The 56th Annual Meeting of the Health Physics Society
26-30 June 2011, West Palm Beach, FL

Single Session



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TAM-A - Medical Health Physics

Room: Ballroom A   8:15 AM - 12:00 PM

Chair(s): Victoria Morris, Mary Ellen Jafari
 
TAM-A.1   08:15  What Dose and Where Does It Come From? V. Morris*, University of Cincinnati ; L. Lemen, University of Cincinnati; M. Gelfand, Cincinnati Children's Hospital/University of Cincinnati

Abstract: The University of Cincinnati radiation safety program has seen a significant increase in the number of young patients undergoing radiation therapy using I-131 labeled metaiodobenzylguanidine (MIBG). A two-part investigation was performed to determine nuclear medicine technologist dose from MIBG patient involvement. First, the average technologist dose received was determined. Second was an investigation of the preparation and administration processes that primarily contributed to this dose. The average dose received was determined using a set of “MIBG” dosimeters worn by the technologist in addition to their standard dosimeters. This set consisted of one whole body and two ring dosimeters. The rules for use were the additional dosimeters were only worn when handling MIBG dosages/patients, and were used for three months or five patients, whichever came first. Data was obtained from two dosimeter sets, involving four different technologists, six patients and 2819 mCi MIBG administered. Results indicated a whole body dose of about 0.09 mrem/mCi, and a hand dose of 0.5 - 1.3 mrem/mCi administered. To determine what task(s) contributed to the dose a more comprehensive dosimeter set that included three whole body dosimeters and eighteen optically stimulated luminescence (OSL) “dots” was used. Each set was used for one patient only. Dosimeters were worn at the chest, waist and upper thigh. One whole body dosimeter was worn at each location throughout the entire MIBG procedure. Pairs of OSL dots were worn at the same locations, but exchanged to separate receipt, preparation, and administration doses. Data was obtained from two technologists and four patients. Results showed the majority of the technologist dose (> 70%) was received during administration. The data are being used to optimize procedures and to purchase additional shielding to minimize technologist dose.

TAM-A.2   08:30  A SmartPhone APP for Tracking Medical CT Doses N Schulte*, Rensselaer Polytechnic Institute ; A Ding, Rensselaer Polytechnic Institute; WM Xu, Rensselaer Polytechnic Institute; PF Caracappa, Rensselaer Polytechnic Institute; XG Xu, Rensselaer Polytechnic Institute

Abstract: X-ray computed tomography (CT) examination has gained popularity in the past decade, causing a concern about the radiation dose to patients. With an accurate and convenient way of estimating and tracking such medical radiation exposures, patients and healthcare personnel will be able to understand and report the level of radiation doses. This paper describes a project to develop a smartphone software application that utilizes many year¡¯s research at RPI on modeling patients and x-ray CT scanners involving a sophisticated Monte Carlo simulation techniques. With this unique radiation dose database, we have developed a graphical user interface targeting users of smart phones that are operated by Android. Our preliminary development had demonstrated the feasibility of adopting 3D patient computational models that are anatomically realistic compared to those used in a few existing software packages. This software improves upon the accuracy and functionality of existing CT dose software. First, VirtualDoseTM incorporates the advanced models for the adult male/female, pregnant female (3-, 6-, and 9-month), with the capability to adjust for body size and shape in order to represent patient populations more accurately. Second, modern CT scanners and protocols, as well as the most recent effective dose algorithms are adopted to keep pace with the multi-detector CT development and regulatory requirements. Third, the software GUI is designed using advanced 3D, objected-oriented programming to improve the user interactivity and reporting functionality including scanning parameter selection and risk comparison. Finally, this is the first software tool available for smartphone users, making it easier to access very accurate and user-friendly CT dose database for reporting purposes. Currently, ~ 100 million CT examinations are performed nationwide each year. The worldwide user market involves an estimated 10 million users that is growing rapidly with this relatively new medical imaging technology. This paper also discusses effort to design multimedia materials for online user and patient education related to Ct dose reduction. *This project is funded by the National Institute of Biomedical Imaging and Bioengineering.

