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Development of nickel-doped lithium formate as potential EPR dosimeter for low dose determination
nstitute of Nuclear Chemistry and Technology, Warsaw, Poland.
Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
Linköpings universitet, Institutionen för medicin och hälsa, Medicinsk radiofysik. Linköpings universitet, Hälsouniversitetet.
2007 (engelsk)Inngår i: Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, ISSN 1386-1425, Vol. 67, nr 5, s. 1370-1373Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

EPR dosimetry employing l-α-alanine has been in vogue during the past few years, due to its tissue equivalence and linear dose response. However, l-α-alanine dosimetry has been improved during the past years, the sensitivity of this material is still too low for clinical applications. Polycrystalline lithium formate doped with NiCl2 was therefore examined for radiation response in the dose range of clinical interest (<5 Gy) using CW EPR and pulse EPR techniques. At equal and moderate settings of microwave power and modulation amplitude lithium formate doped with 1.6 wt% of NiCl2 was almost four times more sensitive compared to l-α-alanine, which is the most common EPR dosimeter standard. It was shown that the nickel-doped lithium formate has an excellent radiation response with a low limit of the measurable dose, and a linear dose response in the range 1–5 Gy. The relaxation and power saturation studies showed that high microwave power can be applied during measurements to improve the sensitivity of this material as an EPR dosimeter. These results show that lithium formate doped with Ni(II) exhibits promising properties required for further development of an EPR dosimeter in the dose range typical for clinical dosimetry.

sted, utgiver, år, opplag, sider
2007. Vol. 67, nr 5, s. 1370-1373
Emneord [en]
EPR, EPR dosimetry, Lithium formate
HSV kategori
Identifikatorer
URN: urn:nbn:se:liu:diva-12962DOI: 10.1016/j.saa.2006.10.026OAI: oai:DiVA.org:liu-12962DiVA, id: diva2:17546
Tilgjengelig fra: 2008-03-03 Laget: 2008-03-03 Sist oppdatert: 2009-04-15
Inngår i avhandling
1. Development of sensitive EPR dosimetry methods
Åpne denne publikasjonen i ny fane eller vindu >>Development of sensitive EPR dosimetry methods
2008 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Institutionen för medicin och hälsa, 2008
Serie
Linköping University Medical Dissertations, ISSN 0345-0082 ; 1044
Emneord
Electron paramagnetic resonance (EPR), Formic acids, pharmacology, Lithium, Nickel, Radiometry, Rhodium
HSV kategori
Identifikatorer
urn:nbn:se:liu:diva-11099 (URN)978-91-7393-975-1 (ISBN)
Disputas
2008-03-13, Eken, Campus US, Linköpings universitet, Linköping, 09:00 (engelsk)
Opponent
Veileder
Tilgjengelig fra: 2008-03-03 Laget: 2008-03-03 Sist oppdatert: 2020-03-29

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