Dose distribution

The worldwide market is approximately 3.0 bHHon in sales, with the pediatric portion accounting for about 35%. Basic, required childhood vaccines (DTP, poHo, measles /MMR, BCG, and TT) account for 3640 x 10 doses of this global market. In the United States doses distributed in the pediatric sector have risen from around 45 x 10 in 1982, covering basic, childhood vaccines, to around 75 x 10 in 1993 due primarily to the addition of vaccines for Haemophilus disease, hepatitis B, and a second dose of MMR to the recommended childhood series (144). The majority of vaccines for the U.S. market are... 

The first inactivated poliovirus vaccine was introduced in the 1950s in an injectable formulation, and replaced in the 1960s by a live oral poliovirus vaccine. The oral poliovirus vaccine not only elicits systemic immunogenicity but also a localized immune response in the intestinal tract. Unfortunately, the oral poliovirus vaccine has the risk of vaccine-associated paralytic poliomyelitis occurring in approximately 1 case of every 2.4 million doses distributed. The risk with the first dose of oral poliovirus vaccine is 1 case in 750,000 doses.11... 

Children less than 12 years of age will have a 97% seroconversion rate following a single vaccination. Adolescents and adults more than 13 years old will only have 78% seroconversion after a single inoculation, but will have 99% conversion after the second vaccination administered 4 to 8 weeks after the first. Antibody titers appear to persist for at least 20 years following immunization. Despite excellent seroconversion rates, breakthrough chickenpox is reported at a rate of 1 case per 10,000 doses distributed. Most cases occurred within the first year following vaccination, and were due to wild-type varicella zoster virus. The majority of breakthrough cases were mild and of short duration.12... 

The VAERS database is continually monitored to determine if the prevalence of reactions is changing and to identify previously unreported reactions to a particular vaccine. One of the limitations of the VAERS data is that it does not contain denominator data. Therefore it is not possible to calculate a true rate of reaction occurrence the number of cases of reaction per dose of vaccine administered. Rates are usually calculated using the number of doses distributed from the manufacture as the denominator. This makes the assumption that each dose distributed is administered. 

M Dolovich. Lung dose, distribution, and clinical response to therapeutic aerosols. Aerosol Sci Technol 18 230-240, 1993. 

The selection of the 1980-82 measurements (Swedjemark and MjOnes, 1984) was made on dwellings built before 1976 and with the aim of determining dose distributions and the collective dose to the Swedish population from the exposure of the short-lived radon decay products. This was done by using the statistical selection made by the National Institute for Building Research intended for an energy study of the Swedish stock of houses. From a selection of 3 100 houses in 103 municipalities, 2 900 were inspected. The data was found to be in substantial conformity with data from the land register and the population census of 1975. For the study of the radon concentration 752 dwellings were selected at random. 

Hofmann, W., Dose Calculations for the Respiratory Tract from Inhaled Natural Radionuclides as a Function of Age - II. Basal Cell Dose Distributions and Associated Lung Cancer Risk, Health Phys. 43 31-44 (1982). 

An external alpha source yields certainly another dose distribution within the blood. Internal alpha sources, as described above,... 

Pohl, E. and J. Pohl-Ruling, Dose Distribution in the Human Organism Due to Incorporation of Radon and Decay Products as a Base for Epidemiological Studies, in Proceedings of the International Radon Specialist Meeting on the Assessment of Radon and Daughters Exposures and Related Biological Effects, Rome, (RD Press)pp. 

SC-52 Conceptual Basis of Calculations of Dose Distributions SC-53 Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Radiation... 

Jacob P. and Likhtarev L, 1996. Transfer factors for mushrooms, in Pathway analysis and dose distributions, Final Report of JSP-5 for the contracts COSU-CT93-0053 and COSU-CT94-0091 of the European Commission, Luxembourg, pp. 63-74. 

By comparing this analysis with estimates of the LD50 (and assuming a similar slope for lethality) one can predict the probable overlap (if any) between the incapacitating and lethal dose distributions (Fig. 13). 

The length of the field usually means that there is a rapidly sloping surface making it difficult to have a homogeneous dose distribution. 

Figure 10 Comparison of the dose distribution of a 1-keV electron at 25 °C (dashed contours) and at 300°C (solid contours). Dose in eV/nm. ...

National Council on Radiation Protection and Measurements Conceptual Basis for Calculations of Absorbed-Dose Distributions Recommendations 168 National Council on Radiation Protection and Measurements Bethesda, MD, 1991. 

As one of the basic formulations accounting for the radial dose distribution in an ion track, the following formulas were given [92] ... 

