Review of RBE values of 15 MeV neutrons for effects on normal tissues

Values of the relative biological effectiveness (RBE) of fast neutrons for effect on normal tissue depend not only on the neutron energy and the dose, but also on the type of tissue irradiated. Values of the RBE of 15 MeV neutrons are reviewed for rapidly proliferating rodent tissue, such as mouse bone marrow, mouse intestine and rat skin treated with single and fractionated irradiations. In addition, RBE values were obtained for rodent tissue with relatively long cell life times, such as the vascular endothelium, the spinal cord and the lung. In general, the normal tissue data indicate that for doses between 50 and 250 rad the RBE values range up to values of about 2, but depend on the fractionation regimen

The relevance of different quantities for risk estimation in diagnostic radiology

At the relatively low dose levels encountered in diagnostic radiology, detrimental effects have not been observed. Based on a linear extrapolation from the available data at high dose, (in excess of 0.3 Gy) a small risk for the occurrence of stochastic effects can, however, not be excluded. In diagnostic radiology the exposure conditions are highly inhomogeneous. When only one type of tissue is exposed, e.g. in the case of mammography, it will be most adequate to quote an average dose to the organ of interest. In nuclear medicine the administered activity, considered by the ICRP as a reference value, can easily be converted into effective dose. For diagnostic radiology with external X ray beams, field parameters such as air kerma free-in-air or the dose-area product (DAP) can be considered as easily measurable quantities. The limitations of the latter parameter are demonstrated on the basis of measurements in paediatric radiology. The DAP increases with age of the children whereas the effective dose remains nearly constant. The absorbed dose at the skin of the patient is not an appropriate quantity for computed tomography. For other techniques this dose value should be complemented by information on beam quality and field dimensions. Although objections have been raised against the use of effective dose, this concept provides a useful means to classify diagnostic procedures in terms of radiation exposure of the patient

Dosimetry for total body irradiation of rhesus monkeys with 300 kV X- rays

Purpose: To obtain more accurate information on the dose distribution in rhesus monkeys for total body irradiation with orthovoltage X-rays. Materials and methods: Dose measurements were performed with an ionization chamber inside homogeneous cylindrical and rectangular phantoms of various dimensions and in phantoms containing lung-equivalent material. The irradiations were carried out with reference to a monitor ionization chamber placed alongside the phantom or the irradiation cage. Results: Correction factors for mass and lung dose relative to the average close in a homogeneous reference phantom, showed linear relationships with the effective diameter of the monkey. The lung close correction factor relative to the homogeneous phantom was about 1.12 for a 3.5 kg monkey. The stated values for the average absorbed dose in the animal of standard weight should be multiplied by a factor of 0.93 for experiments performed before 1983. All publications on total body irradiations of monkeys at TNO after 1983 contain the corrected dose values. Conclusion: Dose distributions are reported for phantoms of different diameters and of cylindrical or rectangular shape. The new dosimetry has also resulted in a revised statement of the LD50 for the occurrence of bone marrow syndrome after X-irradiation; 4.9 Gy instead of 5.3 Gy