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British Journal of Radiology (1992) 65, 167-169
© 1992 British Institute of Radiology
doi: 10.1259/0007-1285-65-770-167
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Magnetic resonance imaging of Fricke-doped agarose gels for the visualization of radiotherapy dose distributions in a lung phantom

S. J. Thomas, MA, MSc I. D. Wilkinson, MSc A. K. Dixon, MD, MRCP, FRCR * and P. P. Dendy, PhD

Medical Physics Department, Addenbrooke's Hospital, Cambridge CB2 2QQ * Department of Radiology, University of Cambridge, Hills Road, Cambridge, UK

This excerpt was created in the absence of an abstract.

When calculating a treatment plan for a radiation beam that passes through an inhomogeneity such as lung, the dose at each point needs to be modified to correct for the effect of the inhomogeneities. Many algorithms exist for making such corrections. Algorithms must be verified by measurements in phantoms. Measurements with an ionization chamber in a solid phantom can only be performed at a limited number of points, giving poor spatial resolution. Film dosimetry gives better spatial resolution, but the introduction of non-tissue equivalent photographic film represents a considerable perturbation of a tissue equivalent phantom.

Shultz et al (1990) and Olsson et al (1990) have recently described techniques for the measurement of absorbed dose using magnetic resonance imaging (MRI) of agarose gels doped with Fricke (iron (II) sulphate) solution. After Fe2+ has been oxidized by irradiation to Fe3+, the gel fixes the position of the ions, so that the distribution of Fe3+ in the gel corresponds to the dose distribution. The gel is then imaged to produce a map of the longitudinal proton relaxation time (T1). As a result of the paramagnetic properties of Fe3+, T1 is inversely proportional to Fe3+ concentration and hence to absorbed dose of radiation.

Thus, the technique provides a method of determining a continuous distribution of radiation dose within a phantom. This paper describes preliminary work using the technique on a phantom containing a volume of low density material designed to simulate lung.

Key Words: Magnetic resonance • Ferrous sulphate dosimetry • Radiotherapy • Treatment planning

Received for publication February 22, 1991. Revision received June 6, 1991. Accepted for publication July 2, 1991.






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