Entrance Skin Exposure Research Articles

SU‐FF‐J‐103: Performance of the Nucletron Simulix Evolution Flat‐Plate Imaging System and CBCT

Purpose: To characterize the performance of the flat‐plate imaging system available on a commercial radiotherapy simulator, to describe some of it's clinical limitations and to present preliminary results when used in cone‐beam CT mode. Method and Materials: Measurements were performed on the Nucletron Simulix Evolution simulator installed at our institution. The Simulix Evolution is equipped with a 40 cm × 40 cm flat‐panel detector. Low contrast measurements were performed with a CDRAD contrast‐detail phantom at the center of varying‐thickness slabs of water‐equivalent material. Cone‐beam CT (CBCT) images were obtained with the AAPM CT and with a 20‐cm diameter water phantoms. Results: The Simulix Evolution performs digital fluoroscopy at a fixed rate of 3 frames/sec. There is no digital radiography mode available currently. In fluoroscopy, two automatic brightness settings are available (ABS1 and ABS2). Entrance skin exposure levels at time of acceptance exceeded 15 R/min. Contrast‐detail measurements with 10‐cm and 20‐cm water‐equivalent phantoms demonstrated that the grid has limited clinical utility since the large air gap present reduces the impact of scatter. Removing the grid reduces patient exposure by a factor of 2. Note that the grid is not used in CBCT. Evaluation of the CBCT mode demonstrated that the system does not currently meet the HU uniformity target of +/− 75 HU for water set by the manufacturer. Ring artifacts are also present and compromise clinical utility. Images and clinical examples will be presented. Conclusion: Lack of a digital radiography mode limits the clinical utility of the Simulix Evolution. With optimization, the system can be operated with clinically‐acceptable fluoroscopy images at exposures below 5 R/min. Cone‐beam CT image quality is currently compromised by the presence of ring artifacts and by poor HU uniformity and low‐contrast discrimination.

Comportamento da dose glandular versus contraste do objeto em mamografia: determinação de formalismo semi-empírico para diferentes combinações alvo-filtro

OBJETIVO: Verificar o efeito da mudança no contraste do objeto, tempo de exposição e dose de radiação quando diferentes espessuras de filtração de molibdênio (Mo) e ródio (Rh) são empregadas em mamógrafos. MATERIAIS E MÉTODOS: Realizaram-se medidas da exposição na entrada da pele com uma câmara de ionização para diferentes espessuras para os filtros de Mo e Rh. Para determinar a dose glandular média foi utilizado simulador de BR12 (50% tecido adiposo e 50% tecido glandular) de diferentes espessuras (4 cm e 8 cm). Energias na faixa de 24 kVp a 34 kVp foram empregadas e filmes Kodak MinR 2000 foram utilizados. RESULTADOS: Os resultados evidenciaram dados de contraste do objeto, dose glandular e tempo de exposição para diferentes espessuras de filtros adicionais e diferentes tensões. Esses dados indicaram aumento nos valores de contraste do objeto e tempo de exposição, com o aumento da espessura dos filtros. A dose glandular apresentou comportamento com diferentes tendências para cada caso analisado. Equações foram definidas para possibilitar a estimativa do contraste do objeto, dose glandular e tempo de exposição para os casos estudados. CONCLUSÃO: Os resultados possibilitaram a estimativa de equações que auxiliam na verificação do comportamento do contraste do objeto e da dose glandular para simuladores com espessura de 4 cm e 8 cm e para os filtros de Rh e Mo. Dessa forma, torna-se possível estimar a figura de mérito (razão entre o contraste do objeto e a dose glandular), podendo auxiliar na análise da relação risco-benefício dos casos estudados.

SU‐FF‐P‐03: Combined Role Of Physicist And Technologist In Optimizing CR, DR Techniques To Meet The Regulations And ALARA!

With advancement of CR and DR, many facilities are switching from regular FILM‐Screen combination to these new technologies. While manufacturers suggest basic techniques for different projections to be used in the radiography rooms, it is our experience, to notice that, some of the prescriptions may not meet the need. Adjusting to a different technique may make the entrance skin exposures for different projections exceed the regulatory limits. It is the responsibility of the Medical Physicist to make sure that ALARA is met in these situations while making sure that image quality is not compromised. Role of the technologist is very important to optimize the exposures. This paper will discuss the failure part and the necessary problem solving steps. Tables for entrance exposures for Filmscreen, CR and DR will be discussed with optimum techniques used in our institution as a model.

