DOSE AND GAMMA-RAY SPECTRA FROM NEUTRON-INDUCED RADIOACTIVITY IN MEDICAL LINEAR ACCELERATORS FOLLOWING HIGH-ENERGY TOTAL BODY IRRADIATION.

Production of radioisotopes in medical linear accelerators (linacs) is of concern when the beam energy exceeds the threshold for the photonuclear interaction. Staff and patients may receive a radiation dose as a result of the induced radioactivity in the linac. Gamma-ray spectroscopy was used to identify the isotopes produced following the delivery of 18 MV photon beams from a Varian 21EX and an Elekta Synergy. The prominent radioisotopes produced include 187W, 63Zn, 56Mn, 24Na and 28Al in both linac models. The dose rate was measured at the beam exit window (12.6 µSv in the first 10 min) following 18 MV total body irradiation (TBI) beams. For a throughput of 24 TBI patients per year, staff members are estimated to receive an annual dose of up to 750 µSv at the patient location. This can be further reduced to 65 µSv by closing the jaws before re-entering the treatment bunker.

Quantification of differences in the effective atomic numbers of healthy and cancerous tissues: a discussion in the context of diagnostics and dosimetry.

PURPOSE: There are a range of genetic and nongenetic factors influencing the elemental composition of different human tissues. The elemental composition of cancerous tissues frequently differs from healthy tissue of the same organ, particularly in high-Z trace element concentrations. For this reason, one could suggest that this may be exploited in diagnostics and perhaps even influence dosimetry. METHODS: In this work, for the first time, effective atomic numbers are computed for common cancerous and healthy tissues using a robust, energy-dependent approach between 10 keV and 100 MeV. These are then quantitatively compared within the context of diagnostics and dosimetry. RESULTS: Differences between effective atomic numbers of healthy and diseased tissues are found to be typically less than 10%. Fibrotic tissues and calcifications of the breast exhibit substantial (tens to hundreds of percent) differences to healthy tissue. Expectedly, differences are most pronounced in the photoelectric regime and consequently most relevant for kV imaging∕therapy and radionuclides with prominent low-energy peaks. Cancerous tissue of the testes and stomach have lower effective atomic numbers than corresponding healthy tissues, while diseased tissues of the other organ sites typically have higher values. CONCLUSIONS: As dose calculation approaches improve in accuracy, there may be an argument for the explicit inclusion of pathologies. This is more the case for breast, penile, prostate, nasopharyngeal, and stomach cancer, less so for testicular and kidney cancer. The calculated data suggest dual-energy computed tomography could potentially improve lesion identification in the aforementioned organs (with the exception of testicular cancer), with most import in breast imaging. Ultimately, however, the differences are very small. It is likely that the assumption of a generic "tissue ramp" in planning will be sufficient for the foreseeable future, and that the Z differences do not notably aid lesion detection beyond that already facilitated by differences in mass density.

Monte Carlo verification of gel dosimetry measurements for stereotactic radiotherapy.

The quality assurance of stereotactic radiotherapy and radiosurgery treatments requires the use of small-field dose measurements that can be experimentally challenging. This study used Monte Carlo simulations to establish that PAGAT dosimetry gel can be used to provide accurate, high-resolution, three-dimensional dose measurements of stereotactic radiotherapy fields. A small cylindrical container (4 cm height, 4.2 cm diameter) was filled with PAGAT gel, placed in the parietal region inside a CIRS head phantom and irradiated with a 12-field stereotactic radiotherapy plan. The resulting three-dimensional dose measurement was read out using an optical CT scanner and compared with the treatment planning prediction of the dose delivered to the gel during the treatment. A BEAMnrc/DOSXYZnrc simulation of this treatment was completed, to provide a standard against which the accuracy of the gel measurement could be gauged. The three-dimensional dose distributions obtained from Monte Carlo and from the gel measurement were found to be in better agreement with each other than with the dose distribution provided by the treatment planning system's pencil beam calculation. Both sets of data showed close agreement with the treatment planning system's dose distribution through the centre of the irradiated volume and substantial disagreement with the treatment planning system at the penumbrae. The Monte Carlo calculations and gel measurements both indicated that the treated volume was up to 3 mm narrower, with steeper penumbrae and more variable out-of-field dose, than predicted by the treatment planning system. The Monte Carlo simulations allowed the accuracy of the PAGAT gel dosimeter to be verified in this case, allowing PAGAT gel to be utilized in the measurement of dose from stereotactic and other radiotherapy treatments, with greater confidence in the future.

Assessment of leakage doses around the treatment heads of different linear accelerators.

