Measurement Of Entrance Skin Dose Research Articles

MEASUREMENT OF ENTRANCE SKIN DOSE AND ABSORBED DOSE TO DIFFERENT ORGANS IN DUAL-ENERGY X-RAY ABSORPTIOMETRY SCANS USING THERMOLUMINESCENCE DOSIMETRY.

Thermoluminescence dosimetry is considered as an effective method in estimating the absorbed doses to organs in different imaging modalities. The present study focuses on dosimetry in dual-energy X-ray absorptiometry scans, for patients, and phantoms in various imaging centres. The cubical LiF (Mg, Ti) thermoluminescence dosemeters were inserted inside the holes of the Rando phantom slabs, to measure the absorbed dose to different organs in the whole body and lumbar scans. According to the results the maximum entrance skin dose was found to be 202.06μGy for Hologic discovery W, which uses the fan beam scanning mode. The Norland XR-800 device took the scans with a much lower dose, as it uses the pencil beam for scanning the patients. The results of the study show that the radiation beam type, patient thickness, imaging technique and scan time may affect the radiation dose received by patient.

Measurement of Entrance Skin Dose in Radiographic Examinations of Pediatric Patients.

This study was conducted to measure the entrance skin dose in radiographic examinations of pediatric patients in King Khalid Hospital, Majmaah, Saudi Arabia. Children have been given special attention since they are often regarded as especially vulnerable to potential hazards. The pediatric population is more susceptible to radiation than the adult population for certain tumor types. The aim of this study is to determine the amount of Entrance Surface Dose (ESD) received by pediatric patients attending the emergency department. Traumatic department registers for pediatric patients admitted to the King Khalid hospital (Majmaah, Saudi Arabia) between 1st February and 31st December 2018 were retrospectively studied for all diagnostic (plain radiographs examinations) imaging did on pediatric (<18 years old) trauma patients. The entrance surface dose was used to calculate the total radiation dose for each patient. One hundred and twenty patients encountered the inclusion criteria of the study and their doses (chest, skull, and extremities) were assessed. The mean of radiation exposure factors were 65.4 ± 7.9 (71.3 - 89.9) and 1.3 ± 0.2 (0.3-2.5) for X-ray tube potential (kVp) and current (mAs), respectively. The measured dose for pediatric patients were 0.10 ± 0.02 (0.09 - 0.37), 0.18 ± 0.04 (0.06 -0.59) and 0.09 ± 0.03 (0.03 -0.45) for chest, skull, and extremities, respectively. The mean Entrance surface dose received by trauma patients was 0.03-0.59 mGy. 51.7% (62 patients) of the patients received ≤ 0.25 mGy while around 48.3% (58 patients) received ≥ 0.26 mGy radiation dose from those examinations. Trauma patients attending to traumatic radiology department obtain substantial Entrance surface dose from chest, skull, and extremities imaging procedures within their initial assessment. The radiation exposure can also be lowered by optimizing each examination, therefore more studies are recommended for this task. The results obtained can be used as the basis for local reference dosages for X-ray examinations.

Chest X-rays of newborns in a medical facility: variation between the entrance skin dose measurements using the indirect and direct methods for clinical dose audit

