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Biological effects of high energy radiation and ultra high dose rates
Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation biology.
1991 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Recently a powerful electron accelerator, 50 MeV race-track microtron, has been taken into clinical use. This gives the opportunity to treat patients with higher x-ray and electron energies than before. Furthermore, treatments can be performed were the entire fractional dose can be delivered in parts of a second.

The relative biological effectiveness (RBE) of high energy photons (up to 50 MV) was studied in vitro and in vivo. Oxygen enhancement ratio (OER) of 50 MV photons and RBE of 50 MeV electrons were investigated in vitro. Single-fraction experiments, in vitro, using V-79 Chinese hamster fibroblasts showed an RBE for 50 MV x-rays of approximately 1.1 at surviving fraction 0.01, with reference to the response to 4 MV x- rays. No significant difference in OER could be demonstrated. Fractionation experiments were carried out to establish the RBE at the clinically relevant dose level, 2 Gy. The RBE calculated for the 2 Gy/fraction experiments was 1.17. The RBEs for 20 MV x-rays and 50 MeV electrons were equal to one. In order to investigate the validity of these results, the jejunal crypt microcolony assay in mice was used to determine the RBE of 50 MV x-rays. The RBE for 50 MV x-rays in this case was estimated to be 1.06 at crypt surviving fraction 0.1. Photonuclear processes are proposed as one possible explanation to the higher RBE for 50 MV x-rays.

Several studies of biological response to ionizing radiation of high absorbed dose rates have been performed, often with conflicting results. With the aim of investigating whether a difference in effect between irradiation at high dose rates and at conventional dose rates could be verified, pulsed 50 MeV electrons from a clinical accelerator were used for experiments with ultra high dose rates (mean dose rate: 3.8 x 10^ Gy/s) in comparison to conventional (mean dose rate: 9.6 x 10"^ Gy/s). V-79 cells were irradiated in vitro under both oxic and anoxic conditions. No significant difference in relative biological effectiveness (RBE) or oxygen enhancement ratio (OER) was observed for ultra high dose rates compared to conventional dose rates.

A central issue in clinical radiobiological research is the prediction of responses to different radiation qualities. The choice of cell survival and dose response model greatly influences the results. In this context the relationship between theory and model is emphasized. Generally, the interpretations of experimental data are dependent on the model. Cell survival models are systematized with respect to their relations to radiobiological theories of cell kill. The growing knowledge of biological, physical, and chemical mechanisms is reflected in the formulation of new models. This study shows that recent modelling has been more oriented towards the stochastic fluctuations connected to radiation energy deposition. This implies that the traditional cell survival models ought to be complemented by models of stochastic energy deposition processes at the intracellular level.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 1991. , 44 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 315
Keyword [en]
Radiobiology, 50 MV x-rays, 50 MeV electrons, in vitro, in vivo, RBE, OER, ultra high dose-rate, radiobiological models, model selection, models of stochastic processes
National Category
Cancer and Oncology
Identifiers
URN: urn:nbn:se:umu:diva-96889ISBN: 91-7174-614-5 (print)OAI: oai:DiVA.org:umu-96889DiVA: diva2:769196
Public defence
1991-11-21, Onkologiska klinikens föreläsningssal, 244, 2 tr., Umeå universitet, Umeå, 09:00
Projects
digitalisering@umu
Note

S. 1-44: sammanfattning, s. 47-130: 5 uppsatser

Available from: 2014-12-16 Created: 2014-12-05 Last updated: 2015-04-10Bibliographically approved
List of papers
1. Relative Biological Effectiveness and Oxygen Enhancement Ratio of 50 MV X-rays
Open this publication in new window or tab >>Relative Biological Effectiveness and Oxygen Enhancement Ratio of 50 MV X-rays
1989 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 28, no 4, 529-535 p.Article in journal (Refereed) Published
National Category
Cancer and Oncology
Identifiers
urn:nbn:se:umu:diva-97399 (URN)A1989AT81600015 ()
Projects
digitalisering@umu
Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2017-12-05Bibliographically approved
2. Relative Biological Effectiveness of High-energy Photons (up tO 50-MV) and Electrons (50-MeV)
Open this publication in new window or tab >>Relative Biological Effectiveness of High-energy Photons (up tO 50-MV) and Electrons (50-MeV)
1991 (English)In: Radiation Research, ISSN 0033-7587, E-ISSN 1938-5404, Vol. 128, no 2, 192-196 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
JSTOR, 1991
National Category
Cancer and Oncology
Identifiers
urn:nbn:se:umu:diva-97401 (URN)10.2307/3578137 (DOI)A1991GM76400010 ()
Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2017-12-05Bibliographically approved
3. Relative biological effectiveness of 50-MV X-rays on jejunal crypt survival in vivo
Open this publication in new window or tab >>Relative biological effectiveness of 50-MV X-rays on jejunal crypt survival in vivo
1992 (English)In: Radiation Research, ISSN 0033-7587, Vol. 132, no 1, 112-114 p.Article in journal (Refereed) Published
Abstract [en]

