Initial experiments with gel-water: towards MRI-linac dosimetry and imaging.
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 TPR20/10and 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.
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia. sjh190@uowmail.edu.au.|Ingham Institute for Applied Medical Research, Sydney, Australia. sjh190@uowmail.edu.au.
Sarah J
SJ
Alnaghy
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Maegan
M
Gargett
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.|Ingham Institute for Applied Medical Research, Sydney, Australia.|Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Sydney, Australia.|South Western Sydney Clinical School, University of New South Wales, Sydney, Australia.
Gary
G
Liney
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Marco
M
Petasecca
Ingham Institute for Applied Medical Research, Sydney, Australia.|Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Sydney, Australia.|South Western Sydney Clinical School, University of New South Wales, Sydney, Australia.
Jarrad
J
Begg
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Anthony
A
Espinoza
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Matthew K
MK
Newall
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Mitchell
M
Duncan
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.|Ingham Institute for Applied Medical Research, Sydney, Australia.|Department of Medical Physics, Liverpool and Macarthur Cancer Therapy Centre, Sydney, Australia.|South Western Sydney Clinical School, University of New South Wales, Sydney, Australia.|Institute of Medical Physics, University of Sydney, Sydney, Australia.|Sydney Medical School, University of Sydney, Sydney, Australia.
Lois
L
Holloway
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Michael L F
ML
Lerch
Computerized Imaging Reference Systems Inc (CIRS), Norfolk, USA.
Mircea
M
Lazea
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.
Anatoly B
AB
Rosenfeld
Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, 2522, Australia.|Ingham Institute for Applied Medical Research, Sydney, Australia.
Peter
P
Metcalfe
D004307:Dose-Response Relationship, Radiation; D004583:Electrons; D005782:Gels / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011874:Radiometry; D014057:Tomography, X-Ray Computed; D014867:Water / Q000737:chemistry*
D005782:Gels; D014867:Water
Dosimetry; Gel phantom; Image-guidance; MRI-linac; Silicon array detector