SU‐FF‐I‐74: Comparison of Image Quality in Contact and Magnification Modes in Digital Mammography

Purpose: To compare image quality in contact and magnification modes in digital mammography. Method and Materials: Images of three anthropomorphic breast phantoms were acquired using a Hologic FFDM system. First, images were acquired in contact mode with grid. The exposure parameters were determined by AEC. Second, images were acquired in 1.5x magnification mode without grid. The exposure parameters were selected such that the detector entrance exposures were the same as those in the first experiment. The third, images were acquired in contact mode with grid and with the same patient doses in magnification mode. Image quality was analyzed using MIPAV software. Results: 9lp/mm and 6lp/mm were resolved in the magnification mode and in the contact mode respectively. However, the smallest specks group in the phantoms (0.13 mm) could be detected in all modes. For masses and fibers, more features were detected in the magnification mode when the detector entrance exposures were fixed at those determined in the contact mode. More masses and fibers were detected in contact mode when the breast skin entrance exposures were the same as those in the magnification mode. Conclusion: At the same patient dose, the contact mode provides better detectability of masses and fibers. The detectability of microcalcification above 0.13 mm is not improved by using the magnification mode. The detectability of smaller microcalcifications (<0.13 mm) needs further investigation.

Applicability of ACR breast dosimetry methodology to a digital mammography system

Determination of mean glandular dose (MGD) to breast tissue is an essential aspect of mammography equipment evaluations and exposure controls. The American College of Radiology (ACR) Quality Control Manual outlines the procedure for MGD determination in screen-film mammography based upon conversions of entrance skin exposures (ESEs) measured with an ionization chamber (IC). The development of digital mammography has increased with the demand for improved object resolution and tissue contrast. This change in image receptor from screen-film to a solid-state detector has led to questions about the applicability of the ACR MGD methodology to digital mammography. This research has validated the applicability of the ACR MGD methodology to digital mammography in the GE digital mammography system Senographe 2000D. MGD was determined using light output measurements from thermoluminescent dosimeters (MGDTL), exposure measurements from an IC (MGD(IC)) and conversion factors from the ACR Mammography Quality Control Manual. MGD(TL) and MGD(IC) data indicate that there is a statistically significant difference between the two measurements with the Senographe 2000D. However, the applicability of the ACR's methodology was validated by calculating MGD at various depths in a 50/50 breast phantom. Additionally, the results of backscatter measurements from the image receptors of both mammography modalities indicate there is a difference (all P values < 0.001) in the radiation backscattered from each image receptor.

Effective dose evaluation for chest and abdomen X-ray tests

The radiation doses resulting from diagnostic X-ray examinations are routinely measured in terms of entrance skin exposure (ESE). In this study, for the purpose of radiation protection, the radiation doses received from chest and abdomen X-ray tests were evaluated in terms of equivalent dose and effective dose. The dose calculations were conducted by using the MCNP Monte Carlo code and an adult hermaphrodite mathematical phantom. The effects of both operating high voltage and projection geometry on the effective dose were investigated. The absolute values of the effective doses may be provided from the national average ESE.

Dual‐energy digital mammography for calcification imaging: Scatter and nonuniformity corrections

Mammographic images of small calcifications, which are often the earliest signs of breast cancer, can be obscured by overlapping fibroglandular tissue. We have developed and implemented a dual-energy digital mammography (DEDM) technique for calcification imaging under full-field imaging conditions using a commercially available aSi:H/CsI:Tl flat-panel based digital mammography system. The low- and high-energy images were combined using a nonlinear mapping function to cancel the tissue structures and generate the dual-energy (DE) calcification images. The total entrance-skin exposure and mean-glandular dose from the low- and high-energy images were constrained so that they were similar to screening-examination levels. To evaluate the DE calcification image, we designed a phantom using calcium carbonate crystals to simulate calcifications of various sizes (212-425 microm) overlaid with breast-tissue-equivalent material 5 cm thick with a continuously varying glandular-tissue ratio from 0% to 100%. We report on the effects of scatter radiation and nonuniformity in x-ray intensity and detector response on the DE calcification images. The nonuniformity was corrected by normalizing the low- and high-energy images with full-field reference images. Correction of scatter in the low- and high-energy images significantly reduced the background signal in the DE calcification image. Under the current implementation of DEDM, utilizing the mammography system and dose level tested, calcifications in the 300-355 microm size range were clearly visible in DE calcification images. Calcification threshold sizes decreased to the 250-280 microm size range when the visibility criteria were lowered to barely visible. Calcifications smaller than approximately 250 microm were usually not visible in most cases. The visibility of calcifications with our DEDM imaging technique was limited by quantum noise, not system noise.

