Whole-body dose irradiation

The W used in calculating the effective dose is proportional to the total detriment given in Table 3.2 and, thus, takes into account fatal cancers and severe hereditary effects, weighted nonfatal cancers, and the relative severity of all fatal responses. When the whole body is irradiated uniformly, the value of wT for a particular organ is the fraction of the total detriment resulting from irradiation of that organ. Thus, the effective dose is intended to be proportional to total... 

Since nonstochastic effects have a threshold, all that is needed to satisfy requirement 2 is to set the exposure limits below that threshold. For nonstochastic effects, the maximum allowed dose is set at 0.5 Sv (50 rem) for any tissue, except for the lens of the eye, for which the limit is set at 0.15 Sv (15 rem). For stochastic effects the limits are set at an acceptable level of risk. Ideally, the limit should be zero, since any exposure is supposed to increase the probability for stochastic effects to occur. Obviously, a zero limit is not practical. For stochastic effects the 10CFR20 sets the limiting exposure on the basis that the risk should be equal regardless of whether the whole body is irradiated uniformly or different tissues receive different doses. Recognizing the fact that different tissues have different sensitivities and, therefore, the proportionality constant between dose and effect is not the same for all tissues, the limit is expressed in terms of the effective dose equivalent (Ffg), defined as... 

Two staff died immediately in the accident, either in the explosion or in the subsequent fire. Twenty-nine others died in the following few days as a result of intense / -exposure causing extensive radiation burns of the skin. Two hundred and seventy-one other people were admitted to hospital of whom 174 suffered symptoms of acute radiation syndrome, having received whole-body y-irradiation doses between 2 and 16 gray. 

Further, the exposure period of 30 min at a distance of 1 m is a cautious judgement of the incidental exposure of persons initially present at the scene of an accident, it being assumed that subsequent recovery operations take place under health physics supervision and control. This is considered to be more realistic than the earlier assumption of exposure for 3 h at a distance of 3 m. Coupled with the dose limits cited above this leads to a limiting dose rate from the damaged package for whole body photon irradiation of 0.1 Sv/h at 1 m. 

In the late 1960s, another compound of this type adrenochrome mono-guanylhydrazone methanesulphonate (S-Adchnon), was shown to be effective at doses well below the toxic level in reducing mortality produced by whole body X-irradiation in mice [425-428]. Recent reports [429, 430] describe the clinical usefulness of S-Adchnon, which can be administered either orally or intraperitoneally and is effective at a dose level of 5 mg/kg. No undesirable side-effects have been reported so far. 

B.5.3 Effective Dose Equivalent and Effective Dose Equivalent Rate. The absorbed dose is usually defined as the mean absorbed dose within an organ or tissue. This represents a simplification of the actual problem. Normally when an individual ingests or inhales a radionuclide or is exposed to external radiation that enters the body (gamma), the dose is not uniform throughout the whole body. The simplifying assumption is that the detriment will be the same whether the body is uniformly or nonuniformly irradiated. In an attempt to compare detriment from absorbed dose of a limited portion of the body with the detriment from total body dose, the ICRP (1977) has derived a concept of effective dose equivalent. 

A wide diversity of dose-response (incidence) relationships has been observed among the neoplasms induced experimentally by chemicals (Zeise et al., 1987), radiation (UNSCEAR, 1977) or both. Although neoplasms of virtually every type have been induced in one experiment ra- another, not all types of neoplasms are observed in animals of any one species or strain. Under some conditions, moreover, the incidence of certain neoplasms has actually been observed to decrease with increasing dose of whole-body irradiation (see Figure 3.1). 

For routine exposures of the public, ICRP recommends a total detriment per unit equivalent dose from uniform whole-body irradiation of 7.3 X 10 2 Sv 1, as shown in Table 3.2. Of this, the recommended probability coefficient for fatal cancers is 5.0 X 10 2 Sv-1, or about two-thirds of the total detriment, and the contributions from severe hereditary responses and weighted nonfatal cancers are 1.3 X 10 2 Sv-1 and 1.0 X 10 2 Sv, respectively. These probability coefficients are summarized in Table 3.3, and their use in radiation protection is discussed in the following section. As noted previously, the probability coefficient for weighted nonfatal cancers is not the same as the probability coefficient for incidence of nonfatal cancers. The probability coefficient for fatal cancers also gives the probability of a fatal cancer per unit effective dose. The effective dose was developed to describe nonuniform irradiations of the body and is discussed below. 

