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Radiation dose measurements with alanine/agarose gel and thin alanine films around a 192Ir brachytherapy source, using ESR spectroscopy
Östergötlands Läns Landsting, Centre of Surgery and Oncology, Department of Radiation Physics. Linköping University, Faculty of Health Sciences.
Department of Physics, University of Oslo, Norway.
Medical Radiation Physics, Stockholm University and Karolinska Institute, Stockholm, Sweden.
Department of Physics, University of Oslo, Norway.
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2002 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 47, no 8, 1333-1356 p.Article in journal (Refereed) Published
Abstract [en]

Alanine/agarose gel and alanine films in stacks have been used for measurements of absorbed dose around an HDR 192Ir source in a vaginal cylinder-applicator, with and without a 180° tungsten shield. The gel and the films were analysed by means of ESR spectroscopy and calibrated against an ion chamber in a 4 MV photon beam to obtain absolute dose values. The gel serves as both dosimeter and phantom material, and the thin (130 μm) films are used to achieve an improved spatial resolution in the dose estimations.

Experimental values were compared with Monte Carlo simulations using two different codes. Results from the measurements generally agree with the simulations to within 5%, for both the alanine/agarose gel and the alanine films.

Place, publisher, year, edition, pages
2002. Vol. 47, no 8, 1333-1356 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-27010DOI: 10.1088/0031-9155/47/8/308Local ID: 11651OAI: diva2:247561
On the day of the defence day the status of this article was submitted.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.
Linköping University Medical Dissertations, ISSN 0345-0082 ; 701
National Category
Medical and Health Sciences
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)
Available from: 2009-10-08 Created: 2009-10-08 Last updated: 2012-10-17Bibliographically approved

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