SU-FF-I-58: Effects of Prepatient Filtration On Contrast, Scatter and Dose in CR Chest Exams: A Phantom Study

Purpose: To establish a convenient method for objective comparison of the consequences of exposure conditions and filtration on image quality and patient dose in adult and pediatric thoracic computed radiography (CR) examinations. Method and Materials: Computer simulation (MATLAB) was utilized for approximating the x-ray spectrum and its modification by pre-patient filtration, predicting the attenuation by the phantom, predicting pixel values in the CR image, calculating expected contrast-to-noise ratio (CNR), and estimating patient dose. CDRH LucAl Chest and Pediatric phantoms with the Al quality insert were imaged at 125 kVp with beam filters (Z=29, 57, 75) with a grid and 75 kVp with beam filters (Z=13, 29, 50) tabletop, respectively. Entrance Skin Exposure (ESE) and detector exposure were measured. Fuji FCR 5000 CR images were developed with L=4 in fixed EDR Mode. Pixel ROI and SD were extracted from DICOM images. Doses were estimated by calculating absorption of the attenuated spectra in water of 20 cm (adult) and 10 cm (pediatric) thickness. Scatter-to-primary ratios (SPR) were estimated for each case using beam blocks. Results: Filtration increased half-value layer (HVL) reducing ESE and contrast. Contrast-to-Noise Ratio (CNR) can increase, depending on Z and the thickness of the filter. The same CNR produced by the unfiltered beam using Automatic Exposure Control (AEC) can be accomplished at 23% lower ESE. Even with a lower ESE, higher HVL increases exposure-to-dose conversion, resulting in higher dose absorbed by the patient to produce the same receptor exposure. No filtered case had CNR superior to the unfiltered case at the same patient dose. SPR also increased with filtration. Conclusion: LucAl Chest and Pediatric phantoms provide standardized platforms for investigating effects of exposure conditions on image quality and patient dose in digital chest radiography. Filtration can provide identical CNR at lower ESE, but may also deliver higher patient dose.

TU‐E‐I‐611‐01: Comparison of Radiation Dose Using Full Field Digital and Conventional Screen‐Film Mammography in a Screening Clinic

Purpose: To evaluate radiation doses delivered by an amorphous selenium based full‐field digital mammography (FFDM) system, and to determine if the expected reduction in average glandular dose (AGD) resulting from the increased efficiency of the digital detector is realized in clinical practice. A secondary purpose was to determine clinical exposure parameters for digital mammography that maintain a level of image noise consistent with screen/film mammography. Method and Materials: Phantom material that approximates breast tissue (50% adipose, 50% glandular) was used for direct comparison of dose between the two clinical mammography units, one digital and one conventional. The mammographic view, compressed breast thickness, kilovoltage, milliampere‐second product, and K‐edge filter were recorded for images of randomly‐selected patients examined on each machine. Entrance skin exposure was calculated from measurements, and AGD was estimated using normalized exposure‐to‐dose conversion factors that assume 50% adipose and 50% glandular breast composition. A two‐tailed student t‐test was used to compare the patient doses. Results: No difference was observed in the mean AGD delivered by the two mammography units over a wide range of compressed breast thicknesses and compositions. For compressed breast thickness above 7 cm, the dose was significantly lower for the FFDM unit (P&lt;0.05) due to the use of higher kilovoltage and rhodium filtration, and correspondingly lower values of mAs. Conclusion: The exposure parameter selection algorithm employed by the FFDM unit does not reduce dose compared with a conventional mammography unit for a wide range of breast thicknesses. Users wishing to reduce AGD should consider using manual techniques, and developing technique charts to achieve the desired compromise between dose and image quality. The algorithm used by the conventional mammography unit to automatically select kVp resulted in extended exposure times and unnecessarily high values of mAs and AGD because of its relatively low upper bound on kVp.

