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Lithium formate EPR dosimetry for verifications of planned dose distrubutions prior to intensity modulated radiation therapy
Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
Linköping University, Department of Medicine and Health Sciences, Radiation Physics . Linköping University, Faculty of Health Sciences.
2008 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, Vol. 53, no 17, 4667-4682 p.Article in journal (Refereed) Published
Abstract [en]

The objective of the present investigation was to evaluate lithium formate electron paramagnetic resonance (EPR) dosimetry for measurement of dose distributions in phantoms prior to intensity-modulated radiation therapy (IMRT). Lithium formate monohydrate tablets were carefully prepared, and blind tests were performed in clinically relevant situations in order to determine the precision and accuracy of the method. Further experiments confirmed that within the accuracy of the current method, the dosimeter response was independent of beam energies and dose rates used for IMRT treatments. The method was applied to IMRT treatment plans, and the dose determinations were compared to ionization chamber measurements. The experiments showed that absorbed doses above 3 Gy could be measured with an uncertainty of less than 2.5% of the dose (coverage factor k = 1.96). Measurement time was about 15 min using a well-calibrated dosimeter batch. The conclusion drawn from the investigation was that lithium formate EPR dosimetry is a promising new tool for absorbed dose measurements in external beam radiation therapy, especially for doses above 3 Gy.

Place, publisher, year, edition, pages
2008. Vol. 53, no 17, 4667-4682 p.
National Category
Medical and Health Sciences
URN: urn:nbn:se:liu:diva-12963DOI: 10.1088/0031-9155/53/17/014OAI: diva2:17547
Available from: 2008-03-03 Created: 2008-03-03 Last updated: 2009-04-28
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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