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Microdosimetric spread for cell-sized targets exposed to 60Co, 192Ir and 125I sources
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Medical Radiation Sciences. (Medical Radiation Sciences)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Medical Radiation Sciences. (Medical Radiation Sciences)
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Radiology, Oncology and Radiation Science, Medical Radiation Sciences. (Medical Radiation Sciences)
2015 (English)In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 166, no 1-4, 365-368 p.Article in journal (Refereed) Published
Abstract [en]

The magnitude of the spread in specific energy deposition per cell may be a confounding factor in dose–response analysis motivating derivation of explicit data for the most common brachytherapy isotopes 125I and 192Ir, and for 60Co radiation frequently used as reference in RBE studies. The aim of this study is to analyse the microdosimetric spread as given by the frequency distribution of specific energy for a range of doses imparted by 125I, 192Ir and 60Co sources. An upgraded version of the Monte Carlo code PENELOPE was used for scoring energy deposition distributions in liquid water for each of the radiation qualities. Frequency distributions of specific energy were calculated according to the formalism of Kellerer and Chmelevsky. Results indicate that the magnitude of the microdosimetric spread increases with decreasing target size and decreasing energy of the radiation quality. Within the clinical relevant dose range (1 to 100 Gy), the spread does not exceed 4 % for 60Co, 5 % for 192Ir and 6 % for 125I. The frequency distributions can be accurately approximated with symmetrical normal distributions at doses down to 0.2 Gy for 60Co, 0.1 Gy for 192Ir and 0.08 Gy for 125I.

Place, publisher, year, edition, pages
2015. Vol. 166, no 1-4, 365-368 p.
National Category
Cancer and Oncology Radiology, Nuclear Medicine and Medical Imaging
Identifiers
URN: urn:nbn:se:uu:diva-259745DOI: 10.1093/rpd/ncv200ISI: 000361806600075OAI: oai:DiVA.org:uu-259745DiVA: diva2:845266
Funder
Swedish National Infrastructure for Computing (SNIC), p2011144
Available from: 2015-08-11 Created: 2015-08-11 Last updated: 2017-12-04
In thesis
1. Micro/nanometric Scale Study of Energy Deposition and its Impact on the Biological Response for Ionizing Radiation: Brachytherapy radionuclides, proton and carbon ion beams
Open this publication in new window or tab >>Micro/nanometric Scale Study of Energy Deposition and its Impact on the Biological Response for Ionizing Radiation: Brachytherapy radionuclides, proton and carbon ion beams
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Research in radiotherapy for cancer treatment focuses on finding methods that can improve the compromise between tumour cell inactivation versus damage to the surrounding healthy tissue. As new radiation modalities such as proton therapy become accessible for everyday clinical practice, a better understanding of the variation in biological response of the tumour and healthy tissues would improve treatment planning to achieve optimal outcome. The development of radiobiological models capable of accurate predictions of biological effectiveness is needed.

Existing radiation quality descriptors such as absorbed dose and LET are insufficient to explain variation in biological effectiveness for different treatment modalities. The stochastic nature of ionizing radiation creates discrete patterns of energy deposition (ED) sites which can now be analysed through sophisticated computer simulations (e.g. Monte Carlo track structure codes). This opens the possibility to develop a nanometre characterization of radiation quality based on the spatial cluster patterns of ED.

The aim of this thesis is to investigate the track structure (ED spatial pattern) properties of several radiation qualities at a micro- and nanometric scale while exploring their influence in biological response through correlations with published experimental data. This work uses track structure data simulated for a set of 15 different radiation qualities: 4 commonly used brachytherapy sources, 6 different proton energies, 4 different carbon ion energies, and 60Co photons used as reference radiation for quantification of biological effectiveness.

At a micrometre level, the behaviour of the microdosimetric spread in energy deposition for target sizes of the order of cell nuclei was analysed. The degree of the influence it had in the biological response was found to be negligible for photon sources but for protons and carbon ions the impact increased with decreasing particle energy suggesting it may be a confounding factor in biological response.

Finally, this thesis outlines a framework for modelling the relative biological effectiveness based on the frequency distribution of cluster order as a surrogate for the nanometre classification for the physical properties of radiation quality. The results indicate that this frequency is a valuable descriptor of ionizing radiation. The positive correlation across the different types of ionizing radiation encourages further development of the framework by incorporating the behavior of the microdosimetric spread and expanding tests to other experimental datasets.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 53 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Medicine, ISSN 1651-6206 ; 1188
Keyword
Ionizing radiation, Monte Carlo track structure code, Microdosimetric spread, Energy deposition clustering, RBE
National Category
Cancer and Oncology
Research subject
Medical Radiophysics
Identifiers
urn:nbn:se:uu:diva-279385 (URN)978-91-554-9495-7 (ISBN)
Public defence
2016-04-22, Skoogssalen, Akademiska Sjukhuset, Ing. 78-79, Uppsala, 09:30 (English)
Opponent
Supervisors
Available from: 2016-04-01 Created: 2016-03-01 Last updated: 2016-04-05

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Villegas, FernandaTilly, NinaAhnesjö, Anders

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