Metal Oxide Semiconductor Field Effect Transistor Dosimeters Research Articles

Patient dosimetry for total body irradiation using single‐use MOSFET detectors

We studied the usefulness of a new type of solid‐state detector, the OneDose single‐use MOSFET (metal oxide semiconductor field effect transistor) dosimeter, for entrance dose measurements for total body irradiation (TBI). The factory calibration factors supplied by the manufacturer are applicable to conventional radiotherapy beam arrangements and therefore may not be expected to be valid for TBI dosimetry because of the large field sizes and extended source‐to‐axis distances used. OneDose detectors were placed under a 1‐cm thick bolus at the head, neck, and umbilicus of 9 patients undergoing TBI procedures. Thermoluminescent dosimeters (TLDs) were placed beside the detectors. We found that the OneDose readings differed from the TLD readings by 4.6% at the head, 1.7% at the neck, and 3.9% at the umbilicus, with corresponding standard deviations of 3.9%, 2.2%, and 2.7%. For all patient measurements, 95% of the OneDose readings fell within 3.3%±6.0% of the TLD readings. Anthropomorphic phantom measurements showed differences of −0.1% at the neck and −1.2% midway between the phantom's carina and umbilicus. Our results suggest that these detectors could be used for TBI quality assurance monitoring, although TLDs should remain the standard when critical dose measurements are performed. If OneDose detectors are to be used for TBI, the use of more than one at each location is strongly recommended. Because the detectors are designed for single use, they cannot be individually calibrated. However, to obtain institution‐specific correction factors for better applicability to TBI dosimetry, measurements of several detectors taken from a particular lot could also be obtained in phantom with the TBI geometry configurations used for patient treatment.PACS numbers: 87.53.Bn, 85.30.Tv, 87.55.‐x

Energy Correction Factors for Silicon Semiconductor Dosimeter in Adult-male Phantom for Accurate Measurement of Organ Doses

Metal oxide semiconductor field effect transistor (MOSFET) dosimeters are used to measure radiation dose in various medical applications and radiation safety. The advantage of the MOSFET dosimeter is that it is very small and provides practically real-time reading. However, given the fact that it is made mainly of silicon and epoxy, which are not ideally tissue equivalent, the MOSFET dosimeter shows some energy dependence for low-energy photons and will overestimate the energy deposition or absorbed dose in tissue when it is used in a phantom, due to the existence of scattered low-energy photons in the phantom. The present study determined, by Monte Carlo simulations with MCNPX, the relative response of the MOSFET dosimeter to the tissue dose, and thereby the energy correction factors, at various dosimeter locations in the ATOM adult-male phantom, in order to be able to accurately measure organ and tissue doses. The calculated values of relative response were 1.0-1.2 and 1.0-1.1 for 0.662 MeV and 1.25 MeV photons, respectively, which shows that if we do not use appropriate correction factors, the measurement of an organ dose could be overestimated by 10-20%, depending on the measurement condition. The result in study also shows that the energy correction factors are not very sensitive to the detailed energy spectrum of the photon field, and that the energy correction factors determined from the 0.662 MeV and 1.25 MeV photons can be used in the radiation fields in nuclear power plants without significant errors.

Monte Carlo simulation of MOSFET dosimeter for electron backscatter using the GEANT4 code

The aim of this study is to investigate the influence of the body of the metal-oxide-semiconductor field effect transistor (MOSFET) dosimeter in measuring the electron backscatter from lead. The electron backscatter factor (EBF), which is defined as the ratio of dose at the tissue-lead interface to the dose at the same point without the presence of backscatter, was calculated by the Monte Carlo simulation using the GEANT4 code. Electron beams with energies of 4, 6, 9, and 12 MeV were used in the simulation. It was found that in the presence of the MOSFET body, the EBFs were underestimated by about 2%-0.9% for electron beam energies of 4-12 MeV, respectively. The trend of the decrease of EBF with an increase of electron energy can be explained by the small MOSFET dosimeter, mainly made of epoxy and silicon, not only attenuated the electron fluence of the electron beam from upstream, but also the electron backscatter generated by the lead underneath the dosimeter. However, this variation of the EBF underestimation is within the same order of the statistical uncertainties as the Monte Carlo simulations, which ranged from 1.3% to 0.8% for the electron energies of 4-12 MeV, due to the small dosimetric volume. Such small EBF deviation is therefore insignificant when the uncertainty of the Monte Carlo simulation is taken into account. Corresponding measurements were carried out and uncertainties compared to Monte Carlo results were within +/- 2%. Spectra of energy deposited by the backscattered electrons in dosimetric volumes with and without the lead and MOSFET were determined by Monte Carlo simulations. It was found that in both cases, when the MOSFET body is either present or absent in the simulation, deviations of electron energy spectra with and without the lead decrease with an increase of the electron beam energy. Moreover, the softer spectrum of the backscattered electron when lead is present can result in a reduction of the MOSFET response due to stronger recombination in the SiO2 gate. It is concluded that the MOSFET dosimeter performed well for measuring the electron backscatter from lead using electron beams. The uncertainty of EBF determined by comparing the results of Monte Carlo simulations and measurements is well within the accuracy of the MOSFET dosimeter (< +/- 4.2%) provided by the manufacturer.