WE-B-I-611-01: Evaluation and Consulting On Patient Dose In Diagnostic Imaging

One of the responsibilities of a clinical medical physicist in diagnostic imaging is to provide both dose and risk information about x-ray examinations. This is required for several reasons including advising medical staff of the doses and risks associated with specific examinations, consulting with institutional review boards (IRBs) relative to research uses of radiation, and determining specific organ doses such as uterine or fetal doses to assist in medical decision making. In order to provide dose and risk estimates four types of information are necessary including: 1) patient entrance skin exposures; 2) specific organ doses based on these exposures; 3) effective dose which is calculated based upon specific organ doses; and 4) estimation of risk based upon the effective dose. Unfortunately, there is no concise source of the information regarding doses and risk so it is necessary to have access to and knowledge of the sources that are available. This refresher course will provide an overview of resources and methods for determining patient risk from ionizing radiation in medical imaging. Several examples will be provided showing how doses and risks can be reduced easily and inexpensively for both clinical and research applications.

Patient exposure and associated radiation risks from fluoroscopically guided vertebroplasty or kyphoplasty.

To derive normalized data for the estimation of effective, gonadal, and peak skin doses to patients undergoing vertebroplasty or kyphoplasty and to investigate the potential for cancer induction, genetic effects, and radiation-induced skin injury after such procedures. Dose values normalized over dose-area product were determined for all radiosensitive organs and tissues by using a humanoid phantom and thermoluminescence dosimetry separately for anteroposterior and lateral projections. Measurements were obtained for treatments of the fifth, eighth, and 11th thoracic vertebrae and the first, third, and fifth lumbar vertebrae. Total fluoroscopy time and resultant dose-area product from each fluoroscopic exposure were monitored in 11 consecutive patients (seven women and four men) undergoing kyphoplasty. The age range of these patients was 41-78 years, and the mean age was 58 years. Mean total fluoroscopy time for kyphoplasty was 10.1 minutes +/- 2.2 (standard deviation). Mean effective dose to patients from kyphoplasty was 8.5-12.7 mSv, and mean gonadal dose was 0.04-16.4 mGy, depending on the level of the treated vertebra. Skin injuries after kyphoplasty are improbable if source-to-skin distance is 35 cm or more; however, such injuries may occur if the total fluoroscopy time per projection is extended and/or the source-to-skin distance is less than 35 cm during the procedure. Patient radiation exposure and associated risks from vertebroplasty or kyphoplasty may be considerable. Data obtained in the current study may be used to establish patient effective dose, gonadal dose, and entrance skin exposure, as well as associated risks, from these fluoroscopically guided surgical treatments of spinal disorders.

マンモグラフィによる被曝線量に対する乳腺割合の影響

Software for the estimation of patient exposure from mammography has been developed. Because it adopts average glandular dose, the estimation of patient exposure must take advantage of D(gN) (average glandular dose per unit entrance skin exposure). D(gN) depends on X-ray quality, compressed breast thickness, and breast composition. The software that was previously reported required information about breast composition. However, the new software that estimates breast composition uses a phantom with known breast composition to estimate average glandular dose and entrance surface dose. The authors were able to calculate average glandular dose that takes account of breast composition using this software. In addition, in a comparison with the mammogram in terms of the classification of mammary gland substance, the software showed high precision in terms of agreement. This software has sufficient utility because only the mammographic conditions are entered, and patient exposure can be easily estimated. Moreover, the half-value layer, incident exposure in air, D(gN), and breast composition can be specifically calculated.

Dosimetric Evaluation of the Mean Glandular Dose for Mammography in Korean Women: A Preliminary Report

The purpose of this study was to evaluate the thickness of the compressed breast in mediolateral oblique (MLO) and craniocaudal (CC) mammograms, to relate these thickness and breast patterns to mean glandular dose (MGD) in Korean women, and to evaluate the suitability of using the American College of Radiology's Recommendations for Korean women from a quality assurance standpoint. The study population consisted of 92 paired MLO and CC mammograms obtained on one mammographic unit. The digital readouts of compressed breast thickness, applied compression force and tube voltage were recorded. Entrance skin exposure was measured by dosimetry. MGD was calculated by multiplying entrance skin exposure by the exposure-to-absorbed dose conversion factor. The range of breast thickness was 1.3-6.2 cm in CC mammograms with a mean breast thickness of 3.6 cm, and 1.6-6.5 cm in MLO mammograms with a mean breast thickness of 3.9 cm. MGDs in CC and MLO mammograms were 1.77 mSv and 1.88 mSv per view, respectively. Breast composition patterns were divided into 4 groups according to ACR BI-RADS; P1 (n=20), P2 (n=16), P3 (n=48) and P4 (n=8). The MGDs for these groups were: 1.82, 1.84, 1.84, and 1.91 mSv, respectively. When subjects were subdivided by breast thickness into three groups, namely, below 3 cm, 3 cm to 4.2 cm, aaa and above 4.2 cm, the corresponding MGDs were 1.83, 1.86, and 1.91 mSv. According to our initial trial, the mean breast thickness and the MGDs of Korean women are lower than recommended by the American College of Radiology, which are commonly used for quality assurance purposes.

