Experimental determination of the relative biological effectiviness of theral neutrons

Transkript

1 Experimental determination of the relative biological effectiviness of theral neutrons PD Dr. Thomas Schmid Department Radiotherapy and Radiooncology SAAGAS 24 February 28, 2013

2 Radiation effects 2 nm

3 1 Gy gamma-rays 3000 base damages per cell 1000 single strand breaks 40 double strand breaks However: repair mechanisms

4 DNA repair DSB Ku70, Ku80 RAD50 DNA-PKcs MRE11, NBS1 Artemis XRCC4, Ligase IV Repair errors: chromosome aberrations Non-homologuous endjoining

5 Chromosome-aberrations Interchromosomal: normal dicentric translocation insertion complex aberrations

6 Dicentric chromosomes

7 Method: The induction dicentrics in human lymphocytes is the gold standard in biological dosimetry Whole blood was irradiated using the larger of two fields available at PGAA with a cold neutron flux of 6.54x10 9 cm -2 s -1 free in air. The absorbed energy dose was calculated from all possible interactions of the constituents of blood. For the evaluation of the biological data, the linear-quadratic dose-response law was used.

8 1.0 thermally equivalent neutron fluence (10 12 cm -2 ) dicentrics per cell neutron dose / Gy

9 Our linear coefficients for induction of dicentrics in human lymphocytes by different photons (demonstrated by ICRP publication 92 and BEIR VII report) 0.1 Dicentrics per cell / Gȳ kV dicentrics 29kV 60kV 220kV 137 Cs 60 Co mean photon energy / kev

10 Relative Biological Effectiveness (RBE) RBE = [Dose from standard radiation to produce a given biol. effect] / [dose from test radiation to produce same effect]. Units: RBE is dimensionless

11 The maximal RBE (RBE M ) In biological studies, a maximum low-dose RBE (RBE M ) is estimated from the ratio between the α coefficients of dose-response curves for the radiation of interest and a reference radiation At very low doses (where the quadratic term can be ignored), the slopes of the radiation qualities are determined

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13 RBE of different neutron energies for induction of chromosome aberrations in human lymphocytes Neutron energy Neutron spectrum Linear coefficient SE (Gy -1 ) Quadratic coefficient β SE (Gy -2 ) RBE M SE relative to 60 Co rays ev Thermal MeV Monoenergetic MeV Monoenergetic MeV Monoenergetic MeV Monoenergetic MeV Fission MeV Monoenergetic MeV Monoenergetic MeV Monoenergetic MeV Monoenergetic

14 Conclusions For the evaluation of the biological data, the linear-quadratic dose-response law was used. It delivers a maximum low-dose RBE M of with respect to 60 Co -rays

15 Acknowledgement Department of Radiotherapy and Radiooncology University Hospital rechts der Isar Technische Universität Muenchen, Germany Michael Molls Gabriele Multhoff Jan Wilkens Olga Zlobinskaya Mathias Gehrmann Daniela Schilling Christine Bayer Radiobiological Institute Ludwig-Maximilians-Universität Muenchen Ernst Schmid Forschungs-Neutronenquelle Heinz Maier- Leibnitz (FRM II), Technische Universität München, Garching, Germany Franz Wagner Lea Canella Federal Office for Radiation Protection, Oberschleissheim Horst Romm