Technical Evaluation of Radiation Dose Delivered in Prostate Cancer Patients as Measured by an Implantable MOSFET Dosimeter

To perform a comparison of the daily measured dose at depth in tissue with the predicted dose values from treatment plans for 29 prostate cancer patients involved in a clinical trial. Patients from three clinical sites were implanted with one or two dosimeters in or near the prostatic capsule. The implantable device, known as the DVS, is based on a metal-oxide-semiconductor field effect transistor (MOSFET) detector. A portable telemetric readout system couples to the dosimeter antenna (visible on kilovoltage, computed tomography, and ultrasonography) for data transfer. The predicted dose values were determined by the location of the MOSFET on the treatment planning computed tomography scan. Serial computed tomography images were taken every 2 weeks to evaluate any migration of the device. The clinical protocol did not permit alteration of the treatment parameters using the dosimeter readings. For some patients, one of several image-guided radiotherapy (RT) modalities was used for target localization. The evaluation of dose discrepancy showed that in many patients the standard deviation exceeded the previous values obtained for the dosimeter in a phantom. In some patients, the cumulative dose disagreed with the planned dose by > or =5%. The data presented suggest that an implantable dosimeter can help identify dose discrepancies (random or systematic) for patients treated with external beam RT and could be used as a daily treatment verification tool for image-guided RT and adaptive RT. The results of our study have shown that knowledge of the dose delivered per fraction can potentially prevent over- or under-dosage to the treatment area and increase the accuracy of RT. The implantable dosimeter could also be used as a localizer for image-guided RT.

TH‐C‐M100E‐10: A Correction Method for the MOSFET Energy Dependence Response to Therapeutic Proton Beams

The energy‐dependence response of the metal oxide semiconductor field‐effect transistor (MOSFET) dosimeter has been investigated with regard to therapeutic proton beams. The MOSFET configurations used include the commercial standard MOSFET (TN‐502RD), the microMOSFET (TN‐502RDM) dosimeters, and a prototype MOSFET with no encapsulation. Proton beams of non‐modulated pristine and modulated Spread‐Out Bragg Peak (SOBP) of 5 cm and 10 cm widths were used with beam ranges of 8.9cm, 15.9cm and 25.9cm in water. Each MOSFET dosimeter was calibrated at the center of the modulated 10 cm SOBP proton beam with conditions of 1 cGy per MU. The MOSFET energy‐dependence response was quantitatively evaluated by the ratio of measured doses between the MOSFET and an ionization chamber in a same condition. The three dosimeters showed a similar response for the pristine proton beams at various beam ranges. This indicates that the variation in dosimeter response is dominated by the change of the linear energy transfer (LET) for the used proton beam and not by the MOSFET encapsulation thickness. The observed MOSFET trends for various pristine proton beams have been modeled by an analytical function , where Rres is the residue range (distance to the distal 90% level dose), and A, B, C are constants. A similar modeling has been performed for modulated SOBP proton beams at different widths and for various beam ranges. The k (Rres) function has been used as a correction factor for patient dose measured by MOSFETs for corresponding residue ranges; this resulted in dose measurements with an uncertainty of less than 3.0% for various proton beams.