TAM-A.3   08:45  To Shield or Not to Shield CT Patients? Paul G. Johnson*, Cleveland Clinic ; Frank Dong, Cleveland Clinic; William J. Davros, Cleveland Clinic

Abstract: This study is conducted to determine whether lead shielding (i.e., lead aprons of 0.25mm or 0.5mm lead equivalent thickness) is effective in significantly lowering the dose to the reproductive organs of individuals who have reached puberty. Estimates of dose will be obtained using a Rando-Alderson anthropomorphic tissue equivalent phantom. The phantom consists of 34 individual sections ranging from the head through the pelvis (overall height of 163 cm, weight of 53 Kg, density of 0.985 g/cm, and an effective atomic number of 7.3). Thermoluminescent dosimeters (TLDs) will be inserted into the phantom material at specific locations (ovaries and testicals) to measure relative organ dose. In addition, TLDs will be placed near the skin surface to measure entrance skin exposure. The effects of collimation ranging from approximately 1 cm to 6 cm, lead placement and scan range will also be evaluated. Typical chest and abdomen protocols will be utlized. The study will be carried out using two manufacturers computed tomography mutiple slice scanners.

TAM-A.4   09:00  Reducing CT Radiation Dose; a Community Hospital’s Experience Mary Ellen Jafari*, Gundersen Lutheran Health System

Abstract: Although CT is an essential diagnostic tool, it is associated with radiation doses that can be higher than those in conventional x-ray imaging. It is good practice and in the interest of patient safety for medical facilities to reduce CT radiation dose to the lowest level necessary for accurate diagnosis. These efforts need not be limited to research institutions or large facilities. Despite staffing and time limitations, CT radiation dose can be reduced at community hospitals by implementation of practical actions based on a system of key strategies, as demonstrated by the facility in this presentation. These strategies include ensuring proper CT scanner functionality and appropriate trained staff, monitoring and evaluation of radiation dose, optimization of CT acquisition protocols, and education of referring physicians and patients. We believe this program can be used successfully at other community hospitals and smaller medical centers.

TAM-A.5   09:15  Federal Guidance for Diagnostic and Interventional X-Ray Procedures LS KEITH*, Agency for Toxic Substances and Disease Registry ; M BOYD, Environmental Protection Agency; ST SEARS, US Navy; DL MILLER, Food and Drug Administration; EM LEIDHOLDT, Department of Veterans Affairs; DG HILL, Department of Labor, Occupational Safety and Health Administration; JP WINSTON, Commonwealth of Pennsylvania

Abstract: At the 2010 annual meeting we addressed efforts by the Medical Workgroup of the Interagency Steering Committee on Radiation Standards to develop updated radiation protection guidance for x-ray procedures. This presentation is an update on what is now slated to become Federal Guidance Report No. 14. The draft document modernizes radiation protection guidance issued in 1976 by the Environmental Protection Agency (which replaced the Federal Radiation Council) and was signed by the President. It expands the scope beyond diagnostic work to include interventional x-ray procedures. Also, it covers a wide range of modalities, including radiography, CT, fluoroscopy, bone densitometry, dentistry, and veterinary practice. The document in general covers new radiation protection concerns raised by digital radiography, shielding, requesting and performing studies, procedure justification, and dose optimization, The modality-specific guidance is presented in terms of equipment, testing and quality assurance, personnel, and procedures. The global shift from film to digital mode has provided an opportunity for improving image quality while at the same time either increasing or decreasing radiation dose to the patient receptor. The medical use of x-rays is steadily increasing, and was estimated in 2006 to deliver 2.2 mSv or approximately 35% of the 6.2 mSv radiation dose a member of the public receives each year from all sources. With CT scans alone increasing at the rate of 10% per year, these x-ray doses will likely exceed 40% of the U.S. total in 2011. Such a rapid increase raises awareness and provides a wake-up call to ensure that the appropriate image quality is requested and that the appropriate dose is delivered to each patient. The status of this effort is changing as its review continues and comments are addressed. Comment periods planned for the medical, dental, and veterinary communities are aimed at making the guidance valuable to all Federal agencies and adoptable by the private sector.

TAM-A.6   09:30  Heart Shift and Reduction in Heart Dose to Left-Breast Cancer Patients Using the Deep Inspiration Breath Hold Technique J. A. Vognetz*, Bloomsburg University of Pennsylvania ; N. Fallahian, Bloomsburg University of Pennsylvania; A. O. Jones, Geisinger Medical Center, Pennsylvania; T. J. Gergel, Geisinger Medical Center, Pennsylvania; C. J. Veale, Geisinger Medical Center, Pennsylvania; J. B. Treas, Geisinger Medical Center, Pennsylvania; D. R. Simpson, Bloomsburg University of Pennsylvania