This study aims to determine the mean and 75th percentile entrance skin dose (ESDcal) from anteroposterior (AP) chest X-rays using machine parameters (indirect method). Also, a comparison was made between the ESDcaland already determined thermoluminescent dosimeter (TLD) measurements (ESDTLD) from a previous study from the same patients' data. In addition, the results were compared to similar articles, where the direct and indirect methods were used in estimating ESD to newborns. The study determined the digital radiography (DR) X-ray machine output using a calibrated XR Multidetector (silicon photodiode). X-ray machine milliampere-seconds (mAs), peak kilovoltage (kVp), focus to detector distance (FDD) and focus to skin distance (FSD) were used from a previous study. The mean kVp and mAs were 56.63 (52-60) and 5.7 (5-6.3) and the patient thickness was 9.5 (8-11.5) cm. The mean ESDs of the newborn between 0 and 28days were 0.67 ± 0.09mGy, and the 75th percentile was 0.75mGy. The effective dose (E) for the 40 patients was 0.19mSv and the estimated prenatal cancer risk ranged from (5-24.7) 10-6 Sv-1. The variation between the indirect and the direct methods for assessing ESD was 39.6 (33.7-45.1)%. The 75th percentile ESD was the highest compared to the American College of Radiology-American Association of Physicists in Medicine-Society for Pediatric Radiology (ACR-AAPM-SPR), European Commission (EC) and United Kingdom (UK) reports. Comparison of both methods for assessing ESD was within 40% as compared to other studies. Based on the above results, the indirect method can be implemented for clinical dose audit.

Measurement of Entrance Skin Dose and the Dose Received by Different Organs in Panoramic Dental Imaging.

Background: Thermoluminescence dosimetry(TLD) has been known as one of the most effective methods for dose estimation in diagnostic radiology. Orthopantomogram (OPG) imaging is used by many dentists, oral and maxillofacial surgeons as an effective tool for choosing an appropriate treatment plan.Objective: This study aims to measure the entrance skin dose and the dose values received by different head and neck organs in OPG imaging using TLD dosimeters (TLD-100).Material and Methods: In this experimental study, the entrance skin dose and doses of various organs during imaging were measured by TLD dosimeters inside and on the surface of the Rando-Phantom. Doses to various organs, including thyroid, eye, esophagus, parotid and sublingual and submandibular salivary glands were measured. The measurements were repeated twice, and the dose values obtained in the two steps were compared.Results: Based on the results obtained in this study, the minimum dose values were found in Esophagus; 65.81, and 59.31 µGy, respectively. The maximum organ dose value was found for left parotid glands, 3842.42, and 3399.58 for the two measurements, respectively. Conclusion: The results show that the dose values can vary based on devices, exposure conditions, and TLD positioning.

Entrance Skin Dose Measurement for Diagnostic Spinal Radiographic Examinations in King Khalid Hospital, Saudi Arabia: A Prospective Study

Entrance Skin Dose Measurement for Diagnostic Spinal Radiographic Examinations in King Khalid Hospital, Saudi Arabia: A Prospective Study

Estimation of fetal radiation absorbed dose during the prophylactic use of aortic occlusion balloon for abnormally invasive placenta

Purpose Abnormally invasive placenta is an important cause of maternal morbidity, and its primary complication is massive bleeding. Strategies for preventing bleeding include arterial endovascular occlusion. One concern with the use of intra-arterial occlusion balloons is radiation exposure to the fetus, which occurs while determining balloon position. In this study, we sought to determine the radiation absorbed dose by the fetus during intra-aortic occlusion balloon placement in patients with abnormally invasive placenta. Materials and methods We estimated the fetal absorbed dose and the entrance skin dose in the vaginal fundus and lumbar skin, respectively, using thermoluminescent dosimeter crystals, during intra-aortic balloon positioning using the mobile X-ray image intensifier system (C-arm) in digital radiography mode, directly in surgery room, without transfer to angiographic suite. We also performed a mannequin-based simulation to validate the entrance skin dose measurement technique. Results Ten women undergoing surgical management of an abnormally invasive placenta, in whom the location of the intra-aortic occlusion balloon was verified using plain radiography with C-arm in the surgery room, were included in the study. Following maternal and fetal radiation exposure, the entrance skin dose and radiation absorbed dose by the fetus were 1.31 ± 0.96 mGy and 0.27 ± 0.28 mGy, respectively, with radiation exposure durations of <1 s. Conclusions There were no complications with the use of REBOA, the radiation absorbed dose by the fetus, entrance skin dose, and duration of radiation exposure during intra-aortic occlusion balloon placement were lower than those reported for other vascular occlusion techniques, being this a safe procedure.