Experimental evaluation of a MOSFET dosimeter for proton dose measurements

The metal oxide semiconductor field-effect transistor (MOSFET) dosimeter has been widely studied for use as a dosimeter for patient dose verification. The major advantage of this detector is its size, which acts as a point dosimeter, and also its ease of use. The commercially available TN502RD MOSFET dosimeter manufactured by Thomson and Nielsen has never been used for proton dosimetry. Therefore we used the MOSFET dosimeter for the first time in proton dose measurements. In this study, the MOSFET dosimeter was irradiated with 190 MeV therapeutic proton beams. We experimentally evaluated dose reproducibility, linearity, fading effect, beam intensity dependence and angular dependence for the proton beam. Furthermore, the Bragg curve and spread-out Bragg peak were also measured and the linear-energy transfer (LET) dependence of the MOSFET response was investigated. Many characteristics of the MOSFET response for proton beams were the same as those for photon beams reported in previous papers. However, the angular MOSFET responses at 45, 90, 135, 225, 270 and 315 degrees for proton beams were over-responses of about 15%, and moreover the MOSFET response depended strongly on the LET of the proton beam. This study showed that the angular dependence and LET dependence of the MOSFET response must be considered very carefully for quantitative proton dose evaluations.

A tomographic physical phantom of the newborn child with real-time dosimetry. II. Scaling factors for calculation of mean organ dose in pediatric radiography

Following the recent completion of a tomographic physical newborn dosimetry phantom with incorporated metal-oxide-semiconductor field effect transistor (MOSFET) dosimetry system, it was necessary to derive scaling factors in order to calculate organ doses in the physical phantom given point dose measurements via the MOSFET dosimeters (preceding article in this issue). In this study, we present the initial development of scaling factors using projection radiograph data. These point-to-organ dose scaling factors (SF(POD)) were calculated using a computational phantom created from the same data set as the physical phantom, but which also includes numerous segmented internal organs and tissues. The creation of these scaling factors is discussed, as well as the errors associated when using only point dose measurements to calculate mean organ doses and effective doses in physical phantoms. Scaling factors for various organs ranged from as low as 0.70 to as high as 1.71. Also, the ability to incorporate improvements in the computational phantom into the physical phantom using scaling factors is discussed. An comprehensive set of SF(POD) values is presented in this article for application in pediatric radiography of newborn patients.

Radiological Characterization of Semiconductor Materials in Field Effect Transistor Dosimeter by Monte Carlo Method

The use of semiconductor materials in radiation processing, radiation therapy and diagnostics, and detection of cosmic radiation motivated development of numerical methods for its radiological characterization. This paper presents the application of the Monte Carlo method using the FOTELP-2K4 code for radiological characterization of Metal Oxide Semiconductor Field Effect Transistor (MOSFET) dosimeter. The advantages of MOSFET dosimeters include small size, immediate readout, and ease of use for a wide photon energy range. In order to determine the dosimeter response accurately, distribution of the absorbed dose in the MOSFET structure has been investigated. Our results show that the absorbed dose distribution calculated by the presented simulation model compares well with the published data.

MOSFET 선량계를 이용한 In-vivo 선량의 확인

In-vivo dosimetry is an essential tool of quality assurance programs in radiotherapy. The most commonly used techniques to verify dose are thermoluminescence dosimeter (TLD) and diode detectors. Metal oxide semiconductor field-effect transistor (MOSFET) has been recently proposed for using in radiation therapy with many advantages. The reproducibility, linearity, isotropy, dose rate dependence of the MOSFET dosimeter were studied and its availability was verified. Consequently the results can be used to improve therapeutic planning procedure and minimize treatment errors in radiotherapy.

MOSFET dosimeter depth‐dose measurements in heterogeneous tissue‐equivalent phantoms at diagnostic x‐ray energies

The objective of the present study was to explore the use of the TN-1002RD metal-oxide-semiconductor field effect transistor (MOSFET) dosimeter for measuring tissue depth dose at diagnostic photon energies in both homogeneous and heterogeneous tissue-equivalent materials. Three cylindrical phantoms were constructed and utilized as a prelude to more complex measurements within tomographic physical phantoms of pediatric patients. Each cylindrical phantom was constructed as a stack of seven 5-cm-diameter and 1-cm-thick discs of materials radiographically representative of either soft tissue (S), bone (B), or lung tissue (L) at diagnostic photon energies. In addition to a homogeneous phantom of soft tissue (SSSSSSS), two heterogeneous phantoms were constructed: SSBBSSS and SBLLBSS. MOSFET dosimeters were then positioned at the interface of each disc, and the phantoms were then irradiated at 66 kVp and 200 mAs. Measured values of absorbed dose at depth were then compared to predicated values of point tissue dose as determined via Monte Carlo radiation transport modeling. At depths exceeding 2 cm, experimental results matched the computed values of dose with high accuracy regardless of the dosimeter orientation (epoxy bubble facing toward or away from the x-ray beam). Discrepancies were noted, however, between measured and calculated point doses near the surface of the phantom (surface to 2 cm depth) when the dosimeters were oriented with the epoxy bubble facing the x-ray beam. These discrepancies were largely eliminated when the dosimeters were placed with the flat side facing the x-ray beam. It is therefore recommended that the MOSFET dosimeters be oriented with their flat sides facing the beam when they are used at shallow depths or on the surface of either phantoms or patients.

