Using personal monitoring data to derive organ doses for medical radiation workers in the Million Person Study-considerations regarding NCRP Commentary no. 30.

The study of low dose and low-dose rate exposure is of central importance in understanding the possible range of health effects from prolonged exposures to radiation. The One Million Person Study of Radiation Workers and Veterans (MPS) of low-dose health effects was designed to evaluate radiation risks among healthy American workers and veterans. The MPS is evaluating low-dose and dose-rate effects, intakes of radioactive elements, cancer and non-cancer outcomes, as well as differences in risks between women and men. Medical radiation workers make up a large group of individuals occupationally exposed to low doses of radiation from external x-ray/gamma exposures. For the MPS, about 100 000 United States medical radiation workers have been selected for study. The approach to the complex dosimetry circumstances for such workers over three to four decades of occupation were initially and broadly described in National Council on Radiation Protection and Measurements (NCRP) Report No. 178. NCRP Commentary No. 30 provides more detail and describes an optimum approach for using personal monitoring data to estimate lung and other organ doses applicable to the cohort and provides specific precautions/considerations applicable to the dosimetry of medical radiation worker organ doses for use in epidemiologic studies. The use of protective aprons creates dosimetric complexity. It is recommended that dose values from dosimeters worn over a protective apron be reduced by a factor of 20 for estimating mean organ doses to tissues located in the torso and that 15% of the marrow should be assumed to remain unshielded for exposure scenarios when aprons are worn. Conversion coefficients relating personal dose equivalent,Hp(10) in mSv, to mean absorbed doses to organs and tissues,DTin mGy, for females and males for six exposure scenarios have been determined and presented for use in the MPS. This Memorandum summarises several key points in NCRP Commentary No. 30.

Abnormal response of tumor vasculature to vasoactive drugs.

The effects of the vasoconstrictor phenylephrine and the vasodilator hydralazine on blood flow to tumor were studied and compared to those on blood flow to normal tissues in vivo. Regional blood flow and cardiac output were measured with the use of radioactive microspheres in 150- to 250-g inbred Harlan F344 rats bearing subcutaneous nodules of two types of transplantable carcinoma ("hard" and "soft") with microscopically different vascular patterns. Three groups of rats were treated with hydralazine, saline, or phenylephrine, and regional blood flow was determined at the time of maximum blood pressure response. Results were correlated with quantitative morphometric analysis of arteriolar and capillary wall thickness in tumor and normal tissue. Phenylephrine decreased and hydralazine increased normal tissue perfusion as indicated by cardiac output. Tumor blood flow remained low and was not significantly influenced by drug treatment, except for the phenylephrine effect on hard tumors. Histologic study of tumor vessel walls revealed an absence of smooth muscle capable of responding to the vasoactive drugs by constriction or dilation. Evidently, by their selective action on normal vessels, vasoactive drugs can change the ratio of tumor:normal tissue perfusion. In particular, the increase of normal tissue: tumor blood flow by vasodilator drugs may enhance the selectivity of local heat therapy.

Effect of pulsed progressive fluoroscopy on reduction of radiation dose in the cardiac catheterization laboratory.

The increased application of therapeutic interventional cardiology procedures is associated with increased radiation exposure to physicians, patients and technical personnel. New advances in imaging techniques have the potential for reducing radiation exposure. A progressive scanning video system with a standard vascular phantom has been shown to decrease entrance radiation exposure. The effect of this system on reducing actual radiation exposure to physicians and technicians was assessed from 1984 through 1987. During this time, progressive fluoroscopy was added sequentially to all four adult catheterization laboratories; no changes in shielding procedures were made. During this time, the case load per physician increased by 63% and the number of percutaneous transluminal coronary angioplasty procedures (a high radiation procedure) increased by 244%. Despite these increases in both case load and higher radiation procedures, the average radiation exposure per physician declined by 37%. During the same time, the radiation exposure for technicians decreased by 35%. Pulsed progressive fluoroscopy is effective for reducing radiation exposure to catheterization laboratory physicians and technical staff.

Dosimetry and biodistribution of an iodine-123-labeled somatostatin analog in patients with neuroendocrine tumors.