Abstract: One of the challenges in breast cancer radiotherapy includes delivering the prescribed dose to a tumor within the breast mass while attempting to limit the dose to healthy organs within the chest wall such as the heart and lungs. The volume of the patient’s exposed chest and organs within the photon beam fluctuates during treatment due to the patient’s breathing pattern, and this will essentially dictate the volume of the tissue exposed to the beam. This study implemented a technique known as deep inspiration breath hold (DIBH), which involves the patient holding her breath during the radiation treatment in order to limit the amount of heart movement into the photon beam. Two CT scans were taken for each of the 35 left-breast cancer patients; one as the patient breathed normally, and the other as the patient performed the DIBH technique. The radiation treatment planning software (Pinnacle from Philips Medical) was then used to fuse the two CT scans by targeting the fusion of the breast tissue. A standardized dose of 5000cGy was applied to each patient’s treatment plan and comparisons were made between the normal breathing heart dose and the DIBH heart dose. The DIBH technique resulted in an average heart shift of 2.82 cm with a mean dose reduction of 215cGy to the heart. This is corresponding to an average of 62% reduction in heart dose. Data showed that all patients benefited from the DIBH technique, effectively reducing the heart dose.

TAM-A.7   10:15  Sestamibi Redistribution Measurement Defines Ischemic Coronary Artery Lumen Disease. RM Fleming*, Cardiovascular Consulting ; GM Harrington, UNI

Abstract: Objectives: Quantitative measurement of changes in isotope concentration originally described by Blumgart in 1925 yielded important diagnostic information for heart disease. Qualitative comparisons of rest stress images are associated with frequent errors including false negatives and false positives. Using methods previously described we compared quantitative changes in isotope measurement under stress conditions with qualitative results from rest stress comparisons. Methods: One hundred twenty men and women between the age of 25 and 82 years of age underwent coronary angiography for evaluation of coronary artery (CAD) disease. Subjects underwent both rest stress qualitative comparisons and quantitative measurement of technetium-99m isotope concentrations under stress stress conditions. These results were compared with angiographic evaluation of CAD. Results: Qualitative evaluation of ischemic CAD cannot be quantitatively compared with angiographic measurement of percent diameter (% DS) stenosis (CAD). Sensitivity and specificity could be determined using 50 %DS as the marker of angiographic disease. Rest stress qualitative comparisons showed a sensitivity of 67% with 22 individuals being told they did not have CAD when in fact they did. Four of these individuals had �critical� disease. The specificity was 88 percent. Quantitative comparisons (FHRWW) of actual technetium-99m isotope count changes during stress (5 minutes) stress (60 minutes) imaging revealed a parabolic relationship between quantitative findings and angiographic (% DS) measurement of CAD. The odds ratio (OR) for rest stress comparisons detection of CAD was 4.88 (C.I. 95%: 2.3-10.3), while the OR for FHRWW was 56.7 (C.I. 95% 27.5-117.2). Conclusions: Rest stress comparisons provide qualitative evaluation of CAD, which missed 1/3rd of all patients studied who in fact had ischemia, more than 3% of whom had �critical� disease. By comparison, measurement of technetium-99m isotope redistribution (FHRWW) provides a quantitative relationship between changes in SPECT myocardial perfusion imaging under stress conditions, which changes the question from does the patient have CAD, to how much CAD does the patient have. In addition, this approach reduces the amount of radiation the patient is exposed to.

TAM-A.8   10:30  Use of Hybrid Phantoms for Individualized Dose Monitoring in Interventional Fluoroscopy WE Bolch*, University of Florida ; P Johnson, University of Florida; D Borrego, University of Florida; K Johnson, University of Florida; D Siragusa, University of Florida