Out-of-field doses to untargeted organs may have long-term detrimental health effects for patients treated with radiotherapy. It has been observed that equivalent treatments delivered to patients with different accelerators may result in significant differences in the out-of-field dose. In this work, the points of leakage dose are identified about the gantry of several treatment units. The origin of the observed higher doses is investigated. LiF:Mg,Cu,P thermoluminescent dosimetry has been employed to quantify the dose at a several points around the linac head of various linear accelerators (linacs): a Varian 600C, Varian 21-iX, Siemens Primus and Elekta Synergy-II. Comparisons are also made between different energy modes, collimator rotations and field sizes. Significant differences in leaked photon doses were identified when comparing the various linac models. The isocentric-waveguide 600C generally exhibits the lowest leakage directed towards the patient. The Siemens and Elekta models generally produce a greater leakage than the Varian models. The leakage 'hotspots' are evident on the gantry section housing the waveguide on the 21-iX. For all machines, there are significant differences in the x and y directions. Larger field sizes result in a greater leakage at the interface plate. There is a greater leakage around the waveguide when operating in a low-energy mode, but a greater leakage for the high-energy mode at the linac face. Of the vendors investigated, the Varian 600C showed the lowest average leakage dose. The Varian 21-iX showed double the dose of the 600C. The Elekta Synergy-II had on average four times the dose leakage than the 600C, and the Siemens Primus showed an average of five times that of the 600C. All vendors show strong differences in the x and y directions. The results offer the potential for patient-positioning strategies, linac choice and shielding strategies to reduce the leakage dose to patients.

Adapting a generic BEAMnrc model of the BrainLAB m3 micro-multileaf collimator to simulate a local collimation device.

This work is focussed on developing a commissioning procedure so that a Monte Carlo model, which uses BEAMnrc's standard VARMLC component module, can be adapted to match a specific BrainLAB m3 micro-multileaf collimator (microMLC). A set of measurements are recommended, for use as a reference against which the model can be tested and optimized. These include radiochromic film measurements of dose from small and offset fields, as well as measurements of microMLC transmission and interleaf leakage. Simulations and measurements to obtain microMLC scatter factors are shown to be insensitive to relevant model parameters and are therefore not recommended, unless the output of the linear accelerator model is in doubt. Ultimately, this note provides detailed instructions for those intending to optimize a VARMLC model to match the dose delivered by their local BrainLAB m3 microMLC device.

Systematic variations in polymer gel dosimeter calibration due to container influence and deviations from water equivalence.

There are a number of gel dosimeter calibration methods in contemporary usage. The present study is a detailed Monte Carlo investigation into the accuracy of several calibration techniques. Results show that for most arrangements the dose to gel accurately reflects the dose to water, with the most accurate method involving the use of a large diameter flask of gel into which multiple small fields of varying dose are directed. The least accurate method was found to be that of a long test tube in a water phantom, coaxial with the beam. The large flask method is also the most straightforward and least likely to introduce errors during the set-up, though, to its detriment, the volume of gel required is much more than other methods.

Decontamination assessment of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surfaces using a hydrogen peroxide gas generator.

AIMS: To evaluate the decontamination of Bacillus anthracis, Bacillus subtilis, and Geobacillus stearothermophilus spores on indoor surface materials using hydrogen peroxide gas. METHODS AND RESULTS: Bacillus anthracis, B. subtilis, and G. stearothermophilus spores were dried on seven types of indoor surfaces and exposed to > or =1000 ppm hydrogen peroxide gas for 20 min. Hydrogen peroxide exposure significantly decreased viable B. anthracis, B. subtilis, and G. stearothermophilus spores on all test materials except G. stearothermophilus on industrial carpet. Significant differences were observed when comparing the reduction in viable spores of B. anthracis with both surrogates. The effectiveness of gaseous hydrogen peroxide on the growth of biological indicators and spore strips was evaluated in parallel as a qualitative assessment of decontamination. At 1 and 7 days postexposure, decontaminated biological indicators and spore strips exhibited no growth, while the nondecontaminated samples displayed growth. CONCLUSIONS: Significant differences in decontamination efficacy of hydrogen peroxide gas on porous and nonporous surfaces were observed when comparing the mean log reduction in B. anthracis spores with B. subtilis and G. stearothermophilus spores. SIGNIFICANCE AND IMPACT OF THE STUDY: These results provide comparative information for the decontamination of B. anthracis spores with surrogates on indoor surfaces using hydrogen peroxide gas.

Primary care providers need a variety of nutrition and wellness patient education materials.