Po‐Poster ‐ 12: Evaluation of MOSFETS for Gamma Knife® helmet factor measurements

The Gamma Knife ® is calibrated annually using the 18 mm collimator helmet; the dose rates for the other helmets are determined by measuring the radiation output relative to the 18 mm helmet. These relative measurements yield a helmet factor for each collimator helmet, which is incorporated into the treatment planning software, and is validated during annual quality assurance testing. Traditionally, helmet factors have been measured using 1×1×1 mm3 thermoluminescent dosimeters (TLDs). Determining helmet factors using this technique is a challenging process since the TLDs are small and fragile, and their preparation, calibration and readout is very time consuming. They also have a large uncertainty of 2 to 5%. The goal of this research is to investigate the use of metal oxide semiconductor field effect transistor dosimeters (MOSFETs) for Gamma Knife® helmet factor measurements. The MOSFET linearity and reproducibility was first characterized using a teletherapy unit; the linearity and reproducibility were both found to be within 2%. The helmet factors were then measured using TLDs, and again using MOSFETs. The TLD results gave helmet factors within 2.5% of the manufacturer's values; the MOSFETs provided helmet factors within 1.3% of the manufacturer's values, in a fraction of the time it took to generate the TLD results. This investigation confirms that MOSFETs can be used to measure Gamma Knife® helmet factors more quickly and accurately than TLDs.

SU-FF-T-226: A Dosimetric Evaluation of a New MOSFET Radiation Dosimeter for Total Body Irradiation

Purpose: To evaluate the use of a new metal oxide semiconductor field effect transistor (MOSFET) as an in vivo dosimeter for patients receiving total body irradiation (TBI). Method and Materials: The dose responses of the MOSFET dosimeters are compared to that of thermoluminescent dosimeters (TLDs) during TBI treatments of 4 patients. Each patient is treated AP/PA with 60Co irradiation, a field size of 44 × 44 cm2 at isocenter, and an SAD of 338.2 cm. One MOSFET dosimeter and 4 TLD crystals are placed at the entrance and exit of five anatomical sites: head, chest, lung, umbilicus, and pelvis. Additionally, the dosimeters are positioned at a calibration point in air to normalize the dosimeter readings. The MOSFET dosimeters are read instantaneously with a digital hand held reader, and the TLDs are measured with a TLD reader. Results: The measured midline dose rates and calculated treatment times of the MOSFET dosimeters and TLDs are compared. The average deviations of the MOSFETs from the TLDs are 6% at the head, 7% at the chest, 3% at the lung, 1% at the umbilicus, and 4% at the pelvis. The maximum deviation of the MOSFETs from the TLDs is 11.5%, and the minimum deviation is 0.94%. The MOSFET calculated treatment times are within 5% of the TLD calculated treatment times. Three dosimeters failed during the treatments. Conclusion: These results show that the new MOSFET dosimeters are an adequate and efficient measurement system for TBI treatments. The cause of dosimeter failure has not been determined as further analysis and experience with the MOSFET dosimeters are necessary. It is recommended that more than one MOSFET dosimeter is used per site for TBI treatment in case of dosimeter failure.