Quantifying entrance skin dose for early diagnose of lung cancer

Lung cancer is disease that can cause death in a short time, but it is almost never detected at an early stage, because its symptons are not specific, such as coughing and lack of appetite. In some patients who have a smoking habit, it is easier to be suspected of having a tumor or lung cancer. In order to detect a tumor or lung cancer, a chest X-ray examination is generally done as an early diagnosis. As we have already known, exposure of X-ray radiation to the body can have a negative impact, therefore the dose of X-ray radiation exposure must be minimized. In this study a measurement of entrance skin dose (ESD) was performed on chest X-ray examination in patients suspected of having a tumor or lung cancer. The results showed that patients who had symptoms similar to those of tumor or lung cancer had higher ESD than those who did not. Although the radiation dose is higher than dose on routine chest X-ray examination, it only shows abnormality of radiological photogaraph but do not accurately indicate the presence of tumor or cancer.

Measuring skin dose in CT examinations under complex geometries: Instruments, methods and considerations

ObjectiveTo investigate skin dose in Computed Tomography (CT) and its dependence on scanning geometry. Materials and methodsMeasurements of entrance surface air kerma (ESAK) in free air and entrance skin dose (ESD) on an anthropomorphic phantom were performed in a 64-slice CT scanner, using two different instruments: the Dose Profiler (DP) and the QED skin diode (QEDSD). Using DP and QEDSD, the ESAK rate profiles at the isocenter and at different distances from it, were measured using axial scans. Using DP and helical scans the ESAK rate profile in the Z-axis was acquired. The same profile was acquired with the QEDSD also, using many axial scans and manual table translation. ESD measurements were performed with the DP and QEDSD, in axial and helical scan mode. ResultsESAK measurements with DP and QEDSD were in good agreement, for both point dose and profile measurements. The agreement was also good for ESD measurements but not for helical scans, due to variable X-ray beam overlapping and different tube angular positions at each scan start. It was observed that the ESD values at different Y-axis offsets were comparable to the respective ESAK values recorded at the same Y-axis offset distances without the phantom. ConclusionsBoth DP and QEDSD were proven suitable for performing point ESD measurements. However, calculating the skin dose distribution in CT examinations is a very challenging task. A practical approach would be for CT scanners to provide a conservative estimate of the peak skin dose using the isocenter ESAK value.

Practical calibration curve of small-type optically stimulated luminescence (OSL) dosimeter for evaluation of entrance skin dose in the diagnostic X-ray region.

For X-ray diagnosis, the proper management of the entrance skin dose (ESD) is important. Recently, a small-type optically stimulated luminescence dosimeter (nanoDot OSL dosimeter) was made commercially available by Landauer, and it is hoped that it will be used for ESD measurements in clinical settings. Our objectives in the present study were to propose a method for calibrating the ESD measured with the nanoDot OSL dosimeter and to evaluate its accuracy. The reference ESD is assumed to be based on an air kerma with consideration of a well-known back scatter factor. We examined the characteristics of the nanoDot OSL dosimeter using two experimental conditions: a free air irradiation to derive the air kerma, and a phantom experiment to determine the ESD. For evaluation of the ability to measure the ESD, a calibration curve for the nanoDot OSL dosimeter was determined in which the air kerma and/or the ESD measured with an ionization chamber were used as references. As a result, we found that the calibration curve for the air kerma was determined with an accuracy of 5%. Furthermore, the calibration curve was applied to the ESD estimation. The accuracy of the ESD obtained was estimated to be 15%. The origin of these uncertainties was examined based on published papers and Monte-Carlo simulation. Most of the uncertainties were caused by the systematic uncertainty of the reading system and the differences in efficiency corresponding to different X-ray energies.

Characterization of a MOSkin detector for in vivo skin dose measurements during interventional radiology procedures.

