Dicentric dose estimates for patients undergoing radiotherapy in the RTGene study to assess blood dosimetric models and the new Bayesian method for gradient exposure
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The RTGene study was focused on the development and validation of new transcriptional biomarkers for prediction of individual radiotherapy (RT) patient responses to ionising radiation (IR). In parallel, for validation purposes, the study has incorporated conventional biomarkers of radiation exposure, including the dicentric assay (DCA). Peripheral blood samples were taken with ethical approval and informed consent from a total of 20 patients undergoing external beam RT for breast, lung, gastrointestinal or genitourinary tumours. For the DCA, two samples were taken from each patient: prior to RT and before the last fraction. Blood samples were set up using standard methods for the DCA. All the baseline samples have dicentric frequencies consistent with the expected background for the normal population. For blood taken before the final fraction, all the samples display distributions of aberrations which are indicative of partial body (PB) exposures. Whole body (WB) and PB cytogenetic doses were calculated with reference to Public Health England (PHE) 250 kVp X-ray calibration curve and then compared to the total dose to blood derived using two newly developed blood dosimetric models. Initial comparisons indicate the relationship between these measures of dose looks very promising, with a correlation of 0.860 (p=0.001). A new Bayesian zero-inflated Poisson finite mixture method has been applied to the dicentric data and PB dose estimates show no significant difference (p<0.001) with those calculated by the contaminated Poisson technique. The next step will be further development and validation in a larger patient group.