Radiation quality

During many years in Scientific Research Institutes of Nuclear Physics and Introscopy at Tomsk Polytechnical University (TPU) researches into induction electron accelerators and their uses for non-destructive radiation quality control of materials and articles have been conducted. Control sensitivity and efficiency detection experimental researches have been conducted with the high-current stereo-betatron modifications [1], and KBC-25 M and BC-50 high-current betatrons [2,3] in range of 11 MeV and 25-50 MeV radiation energy. 

Tvne of radiation Quality factor (O) Absorbed dose equal to a unit dose equivalent ... 

Samuel and Magee (1953) employed a 1-radical model to find the relative forward yield in water radiolysis as a function of radiation quality. In such models, no distinction is made between reactive radicals or molecular products. The products of radiolysis are called forward (F) to denote observable molecular yield or radical (R), denoting yield of scavenger reaction at small concentration. The aim of the theory is to calculate the relative forward yield G(F)/[G(F) + G(R)], where the G values refer to the respective yields for 100 eV energy absorbed in... 

Sangster, D.F. In Biophysical Aspects of Radiation Quality International Atomic Energy Agency Vienna, 1971 p. 481-496. 

Frequency of energy deposition in volumes of dimensions similar to DNA and other biological molecules provides a method of interpretation of mechanism of radiation effects. In this method, the assumption is that radiation quality effects are mostly because of the spatial properties of the radiation on a microscopic scale. The database of absolute frequencies of energy depositions in cylindrical targets of dimensions 1-100 nm include ... 

Improving the radiobiological differential effect between the cancer and normal cell populations. This second approach is more complex and involves radiobiological considerations. New and different radiation qualities have been considered such as high-LET radiations. Some of the radiobiological issues involved in the use of high-LET radiation, in particular the RBE concept, are discussed in Sec. 3. 

Radiation quality is defined by the nature, charge, and energy spectrum of the particles and can be characterized by the linear energy transfer (LET) or, alternatively, by the micro-dosimetric spectra at the point of interest under the actual irradiation conditions. 

With hadrons (i.e., neutrons, protons, and heavy ions), new radiation qualities are introduced in therapy. The distributions of the ionizations (and energy deposition events) along the particle tracks are different, and, as a result, different and increased biological effects (at equal absorbed dose) may be expected compared with the conventional photon beams. Fig. 1 illustrates the differences in dose necessary to produce a given biological effect as a function of radiation quality [15]. 

These large differences in energy distribution, at the microscopic level, between radiation qualities at equal absorbed dose, produce different biological effects this leads to the concept of RBE. 

The RBE is defined as a dose ratio, between two doses delivered with two radiation qualities, which produces the same effect on a given biological system, under the same conditions. ... 

The RBE of a given radiation quality relative to Co gamma rays is not a unique value but varies to a large extent with dose, biological system, and effect. 

A high RBE of a new radiation quality does not per se imply a therapeutic advantage. The therapeutic gain is actually the ratio of the RBE for the effects on the cancer cell population and the RBE for the effects on the normal tissues (under the actual irradiation conditions). 

In hadron therapy, a similar approach and symbolism are presented to take into account the RBE differences. RBE values for neutrons are well documented, and reliable data are now becoming available for protons and heavy ions, on which safe weighting factors IErbe can be based. Besides radiobiological determinations, microdosimetry brings independently additional information on the radiation quality and improves confidence in both sets of data. Microdosimetry provides an objective description of the radiation quality at the point of interest under the actual irradiation conditions. Correlation between this set of information and the experimental RBE results is of great scientific and clinical value in hadron therapy [24,25]. 

This brings us to an important question has the efficacy of photon beam therapy now reached a plateau (at least as far as physical selectivity is concerned) If this is the case, little additional clinical benefit can be expected from further technical improvements with photons, and one has to search for other beam or radiation qualities to further improve the effectiveness of radiation therapy. 

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. 

A number of radiation fields spanning a range of radiation qualities are used to accommodate the range of radiation qualities encountered in the workplace. 

W0HNI, T. and STRANDEN, E. (1979). The new ICRP concept of person-dose related to the film-badge exposure for some geometries and radiation qualities used in medical x-ray, Health Phys. 36, 71-73. 

The modalities of exposure for which there are at least s(xne hiunan data include the part of the body exposed to radiation, the dose to an organ or tissue, tl e distribution of the dose over time (dose-rate and fractionation), and the radiation quality defined in terms of LET. 

Ullrich, R.L. and Storer, J.B. (1978). Influence of dose, dose-rate and radiation quality on radiation carcinogenesis and life shortening in RFM and BALB/C mice, in Late Biological Effects of Ionizing Radiation, VoL II., Proceedings of a Symposium, Vienna, 1978, (International Atomic Energy Agency, Vienna). 

Good heat radiating qualities are an asset to an incendiary agent, that is, the spread of luminosity for good distances greatly increases the probability of fire raising. 

Porschen W, Bosiljanoff P, Gewehr K, Muhlensiepen H, Weber HJ, Dietzel F, Feinendegen LE (1977) In vivo assay of the radiation sensitivity of hypoxic tumour cells. Influence of radiation quality and hypoxic sensitization. In Radiobiological research and radiotherapy, Vol. 1. International Atomic Agency, Vienna, pp 181-194... 

These observations have prompted speculation about the role of radiation quality and intensity in regulating MAA content. 

In the field of radiation safety of the environment - regulated, in particular, by the Federal Law On the Environmental Protection - the legislation does not address the issues of standardization of radiation quality of objects of environment. Moreover, a number of the law provisions contradicts the existing legislation and real practice of radiation protection of the environment which use the sanitary-hygienic approach where if man is protected, the environment is protected too , as per the ICRP Recommendations in force (Publication 60). 

The density of excitation and ionization is not necessarily the same for all radiation qualities. For example, it is greater along the track of an a-par-ticle than for an electron track. For a primary-recoil electron produced by Co 7-rays in water, the distance between successive ionizations is about 1000 A. TTie ionized track is, therefore, sparse. At each point of ionization, secondary electrons give rise to further ionizations, forming a group of ion-pairs. In contrast, a-particles form a continuous track as a result of overlapping between the spheres of ionization. 

Type of Murmur Examples Location Pitch Radiation Quality... 

Stopping power can not be the universal parameter though it is still good one, that is, even at a fixed stopping power, the velocity of ions can severely affect the irradiation effects [41, 97]. The similar example was already found for liquid hydrocarbons as seen in the previous section [68], These findings have evoked the concept of radiation-quality effect, as a natural extension of LET effect. 

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