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Radiation-induced radicals in lithium formate monohydrate (LiHCO2·H2O). EPR and ENDOR studies of X-irradiated crystal and polycrystalline samples
Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Physics, Chemistry and Biology, Chemical Physics . Linköping University, The Institute of Technology.
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2004 (English)In: PCCP : physical chemistry chemical physics, ISSN 1463-9076, Vol. 6, 3017-3022 p.Article in journal (Refereed) Published
Abstract [en]

Single crystals and polycrystalline samples of lithium formate monohydrate (HCO2Li·H2O) were X-irradiated at 295 K and studied using X-band EPR, ENDOR, and ENDOR-induced EPR (EIE) spectroscopy at 200 or 295 K. Two different radical species were observed. The overall dominating species is the CO2 radical trapped in the crystal matrix at an orientation not very different from that of the parent CO2 fragment in the unirradiated matrix. The g- and 13C hyperfine coupling tensors of the CO2 radical were determined. The large linewidth (about 1.5 mT) of the polycrystalline EPR spectrum is due to extensive hyperfine couplings with lithium ions and protons in the environment. Four lithium couplings and four proton couplings associated with the CO2 radical were measured, and all couplings were assigned to specific matrix nuclei. The spectra yield evidence for a second radical in low relative abundance. One small lithium hyperfine interaction detected was ascribed to this radical. Spectral simulations of the EPR and ENDOR spectra support the conclusions made.

Place, publisher, year, edition, pages
2004. Vol. 6, 3017-3022 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-12960DOI: 10.1039/b402846eOAI: diva2:17544
Available from: 2008-03-03 Created: 2008-03-03 Last updated: 2009-06-08
In thesis
1. Development of sensitive EPR dosimetry methods
Open this publication in new window or tab >>Development of sensitive EPR dosimetry methods
2008 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Electron paramagnetic resonance (EPR) dosimetry using the well established dosimeter material alanine is a generally accepted dosimetric method for measurements of high absorbed doses. Alanine EPR dosimetry is however not sensitive enough for high precision measurements of low (< 5 Gy) absorbed doses using reasonably measurement times and small dosimeters. It has therefore not been possible to fully exploit the benefits of EPR dosimetry for applications in radiation therapy.

The aim of this thesis was to show that sensitive EPR dosimetry is a competitive method for applications in radiation therapy fulfilling the requirements of measurement precision. Our strategy for reaching this goal was to search for new, more sensitive, EPR dosimeter materials fulfilling the criteria of being tissue equivalent, having a high radical yield and having a narrow EPR spectrum suitable for dosimetry. The best materials were found among formates and dithionates. Doping with small amounts of metal ions and recrystallisation in D2O were tested to further increase the sensitivity. Four promising candidate materials were tested regarding radical stability and dose response and among them lithium formate was chosen for dosimetry in radiation therapy applications.

A high precision EPR dosimetry method was developed using lithium formate. The method included the development of a production method for EPR dosimeters with very homogenous shape, mass and composition. A read-out process was developed with maximal measurement precision for reasonably short measurement times. The method also included a dosimeter quality control before actual dose measurements. Measurement accuracy was controlled for every new dosimeter batch.

This high precision lithium formate EPR dosimetry method was evaluated for pretreatment verifications of intensity modulated radiation therapy (IMRT) treatment plans. The precision and accuracy was shown to be sufficient (< 5 %) for measurements of doses above 1.5 Gy using one single dosimeter and a measurement time of 15 minutes. The described evaluation is therefore a demonstration of the improved precision at low dose determinations that is available with our sensitive EPR dosimeter materials.

While the EPR signal intensity is proportional to absorbed dose, the signal shape is in some cases dependent on the radiation quality. A new method is presented for simultaneous measurements of beam LET (linear energy transfer) and absorbed dose in heavy charged particle beams using potassium dithionate EPR dosimetry. The study shows that when irradiating a dosimeter with 35 MeV carbon ions, the ratio of the signal amplitudes from two radicals in potassium dithionate vary along the track indicating a dependence on linear energy transfer, LET. Potassium dithionate may therefore be a promising EPR dosimeter material for simultaneous measurements of absorbed dose and LET in heavy charged particle radiation fields.

Place, publisher, year, edition, pages
Institutionen för medicin och hälsa, 2008
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1044
Electron paramagnetic resonance (EPR), Formic acids, pharmacology, Lithium, Nickel, Radiometry, Rhodium
National Category
Medicinal Chemistry
urn:nbn:se:liu:diva-11099 (URN)978-91-7393-975-1 (ISBN)
Public defence
2008-03-13, Eken, Campus US, Linköpings universitet, Linköping, 09:00 (English)
Available from: 2008-03-03 Created: 2008-03-03 Last updated: 2009-08-21

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Gustafsson, HåkanLund, Anders
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