Assessment of the micronucleus assay as a biological dosimeter using cytokinesis-blocked lymphocytes from cancer patients receiving fractionated partial body-radiotherapy
Purpose: To assess the suitability of the cytokinesis block micronucleus assay as a biological dosimeter following in-vivo radiation using cancer patients undergoing radiotherapy. Methods: Blood from 4 healthy donors was irradiated in vitro with γ-rays and the dose response of induced micronuclei in binucleate lymphocytes following cytokinesis block was determined. Micronucleus frequency was ascertained before and at intervals during radiotherapy treatment in 6 patients with various tumors in the pelvic region. Equivalent whole body doses (physical doses) at these times were calculated from radiation treatment plans and cumulative dose volume histograms. Results: Linear dose response relationships were found for induced micronucleus frequency in lymphocytes resulting from both in-vitro and in-vivo irradiation. Doses resulting from in-vivo irradiation (biological doses) were estimated by substitution of micronucleus frequency observed in radiotherapy patients into the dose response curve from in-vitro irradiation of blood. The relationship between the biologically estimated dose (BD) and the calculated equivalent whole body dose (PD) was BD = 0.868(± 0.043)PD + 0.117(± 0.075). Conclusion: The micronucleus assay appears to offer a reliable and consistent method for equivalent whole body radiation dose estimation, although our findings should be confirmed using lymphocytes from radiotherapy patients with tumors at anatomical sites other than the pelvis. Except at doses lower than about 0.4 Gy, the method yields dose estimates acceptably close to 'true' physically determined doses. The assay can be performed relatively rapidly and can be used as a 'first line' biological dosimeter in situations where accidental exposure to relatively high radiation doses has occurred.