The MOSkin is a MOSFET detector designed especially for skin dose measurements. This detector has been characterized for various factors affecting its response for megavoltage photon beams and has been used for patient dose measurements during radiotherapy procedures. However, the characteristics of this detector in kilovoltage photon beams and low dose ranges have not been studied. The purpose of this study was to characterize the MOSkin detector to determine its suitability for in vivo entrance skin dose measurements during interventional radiology procedures. The calibration and reproducibility of the MOSkin detector and its dependency on different radiation beam qualities were carried out using RQR standard radiation qualities in free-in-air geometry. Studies of the other characterization parameters, such as the dose linearity and dependency on exposure angle, field size, frame rate, depth-dose, and source-to-surface distance (SSD), were carried out using a solid water phantom under a clinical x-ray unit. The MOSkin detector showed good reproducibility (94%) and dose linearity (99%) for the dose range of 2 to 213 cGy. The sensitivity did not significantly change with the variation of SSD (± 1%), field size (± 1%), frame rate (± 3%), or beam energy (± 5%). The detector angular dependence was within ± 5% over 360° and the dose recorded by the MOSkin detector in different depths of a solid water phantom was in good agreement with the Markus parallel plate ionization chamber to within ± 3%. The MOSkin detector proved to be reliable when exposed to different field sizes, SSDs, depths in solid water, dose rates, frame rates, and radiation incident angles within a clinical x-ray beam. The MOSkin detector with water equivalent depth equal to 0.07 mm is a suitable detector for in vivo skin dosimetry during interventional radiology procedures.

Measurement of Entrance Skin Dose and Calculation of Effective Dose for Common Diagnostic X-Ray Examinations in Kashan, Iran.

The knowledge of the radiation dose received by the patient during the radiological examination is essential to prevent risks of exposures. The aim of this work is to study patient doses for common diagnostic radiographic examinations in hospitals affiliated to Kashan University of Medical sciences, Iran. The results of this survey are compared with those published by some national and international values. Entrance surface dose (ESD) was measured based on the exposure parameters used for the actual examination and effective dose (ED) was calculated by use of conversion coefficients calculated by Monte Carlo methods. The mean entrance surface dose and effective dose for examinations of the chest (PA, Lat), abdomen (AP), pelvis (AP), lumbar spine (AP, Lat) and skull (AP, Lat) are 0.37, 0.99, 2.01, 1.76, 2.18, 5.36, 1.39 and 1.01 mGy, and 0.04, 0.1, 0.28, 0,28, 0.23, 0.13, 0.01 and 0.01 mSv, respectively. The ESDs and EDs reported in this study, except for examinations of the chest, are generally lower than comparable reference dose values published in the literature. On the basis of the results obtained in this study can conclude that use of newer equipment and use of the proper radiological parameter can significantly reduce the absorbed dose. It is recommended that radiological parameter in chest examinations be revised.

多施設間IVR被ばく線量解析研究を支援するためのシステム構築

Although measurement and management of angiographic entrance skin dose (ESD) are deemed extremely important, accurate determination of maximum ESD and its location is generally difficult because of the dependence on therapeutic technique and position. Following our development of body-mounted gear bearing radiophotoluminescence glass dosimeter (RPLD) arrays for direct measurement of ESD in cranial and cardiovascular angiography and interventional radiology (IVR), our focus next turned to the limited number of facilities equipped to read RPLD outputs and the need for methods to effectively provide feedback to clinical facilities. As described here, we first constructed an RPLD reading facility capable of sending and receiving RPLDs by post, offering the potential to enable utilization of the developed gear at all hospitals in Japan that perform angiography and IVR. We next developed specialized web-based system to generate dose maps from RPLD dose data, thereby enabling any facility to perform trial system analysis, evaluation, and implementation; and investigated the results and related problems.

