1983年 · 第03卷第05期

The techniques of preparing rat bone marrow tissue for scanning electron microscopy are described. Thiopental sodium and heparin sodium were adminstered intraperitoneally for anesthesia and anticoagulation. Vascular perfusion or immersion solution used for fixation was 2.5% glutaraldehyde in 0.1 M phosphate buffer. In addition, 1 % buffered osmium tetroxide solution was used for postfixation of some part of tissues. After fixation tissues were dehydrated in a series of ethanol of increasing concentrations, dried in a critical point dryer and coated with a thin layer of gold in ion sputterer. Finally, the specimen was studied under scanning electron microscope, and satisfactory ultrastructural pictures were obtained.

The mechanism of micronucleus formation in human peripheral blood lymphocytes irradiated in vitro with ⁶⁰Co-rays from 0 to 600 rad was studied. The mechanism of its formation and some of its properties are as follows.

1. The micronucleus structure produced by DNA substance had the ability of self-reproduction. This process might occur simultaneously with that of main nuclei, or be delayed and completed independently.

2. The factor affecting the number and distribution of micronuclei in the cytoplasm seemed to be the dynamics of cell division and reproduction.

3. Micronuclei about 1/3~1/2 the size of main nuclei could be seen in the irradiated lymphocytes. They did not derive from simple chromosomal fragments, but from the fusion of various components of aberrant chromosomes (such as acentric rings, microbodies, acentric fragments, mitosome-containing chromosomes, etc.) in the cytoplasm.

4. Micronuclei could also develop from nuclear budding which twisted and dropped in the cytoplasm.

5. Atypical lymphocytes formed after irradiation tended to foster micronucleus formation.

A follow-up study of chromosome aberrations in peripheral blood lymphocytes was carried out on 14 hyper thyroid patients treated with different doses of ¹³¹I (4 to 11 mCi) orally. The results obtained 24 hours to one year after treatment showed that the frequencies of chromosome aberrations in these patients were significantly greater than those before treatment (t>1.96, p<0.05). But during the post-treatment period the levels of chromosome aberrations determined at 8 separate examinations displayed no significant difference (t<1.96, p>0.05). In comparison with external irradiation, the patients treated with ¹³¹I had the same types but quite different statistical distributions of chromosome aberrations in lymphocytes. The chromosome aberrations induced by ¹³¹I deviated from Poisson's distribution significantly.

In order to improve the situation of clinical dosimetry, mailing intercomparison of absorbed doses in water phantom was carried out with thermoluminescent dosimeters for ⁶⁰Co gamma-rays. The errors of measurements could be controlled within 5%.

Scheduled and unscheduled comparisons among hospitals engaged in radiotherapy can avoid the error of overestimating radiation dose in clinical practice.

According to the concept of effective dose equivalent described in ICRP publication No. 26, a homogeneous tissue equivalent phantom made from MixD was used for measuring the low energy X-ray direct beam field and scarttered beam field. Under the latter condition, physicians in clinical practice perform cardiac catheterizations and certain special gastrointestinal examinations. The relationships among the effective dose equivalent, personal dosimetric readings and free air dose from field monitoring instrument were established, so that it was possible to estimate the effective dose equivalent and organ absorbed dose from the corresponding monitoring data previously obtained. Furthermore, a dose-depth curve was constructed with the phantom. By dint of this curve, organabsorbed dose could be determined if the dose of body-surface was known.

The personal exposure doses to 201 nuclear medical workers in Beijing were surveyed by means of CaSO₄ and LiF TLD within eight months in 1982. Ninety per cent of them wore the dosimeters throughout the period while the remainder only for 3~4months. The results showed that the average personal dose equivalent was 0.49mSv per year. The individual doses followed a lognormal distribution.