The biological effectiveness of dose depends on the type of radiation and also on the mass and sensitivity of the irradiated tissue. For alpha irradiation, a quality factor of 20 is assumed (ICRP, 1981), and the dose in Sieverts is 20 times the dose in Grays. In addition, ICRP recommends a weighting factor of 0.12 for irradiation of the whole lung and 0.06 for irradiation of bronchial epithelium only. Thus the effective dose equivalent , symbol HE, is defined as the dose to the whole body which carries the same risk as the given dose to the organ or tissue. This, for irradiation of bronchial tissue is 20 x 0.06 = 1.2 times the dose to the organ in Gy. 

It is now usual to calculate the effective dose equivalent (Appendix 1.2). The dose equivalent measured in Sieverts (Sv), takes into account the relative biological efficiency of different radiations. For gamma and beta radiation, the conversion factor is unity, but for alpha radiation it is 20. The effective dose equivalent allows also for the relative importance of irradiation of various organs to the risk of cancer. To convert thyroid dose from beta particles, measured in Gy, to effective dose equivalent, a factor 0.03 is applied. Thus the maximum thyroid doses estimated by Loutit et al. correspond to effective dose equivalents of 4.8 mSv (child) and 1.2 mSv (adult). Adding the external whole body gamma radiation, for which the conversion factor is unity, gives 5.4 mSv (child) and 1.8 mSv (adult). 

CBC and differential STAT, followed by Radiation dose assessment establish absolute lymphocyte counts every 6 hrs. for baseline (initial counts) tor comparison with 48 hrs. if whole-body irradiation possible. later counts to assess degree ot injury. Draw blood from noncontaminated area, cover puncture site afterward. 

The survivors of the bombs dropped over Japan in 1945 are the most important source of information about human whole-body irradiation. The health of about 76 000 persons who had been exposed to doses of up to 7-8 Gy of instantaneous neutron and y radiation and that of their children has been investigated in detail for... 

Radiophosphorus ( P, sodium radiophosphate) is given i.v. Phosphorus is concentrated in bone and in cells that are dividing rapidly, so that the erythrocyte precursors in the bone marrow receive most of the P-irradiation. The effects are similar to those of whole-body irradiation, and in PRV, P is a treatment option for those > 65 years (acaunulation in the gonads precludes its use in younger patients). The maximum effect on the blood count is delayed 1-2 months after a single dose that usually provides control for 1-2 years. It reduces vascular events and delays progression to myelofibrosis. Excessive depression of the bone marrow including leucocytes and platelets is the main adverse effect, but is seldom serious. Acute myeloid leukaemia occurs more frequently in patients treated with P especially when used in combination with hydroxyurea. 

Rosentein et al. [21] injected high dose IL-2 into mice followed by intravenous bovine serum albumin as a marker of capillary leak. The severity of the vascular leak syndrome was dependent upon the number of days of treatment and the dose given. Severity could be reduced by immune suppression with cyclophosphamide, corticosteriods, or whole body irradiation implying that lymphokines released by lymphocytes placed a role in the induction of the vascular leak phenomenon. 

Some skin damage frequently accompanies ARS. However, the cutaneous syndrome can also result from localized acute radiation exposure to the skin, usually from direct handling of radioactive sources or from contamination of the skin or clothes (2,8) (see Figs. 4.1 and 4.2) With localized exposure, even with high doses, the victim frequently survives, because the whole body usually does not receive the localized dose. However, if a patient with localized radiation induced cutaneous injury has also received whole body irradiation from an external source, the cutaneous damage increases the risk for death from the whole body exposure (2). Patients with the hematopoietic syndrome due to whole body irradiation will recover more slowly, if at all, from cutaneous injury due to bleeding, infection and poor wound healing (2). 

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