Abstract: Interventional fluoroscopy uses ionizing radiation to guide small instruments such as catheters through blood vessels or other body pathways. The technique represents a tremendous advantage over invasive surgical procedures, as it requires only a small incision, thus reducing the risk of infection and providing for shorter recovery times in comparison to surgical alternatives. The growing use and increasing complexity of interventional fluoroscopic procedures, however, has resulted in public health concerns regarding radiation exposures, particularly with respect to localized skin dose. Tracking and documenting patient-specific skin and internal organ dose has been specifically identified for interventional fluoroscopy where extended irradiation times, multiple projections, and repeat procedures can lead to some of the largest doses encountered in radiology. Furthermore, in-procedure knowledge of localized skin doses can be of significant clinical importance to managing patient risk. Two recent and innovative developments are used to make individualized dose monitoring in interventional fluoroscopy a clinical reality. The first is the development of a library of patient-dependent hybrid computational phantoms that cover a range of body shapes and sizes within the US adult population. The second is the release of the new DICOM Radiation Dose Structured Report (RDSR) which has the potential for near real-time documentation of all factors required for reconstruction of skin and internal organ dose. In this study, the RDSR is read from the Artis Zee fluoroscopic system from Siemens Medical Solutions. Reference point air kerma values are extracted during each radiation event, mapped onto a 1 x 1 cm2 grid of surface voxels for a patient-matched hybrid phantom, adjusted by an energy-dependent photon backscatter factor, with further corrections for both table and pad attenuation. Assessments of internal organ doses are performed via Monte Carlo radiation transport using the RDSR and selected patient morphometry information to uniquely specify the irradiation geometry. The techniques presented thus provide for patient dose monitoring in interventional fluoroscopic procedures in a manner that accounts for both the anatomic diversity of the patient population and the complex, dynamic, and individually unique nature of these procedures.

TAM-A.9   10:45  Radiopharmaceutical dose estimates reflecting recent model changes MG Stabin*, Vanderbilt University

Abstract: Three recent model changes will affect standardized dose estimates for radiopharmaceuticals, namely (1) introduction of new, anatomically realistic phantoms based on non-uniform rational b-splines (NURBS), using the new ICRP 89 recommended organ masses, (2) replacement of the traditional ICRP 30 GI tract model with the ICRP human alimentary tract (HAT) model and (3) use of ICRP 103 tissue weighting factors for calculating effective dose. The RADAR Task Group has recalculated organ dose estimates and effective doses for most important radiopharmaceuticals currently in use, entering results from biokinetic models suggested by the ICRP Task Group on Radiopharmaceutical Dosimetry into the OLINDA/EXM version 2 software, which implements the three new modeling approaches. Most organ and effective doses do not change profoundly, although differences can be noted due to the closer proximity of organs in the realistic models and the explicit treatment of electron transport, compared to approaches used in the previous generation of 'stylized' mathematical phantoms. Several important organs not available in the previous generation phantoms (e.g. esophagus, salivary glands, prostate) allow for a more complete treatment of dosimetry and calculation of effective dose. The different definitions of the lower intestinal regions in the HAT model, compared to the previous ICRP 30 model, will present some difficulties in direct comparisons of dose estimates. The new dose estimates will be made generally available to the user community via the RADAR web site.

TAM-A.10   11:00  The UF Family of Pediatric Patient-Dependent Phantoms for Medical Dose Reconstruction A Dziadon*, University of Florida ; A Geyer, University of Florida; C Lee, National Cancer Institute; P Johnson, University of Florida; M Wayson, University of Florida; W Bolch, University of Florida

Abstract: Based on data released in 2009, the National Council on Radiation Protection (NCRP) estimates that since 1982, the average effective patient dose from medical imaging has increased by nearly 600%. The need for organ dose assessment and tracking has motivated the University of Florida’s research in computational anatomical phantoms. The UF family of computational hybrid phantoms was created using various methods such as retrospective patient image reviews, national anthropometric databases, and ICRP literature coupled with modern-day computer animation software. The UF pediatric family was originally designed to be consistent with reference individuals as defined in ICRP Publication 89 and which included models for the newborn, 1-year, 5-year, 10-year, and 15-year male and female child. In the study by Johnson et al [Proceedings of the IEEE, vol. 97, No. 12, pp. 2060-2075], data from the CDC’s National Center for Health Statistics over the period 1988 to 1994 were used to create targeted values of standing height, sitting height, total body weight, and various secondary circumferential values in which an expanded library of 50 adult phantoms – 25 males and 25 females – were generated at five different standing heights and for each standing height, five different weight percentiles – 10th, 25th, 50th, 75th, and 90th – as needed for improved matching of dosimetry phantom to individual patient. The study additionally targeted the development of some 100 pediatric patients – 50 males and 50 females – also at different heights and weights. The purpose of the present study is to update this phantom library of pediatric models to conform to body morphometry data of the US population collected over the more recent period 1999 to 2010. This effort is required as increasing obesity rates in US children have been observed over the past 20 years, and corresponding changes in the UF phantom library are warranted.

