Trends in radiation protection of medical workers.

Medical workers constitute the largest group of individuals occupationally exposed to radiation, and their collective dose equivalent is exceeded only by persons employed in the nuclear fuel cycle. Although medical workers have increased in number by about 50% over the past two decades, their collective dose has steadily declined. Factors that contribute to changes in the exposure patterns of medical workers include variations in demand for medical imaging procedures, changes in the way these procedures are administered to patients, and development of devices that utilize radiation more efficiently and display radiation-derived information more effectively. Trends such as the movement of imaging procedures into nonradiologic disciplines and nonhospital settings, and the imposition of economic and legal considerations into decisions about patient management and health care, may also ultimately affect the exposure of medical workers to radiation.

Dose-response models and methods of risk prediction and causation estimation.

Dose-response models are mathematical expressions that describe the relationship between absorbed dose and radiogenic effects. The limited quality and quantity of human dose-response data make it necessary to use fairly simplistic models. Most current low-LET data support the linear-quadratic model in which radiogenic effects are linearly dependent at low doses and then become quadratically curved at higher doses. Some types of effects never exhibit a quadratic component, remaining linear over a wide range of absorbed dose. Future progress in developing more refined dose-response models is more likely to come from a better understanding of the fundamentals of radiation carcinogenesis rather than better data or better curve-fitting techniques. The risk of radiation injury is a prospective estimation of the probability that some harm will result in the future as a consequence of having been irradiated. Quantitative risk estimates for the carcinogenic, genetic, and fetal effects of low level radiation that have been determined by national and international organizations are of the order of magnitude of one chance fatality in 10,000/rem. Causation estimation is the retrospective analysis of the probability that cancer observed in an irradiated individual was caused by radiation as opposed to some other agent. Depending on the dose type of cancer, gender, age at time of irradiation, and time since irradiation, the probability of causation can range from 0% to 100%. Methods for calculation of the probability of causation for certain types of cancer and irradiation circumstances have been developed recently by the National Institutes of Health.

ALARA and an integrated approach to radiation protection.

Exposures of individuals to ionizing radiation have been restricted for many years by a number of guidelines and rules developed by various advisory and regulatory groups. Accompanying these restrictions has been an evolving principle that exposures to individuals and groups should be kept "as low as reasonably achievable" (ALARA), consistent with provision of the benefits of radiation use to society. Although the ALARA concept is a laudable goal in principle, its implementation in a clinical facility has not been a straightforward process. Problems of implementing ALARA have been confounded further by the efforts of regulatory agencies to incorporate the ALARA concept into regulations governing radiation exposures. To facilitate the implementation of ALARA as a workable construct in a clinical facility, guidelines are needed for its application to both individual and collective exposures to radiation. The provision of such guidelines, including action and inaction levels for both individual and collective exposures, are presented here.

Preliminary observations on the results of combined 125iodine seed implantation and external irradiation for carcinoma of the prostate.

Fifty-seven patients with localized carcinoma of the prostate were treated with pelvic lymphadenectomy and a reduced 125iodine implant dosage, supplemented by a moderate dose of external beam radiotherapy to the whole pelvis delivered 4 to 6 weeks later. The incidence of pelvic nodal metastases was 28 per cent and the operative morbidity was 15 per cent. Late radiation sequelae developed in 18 patients, including 15 patients with radiation proctitis (29 per cent), among whom 2 (4.6 per cent) suffered rectal ulceration and required diverting colostomy. Followup has been 2 years or longer (median 33 months) in 26 patients, of whom 22 (85 per cent) are free of disease. Three patients are living with osseous metastases or local disease and there has been 1 death of prostatic carcinoma, for an absolute 2-year survival rate of 95 per cent. Of the 7 patients with poorly differentiated tumor and of the 8 patients with positive pelvic lymph nodes 5 and 6, respectively, remain free of disease after a minimum 2-year followup. Potency has been lost in 20 per cent and reduced significantly in 30 per cent of the patients followed 18 months or longer. Prostatic biopsies on 28 asymptomatic patients 12 to 30 months after completion of therapy showed no tumor in 21 (75 per cent).

Automatic outlining of regions on CT scans.

A computer software system for automatic outlining of borders between regions of differing CT numbers on computed tomography scans has been developed. The technique was originally intended for application in defining inhomogeneities for radiation therapy treatment planning; however, several other applications are possible. The system scans an image using a simple threshold model to locate initial outline points and then completes the outline with a border-following algorithm. Results of the automatic outlining system are given along with histograms of the enclosed regions, demonstrating several further applications of these techniques.

Combined I125 seed implant and external irradiation for carcinoma of prostate.

Localized carcinoma of the prostate was treated in 20 patients by pelvic lymph node dissection, radioactive iodine implant and external radiotherapy. Treatment was well tolerated. Pelvic lymph node involvement was present in 35% of the patients. Well-differentiated cancers were essentially in small prostates (3 cm), stages T1 or T2. They had a lower possibility (10%) of metastasis to only one pelvic lymph node. None had more than one lymph node involved. Moderately or poorly-differentiated cancers occurred in larger prostates (4 cm or more), stage T3. They had a high likelihood (60%) of pelvic node involvement.

Radiation exposure to medical personnel during iodine-125 seed implantation of the prostate.

Radiation exposure to operating room personnel was measured by thermoluminescent dosimeters and an ionization chamber during a simulated iodine-125 seed implantation of the prostate gland. The exposure rates at points around the implanted phantom were measured and compared with the calculated values. The data suggested that even with a schedule of 25 prostate implants per year, exposure levels would not exceed 5% of the recommended maximum limits for occupationally exposed personnel.

Irradiation of the microvasculature with fast neutrons.