A modified method for the preparation of a radiolabeled analog of somatostatin (123I-octreotide) is described. The pharmacokinetics and dosimetry of this analog were evaluated in patients with neuroendocrine tumors. Thirty patients had multiple blood and urine samples and sequential anterior and posterior whole-body scintigraphy up to 40 hr postinjection of 123I-octreotide. Region of interest analysis of the whole-body images was used to determine organ and tumor doses. The 123I-octreotide was rapidly cleared from the blood with a T 1/2 of 10 min by the hepatobiliary system. By 40 hr, approximately 55% was eliminated in the feces. The gallbladder wall received the highest dose (0.48 rad/mCi), with other organs receiving doses of 0.12 rad/mCi or less. Tumors were identified in 25 of 28 satisfactory studies. Tumor doses ranged from 0.1 to 0.6 rad/mCi. Calculations with 131I instead of 123I indicated that the gallbladder wall would receive 2 rad/mCi, while average tumor doses would range from 0.9 to 5.0 rad/mCi. Iodine-123-octreotide is a useful agent for the visualization of neuroendocrine tumors. The rapid washout of this agent from tumors precludes the possibility of radiotherapy with 131I-octreotide in these patients.

Measurement of body potassium with a whole-body counter: relationship between lean body mass and resting energy expenditure.

We conducted studies to determine whether the Mayo whole-body counter could be used to measure body potassium, and thus lean body mass (LBM), and whether moderate obesity alters resting energy expenditure when corrected for LBM. Twenty-four nonobese and 18 moderately obese adults underwent body potassium (40K) counting, as well as tritiated water space measurement and indirect calorimetry. LBM values predicted from 40K counting and tritiated water space measurements were highly correlated (P = 0.001; r = 0.88). Resting energy expenditure was closely related to LBM (P less than 0.0001; r = 0.78): kcal/day = 622 kcal + (LBM.20.0 kcal/kg LBM). In this relationship, the obese subjects did not differ from nonobese subjects. In summary, the Mayo whole-body counter can accurately measure LBM, and moderate obesity has no detectable effect on corrected resting energy expenditure.

The radiation dosimetry and normal value study of 99mTc-HMPAO-labeled leukocytes.

RATIONALE AND OBJECTIVES: Indium-111 (111In)-labeled leukocyte scanning has been used frequently in patients suspected of having infections. Recently, technetium-99m hexamethylpropylene amine oxime (99mTc-HMPAO) has been used to label leukocytes. This study was undertaken to determine the distribution and dosimetry of 99mTc-HMPAO leukocytes in healthy subjects. METHODS: Five healthy volunteers had leukocytes labeled with 99mTc-HMPAO. After injection of the labeled leukocytes, whole body images and blood and urine samples were obtained at multiple time points. RESULTS: Visual interpretation of the images demonstrated significant bowel activity as early as 2 hours and increasing with time such that one the 8- and 24-hour images, the amount of bowel activity would preclude using 99mTc-HMPAO leukocyte scanning for abdominal processes. The dosimetry for this study is similar to that of other studies and is in an acceptable diagnostic range. CONCLUSIONS: 99mTc-HMPAO leukocyte studies are an acceptable alternative to 111In-labeled leukocyte studies in terms of dosimetry. Use of such studies in the abdomen should be limited to early images, usually before 2 hours, to avoid confusion with the normal route of excretion in the bowel.

Regulations for radioiodine therapy in the United States: current status and the process of change.

Radioiodine therapy has been used for many years to treat thyroid disease. The use of 131I sodium iodide in mCi dosages poses potential hazards to health care personnel, family or close friends of the patient, and the general public. The US Nuclear Regulatory Commission (NRC) is charged with protection of health and safety from various radioactive materials including 131I. The NRC accomplishes its mission through regulations and license conditions placed on the authorized use of radioiodine. Current regulations limit annual whole body dose of 1 mSv (100 mrem) for members of the public and 50 mSv (5,000 mrem) for radiation workers. To protect patients from dispensing errors, the NRC promulgated regulations on possession use, calibration, and check of dose calibrators and outlined procedures to follow if an error is made. This paper discusses these requirements, methods for meeting them, the process used by the NRC to change its regulations, a proposed rule on release of patients who contain therapeutic radionuclides, and some commentary from the National Council on Radiation Protection and Measurements that medical licensees may find useful.

Flexible polyimide-based intracortical electrode arrays with bioactive capability.

The promise of advanced neuroprosthetic systems to significantly improve the quality of life for a segment of the deaf, blind, or paralyzed population hinges on the development of an efficacious, and safe, multichannel neural interface for the central nervous system. The candidate implantable device that is to provide such an interface must exceed a host of exacting design parameters. We present a thin-film, polyimide-based, multichannel intracortical Bio-MEMS interface manufactured with standard planar photo-lithographic CMOS-compatible techniques on 4-in silicon wafers. The use of polyimide provides a mechanically flexible substrate which can be manipulated into unique three-dimensional designs. Polyimide also provides an ideal surface for the selective attachment of various important bioactive species onto the device in order to encourage favorable long-term reactions at the tissue-electrode interface. Structures have an integrated polyimide cable providing efficient contact points for a high-density connector. This report details in vivo and in vitro device characterization of the biological, electrical and mechanical properties of these arrays. Results suggest that these arrays could be a candidate device for long-term neural implants.