Estimating cancer risk from dental cone-beam CT exposures based on skin dosimetry

The aim of this study was to measure entrance skin doses on patients undergoing cone-beam computed tomography (CBCT) examinations, to establish conversion factors between skin and organ doses, and to estimate cancer risk from CBCT exposures. 266 patients (age 8–83) were included, involving three imaging centres. CBCT scans were acquired using the SCANORA 3D (Soredex, Tuusula, Finland) and NewTom 9000 (QR, Verona, Italy). Eight thermoluminescent dosimeters were attached to the patient's skin at standardized locations. Using previously published organ dose estimations on various CBCTs with an anthropomorphic phantom, correlation factors to convert skin dose to organ doses were calculated and applied to estimate patient organ doses. The BEIR VII age- and gender-dependent dose-risk model was applied to estimate the lifetime attributable cancer risk. For the SCANORA 3D, average skin doses over the eight locations varied between 484 and 1788 µGy. For the NewTom 9000 the range was between 821 and 1686 µGy for Centre 1 and between 292 and 2325 µGy for Centre 2. Entrance skin dose measurements demonstrated the combined effect of exposure and patient factors on the dose. The lifetime attributable cancer risk, expressed as the probability to develop a radiation-induced cancer, varied between 2.7 per million (age >60) and 9.8 per million (age 8–11) with an average of 6.0 per million. On average, the risk for female patients was 40% higher. The estimated radiation risk was primarily influenced by the age at exposure and the gender, pointing out the continuing need for justification and optimization of CBCT exposures, with a specific focus on children.

Study on the development of a patient dosimetry gown for interventional cardiology procedures

In recent years, dose justification and optimization have been attempted in percutaneous coronary intervention (PCI); however, deterministic effects have been reported. To prevent radiation skin injuries in PCI, it is necessary to measure the patient entrance skin dose (ESD), but an accurate dose measurement method has not yet been established. In this study, we developed a dosimetry gown that can measure the ESD during PCI using multiple radiophotoluminescence dosimeters (RPLDs). The RPLDs were placed into 84 pockets that were sewn into a dosimetry gown. Patients wear the original dosimetry gown during the procedures, after which we obtain accurate ESD measurements. We believe that this method using RPLDs and a newly-designed dosimetry gown provides accurate ESD measurements during PCI. We expect this system to become a standard method for measuring ESD during PCI.

Fundamental study on the characteristics of a radiophotoluminescence glass dosemeter with no energy compensation filter for measuring patient entrance doses in cardiac interventional procedures

Cardiac interventional procedures have been increasing year by year. However, radiation skin injuries have been still reported. There is a necessity to measure the patient entrance skin dose (ESD), but an accurate dose measurement method has not been established. To measure the ESD, a lot of radiophotoluminescence dosemeters (RPLDs) provide an accurate measurement of the direct actual ESD at the points they are arrayed. The purpose of this study was to examine the characteristics of RPLD to measure the ESD. As a result, X-ray permeable RPLD (with no tin filter) did not interfere with the percutaneous coronary intervention procedure. The RPLD also had good fundamental performance characteristics. Although the RPLD had a little energy dependence, it showed excellent dose and dose-rate linearity, and good angular dependence. In conclusion, by calibrating the energy dependence, RPLDs are useful dosemeter to measure the ESD in cardiac intervention.

Characterization of a cable‐free system based on p‐type MOSFET detectors for “in vivo” entrance skin dose measurements in interventional radiology