TAM-A.11   11:15  The Effect of Patient Obesity on PET/CT Imaging Dose Using a Phantom with a Body Mass Index of 45 MM Mille*, Rensselaer Polytechnic Institute, Troy, NY ; A Ding, Rensselaer Polytechnic Institute, Troy, NY; T Liu, Rensselaer Polytechnic Institute, Troy, NY; YH Na, Rensselaer Polytechnic Institute, Troy, NY; PF Caracappa, Rensselaer Polytechnic Institute, Troy, NY; XG Xu, Rensselaer Polytechnic Institute, Troy, NY

Abstract: The average medical radiation exposure to the U.S. population has risen dramatically over the last few decades due, in large part, to an increase in the number of x-ray computed tomography (CT) and positron emission tomography (PET) exams performed annually. This trend has drawn attention to the need for improved reporting of patient imaging dose. Such dose estimates are often derived from Monte Carlo simulations involving computational human body phantoms that represent the quintessential “average” adult. Nonetheless, it also important to study the range of doses received by patients who may differ in size and stature. In particular, few phantoms exist for calculating dose to obese patients who, because of their greater body thickness, can require special imaging protocols to maintain image quality. The purpose of this work was to study the effect of obesity on the imaging dose of patients undergoing whole-body diagnostic CT and F-18 FDG PET scans. The RPI-Adult Male phantom with a body mass index (BMI) of 24 (normal weight) was modified by adding subcutaneous fat superficially to the torso and by packing visceral fat between the organs in the abdominal cavity. The resulting phantom had a BMI of 45 (morbidly obese). CT organ doses for a GE Lightspeed scanner (tube voltage 120 kVp) were calculated for the 2 phantoms in the MCNPX code. Similarly, PET organ doses were calculated using S-values computed in MCNPX along with the ICRP-106 FDG biokinetic model. For the same tube current, the obese phantom was found to have CT organ doses which were on average a factor of 0.7 times smaller than that of the normal weight phantom because of shielding by the extra fat. For the same injected activity, the average PET organ dose ratios were 0.95 and 0.65 for source and non-source organs, respectively. These differences are due primarily to the obese phantom’s smaller remainder source S-values which arise from the addition of the extra fat to the remainder compartment. These results translate into higher imaging exposures for obese patients after accounting for the greater tube current and radiopharmaceutical dosages such patients typically receive. Ongoing studies are considering more obese phantoms. Acknowledgement: Mr. Mille is supported by a U.S. Department of Energy Nuclear Energy University Program Graduate Fellowship.

TAM-A.12   11:30  Statistical and Dose Trend Analysis of Occupational Doses : A 20-year Review A.N. Al-Haj*, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia ; I. Al-Gain, King Faisal Specialist Hosptial & Research Centre, Riyadh, Saudi Arabia; A.M. Lobriguito, King Fahad Medical City, Riyadh, Saudi Arabia

Abstract: The King Faisal Specialist Hospital & Research Centre (KFSHRC) in Riyadh is the largest medical centre equipped with state of the art imaging systems with the biggest cyclotron facility in the Gulf region. This study aims to analyze the dose trends from year 1990 to 2009 and investigate the causes in staff dose increase in three occupational categories: cardiac catheterization, angiography and cyclotron. Dose records were retrieved and correlation of the mean and collective doses with several factors such as patient workload was investigated. Data showed that the doses of cardiac catheterization staff were reduced by a factor of two while there is an increasing dose trend for angiography. The dose trend for cyclotron was increasing during the first 10 years but was reduced by a factor of two in the second 10 year. A significant correlation (r= 0.95) exists between the annual collective dose and the number of radiation workers. There is a need to review the protocols for angiography and develop techniques for staff dose reduction in cyclotron.

TAM-A.13   11:45  PET/CT Patient Doses and Staff Exposures : Is there a Need for Optimization? A.N. Al-Haj*, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia ; A.M. Lobriguito, King Fahad Medical City, Riyadh, Saudi Arabia; A. Arafah, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia; R. Parker, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia

Abstract: The first PET/Ct was installed at King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia in 2006. ööIt has a yearly workload of about 4,000 patients. The study aims to evaluate the variation in patient and staff doses during whole body imaging. It also aims to investigate the causes for high doses in patients and staff and provide recommendations for dose optimization. A total of 500 pediatric and adult patients were included in the study. CT doses were estimated using the IMPACT dose calculator. PET doses were estimated using the ICRP 80 dose conversion coefficients. Staff doses were estimated from TLD readings deployed for 18 months and were verified using measured dose levels. The mean effective dose is highest for neonates (15.5 mSv) and age group 1 year old (15.9mSv). The estimated effective dose for adult patients is 18 mSv. Results show that a review of the PET/CT patient protocols and staff work planning is needed for dose reduction.



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