Title

Initial experiments with gel-water: towards MRI-linac dosimetry and imaging

RIS ID

110520

Publication Details

Alnaghy, S. J., Gargett, M., Liney, G., Petasecca, M., Begg, J., Espinoza, A., Newall, M. K., Duncan, M., Holloway, L., Lerch, M. L F., Lazea, M., Rosenfeld, A. B. & Metcalfe, P. (2016). Initial experiments with gel-water: towards MRI-linac dosimetry and imaging. Australasian Physical and Engineering Sciences in Medicine, 39 (4), 921-932.

Abstract

Tracking the position of a moving radiation detector in time and space during data acquisition can replicate 4D image-guided radiotherapy (4DIGRT). Magnetic resonance imaging (MRI)-linacs need MRI-visible detectors to achieve this, however, imaging solid phantoms is an issue. Hence, gel-water, a material that provides signal for MRI-visibility, and which will in future work, replace solid water for an MRI-linac 4DIGRT quality assurance tool, is discussed. MR and CT images of gel-water were acquired for visualisation and electron density verification. Characterisation of gel-water at 0 T was compared to Gammex-RMI solid water, using MagicPlate-512 (M512) and RMI Attix chamber; this included percentage depth dose, tissue-phantom ratio (TPR20/10), tissue-maximum ratio (TMR), profiles, output factors, and a gamma analysis to investigate field penumbral differences. MR images of a non-powered detector in gel-water demonstrated detector visualisation. The CT-determined gel-water electron density agreed with the calculated value of 1.01. Gel-water depth dose data demonstrated a maximum deviation of 0.7% from solid water for M512 and 2.4% for the Attix chamber, and by 2.1% for TPR20/10 and 1.0% for TMR. FWHM and output factor differences between materials were ≤0.3 and ≤1.4%. M512 data passed gamma analysis with 100% within 2%, 2 mm tolerance for multileaf collimator defined fields. Gel-water was shown to be tissue-equivalent for dosimetry and a feasible option to replace solid water.

Grant Number

NHMRC/1036078

Grant Number

ARC/DP110104007

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