In vivo measurements with MOSFET detectors in oropharynx and nasopharynx intensity-modulated radiation therapy

To evaluate the feasibility of in vivo measurements with metal oxide semiconductor field effect transistor (MOSFET) dosimeters for oropharynx and nasopharynx intensity-modulated radiation therapy (IMRT). During a 1-year period, in vivo measurements of the dose delivered to one or two points of the oral cavity by IMRT were obtained with MOSFET dosimeters. Measurements were obtained during each session of 48 treatment plans for 21 patients, all of whom were fitted with a custom-made mouth plate. Calculated and measured values were compared. A total of 344 and 452 measurements were performed for the right and left sides, respectively, of the oral cavity. Seventy percent of the discrepancies between calculated and measured values were within +/-5%. Uncertainties were due to interfraction patient positions, intrafraction patient movements, and interfraction MOSFET positions. Nevertheless, the discrepancies between the measured and calculated means were within +/-5% for 92% and 95% of the right and left sides, respectively. Comparison of these discrepancies and the discrepancies between calculated values and measurements made on a phantom revealed that all differences were within +/-5%. Our experience demonstrates the feasibility of in vivo measurements with MOSFET dosimeters for oropharynx and nasopharynx IMRT.

Measurement of ionizing radiation using carbon nanotube field effect transistor

Single-walled carbon nanotubes (SWNTs) are a new class of highly promising nanomaterials for future nano-electronics. Here, we present an initial investigation of the feasibility of using SWNT field effect transistors (SWNT-FETs) formed on silicon-oxide substrates and suspended FETs for radiation dosimetry applications. Electrical measurements and atomic force microscopy (AFM) revealed the intactness of SWNT-FET devices after exposure to over 1 Gy of 6 MV therapeutic x-rays. The sensitivity of SWNT-FET devices to x-ray irradiation is elucidated by real-time dose monitoring experiments and accumulated dose reading based on threshold voltage shift. SWNT-FET devices exhibit sensitivities to x-rays that are at least comparable to or orders of magnitude higher than commercial MOSFET (metal-oxide semiconductor field effect transistor) dosimeters and could find applications as miniature dosimeters for microbeam profiling and implantation.

Effects of temperature variation on MOSFET dosimetry

This note investigates temperature effects on dosimetry using a metal oxide semiconductor field effect transistor (MOSFET) for radiotherapy x-ray treatment. This was performed by analysing the dose response and threshold voltage outputs for MOSFET dosimeters as a function of ambient temperature. Results have shown that the clinical semiconductor dosimetry system (CSDS) MOSFET provides stable dose measurements with temperatures varying from 15 °C up to 40 °C. Thus standard irradiations performed at room temperature can be directly compared to in vivo dose assessments performed at near body temperature without a temperature correction function. The MOSFET dosimeter threshold voltage varies with temperature and this level is dependent on the dose history of the MOSFET dosimeter. However, the variation can be accounted for in the measurement method. For accurate dosimetry, the detector should be placed for approximately 60 s on a patient to allow thermal equilibrium before measurements are taken with the final reading performed whilst still attached to the patient or conversely left for approximately 120 s after removal from the patient if initial readout was measured at room temperature to allow temperature equilibrium to be established.

Characterization of high-sensitivity metal oxide semiconductor field effect transistor dosimeters system and LiF:Mg,Cu,P thermoluminescence dosimeters for use in diagnostic radiology

Monitoring radiation exposure during diagnostic radiographic procedures has recently become an area of interest. In recent years, the LiF:Mg,Cu,P thermoluminescence dosimeter (TLD-100H) and the highly sensitive metal oxide semiconductor field effect transistor (MOSFET) dosimeter were introduced as good candidates for entrance skin dose measurements in diagnostic radiology. In the present study, the TLD-100H and the MOSFET dosimeters were evaluated for sensitivity, linearity, energy, angular dependence, and post-exposure response. Our results indicate that the TLD-100H dosimeter has excellent linearity within diagnostic energy ranges and its sensitivity variations were under 3% at tube potentials from 40 Vp to 125 kVp . Good linearity was also observed with the MOSFET dosimeter, but in low-dose regions the values are less reliable and were found to be a function of the tube potentials. Both dosimeters also presented predictable angular dependence in this study. Our findings suggest that the TLD-100H dosimeter is more appropriate for low-dose diagnostic procedures such as chest and skull projections. The MOSFET dosimeter system is valuable for entrance skin dose measurement with lumbar spine projections and certain fluoroscopic procedures.

