Purpose: To harmonize X-ray dosimetry in radiobiology to allow a direct comparison of radiobiological studies performed at institutes cooperation within the framework of the European Late Effects Project Group (EULEP). Materials and methods: The 1985 EULEP protocol for X-ray dosimetry and exposure arrangements employed for studies of late somatic effects in mammals required serious revision, e.g. due to the replacement of calibration of dosemeters in terms of exposure by calibration in terms of air kerma free-in-air. An action group established by EULEP and the European Radiation Dosimetry Group (EURADOS) updated the 1985 protocol. Results: The new EULEP EURADOS protocol for X-ray dosimetry in radiobiology including the code of practice for irradiation of small animals and related dosimetry. The present protocol includes the changes in calibration procedures and dosimetric concepts for irradiation with medium energy X-rays since 1985. Accuracy and precision are replaced by the concept of combined (standard) uncertainty. The revised supplements provide more detailed background information. New appendices contain definitions of general terms used for measurements and mathematical expressions of the relative variances. Conclusion: Adherence to the present protocol will result in improved dosimetry and facilitates the comparison of results of radiobiological experiments obtained at different institutes.

Protocol for X-ray dosimetry in radiobiology

The effect of cortisone treatment on the ability of bone marrow cells to repopulate X-irradiated thymus was investigated In one experimental series, groups of mice were treated first with cortisone and then irradiated with or without bone marrow protection Mice treated with either cortisone or radiation alone served as controls During an initial, bone marrow independent phase of thymus regeneration, cortisone had a stronger inhibitory effect on the cellular regeneration of the organ than irradiation On the other hand, during a subsequent bone marrow dependent phase, thymus regeneration was impaired by radiation exposure but not by cortisone treatment In another experimental series, irradiated mice were transplanted with bone marrow cells in different numbers from syngeneic donors which had either been treated with cortisone or were left untreated Twenty days later the cell number was consistently larger in the thymus of animals which has been transplanted with cortisone treated bone marrow than in the animals transplanted with untreated bone marrow It is concluded that the thymus lymphocyte precursors in the bone marrow and the early precursors of thymocytes in the thymus differ with regard to their sensitivity to cortisone and radiation and, therefore, may represent two distinct cell types

Effect of cortisone and X-irradiation on cellular depletion and regeneration in the thymus of mice: Experimental discrimination between thymus lymphocyte precursors in the bone marrow and in the thymus

Summary In one series of experiments, the cellular repopulation of the thymus was investigated in mice exposed first to 200 R on the whole body and, after various intervals, to 700 R with one leg protected or unprotected during the exposure. When no protection was made, the mice were transplanted with syngeneic bone marrow cells in a defined number immediately after irradiation. Repopulation was fastest when the interval between exposures was 5 days, and most delayed when it was 14 days; with a 30 day interval the speed of repopulation was intermediate, and resembled that of a control group exposed to only the second dose. In another experimental series, thymus repopulation was studied after exposure of mice first to 200 R with one leg protected or unprotected and, after an interval of 5, 14 or 30 days, to a second dose of 700 R on the whole body. In all cases, syngeneic bone marrow cells were grafted intravenously after the second irradiation. The thymus repopulation was enhanced by protection of the leg when 14 day interval separated the exposures. In the other cases, no enhancement was noted. The findings were interpreted to indicate that the cellular composition of the thymus and, in particular, the frequency of the proliferating stem cells at the time of the exposure determines thymic repopulation for about two weeks after irradiation. After this period, repopulation is due to new precursors from the bone marrow which seeded the thymus.

The role of bone marrow in different phases of the cellular repopulation of irradiated mouse thymus.

During the last few years partial-body irradiation techniques have become more extensively used in several types of radiobiological experiments, such as studies of the radiosensitivity of individual organs and tumours, studies on the carcinogenic action of collimated radiation beams, etc. Such techniques entail the use of lead shields of various shapes, in order to achieve the best approximation to the ideal of zero-dose in the shielded tissues. Unfortunately, scattered radiation coming from the adjacent unshielded parts of the body cannot be prevented from reaching the shielded regions and giving there a more or less significant dose. In order to undertake a detailed study of the resulting dose distribution in small animals such as mice, dosimeters with a very high spatial resolution are required. Thermoluminescent dosimeters (TLD) are very useful devices in this respect. Modern sintered TLDs (either pure or Teflon-mixed) are quite small and easy to handle. Some of them, such as LiF and BeO, are also tis...

Use of thermoluminescent dosimeters for measuring dose distribution with high spatial resolution in partial-body irradiation of small animals

Response of Stem Cell System to Whole Body and Partial Body Irradiation1

Dose from Scattered Roentgen Radiation to a Protected Part of a Mouse Phantom

Frozen mouse cadavers were exposed to 220 kV roentgen irradiation with the thymic area covered with a lead plate sized 18 mm X 24 mm X 4 mm oe 18 mm X 12 mm X 4 mm. Lif-Telfon rods were used for dose measurements. With larger plate the mean dose from scattered radiation, in percent of that in the uprotected abdomen, was 12.77 (thymic lobes) and 18.34 (vertebra). With the smaller shield the figures were markedly increased, 16.70 and 23.77, respectively. Since the percentage dose is relatively high, the amount of scattered radiation may have biologic significance.

I. Bojtor

Papers

Dose from Scattered Roentgen Radiation to a Protected Part of a Mouse Phantom

Dose to the shielded thymic region of irradiated mouse cadavers.