Portable chest radiographs in the intensive care units: referral patterns and estimated cumulative radiation exposures.

The objective of this article was to determine the frequency of referrals for portable chest radiographs from medical and (noncardiac) surgical intensive care units (NICU and SICU) and their respective stepdown units (NICA and SICA). Additionally, the cumulative entrance skin exposure (ESE) using an ion chamber was determined. We retrospectively reviewed the medical records of all adult patients admitted to the MICU, SICU, MICA, and SICA at a tertiary referral center during a 6-month interval. The duration of stay and the number of portable chest radiographs were determined for each patient. The measured ESEs from all portable radiography units ranged from 5 to15 mR (average: 10mR). The cumulative radiation exposure for each patient was calculated. There were 567 patients admitted to the units: 146 surgical and 421 medical. Their ages ranged from 15 to 87 years. The duration of stay varied from 1 to 68 days. A total of 3,794 portable chest radiographs were obtained. The number of radiographs per patient varied from 1 to 94. The number of radiographs and the corresponding cumulative radiation doses were as follows: 406 patients (72%) had fewer than five radiographs (<50 mR); 76 (13%) had five to 10 radiographs (<100 mR); 35 (6%) had 11 to 20 (<200 mR); and 50 (9%) had more than 20 chest radiographs (>200 mR). The cumulative ESE ranged from 10 to 940 mR. It exceeded 450 mR in only nine (1.5%) patients. Most (73%) patients undergoing intensive care undergo fewer than five radiographs during their stay in the units. Patient exposure from portable chest radiographs in this population is less than the average annual exposure from background radiation in the USA (450-500 mR), and is much less than the average annual exposure from teratogenic radiation.

Fluoroscopy: patient radiation exposure issues.

Fluoroscopic procedures (particularly prolonged interventional procedures) may involve high patient radiation doses. The radiation dose depends on the type of examination, the patient size, the equipment, the technique, and many other factors. The performance of the fluoroscopy system with respect to radiation dose is best characterized by the receptor entrance exposure and skin entrance exposure rates, which should be assessed at regular intervals. Management of patient exposure involves not only measurement of these rates but also clinical monitoring of patient doses. Direct monitoring of patient skin doses during procedures is highly desirable, but current methods still have serious limitations. Skin doses may be reduced by using intermittent exposures, grid removal, last image hold, dose spreading, beam filtration, pulsed fluoroscopy, and other dose reduction techniques. Proper training of fluoroscopic operators, understanding the factors that influence radiation dose, and use of various dose reduction techniques may allow effective management of patient dose.

Determination of guidance levels of dose for diagnostic radiography in Taiwan.

The International Atomic Energy Agency has recommended guidance levels of dose for diagnostic radiography for a typical adult patient. These levels were intended to act as thresholds to trigger investigations or corrective actions in ensuring optimized protection of patients and maintaining appropriate levels of good practice. Since guidance levels should be derived from wide scale surveys of exposure factors performed in individual hospitals, a national survey was conducted recently in Taiwan to collect these factors for the most frequent radiographic procedures. A total of 276 completed questionnaires were received and analyzed. In the questionnaire, respondents were asked to check those projections that were routinely performed in their department and to report machine data, patient data, output measurements, and technical factors including kVp, mAs, focus-to-film distance, table-to-film distance, aluminum filtration, and focal spot size. Based on the survey data, entrance skin exposures in air, i.e., free air exposures at the point of intersection of the x-ray central beam with the entrance surface of the patient, were estimated using the RADCOMP program. Entrance surface doses to air and tissue with backscatter were then evaluated by the application of the exposure-dose conversion factor and the backscatter factor obtained from TLD measurements and Monte Carlo simulations. Guidance levels were determined from survey results on the entrance surface dose based on optimization considerations involving the cost-effectiveness analysis. Except for chest PA and LAT and skull LAT procedures, all guidance levels derived in this work are less than those recommended by the International Atomic Energy Agency. Survey data and guidance levels were provided to the national authorities to help them develop quality control and radiation protection programs for medical exposures.

