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In a cooperative study, four laboratories evaluated the micronucleus test in irradiated and non-irradiated lymphocytes with respect to time of storage, the difference between X-ray and gamma exposure and inter-observer variance. The results were compared with parallel studies on dicentric aberrations. No significant differences between laboratories, with respect to storage time or between gamma and X-irradiation were observed for micronuclei and dicentrics using analysis of variance. However, micronuclei are not suitable for an assessment of exposure inhomogeneity because of a significant overdispersion already in controls and homogeneously irradiated samples.

The present experiments were carried out on mixtures of male irradiated and female non-irradiated lymphocytes, using the Y chromosome as a marker. The results demonstrate that in vitro synchronisation of cells by a thymidine block which generally improves the preparation does not interfere with the estimate of the averaged whole body dose after homogeneous exposure or the fraction of the blood irradiated and the dose after inhomogeneous exposure.

Addition of thymidine to culture medium commonly used by laboratories performing medical cytogenetics followed by a release of the block by 2-deoxycitidine increases greatly the mitotic index and the proportion of metaphases suitable for chromosome analysis. The benefit is, however, less evident when the method is applied to culture medium used in laboratories specialized in chromosome aberration dosimetry.

The yield of dicentric chromosomes has been recorded in peripheral blood lymphocytes of patients undergoing telecobalt therapy for glioblastoma. Blood samples were taken by venipuncture, prior to the first radiotherapy session and 24 h after 10, 20 and 30 Gy to the tumor volume. On the basis of the maximum likelihood method, the yield of chromosome aberrations was best fitted by a linear quadratic dose-response relationship. According to this relationship, the dose inducing ten dicentrics at the target volume is 58 Gy, a value considerably higher than those found after radiotherapy for mammary carcinoma (15 Gy) or for pelvic tumors (5.62 Gy). Our results indicate that, in the case of fractionated exposures, confined to a small volume of the body, it is not possible to estimate the total dose administered and that the method only provides an estimate of the proportion of the lymphocytes irradiated.

Peripheral blood lymphocytes of patients undergoing radiation therapy for pelvic tumours have been examined for the presence of dicentric and centric ring chromosomes. Blood samples were taken, by venipuncture, prior to the first radiotherapy session and 24 h after radiotherapy sessions to allow the mixing of the irradiated lymphocytes in the circulating blood. The yield of dicentrics and centric rings was best fitted by a straight line which, according the maximum likelihood method, corresponds to Y = 1.77 +/- 0.0003 10(-2) D. On this basis the dose inducing ten dicentrics or rings is 5.62 Gy at the target volume and, thus, is intermediate between the doses at the target volumes displaying the same effects in patients treated for mammary carcinoma (15 Gy) or for ankylosing spondylitis (2 Gy).

Human whole blood samples were exposed to different doses (1, 2, 4, 6 or 10 Gy) of gamma-radiation and mixed with different volumes of non-irradiated blood before culturing to simulate partial body irradiations. Chromosome aberrations were analysed and the frequency of dicentrics was found to be lower than expected, particularly when irradiated blood was mixed with large volumes of non-irradiated blood and after exposure to high radiation doses. For the mixtures of irradiated and unirradiated blood the deviation from the Poisson distribution depends on the respective proportions and on the doses. The results can be correlated to in vivo aberration frequencies in case of therapeutical treatments, but the yields of aberrations are generally underestimated in vitro.