Experimental approaches to measure the radial dose distribution are also in progress [119], and it was found that the distribution follows r law in the inner region of a critical distance and obeys r law outside of that region. LaVerne and Schuler reported the considerable decrease in the radiation chemical yield for ferric production in the Fricke dosimeter, suggesting a model of a deposited energy density in an ion track, which depends on the LET and the atomic number of an irradiation particle [120,121]. 

The dose distribution in the materials is given as a depth-dose curve. An example of the curve is illustrated in Fig. 4 obtained with the irradiation of electron from 0.5 to 1.0 MeV using cellulose triacetate (CTA) film dosimeter [12]. The existence of the maximum dose is an important characteristic of the depth-dose curve. Irradiation from two opposite sides by using two accelerators was proposed in order to give better uniformity in water [13]. The uniform irradiation is also important for flue gas treatment. Better efficiency of NO removal was proved with both-side irradiation by using three accelerators for coal-fired flue gas than single-side irradiation at the same dose [14]. 

Figure 4 Depth-dose distribution curves in CTA stack films with the irradiation of electron. (From Ref. 11.)...

From a technical point of view, intensity-modulated radiation therapy (IMRT) optimizes several parameters selection of multiple beams and, for each beam, optimization of dose, dose rate, size and shape, etc. Tomotherapy optimizes the dose distribution by IMRT in successive sections with immediate verification gamma knife, cyberknife, and radiosurgery concentrate high radiation doses in well-defined small volumes. 

More generally, the technical conditions in which radiological treatment is delivered (resulting in different dose distributions and different doses to normal tissues)... 

Figure 14 Proton beam irradiation of a deep-seated large tumor. Single Bragg peaks of different energy are combined, in adequate proportions, to obtain a homogeneous dose distribution at the level of the SOBP. The depth-dose curve of a photon beam, shown for comparison, is inferior compared to the proton curve. However, an optimized multifield photon treatment allows to reach better irradiation conditions. (From Ref 43.)...

Of course, like with photons, several intersecting proton beams can be used in order to further improve the final dose distribution. Fixed beams or an isocentric gantry can be used. 

Figure 16 Proton therapy for uveal melanoma. Dose distribution obtained with a beam of 60-MeV protons with an appropriate spread-out Bragg peak (energy modulated from 14-60 MeV). Transverse section through the center of the eye. The position of the tumor [gross tumor volume (GTV)] is indicated by the posterior hatched area. Protons allow to obtain a homogeneous dose over the whole GTV with effective sparing of the normal structures. This implies a great precision in patient-beam positioning. (Courtesy from PSI, cited in Ref. 3.)...

Figure 18 Comparison of photon and proton dose distributions for the treatment of a craniopharyngioma in a child. Typical planning sections for a large suprasellar craniopharyngioma, in a 3-year-old child, treated with photons (A) or protons (B). The planning target volume (PTV) is indicated by the hatched area. For photons and protons, four equally weighted beams are used and the normalization point was chosen at the intersection of the beam axes. For the four proton beams, the Bragg peak was spread over 4 cm. (From Ref. 41.)...

The third approach is the introduction of another type of radiation quality high-LET radiation. Clinical experience with neutrons has demonstrated that high-LET radiations are superior to low-LET radiations for some tumor types or sites. Fast neutrons were indeed the first high-LET radiations to be applied clinically (see Sec. 4.1). Although in the first studies they were applied in suboptimal conditions from a technical or dose distributions point of view, their advantage for some types of tumors is well established, particularly for slowly growing, well-differentiated tumors. Randomized trials have indeed shown their superiority over conventional photons for salivary gland tumors and prostatic adenocarcinomas. 

Proper control of food irradiation applications should fulfill the requirements for both food technologies and radiation technologies. Application of well-established methods for measurement of absorbed radiation dose and the dose distribution helps to provide assurance that the radiation treatment is both effective and legally correct [133]. Computer tomography (CT) can provide detailed, high-resolution, and accurate dose maps for any arbitrary product and package configurations [134]. Such dose maps are an essential part of process validation. 

Radiation cross-linking of polyethylene requires considerably less overall energy and less space, and is faster, more efficient, and environmentally more acceptable. Chemically cross-linked PE contains chemicals, which are by-products of the curing system. These often have adverse effects on the dielectric properties and, in some cases, are simply not acceptable. The disadvantage of electron beam cross-linking is a more or less nonuniform dose distribution. This can happen particularly in thicker objects due to intrinsic dose-depth profiles of electron beams. Another problem can be a nonuniformity of rotation of cylindrical objects as they traverse a scanned electron beam. However, the mechanical properties often depend on the mean cross-link density. ... 

The depth dose distribution is measured by irradiating a stack of radia-chromic film chips with a thickness slightly greater than the practical range at the energy of interest. The depth dose is determined by evaluating the individual chips. 

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