Radiation dose from DXA scanning to reproductive tissues of females.

The objective of this study was to use an anatomically arrayed whole-body phantom to measure radiation exposure to the ovaries and uterus during standard dual-energy Xray absorptiometry (DXA) scanning. DXA instrument manufacturers' published entrance skin exposure is about 3 mR (0.77 microC/kg), which is equivalent to the radiation exposure received during a transcontinental plane trip. Nonetheless, since DXA scanning is used more frequently with very young females, the need for pregnancy testing has become an issue that requires attention and formulation of research guidelines. We attached thermoluminescent dosimeters (TLDs) to anatomically arrayed balloon models for ovaries and the uterus, and placed these in the appropriate sites within a small human skeleton along with appropriate amounts of aqueous and fat soft tissue equivalents. Whole-body scanning with a Hologic QDR-2000W was performed 10 times with the pencil beam mode and, using separate TLD detectors, 10 times with the fan beam mode. Overall, the average exposures at skin entrance were 0.89 mR (0.23 microC/kg) with doses for the ovaries of 0.52 mrad (5.2 microgy) and 0.59 mrad (5.9 microgy) for the uterus. These doses are equivalent to 2 d of ambient background radiation in central Pennsylvania or 1 h of flying at 39,000 ft. Although different DXA models by Hologic and DXA instruments by other manufacturers will have different radiation outputs, we believe that these low radiation levels do not require pregnancy testing or questioning of whether the scan subject might be pregnant.

Patient Dosimetry During Interventional Cardiology Procedures

Interventional cardiology procedures generally require prolonged fluoroscopy time and a series of radiographic exposures which result in increasec radiation doses and risks to patient and personnel In order to assess patients stochastic risk during PTCA, the dose-area product (DAP) was measured and the effective dose was calculated by multiplying the DAP by a lactor of 0.2 mSv.Gy 1 .cm 2 . The risk for deterministic effects was estimated by the skin entrance exposure (SEE) measured either by TLDs placed on the patient's skin or calculated using the DAP value over the mean field size. Finally, the clinical protocols used by two teams of ardiologists during RF catheter ablation were compared and the differences in effective doses delivered to the patient were discussed. Complying with the European Directive on Patient Protection, reference dose levels were tentatively suggested in terms of DAP.

A quantitative analysis of dental radiography quality assurance practices among North Carolina dentists

Objective. The purpose of this study was to assess the level of compliance with dental radiography quality assurance recommendations on the part of dental practitioners in the state of North Carolina and to determine whether the age of the practice was an influential factor affecting compliance. Study Design. On-site survey inspections by state officials using measurement devices and questionnaires were used to assess x-ray machine parameters and gather information about quality assurance practices in private offices in the state of North Carolina. Results. There were approximately three intraoral units per facility, with an average entrance skin exposure of 267 mR per bitewing radiograph. There were no significant differences associated with the age of the practice in quality assurance practices except with respect to the type of processor used: dentists who had been in practice for more than 20 years used manual processing more frequently than those who had been in practice for less than 20 years ( p = 0.001). Conclusions. Most practices showed a high level of compliance with equipment function requirements. North Carolina dentists are making an effort to comply with the American Academy of Oral and Maxillofacial Radiology recommendations. However, the use of faster film and rectangular collimation was much less than expected. Only 9% of the participants reported using E-speed film exclusively, and only 7.33% reported using rectangular collimation.

Exposure and dose in panoramic radiology.

Panoramic radiology entrance skin exposure (ESE) was measured for a Siemens Orthopantomograph 10 E using a thimble chamber and TLDs. Thimble chamber measurements are shown to be inaccurate for the moving, narrow beam panoramic scan geometry due to partial volume and partial charged-particle equilibrium effects. For 75 KVp, 8 mA panoramic scans the TLD measured beam central ray ESE on the scan central plane (patient midsagittal plane) was an approximately constant 20 mR for the first 7.5 cm from the entrance slit. A theoretical model of central plane ESE for a fixed rotation center agrees very well with the TLD measurements and is consistent with all of the known ESE (and dose) properties near rotation centers. Head phantom skin dose measurements demonstrate the dependence of skin dose on exact equipment mode of use and patient anatomy. Central plane, beam central ray ESE is judged to be a convenient, universal measure of panoramic radiology radiation output.