Single- and split-dose irradiation of the eyes of dogs was performed with cyclotron-produced polyenergetic neutrons at a rate of about 0.2 Gy (20 rad) per minute. Neovascularization was subsequently induced surgically in the avascular corneas and stimulated for 7 days to study the response of slowly proliferating capillary endothelial cells. Corneal tissue samples were evaluated quantitatively by morphometric methods. A dose-response curve was drawn by plotting per cent capillary volume versus dose. D0 was 2 Gy (200 rad), and the recovery ability was determined to be equivalent to 1.3 Gy (130 rad). Depending on the level of damage, relative biological effectiveness (RBE) values were 1.9 to 2.3.

A least-squares technique for extracting neutron spectra from Bonner sphere data.

The accurate assessment of neutron flux and dose-rate levels in a medical environment is a topic of much current interest. In this paper, a least-squares data-analysis technique has been used for extracting neutron spectra and related information from Bonner sphere data. This technique, incorporated in the FORTRAN IV code NFLS is worthy of consideration as an alternative to the count-rate ratios and iterative-unfolding techniques used in the past. The analysis provides calculated total neutron flux density, dose-equivalent rate, and average and median-neutron-energy information as well as a plot of integral neutron-flux-density spectra. The method allows the calculation of the statistical uncertainty of each of the above quantities, which has not always been possible with other analytical methods. Results of calibration and experimental data analysis are presented and compared to results of the iterative-unfolding technique.

Effects of motion on the radiological image.

A method to study the loss of resolution of radiological images caused by patient motion is presented. Optical transfer functions (OTF) are computed for motion with uniform velocity and with simple harmonic oscillation. The line spread function (LSF) of a pattern of motion can be generated from the image of a long, narrow moving slit. Once the LSF is known the OTF of the motion can be obtained by Fourier transform.

Use of 48Ca as a stable isotope tracer analyzed by proton activation.

The use of the stable isotope 48Ca as a tracer in biological systems has been studied. Determination of 48Ca concentrations in samples was accomplished by proton activation via the (p,n) reaction with subsequent measurement of gamma-ray spectra from 44-h 48Sc and 4-h 44Sc. With protons of about 5.5 MeV and a Ge(Li) gamma-ray detector, and with no chemical processing of the samples, ratios of these two radioisotopes can be determined with sufficient precision to allow 48Ca tracer studies to be performed with sensitivity at least equivalent to that possible with the common 45Ca radioactive tracer.

Diabetes and associated variables in the South Australian Aboriginal.

Diabetes of a predominant maturity-onset type has been identified as being up to ten times more prevalent in South Australian Aborigines than in Caucasians. On the evidence provided, nutritional status and obesity are thought to be dominant in the aetiology of the hyperglycaemia, although relative hyperinsulinaemia in full blood Aborigines suggests a significant racial genetic effect. It is suggested on these and other grounds that the diabetic genotype may represent a factor of previous survival advantage to the Aboriginal, now rendered deleterious by urbanization. The degree of hyperglycaemia, and its association with hyperlipidaemia, obesity, retinal arteriovenous changes and abnormal electrocardiographic findings, accentuates the significance of the diabetes, and underlines the serious need for ongoing nutritional education in these communities.

Blood pressures and electrocardiographic findings in the South Australian Aborigines.

Blood pressure measurements were recorded in 522 adults and 141 10-19 year-old full and part blood Aborigines in five communities. The means for systolic and diastolic blood pressures at 40 years were close to those reported for Europeans, although below this age, values tended to be lower, and above 40 years tended to be higher than those reported in the Tecumseh study. Hypertension, as defined by the Princeton criteria, was present in 29%, more often in the men (1-6 to 1-0), and eight subjects satisfied the criteria for hypertensive heart disease (HHD). 522 electrocardiograms were recorded on adult subjects at five Aboriginal communities and classified according to categories of the Minnesota code. Of the 210 abnormalities observed, minor T wave inversions and minor S-T segment depression were the most commonly encountered, and were more frequent in female subjects. Q wave changes typical of myocardial infarction was found in 5% of the tracings and occurred mainly in older men. If hypertension and certain ECG codes are assumed to be "risk factors" for the development of clinical ischaemic heart disease (IHD), the urbanized Aboriginal had a higher prevalence compared with Caucasian subjects of the Busselton study. "Probable" and "suspect" ECG changes of IHD, although mainly in the older subjects, were found to be associated with hyperglycaemia, as recognised in Western society. It is postulated that urbanized Aborigines are prone to cardiovascular degenerative disease to a similar or possibly larger extent than Caucasians.

Visual acuity and retinal changes in South Australian Aborigines.

Eye examinations were carried out a four Aboriginal reserves. Of 361 Aboriginal adults tested, 64 had a visual defect (visual acuity of 6/9 or worse) in each eye, a prevalence of 18%, with an additional 79 (22%) with a similar loss of acuity in one eye only; these were more frequently seen at the urbanized reserve of Koonibba. Only one full blood Aboriginal child within the less urbanized communities had a reduced visual acuity, whereas seven (10%) part blood children at a more urbanized reserve had reduced vision in both eyes, with a further nine (13%) in one eye only, not unlike figures quoted for South Australian school children. Vascular changes in the fundus oculi were observed and occurred more often when hypertension and/or hyperglycaemia were present. They consisted of arteriovenous crossing changes (26%), swelling of the retinal veins (3%) and altered light reflex (41%) and were not infrequently seen in the younger adult (20% of adults under 30 years had AV crossing changes and 46% had widened light streak). Analysis suggests that, although hypertension and hyperglycaemia are related to retinal vascular changes, other factors, as yet unidentified, are present in the Aboriginal population under consideration.