Radiation dose-exposure

We tested the response of various fluorescence parameters to radiation. Among all tested values (Fo, Fm> Fy/Fm, area, Fj, Fp etc.) the modification of the area over the fluorescence curve was more relevant at the low radiation dose exposure (Fig. 9). 

This is a very attractive proposition in paediatric radiography, but it can potentially cause problems and in clinical practice considerable effort is needed to maintain standards (Willis and Slovis 2005). The equipment must be set up carefully, to optimise all of the factors under control, and these must be constantly monitored and improved. It is all too easy later on to improve poor images by increasing the radiation dose ( exposure factor creep ) when other adjustments might have been effective. 

Often the success of a decontamination operation is expressed in terms of a cost-benefit analysis, i. e. a comparison of the expenses incurred during execution of the total procedure to the cumulative dose exposure (man-rems) which can be expected to be saved as a consequence of the reduced radiation levels. The problem with such an analysis, which is mainly in use in the USA, lies in the difficulty in translating radiation dose exposures saved into an equivalent amount of money. The result of such an analysis, therefore, depends highly on the equivalent assumed. On the basis of such cost-benefit analyses, substantial radiation exposure savings to the staff have been calculated, in particular when decontamination was carried out prior to inspection, repair or replacement work. As was shortly mentioned above, the initial concerns of the plant owners with regard to the costs, the potential success and the potential hazards of such an action have been largely dissipated and, at many plants, decontamination of particular systems has become a standard technique. However, as the measures taken for reduction of plant contamination buildup (see Sections 4.4.3. and 4.4.4.) will prove to be more and more successful in the future, the need of operational decontamination in the plants is expected to decrease. 

The implications of performing cardiac CT and the corresponding radiation dose exposure are a complex issue with many health policy aspects. Some authors have tried to shed light in those topics. Coles et al. (2006) performed a comparison between 16-slice CTCA and conventional angiography in 91 directly comparable patients. The dose apphed in CTCA of 14.7 2.2 mSv was... 

Very low-risk patients are not good candidates for CT imaging due to the risk of contrast and radiation exposure. Cardiac CT imaging based on the current standard of retrospective helical acquisitions is associated with a radiation dose exposure of 15mSv (three times the average exposure rate of conventional catheterization angiography), precluding use of the method for asymptomatic patients. 

Measurements of the radiation dose exposure to radon and its decay products is carried out by an electronic radon gas personal dosimeter. Such a dosimeter is that named DOSEman (Sarad, Dresden, Germany) (Grundel and Porstendorfer, 2003). Using the dosimeter, the radon concentration is measured in the environment, e.g. in dwellings, mines, caves, etc., and can be converted to a personal dose. The entire measuring system is accommodated in a handy housing, so that it can be carried comfortably on the body. 

The radon concentration indoors in terms of radiation dose exposure is expressed in WL (Working Level, the radiation level of 100 pCi per litre or 3700 Bq per m of Rn in equilibrium with its decay products). Effects of radon are given in terms of WLM (Working Level Months), which is the exposure at 1 WL for one working month, or 170 h. Since there are 365 X 24 = 8760 h per year and 80% of them (7000 h) are spent indoors, the annual time of exposure is 7000/170 = 41 working months . A world-wide representative value adopted by the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR, 1977) is that 1 pCi per litre or 37 Bq per m is the average Rn concentration indoors, with an equilibrium factor (ratio of Rn decay product concentration to their concentration in radioactive decay equilibrium with Rn gas) of 0.5. This corresponds to an average concentration of 0.005 WL or 5 mWL. The annual indoor exposure is then 0.005 WL x 41 WM = 0.205 WLM. 

In order to minimize the radiation dose, the inspection time is limited to 30 seconds of exposure (programmable) after which the X-ray on/off shutter will shutter off the X-rays and the block must be unloaded. A timer will keep the operator informed of the time that has elapsed. 

Radiation protection, ie, the limits on radiation dose to workers and the pubHc are specified. Exposure is maintained as low as reasonably achievable... 

Radiation dose limits at a disposal site boundary are specified by the NRC as 25 x 10 Sv/yr (25 mrem/yr), a small fraction of the average radiation exposure of a person in the United States of 360 x 10 /Sv/yr (360 mrem/yr). Protection against nuclear radiation is fully described elsewhere... 

Most of the data on radiation health effects have come from medical monitoring of Japanese atomic bomb survivors. For survivors who received radiation exposures up to 0.10 Sv, the iacidence of cancer is no greater than ia the geaeral populatioa of Japanese citizens. For the approximately 1000 survivors who received the highest radiation doses, ie, >2 Sv, there have been 162 cases of cancer. About 70 cases would have been expected ia that populatioa from aatural causes. Of the approximately 76,000 survivors, as of 1995 there have beea a total of about 6,000 cases of cancer, only about 340 more cases than would be expected ia a group of 76,000 Japanese citizens who received only background radiation exposure (59). 