Earlier in vitro studies of relative biological effectiveness (RBE) of 50-MV X rays show an RBE of approximately 1.1 compared to 4 MV. No difference in RBE has been found for 20-MV X rays or 50-MeV electrons. The higher RBE for 50 MV can be explained to some extent by the small high linear energy transfer contribution from photonuclear reactions at high X-ray energies. To investigate the validity of the results in vitro, a study of the RBE of 50-MV X rays has been performed in vivo using the jejunal crypt microcolony assay in mice. The reference radiation used in this case was 20-MV X rays. The results confirm the earlier in vitro studies. The RBE for 50-MV X rays was estimated to be 1.06, calculated as the ratio between the slopes of the response curves.

Place, publisher, year, edition, pages
Oak Brook, IL 60521 USA: Radiation Research Society, 1992
National Category
Cancer and Oncology
Identifiers
urn:nbn:se:umu:diva-39967 (URN)10.2307/3578341 (DOI)A1992JU54700016 ()
Available from: 2011-02-11 Created: 2011-02-11 Last updated: 2014-12-16Bibliographically approved
4. Biological Response, in vitro, to Pulsed High-dose Rate Electrons from a Clinical Accelerator
Open this publication in new window or tab >>Biological Response, in vitro, to Pulsed High-dose Rate Electrons from a Clinical Accelerator
1991 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 30, no 6, 747-751 p.Article in journal (Refereed) Published
Abstract [en]

Several studies of biological response to ionizing radiation of high absorbed dose rates have been performed, often with conflicting results. The aim of this study was to establish whether a difference between irradiation at high dose rates and at more conventional dose rates could be verified. Pulsed 50 MeV electrons from a clinical accelerator were used both for the high dose rate experiments (mean dose rate: 3.8 x 10(2) Gy/s) and the reference experiments (mean dose rate: 9.6 x 10(-2) Gy/s). In this study V-79 cells were irradiated in vitro. The experiments were carried out under both oxic and anoxic conditions. No significant difference in relative biological effectiveness (RBE) or oxygen enhancement ratio (OER) was observed at the different dose rates investigated.

Place, publisher, year, edition, pages
Oslo, Norway: Scandinavian University Press, 1991
National Category
Cancer and Oncology
Identifiers
urn:nbn:se:umu:diva-97400 (URN)A1991GP34600014 ()
Projects
digitalisering@umu
Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2017-12-05Bibliographically approved
5. Radiobiological Cell-survival Models: a Methodological Overview
Open this publication in new window or tab >>Radiobiological Cell-survival Models: a Methodological Overview
1992 (English)In: Acta Oncologica, ISSN 0284-186X, E-ISSN 1651-226X, Vol. 31, no 4, 433-441 p.Article in journal (Refereed) Published
Abstract [en]

A central issue in clinical radiobiological research is the prediction of responses to different radiation qualities. The, choice of cell survival and dose-response model greatly influences the results. In this context the relationship between theory and model is emphasized. Generally, the interpretations of experimental data depend on the model. Cell survival models are systematized with respect to their relations to radiobiological theories of cell kill. The growing knowledge of biological, physical, and chemical mechanisms is reflected in the formulation of new models. The present overview shows that recent modelling has been more oriented towards the stochastic fluctuations connected to radiation energy deposition. This implies that the traditional cell survival models ought to be complemented by models of stochastic energy deposition processes and repair processes at the intracellular level.

National Category
Cancer and Oncology
Identifiers
urn:nbn:se:umu:diva-97402 (URN)A1992JF83500011 ()
Projects
digitalisering@umu
Available from: 2014-12-16 Created: 2014-12-16 Last updated: 2017-12-05Bibliographically approved

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