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    The comparisons of random survival forests and Cox regression analysis with simulation and an application related to breast cancer
    (Pergamon-Elsevier Science Ltd, 2009) Omurlu, Imran Kurt; Ture, Mevlut; Tokatli, Fuesun
    The objective of this study was to compare the performances of Cox regression analysis (CRA) and random survival forests (RSF) methods with simulation and a real data set related to breast cancer. In the simulations, we compared across the methods under varying sample sizes by using Monte Carlo simulation method. The results showed that the performance of the CRA was a slightly better for analysis based on Harrell's concordance index than RSF approaches based on log-rank, conservation of events, log-rank score and approximate log-rank splitting rules. In the real data application, a retrospective analysis was performed in 279 breast cancer patients diagnosed. According to Harrell's concordance index, RSF based on approximate log-rank splitting rule to determined major risk factors for disease-free survival (DFS) showed a slightly better performance than other approaches. In general, performances of all the methods were almost similar. The predictive capability of CRA can be used for different sample sizes and potential future suitable survival data problems, whereas RSF provide interpretive results. (C) 2008 Elsevier Ltd. All rights reserved.
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    The Effects of Micronuclei with Whole Chromosome on Biological Dose Estimation
    (Tubitak Scientific & Technological Research Council Turkey, 2008) Pala, Funda S.; Alkaya, Fadime; Tabakcioglu, Kiymet; Tokatli, Fuesun; Uzal, Cem; Parlar, Sule; Alguenes, Cetin
    The total micronucleus (MN) assay has been used for purposes of biological dosimetry for many years. The variable spontaneous incidence of micronuclei in peripheral blood lymphocytes affects the sensitivity of biological dose estimations at low doses. It has been suggested that this problem could be solved by using the micronuclei-centromere assay. In this study. Co-60 gamma ray dose response curves for micronuclei (MN) and micronuclei without centromeres (MNC-) in the range of 0-5.0 Gy were established using a pancentromeric FISH probe on cultured binucleate lymphocytes from 2 donors. There were no significant inter-donor differences in the dose responses for either MN or MNC-. The relative proportions of MN that contained centromeres (MNC+) decreased with radiation dose, which is in line with the proposition that radiation predominately causes chromosomal breakage rather than whole chromosome loss. The a coefficients of MNC- curves decreased to 62% of the values for total MN whilst the beta coefficients were unchanged. MN and MNC+ frequencies of 60 control smoker and 40 non-smoker donors were also compared. No effect of smoking was observed. However the MNC+ spontaneous frequencies showed an age and gender effect with the highest frequencies in older women.