During radiological interventional procedures (RIP) the skin of a patient under examination may undergo a prolonged x-ray exposure, receiving a dose as high as 5 Gy in a single session. This paper describes the use of the OneDose(TM) cable-free system based on p-type MOSFET detectors to determine the entrance skin dose (ESD) at selected points during RIP. At first, some dosimetric characteristics of the detector, such as reproducibility, linearity, and fading, have been investigated using a C-arc as a source of radiation. The reference setting (RS) was: 80 kV energy, 40 cm × 40 cm field of view (FOV), current-time product of 50 mAs and source to skin distance (SSD) of 50 cm. A calibrated PMX III solid state detector was used as the reference detector and Gafchromic(®) films have been used as an independent dosimetric system to test the entire procedure. A calibration factor for the RS and correction factors as functions of tube voltage and FOV size have been determined. Reproducibility ranged from 4% at low doses (around 10 cGy as measured by the reference detector) to about 1% for high doses (around 2 Gy). The system response was found to be linear with respect to both dose measured with the PMX III and tube voltage. The fading test has shown that the maximum deviation from the optimal reading conditions (3 min after a single irradiation) was 9.1% corresponding to four irradiations in one hour read 3 min after the last exposure. The calibration factor in the RS has shown that the system response at the kV energy range is about four times larger than in the MV energy range. A fifth order and fourth order polynomial functions were found to provide correction factors for tube voltage and FOV size, respectively, in measurement settings different than the RS. ESDs measured with the system after applying the proper correction factors agreed within one standard deviation (SD) with the corresponding ESDs measured with the reference detector. The ESDs measured with Gafchromic(®) films were in agreement within one SD compared to the ESDs measured using the OneDose(TM) system, as well. The global uncertainty associated to the OneDose(TM) system established in our experiments, ranged from 7% to 10%, depending on the duration of the RIP due to fading. These values are much lower than the uncertainty commonly accepted for general diagnostic practices (20%) and of about the same size of the uncertainty recommended for practices with high risk of deterministic side effects (7%). The OneDose(TM) system has shown a high sensitivity in the kV energy range and has been found capable of measuring the entrance skin dose in RIP.

Survey of dose area product received by patients undergoing common radiological examinations in four centers in Nigeria

Patient dosimetry studies in diagnostic radiology in Nigeria have been on measurement of entrance skin dose and effective dose. Another important and easy to measure radiation dose descriptor that could be used to assess patient dose in radiological procedures is dose area product (DAP). Knowledge of DAP with location and projection of X‐ray beam allows direct calculation of organ dose and effective dose. In this study, DAP for commonly performed radiological examinations (abdomen, chest, lumbo sacral joint, pelvis, paranasal sinus, and skull) in four diagnostic centers in Nigeria were determined. These centers comprise of three classes of health care center namely tertiary, private, and specialist hospitals. Mathematical method was used to determine DAP received by 336 patients undergoing radiological examinations at the selected diagnostic centers. The DAP received by patient from each radiological examination varies from center to center. The range factor (RF) of DAP for individual patients ranged from 1.55–4.56, while RF of DAP among the selected centers was 2.27–55.84. The highest RF of DAP (55.84) was obtained from X‐ray examination of the chest. This variation was due to the application of anti‐scatter grid, and high kVp and high mAs values for chest examination by only one of the centers. The very wide variation in DAP found among diagnostic centers in this survey showed that there is need to harmonize radiological techniques of common X‐ray examination among different diagnostic centers. This would ensure optimal protection of patient against excessive radiation dose.PACS numbers: 87.53.Bn; 87.59.B

