Akihiro Shiragai

RADIATION EFFECTS ON CELL POPULATIONS IN THE INTESTINAL EPITHELIUM OF MICE AND ITS THEORY

Mice were exposed to 1000 R of X‐rays to their trunks and sacrificed every day up to the tenth day after exposure. Cell counts were made on histological sections of the duodenum. The cell counts in the crypts were reduced to about 50% of the control value on the first day after exposure. The cell counts began to recover on the third day and an overshoot of 170% was observed on the fourth day; thereafter the crypt cell counts tended to return to the control level. The cell counts on the villi reached their minimum value on the third day after exposure. Following an overshoot on the sixth day, the villus cell counts returned to the control level by the tenth day. The above experimental results were analysed using a two‐compartment model with a feedback term. A logistic proliferation was assumed for the proliferative crypt cells, while for the postmitotic villus cells the compartment was assumed to be a first in‐first out type. The calculated results with this model are in general consistent with the experimental ones. The model seems to possess some essential features of the dynamics of cell renewal in the intestinal mucosa.

A Stereological Study on Size and Number of Mitochondria in Zona Fasciculata of Rat Adrenal Cortex after Whole-body X-irradiation

SummaryThe weight of the zona fasciculata in rat adrenal cortex increased to about 50 per cent over the control during the period of 72 hours after whole-body x-irradiation of 1000 R. The mitochondria of the parenchymal cells in the zona fasciculata were reconstructed three-dimensionally by Bachs theory on sphere-size distribution, using electron micrographs recorded at random during the post-irradiation period. The average volume of mitochondria was significantly larger than the control at 24 and 48 hours, but smaller at 72 hours after 1000 R. The total number of these mitochondria in an individual rat decreased to 60 per cent of the control at 24 hours and then increased to about twice the control at 72 hours. The size-distribution histograms showed that small mitochondria with radii shorter than 0·3 μ are practically absent in the control and in the groups at 24 and 48 hours, but present in the rats at 72 hours.

Some Relationships between Dosimetric Quantities in Photon and Electron Beams

Theoretical considerations of photon and electron dosimetry with general cavity are attempted on the basis of partitioning the kerma into its collisional part and its radiative part. A necessary and sufficient condition for the existence of charged-particle equilibrium in a material irradiated by photons is the equality of the collisional kerma with the absorbed dose. The exposure can be determined indirectly without restriction on the photon energies, if a quantity such as the W-value or G-value of the cavity material of the dosimeter is known. The absorbed dose can also be measured by using a dosimeter calibrated in terms of exposure, air kerma, or absorbed dose in the medium. During exposure calibration, air-kerma calibration, or exposure measurement, a material equivalent to the cavity wall must be used as the build-up cap material.

Acute mortality and changes in body-weight of mice after partial-body irradiation with X-rays and fast neutrons

SummaryAcute mortality and changes in body-weight were studied in CRF1 female mice after trunk irradiation with 200 kV X-rays and fast neutrons produced by the Be(d, n) reaction with 2·8 MeV deuterons. For the neutron beam, including its inherent gamma contamination, LD50 values of 412 rads and 527 rads and r.b.e. values of 3·1 and 2·7 were obtained for 30-day mortality and 5-day mortality, respectively. For changes in body-weight of surviving mice, a single minimum was found after trunk irradiation with X-rays as well as neutrons. The minimum weight, the time at which this occurred, and the time of recovery to the initial weight level were correlated with dosage.

Theory of Measurement of Collision Kerma in Photon Beams with an Ionization Chamber

Despite the accepted limitation to the determination of exposure for photons of energies higher than a few MeV, it is shown that the collision kerma for a suitable material or the exposure is a measurable quantity which is useful to describe the high-energy photon field. These quantities are measured at a point in free space or inside a material different from air by using ionization chambers, which have small gas cavities, calibrated in terms of exposure, air kerma or absorbed dose in the cavity gas for photons of a specified quality. As for measurements of collision kerma in soft tissue, the correction factor for attenuation and scatter in the wall and buildup cap of the chamber when exposed in air to the calibration photons or users beams may be experimentally determined if the chamber wall and buildup cap are of tissue-equivalent materials.