For radiation doses <0.5 Sv, there is no clinically observable iacrease ia the number of cancers above those that occur naturally (57). There are two risk hypotheses the linear and the nonlinear. The former implies that as the radiation dose decreases, the risk of cancer goes down at roughly the same rate. The latter suggests that risk of cancer actually falls much faster as radiation exposure declines. Because risk of cancer and other health effects is quite low at low radiation doses, the iacidence of cancer cannot clearly be ascribed to occupational radiation exposure. Thus, the regulations have adopted the more conservative or restrictive approach, ie, the linear hypothesis. Whereas nuclear iadustry workers are allowed to receive up to 0.05 Sv/yr, the ALARA practices result ia much lower actual radiatioa exposure. 

Is the employer using means other than employee rotation to eomply with permissible exposure limits (PELs) or ionizing radiation dose limits, exeept where no other feasible way exists [OSHA Referenee. 120(g)(l)(iii)]... 

State whether the following statements are true or false. If false, explain why. (a) The dose equivalent is lower than the actual dose of radiation because it takes into account the differential effects of different types of radiation, (b) Exposure to 1 X 1 ()x Bq of radiation would be much more hazardous than exposure to 10 Ci of radiation, (c) Spontaneous radioactive decay follows first-order kinetics, (d) Fissile nuclei can undergo fission when struck with slow neutrons, whereas fast neutrons are required to split fissionable nuclei. 

Radiation sterilization Radiochromic chemical Plastic devices impregnated with radiosensitive chemicals which undergo colour changes at relatively low radiation doses Only indicate exposure to radiation... 

Generally, the phenotype that predisposes an individual to an increased risk of skin cancer is red or blond hair, blue eyes, and fair skin. These characteristics are surrogate measure of the sensitivity of the skin to sun exposure and the tendency to develop nevi, freckles, and sunburns based on the skin type. Freckles, which may appear abruptly after the first high dose of UV radiation sun exposure, represent clones of mutated melanocytes, and their presence is associated with an increased risk of melanoma.12 The Fitzpatrick classification of skin type is used to determine the response pattern of the skin to UV radiation and assess the risk for melanoma. There are six Fitzpatrick skin types Type I skin always burns and never tans, type II skin burns easily and tans rarely, type III skin burns sometimes and tans usually, type IV skin burns rarely and always tans, type V skin always tans and is moderately pigmented (brown), and type VI skin always tans and is darkly pigmented (black). Fitzpatrick I and II skin types are commonly affected by NMSC and MM. The susceptibility to skin cancer, both NMSC and MM, is related to the melanin content of the skin and the skin s response to UV radiation. 

Type SR-0 compounds include insoluble and nonreactive gases (e g., inert gases such as H2, He). These compounds do not significantly interact with the respiratory tract tissues, and essentially all compound inhaled is exhaled. Radiation doses from inhalation exposure of SR-0 compounds are assumed to result from the irradiation of the respiratory tract from the air spaces. 

Epidemiological and Human Dosimetry Studies. Epidemiological studies of radiation dose typically involve estimates of exposure that are based on whole-body measurements of internally-deposited americium. A need remains for epidemiological data that can provide quantitative human dose-response information while supplying additional information on the health effects of exposure to ionizing radiation and americium in particular, for cases of known internal exposure. 

Effect. Chromosomal aberrations have been reported in lymphocytes following exposure to 241Am (Bauchinger et al. 1997 Kelly and Dagle 1974). Additionally, high radiation doses from internally deposited americium can cause bone marrow changes and altered blood values (Filipy et al. 1995 Priest et al. 1995). However, none of these effects are specific to americium. 

Robinson B, Heid KR, Aldridge TL, et al. 1983. 1976 Hanford americium exposure incident Organ burden and radiation dose estimates. Health Phys 45(4) 911-921. 

Dosimetry—Quantification of radiation doses to cells, tissues, organs, individuals or populations resulting from specified exposures. 

Characterizing the radiation dose to persons as a result of exposure to radiation is a complex issue. It is difficult to (1) measure internally the amount of energy actually transferred to an organic material and to correlate any observed effects with this energy deposition and (2) account for and predict secondary processes, such as collision effects or biologically triggered effects, that are an indirect consequence of the primary interaction event. 

It should be noted that there is intense controversy as to the health effects of radiation doses below about 100 mSv per year. This estimate of 15,000 annual cancer deaths from indoor radon, as well as estimates of tens of thousands of eventual cancer deaths from Chernobyl exposures, is obtained by applying the linearity hypothesis. This hypothesis has been adopted by most regulatory agencies but is strongly contested by some scientists who believe it overestimates the effects of radiation at low dose levels. Of course, if calculations based on this hypothesis overestimate the deaths from indoor radon, they also overestimate the effects of potential radiation from a waste repository. 

---