caa a22 4500 397503164 CHVBK 20180308164537.0 cr unu---uuuuu 161202e19950801xx s 000 0 eng 10.1093/oxfordjournals.rpd.a082762 doi 0144-8420 pii (NATIONALLICENCE)oxford-10.1093/oxfordjournals.rpd.a082762 Physical Interaction of Ionising Radiations with the Intracellular Macromolecular Target DNA and its Biological Consequences [Elektronische Daten] [C.R. Geard, B.D. Loucas (INVITED)] Chromosomal DNA breaks were evaluated in normal human fibroblasts after irradiation of non-cycling G1 phase cells with 90 keV.µm-1a particles and 250 kVp X rays. Yields were measured using the premature chromosome condensation technique in interphase cells, straight after and 24 h after irradiation, and by mitotic scoring of terminal deletions following cellular release at 24h and progression through the cell cycle. Yields were related to the frequencies of energy deposition events per cell nucleus estimated microdosimetrically for X rays and by relating fluence to nuclear cross-sectional areas for the a particles. Linear relationships were found for both radiations and at all three times post-irradiation. Initial break yields of 1.3 x 100 and 1.6 x 10-2 per energy deposition event for a particles and X rays respectively, changed to residual yields (24h) of 4.0 x 10-1 and 1.3 x 10-3, and for terminal deletions at mitosis to 6.0 x 10-3 and 4.0 x 10-5 per energy deposition event. That is, one 90 keV.µm-1a particle is about 100 times more biologically effective than an electron track from 250 kVp X rays and greater than 99% of initially induced chromosomal DNA breaks are repaired/misrepaired before the next mitosis. Misrepair will involve illegitimate interactions and combinations of pairs of lesions, entitities which pre-dominate at mitosis, which a failure to repair/misrepair resulting in relic DNA double strand breaks is likely to be of minimal consequence. Lesion interaction, proximity dependent, and largely irrespective of LET dependent lesion severity will then be the principal basis for the unwanted biological sequelae from ionising radiations. Radiation Protection Dosimetry Geard C.R. aut Loucas (INVITED) B.D. INVITED aut Radiation Protection Dosimetry Oxford University Press 61/1-3(1995-08-01), 101-106 0144-8420 61:1-3<101 1995 61 rpd https://doi.org/10.1093/oxfordjournals.rpd.a082762 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1093/oxfordjournals.rpd.a082762 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Geard C.R. aut NATIONALLICENCE 700 1- Loucas (INVITED) B.D. INVITED aut NATIONALLICENCE 773 0- Radiation Protection Dosimetry Oxford University Press 61/1-3(1995-08-01), 101-106 0144-8420 61:1-3<101 1995 61 rpd Metadata rights reserved CC BY-NC-4.0 http://creativecommons.org/licenses/by-nc/4.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-oxford