Radiation exposure of fertile women in medical research studies.

Fertile women may be exposed to ionizing radiation as human subjects in medical research studies. If the woman is pregnant, such exposures may result in risk to an embryo/fetus. Fertile women may be screened for pregnancy before exposure to ionizing radiation by interview, general examination, or pregnancy test. Use of the sensitive serum pregnancy test has become common because it offers concrete evidence that the woman is not pregnant (more specifically, that an embryo is not implanted). Evidence suggests that risk to the embryo from radiation exposure before organogenesis is extremely low or nonexistent. Further, demonstrated effects on organogenesis are rare or inconclusive at fetal doses below 50 mSv (5 rem). Therefore, there may be some level of radiation exposure below which risk to the fetus may be considered essentially zero, and a serum pregnancy test is unnecessary. This paper reviews the fetal risks and suggests that consideration be given to establishing a limit to the fetus of 0.5 mSv (50 mrem), below which pregnancy screening need not include the use of a serum pregnancy test.

Reorganization and consolidation of a safety program.

Prior to 1990, the Mayo Safety Program consisted of several autonomous functions, one of which was Radiation Safety. Consolidation and enhancement of these programs began in 1990 with safety coordinators (e.g., health physicists, industrial hygienists, ergonomists) reporting to one safety director who reports to a vice president level administrator. In 1995, the hierarchical structure was replaced with self-directed work teams. These teams have team leaders who replaced conventional work unit supervisors and a Human Resources (HR) Liaison who is responsible for HR issues including time keeping and 360 degrees performance reviews. A Steering Team, consisting of team leaders was established to create a strategic plan, set program goals, and hold teams accountable. In 1997, processes were evaluated and redesigned through an operational restructuring method called process mapping; process mapping is a tool used in reengineering. Value added to the safety program as a result of these efforts includes more program ownership by Safety staff as demonstrated by increased motivation, increased interest in success of the entire safety program, and increased participation in team planning and management. In addition, some economies of scale have been achieved through cross-functional teams.

Update on patient radiation doses at a large tertiary care medical center.

Radiation procedures in diagnostic radiology and nuclear medicine examinations, especially at referral centers, contribute a significant proportion to population dose; hence, there is a presumed detriment. Knowledge of the magnitude of dose from each type of exam is helpful in determining where to implement dose reduction efforts. Additionally, new records of dose data facilitate comparisons with past measurements. In this paper, updated patient exam dose data (frequency and effective dose equivalent) are provided for a large, comprehensive, tertiary care medical center that served more than 340,000 patients in 1997. Patient billing code data were used to study 31 different types of diagnostic exams encompassed in five major categories (angiography, fluoroscopy, radiography, nuclear medicine, and computerized tomography). Organ doses for each radiographic and nuclear medicine exam were estimated using published Monte Carlo conversion factors and appropriate exposure values. Estimates of organ doses were utilized to compute effective dose equivalent (EDE) per ICRP 26 and collective effective dose equivalent. Mean effective dose equivalent was also calculated for each exam category. Total collective effective dose equivalent had decreased from 1988 (2,030 person-Sv) to 1997 (1,817 person-Sv). The largest contributors to collective effective dose equivalent were angiography (768 person-Sv), computerized tomography (447 person-Sv), and nuclear medicine (355 person-Sv). Radiography (150 person-Sv) and fluoroscopy (97 person-Sv) contributed the least to collective effective dose equivalent. Mean effective dose equivalent contributions remained the same, with angiography accounting for the highest component, followed by nuclear medicine, computerized tomography, fluoroscopy, and radiography, respectively. Effective dose equivalent, collective effective dose equivalent, and mean effective dose equivalent values were calculated and tabulated in five major categories. These data provide updated information as to trends in exam and; collective dose from 31 common types of radiologic exams performed at a large medical center, which can be used as an up to date baseline for analyses of trends in U.S. radiation doses due to medical imaging procedures. Although minor changes were observed in comparing the mean effective dose equivalent data to those of a previous study, substantial differences were evident in the collective effective dose equivalent data. This was due primarily to variations in the number of patients examined and changes in technology and practice.