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EPR Dosimetric Properties of 2-Methylalanine: EPR, ENDOR and FT-EPR Investigations
Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics. Linköping University, Faculty of Health Sciences.
Department of Physics, University of Oslo, Oslo, Norway .
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology. Linköping University, The Institute of Technology.
2002 (English)In: Radiation Research, ISSN 0033-7587, Vol. 157, no 2, 113-121 p.Article in journal (Refereed) Published
Abstract [en]

To find an EPR dosimeter material that is sensitive enough for clinical use, the substance 2-methylalanine (2MA) with the chemical structure (CH3)2C(NH3+)COO was tested for its sensitivity to ionizing radiation, dose response, and radical stability over time. At equal and moderate settings of microwave power and modulation amplitude, 2MA was found to be 70% more sensitive than l-α-alanine, which is the most common EPR dosimeter material today. The dose response is linear, at least in the dose range of interest (0.5–100 Gy), and the time-dependent variations in signal intensity are very small and may be corrected for easily. The energy dependence of the stopping power and energy absorption was calculated and was found to be similar to that of alanine. The dependence of the signal intensity on microwave power and modulation amplitude was investigated, and the optimal settings were found to be 25 mW (Bruker ER 4102ST) and 12 gauss, respectively. Single crystals of 2MA were analyzed using ENDOR and ENDOR-induced EPR to identify the radiation-induced radicals that formed. Only one radical, in which the amino group is detached from the original molecule, was identified. This radical is obviously dominating and is apparently the only one relevant for dosimetry purposes. The complete set of coupling parameters for three hyperfine couplings is reported. The power saturation properties and spectral line width are ruled by the relaxation times T1 and T2. To determine the relaxation times of 2MA, pulsed EPR experiments were performed on single crystals. Two different values of T1 were obtained, one in the range 1–3 µs, shown to be of importance for the dosimetry properties, and another that is strongly anisotropic with a value between 10 and 35 µs that does not seem to affect the saturation behavior. T2 was estimated to be of the order of 200–300 ns.

Place, publisher, year, edition, pages
2002. Vol. 157, no 2, 113-121 p.
National Category
Medical and Health Sciences
Identifiers
URN: urn:nbn:se:liu:diva-27098DOI: 10.1667/0033-7587(2002)157[0113:EDPOME]2.0.CO;2Local ID: 11745OAI: oai:DiVA.org:liu-27098DiVA: diva2:247649
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-08-22Bibliographically approved
In thesis
1. ESR dosimetry in the radiation therapy dose range: development of dosimetry systems and sensitive dosimeter materials
Open this publication in new window or tab >>ESR dosimetry in the radiation therapy dose range: development of dosimetry systems and sensitive dosimeter materials
2001 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

ESR dosimetry with L-α-alanine as a dosimeter material is a well known and frequently used method for measuring high absorbed doses, for example at sterilisation and food irradiation. The increased sensitivity of modem spectrometers and an increased knowledge of the radiochemical properties of alanine have lowered the detection limit of ESR/alanine dosimetry to the dose range relevant for radiation therapy. The aim of this thesis is to contribute to an extended use of ESR dosimetry in radiation therapy, including development of an alanine-based gel dosimeter and investigation of alternative dosimeter materials.

The dosimeter material is often a polycrystalline powder, which can be mixed with a binder and formed to solid dosimeters in the shape of tablets, rods or films. It can also be distributed in a gel, to serve as both dosimeter material and phantom material. Thus, problems caused by the detector displacing the medium are avoided. The gel developed in this thesis is based on polycrystalline alanine, distributed in an agarose gel. It was tested for calibrated measurements in a brachytherapy situation. With further development, the alanine/agarose gel was found to have potential as a tool for verification of treatment plans, also at complicated dose distributions. One problem to be solved before the gel can be used at an arbitrary irradiation geometry is the low sensitivity of the gel. At present, the sensitivity puts a limit on the spatial resolution at low doses because of the high demands on measurement precision in radiation therapy.

The low sensitivity of the alanine/agarose gel, and also the need for a high precision at low doses together with a small dosimeter size when using traditional solid dosimeters, have raised the need for alternative, more sensitive, dosimeter materials than alanine. Such a material should form only one radiation induced radical, giving an ESR spectrum with few and narrow lines for easy evaluation. It should also be possible to increase the microwave power and the field modulation amplitude without severe distortion of the spectrum shape. Other important criteria are a low effective atomic number, a signal that is stable over time and, preferably, a linear dose response.

Two compounds are presented; ammonium tartrate and 2-methylalanine. Both  are more sensitive than alanine at low settings of microwave power and modulation amplitude, and fulfil the criteria of a low effective atomic number and a linear dose response. Ammonium tartrate is saturated already at low microwave power levels whereas the modulation amplitude can be increased to very high levels without saturation. However, the spectrum shape is then distorted. The signal-changes over time are rapid during the first hours after irradiation, but are then stabilised and can be corrected for.

The other investigated substance, 2-methylalanine, is more similar to alanine regarding signal stability over time and dependency of microwave power and field modulation amplitude. However, irradiation of 2-methylalanine results in only one detectable radical, where the alanine spectrum is composed of at least two radicals. The less complicated spectrum of 2-methylalanine makes it more safe to increase the microwave power and the modulation amplitude to their saturation levels.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2001. 44 p.
Series
Linköping University Medical Dissertations, ISSN 0345-0082 ; 701
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-27534 (URN)12191 (Local ID)91-7373-145-5 (ISBN)12191 (Archive number)12191 (OAI)
Public defence
2001-11-30, Berzeliussalen, Universitetssjukhuset, Linköping, 13:00 (Swedish)
Opponent
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-10-17Bibliographically approved

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Olsson, SaraLund, Anders

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