Occupational radiation exposure in health care facilities.

BACKGROUND: Radiation, which is used extensively to diagnose and treat human diseases, poses an occupational health risk for the concerned health workers. Personal dosimetry is an important tool to monitor occupational radiation exposures. OBJECTIVE: This study was conducted to reveal and to describe the situation of occupational radiation exposure monitoring among staffs in different health care facilities in Nepal. METHODS: A cross-sectional study was performed among the 35 Health Care Facilities. Information about types and number of X-ray procedures performed, types and number of personnel involved, workload and the availability of personal dosimetry service were collected. RESULTS: Six Health Care Facilities had personal dosimetry service available for a total of 149 personnel. Of a total of nearly one million X-ray procedures performed in the 35 Health Care Facilities in 2007, 76 percent was performed by non-monitored personnel. The majority of the facilities performing high dose procedures, like catheterisation, angiography and intestinal barium procedures did not offer personal dosimetry for the involved personnel. CONCLUSION: There are a limited number of personnel being monitored with personal dosimetry. There are no regulatory dose limits for occupationally exposed staff. Thus, there is an urgent need to establish a national radiation protection authority to regulate the use of radiation in Nepal.

A simplified approach for exit dose in vivo measurements in radiotherapy and its clinical application.

This is a study using LiF:Mg;Ti thermoluminescent dosimeter (TLD) rods in phantoms to investigate the effect of lack of backscatter on exit dose. Comparing the measured dose with anticipated dose calculated using tissue maximum ratio (TMR) or percentage depth dose (PDD) gives rise to a correction factor. This correction factor may be applied to in-vivo dosimetry results to derive true dose to a point within the patient. Measurements in a specially designed humanoid breast phantom as well as patients undergoing radiotherapy treatment were also been done. TLDs with reproducibility of within +/- 3% (1 SD) are irradiated in a series of measurements for 6 and 10 MV photon beams from a medical linear accelerator. The measured exit doses for the different phantom thickness for 6 MV beams are found to be lowered by 10.9 to 14.0% compared to the dose derived from theoretical estimation (normalized dose at dmax). The same measurements for 10 MV beams are lowered by 9.0 to 13.5%. The variations of measured exit dose for different field sizes are found to be within 2.5%. The exit doses with added backscatter material from 2 mm up to 15 cm, shows gradual increase and the saturated values agreed within 1.5% with the expected results for both beams. The measured exit doses in humanoid breast phantom as well as in the clinical trial on patients undergoing radiotherapy also agreed with the predicted results based on phantom measurements. The authors' viewpoint is that this technique provides sufficient information to design exit surface bolus to restore build down effect in cases where part of the exit surface is being considered as a target volume. It indicates that the technique could be translated for in vivo dose measurements, which may be a conspicuous step of quality assurance in clinical practice.

Anopheline mosquito (Diptera: Culicidae) ecology in relation to malaria transmission in the inner and outer terai of Nepal, 1987-1989.

The ecology of Anopheles mosquitoes in relation to malaria transmission was studied at sprayed and unsprayed villages and two unsprayed cattle sheds in the inner terai of Sindhuli District, Central Region, and at two unsprayed villages and one cattle shed in Kanchanpur, Far Western Region of Nepal, from August 1987 to August 1989. Anopheles maculatus was the most abundant of 26 anopheline species collected in Sindhuli District; however, An. fluviatilis was collected most frequently at human bait and was infected most frequently with malaria sporozoites. Residual house spray controlled the indoor resting abundance of the endophilic resting species and protected the population from malaria during midsummer, but had less effect on exophilic resting species and those abundant after and before spray application during the fall and spring, respectively. Malaria at the unsprayed village was detected predominantly in adults of both sexes, perhaps because young children retired early and frequently slept indoors under bed nets during the early evening period of elevated anopheline host-seeking activity. Malaria transmission was verified by the collection of sporozoite infected An. fluviatilis and An. maculatus during spring at cattle sheds in the forested Churia Hills and during the summer monsoon season within the unsprayed village. An. culicifacies was the most abundant of 12 anopheline species collected in Kanchanpur District. Few females of all species were collected at human bait positioned in or out of houses or had human positive blood meals; none were infected with sporozoites. Malaria incidence was higher in the study village positioned along the forest-rice field ecotone than in the cleared rice growing area.

Arbovirus surveillance in northern Colorado, 1987 and 1991.

Arbovirus surveillance was conducted during an epizootic of western equine encephalitis (WEE) during 1987 and during a nonepizootic year, 1991, in the same area in northern Colorado. Mosquitoes were collected in Larimer County, CO, during weeks 33-37 (10 August to 7 September) in 1987 and during weeks 26-35 (24 June to 26 August) in 1991. In total, 13,099 mosquitoes in 694 pools collected during 1987 and 8,672 mosquitoes in 242 pools collected during 1991 were tested for virus. WEE virus was isolated in both years from Culex tarsalis Coquillett and from Cx. pipiens L. in 1987. Infection rates and population levels of Cx. tarsalis were not significantly different in the 2 yr during weeks 33, 34, and 35 (12-26 August). St. Louis encephalitis virus was isolated in 1987 from Cx. tarsalis. Other viruses isolated included Hart Park, Turlock, and Jerry Slough, a variety of Jamestown Canyon virus.

MtDNA polymorphisms among Tharus of eastern Terai (Nepal).

Tharus--a population of Terai (a region with a severe malarial morbidity in the past)--can be subdivided into three main groups: Western, Central and Southern Tharus. They have usually been considered a Mongoloid population and this has been further substantiated by mtDNA findings on Central Tharus. Studies on the distribution of malaria-related genes have shown an extremely high frequency (0.8) of the alpha-thal gene among Western and Central Tharus. This frequency, however, unexpectedly turned out to be only 0.04 in a sample of Eastern Tharus. This raised doubts on the common notion that Tharus are a single anthropological entity. In the present investigation mtDNA markers were studied in the same sample of Eastern Tharus previously examined for the alpha-thal gene. The findings were: 1. the same three features which confirmed the classification of Central Tharus as Mongoloids (i.e., the common occurrence of HpaI-1/HincII-1 and HaeII-5 morphs, and the lack of BamHI polymorphism) were also present in this sample. Since the only neighbouring population accessible to Tharus, until recently, has been Hindu (Caucasoids), this result strongly supports the notion that Tharus are indeed a single anthropological entity; 2. two statistically significant differences between Eastern and Central Tharus--namely, a much higher HaeII morph 5 frequency among Central Tharus, and the absence in the same group of the mutation at 15.487 bp (very common among Eastern Tharus)--together with the results on alpha-tal gene, suggested that Tharu subgroups underwent an effective reproductive isolation.