Estimation of mean-glandular dose from monitoring breast entrance skin air kerma using a high sensitivity metal oxide semiconductor field effect transistor (MOSFET) dosimeter system in mammography

Estimation of mean-glandular dose (MGD) has been investigated in recent years due to the potential risks of radiation-induced carcinogenesis associated with the mammographic examination for diagnostic radiology. In this study, a new technique for immediate readout of breast entrance skin air kerma (BESAK) using high sensitivity MOSFET dosimeter after mammographic projection was introduced and a formula for the prediction of tube output with exposure records was developed. A series of appropriate conversion factors was applied to the MGD determination from the BESAK. The study results showed that signal response of the high sensitivity MOSFET exhibited excellent linearity within mammographic dose ranges, and that the energy dependence was less than 3% for each anode/filter combination at the tube potentials 25–30 kV. Good agreement was observed between the BESAK and the tube exposure output measurement for breasts thicker than 30 mm. In addition, the air kerma estimated from our prediction formula provided sufficient accuracy for thinner breasts. The average MGD from 120 Asian females was 1.5 mGy, comparable to other studies. Our results suggest that the high sensitivity MOSFET dosimeter system is a good candidate for immediately readout of BESAK after mammographic procedures.

Comparison of angular free-in-air and tissue-equivalent phantom response measurements in p-MOSFET dosimeters.

Metal Oxide Semiconductor Field Effect Transistor (MOSFET) radiation dosimeters have found recent application in providing real-time measurement in diagnostic radiology as well as in radiotherapy. Due to the design of the MOSFET dosimeter, the response is dependent on both energy and angulation with respect to the direction of primary radiation. The axial angular dependence has been characterized for both free-in-air and for tissue-equivalent phantoms. However, neither the angular dependence normal (90-degree) to the axial rotation, nor the effects of various tissue compositions on angular dependence, have been investigated for radiation energies in the diagnostic range. To characterize the angular dependence normal to the axial rotation, we exposed three "high sensitivity" MOSFET dosimeters simultaneously to x-rays from a medical diagnostic x-ray unit over a 360-degree rotation, at 22.5-degree increments, for both free-in-air and in lung, skeletal, and soft tissue-equivalent phantoms. The MOSFET dosimeters clearly showed an angular dependence in the orientation normal-to-axial as well as in the axial rotation, both for free-in-air and in tissue-equivalent phantoms. Significant variations in response occurred when the MOSFETs were exposed at incident angles between 90 degrees and 180 degrees normal-to-axial, as compared to the normal position (i.e., the zero-degree position with the bubble-side of the MOSFETs facing the radiation source). A maximum decrease in response to 32% of normal was observed when the distal ends (end opposite the wire lead) of the dosimeters were pointing directly away from the x-ray source (270-degree position). To avoid significant errors in MOSFET dosimeter readings, placement of the dosimeters should be consistent, and care should be taken to avoid orienting the dosimeter with its sensitive region (bubble side) facing away from the source of primary radiation at particular angles.

The characterization of a commercial MOSFET dosimeter system for use in diagnostic x ray.

A commercial patient dose verification system utilizing non-invasive metal oxide semiconductor field effect transistor (MOSFET) dosimeters originally designed for radiotherapy applications has been evaluated for use at diagnostic energy levels. The system features multiple dosimeters that may be used to monitor entrance or exit skin dose and intracavity doses in phantoms in real time. We have characterized both the standard MOSFET dosimeter designed for radiotherapy dose verification and a newly developed "high sensitivity" MOSFET dosimeter designed for lower dose measurements. The sensitivity, linearity, angular response, post-exposure response, and physical characteristics were evaluated. The average sensitivity (free in air, including backscatter) of the radiotherapy MOSFET dosimeters ranged from 3.55 x 10(4) mV per C kg(-1) (9.2 mV R(-1)) to 4.87 x 10(4) mV per C kg(-1) (12.6 mV R(-1)) depending on the energy of the x-ray field. The sensitivity of the "high sensitivity" MOSFET dosimeters ranged from 1.15 x 10(5) mV per C kg(-1) (29.7 mV R(-1)) to 1.38 x 10(5) mV per C kg(-1) (35.7 mV R(-1)) depending on the energy of the x-ray field. The high sensitivity dosimeters demonstrated excellent linearity at high energies (90 and 120 kVp) and acceptable linearity at lower energies (60 kVp). The angular response was significant for free-in-air exposures, as illustrated by the sensitivity differences between the two sides of the dosimeter, but was excellent for measurements within a tissue equivalent cylinder. The post-exposure drift response is a complicated but reproducible function of time. Real-time monitoring requires little if any corrections for the post-exposure drift response. The MOSFET dosimeter system brings some unique capabilities to diagnostic radiology dosimetry including small size, real-time capabilities, nondestructive measurement, good linearity, and a predictable angular response.