영·유아의 입사피부선량 측정을 위한 몬테카를로 시뮬레이션

성인과 달리 영 유아에게 행해지는 방사선 검사 시 투여되는 방사선량의 평가는 활발하게 이루어지지 않고 있다. 따라서 영 유아의 방사선 검사 시 피폭되는 정도를 나타내는 지표로서 입사피부선량을 측정하고 Geant4를 이용한 몬테카를로 시뮬레이션을 통한 결과값을 비교하여 입사피부선량 측정의 재현성을 높이고 다양한 지오메트리 구현의 가능성을 증명하였다. 몬테카를로 시뮬레이션 결과값은 입사피부선량을 선량보정을 위한 정규인자를 통해 추정하였고 단위 X선 조사영역크기로 표준화한 결과 영 유아에게 있어 일회의 방사선 촬영 당 평균 입사피부선량은 <TEX>$78.41{\mu}Gy$</TEX> 였으며 선량계를 통한 측정값과 몬테카를로 시뮬레이션값의 백분율 오차는 최대 -4.77%로 나타났다. 몬테카를로 시뮬레이션을 통한 입사피부선량 평가 방법은 의료기관에서 실제 진단을 위해 내원한 환아를 대상으로 한 입사피부선량 평가의 어려움을 대체할만한 수단으로서의 가능성을 보여준다. Radiation dose estimation on the newborn and infants during radiation examinations, unlike for the adults, is not actively being progressed. Therefore, as an index to present exposure dose during radiation examinations on newborn and infants, entrance skin dose was measured, and the result was compared with results of monte carlo simulation to raise reproducibility of entrance skin dose measurement, and it was proved that various geometry implementation was possible. The resulting values through monte carlo simulation was estimated using normalization factors for entrance skin dose to calibrate radiation dose and then normalized to a unit X ray radiation field size. Average entrance skin dose per one time exposure was <TEX>$78.41{\mu}Gy$</TEX> and the percentage error between measurement by dosimeter and by monte carlo simulation was found to be -4.77%. Entrance skin dose assessment by monte carlo simulation provides possible alternative method in difficult entrance skin dose estimation for the newborn and infants who visit hospital for actual diagnosis.

Accurate skin dose measurements using radiochromic film in clinical applications

Megavoltage x-ray beams exhibit the well-known phenomena of dose buildup within the first few millimeters of the incident phantom surface, or the skin. Results of the surface dose measurements, however, depend vastly on the measurement technique employed. Our goal in this study was to determine a correction procedure in order to obtain an accurate skin dose estimate at the clinically relevant depth based on radiochromic film measurements. To illustrate this correction, we have used as a reference point a depth of 70 micron. We used the new GAFCHROMIC dosimetry films (HS, XR-T, and EBT) that have effective points of measurement at depths slightly larger than 70 micron. In addition to films, we also used an Attix parallel-plate chamber and a home-built extrapolation chamber to cover tissue-equivalent depths in the range from 4 micron to 1 mm of water-equivalent depth. Our measurements suggest that within the first millimeter of the skin region, the PDD for a 6 MV photon beam and field size of 10 x 10 cm2 increases from 14% to 43%. For the three GAFCHROMIC dosimetry film models, the 6 MV beam entrance skin dose measurement corrections due to their effective point of measurement are as follows: 15% for the EBT, 15% for the HS, and 16% for the XR-T model GAFCHROMIC films. The correction factors for the exit skin dose due to the build-down region are negligible. There is a small field size dependence for the entrance skin dose correction factor when using the EBT GAFCHROMIC film model. Finally, a procedure that uses EBT model GAFCHROMIC film for an accurate measurement of the skin dose in a parallel-opposed pair 6 MV photon beam arrangement is described.

Application of Imaging Plates to Cumulative Dosemeter for High X-ray Radiation Fields

The application of imaging plates (IPs), which are highly sensitive two-dimensional radiation sensors, to cumulative dosemeters for measuring high level X-ray radiation has been attempted, aiming at direct measurement of entrance skin dose (ESD) in interventional radiology (IR) .The IP has 103 times greater sensitivity to X-rays than does X-ray emulsion film. The present upper limit of the measurable dose is only less than 1 mGy, which is principally determined by the saturation of the output current of the photomultiplier tube (PMT) and not by the property of IP. To extend the upper limit of the measurable dose without adapting the readout system, a new and simple technique to decrease the occurrence of photostimulated luminescence (PSL) and reduce exposure levels within the dynamic range of the PMT is being developed. The process involves placing a sheet of color cellophane over the IP during the readout process and/or annealing the IP.This process enables extension of the upper limit of the X-ray dose to approximately 102Gy by using three sheets of color cellophane or to 10!Gy by annealing the IPs at 100°C for 70 hours. Combining the conventional way, the dynamic range of an IP can be extended by eight orders of magnitude.