1. Med Phys. 2009 Sep;36(9):4223-9.

X-band EPR imaging as a tool for gradient dose reconstruction in irradiated
bones.

Levêque P, Godechal Q, Bol A, Trompier F, Gallez B.

Biomedical Magnetic Resonance Unit, Université catholique de Louvain, B-1200
Brussels, Belgium.

PURPOSE: Various tools are currently available for dose reconstruction in
individuals after accidental exposure to ionizing radiation. Among the available 
biological analyses, Monte Carlo simulations, and biophysical methods, such as
electron paramagnetic resonance (EPR), the latter has proved its usefulness for
retrospective dosimetry. Although EPR spectroscopy is probably the most sensitive
technique, it does not provide spatial dosimetric data. This information is,
however, highly desirable when steep dose gradient irradiations are involved. The
purpose of this work was to explore the possibilities of EPR imaging (EPRI) for
spatial dose reconstruction in irradiated biological material. METHODS: X-band
EPRI was used to reconstruct ex vivo the relative dose distribution in human bone
samples and hydroxyapatite phantoms after irradiation with brachytherapy seeds or
x rays. Three situations were investigated: Homogeneous, stepwise gradient, and
continuous gradient irradiation. RESULTS: EPRI gave a faithful relative spin
density distribution in bone samples and in hydroxyapatite phantoms. Measured
dose ratios were in close agreement with the actual delivered dose ratios. EPRI
was able to distinguish the dose gradients induced by two different sources (125I
and 192Ir). However, the measured spatial resolution of the system was 1.9 mm and
this appeared to be a limiting factor. The method could be improved by using new 
signal postprocessing strategies. CONCLUSIONS: This study demonstrates that EPRI 
can be used to assess the regional relative dose distribution in irradiated bone 
samples. The method is currently applicable to ex vivo measurements of small size
samples with low variation in tissue density but is likely to be adapted for in
vivo application using L-band EPRI.

PMID: 19810496 [PubMed - in process]