN-1002RDM used in conjunction with their respective high-sensitivity and ultrahigh-sensitivity bias supplies provided the highest sensitivity response of the models evaluated. Either micro MOSFETS model No. TN-1002RDS or TN-1002RDM used in conjunction with the appropriate bias supply provide the best choice for clinical mammography applications. Under these conditions, MOSFET dosimeters can provide a viable option as a dosimeter in the mammography energy range (22-50 kVp). The clinical application of MOSFET dosimeters must take into account the energy dependence and reproducibility to ensure accurate measurements.

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“…Both the simulation and the measurement indicate that the MOSFET dosimeter shows a higher response ͑by ϳ8%͒ for photons coming from the epoxy side, compared with photons from the kapton side. Pomijie et al 28 also observed a similar trend, but their angular dependence was much larger ͑ϳ20%͒. This difference is because they used much lower photon energies ͑90 kVp x rays͒.…”

Section: A Measurement Of Cs-137 From Different Directionsmentioning

confidence: 78%

Monte Carlo modeling of a High‐Sensitivity MOSFET dosimeter for low‐ and medium‐energy photon sources

Wang

Kim

2004

Medical Physics

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Metal-oxide-semiconductor field effect transistor (MOSFET) dosimeters are increasingly utilized in radiation therapy and diagnostic radiology. While it is difficult to characterize the dosimeter responses for monoenergetic sources by experiments, this paper reports a detailed Monte Carlo simulation model of the High-Sensitivity MOSFET dosimeter using Monte Carlo N-Particle (MCNP) 4C. A dose estimator method was used to calculate the dose in the extremely thin sensitive volume. Efforts were made to validate the MCNP model using three experiments: (1) comparison of the simulated dose with the measurement of a Cs-137 source, (2) comparison of the simulated dose with analytical values, and (3) comparison of the simulated energy dependence with theoretical values. Our simulation results show that the MOSFET dosimeter has a maximum response at about 40 keV of photon energy. The energy dependence curve is also found to agree with the predicted value from theory within statistical uncertainties. The angular dependence study shows that the MOSFET dosimeter has a higher response (about 8%) when photons come from the epoxy side, compared with the kapton side for the Cs-137 source.

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COMPARISON OF ANGULAR FREE-IN-AIR AND TISSUE-EQUIVALENT PHANTOM RESPONSE MEASUREMENTS IN p-MOSFET DOSIMETERS

Cited by 22 publications

References 6 publications

Evaluation of a low-cost commercial mosfet as radiation dosimeter

Evaluation of a low-cost commercial mosfet as radiation dosimeter

Characterization of metal oxide semiconductor field effect transistor dosimeters for application in clinical mammography

Monte Carlo modeling of a High‐Sensitivity MOSFET dosimeter for low‐ and medium‐energy photon sources

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