OBJECTIVE: To assess and document the need for nutrition and wellness patient education materials. DESIGN: The results of open-ended interviews and focus groups were used to develop a mail-type survey. The 46-item survey addressed barriers to using nutrition and wellness education materials as well as format, education/reading level, foreign languages, and topics needed. North Carolina Cooperative Extension Service (NCCES) family and consumer education agents distributed surveys to family and general practices throughout North Carolina. SUBJECTS: Of the 721 primary care providers surveyed, 303 (42%) returned usable surveys. Respondents practiced in 89 of the 100 counties of the state served by NCCES family and consumer education agents. STATISTICAL ANALYSIS PERFORMED: Descriptive statistics and independent sample t tests were used to analyze survey results. RESULTS: Limited time with patients and inability to obtain materials because of cost or being unsure of sources were most often identified as barriers to using nutrition and wellness materials. Of the 26 topics surveyed, 6 had mean levels of need greater than or equal to high need (mean score > or = 4): weight control for adults, smoking cessation, changing dietary fat intake, exercise guidelines for healthy adults, general stress management guidelines, and healthful eating for older adults. Twenty-four of the 26 topics had mean levels of need greater than or equal to moderate need (mean score > or = 3). Topics with moderate need included guidelines for overweight children and adolescents, nutrition for chronic disease prevention, and healthful eating for various stages of the life cycle. The combined mean score for topics dealing with weight control and exercise for adults, adolescents, and children was greater than the score for high need (mean score > 4). Eighty-three percent of respondents preferred 1-page, printed handouts. Forty-five percent requested materials in Spanish. APPLICATIONS: Dietitians who work in a variety of settings can use techniques similar to those described here to determine the patient education materials practitioners need for the populations they serve. The information obtained from this study will be used to develop 1-page, printed handouts. A registered dietitian and a food and nutrition specialist with NCCES will develop and pilot-test the handouts. These materials will be made available to primary care providers in North Carolina via local NCCES family and consumer education agents, many of whom are registered dietitians.

Biological and sociocultural approaches of histoplasmosis in the State of Guerrero, Mexico.

Histoplasmosis is a deep mycosis with a high prevalence in America. Its aetiological agent, Histoplasma capsulatum, is found in Mexico, mainly in confined spaces, where it grows on bat guano or bird droppings. A research project has been developed in the State of Guerrero, Mexico, where many contaminated caves and mines are visited by individuals and epidemic outbreaks have been recorded. Data concerning human skin test response to histoplasmin antigen, host genetic predisposition to Histoplasma infection, sociocultural, socioeconomical and ethnobiological aspects of the disease in Guerrero are summarized in this paper.

The role of a community coalition in the development of health services for the poor and uninsured.

Access to primary health care for indigent citizens presents a dilemma for many communities in the United States. In response, communities have developed a variety of strategies to effectively deal with the problem. This article describes the evolution of a small free clinic into a comprehensive primary care clinic developed through the actions of a community-based coalition. The clinic originated within an umbrella organization for indigent residents as free medical service provided at a night shelter by a local physician once a week. Through a coalition of business, religious, medical, hospital, foundation, lay volunteer, county health department, and chamber of commerce representatives, the service was enlarged into a formal clinic operation with a small staff and volunteers providing services for about 3,500 patient visits each year. As the demand for services increased beyond resources, an expanded coalition created HealthServe Medical Center, a comprehensive primary care clinic operating 40 hours per week. The HealthServe Board is currently active in supporting service delivery at the clinic, with plans to serve 24,000 medical and dental visits annually by mid-1995. The evolution process was based upon the characteristics of effective community coalitions and the commitment of individuals from diverse community sectors.

The effect of fluoride on the patterns of adherence of osteoclasts cultured on and resorbing dentine: a 3-D assessment of vinculin-labelled cells using confocal optical microscopy.

Osteoclasts were isolated mechanically from chick long bones and cultured on dentine for three days in MEM/10% FCS with or without 1 mg/l NaF, (near to therapeutic ranges for serum fluoride levels) or 15 mg/l NaF (which has been found to reduce the volume:plan-area ratios of resorption pits in vitro). The distribution of close contacts with the substratum was determined by immunolabelling of vinculin and confocal fluorescence microscopy. Four characteristic patterns of contacts were observed: infilled discs, rings, crescents and patches: these reflect the progress of the cell in the process of pit formation. Cell-substratum adherence was more extensive than previously reported with contacts often extending down the sides of pits and sometimes across the floor. This distribution explains the curved shape of unilocular pits and the kidney-shaped extensions of multilocular pits. The peripheral creeping of the contact region was more marked in the osteoclasts of the 15 mg/l NaF cultures, and these cultures showed a decrease in pit depth and inhibition of osteoclastic movement in the presence of fluoride.