Abstract
The Australian MRI-Linac consists of a fixed horizontal photon beam combined with a MRI. Commissioning required PDD and profiles measured in a horizontal set-up using a combination of water tank measurements and gafchromic film. To validate the methodology, measurements were performed comparing PDD and profiles measured with the gantry angle set to 0 and 90° on a conventional linac. Results showed agreement to within 2.0% for PDD measured using both film and the water tank at gantry 90° relative to PDD acquired using gantry 0°. Profiles acquired using a water tank at both gantry 0 and 90° showed agreement in FWHM to within 1 mm. The agreement for both PDD and profiles measured at gantry 90° relative to gantry 0° curves indicates that the methodology described can be used to acquire the necessary beam data for horizontal beam lines and in particular, commissioning the Australian MRI-linac.
Highlights
The Australian MRI-Linac Program [1] is developing a 1 T split-bore MRI/6 MV linac using a Varian Linatron-MP (Palo Alto, USA) horizontal 6 MV beam
The Australian MRI-Linac consists of a fixed horizontal photon beam combined with a MRI
Profiles acquired using a water tank at both gantry 0 and 90° showed agreement in full width half maximums (FWHM) to within 1 mm. The agreement for both PDD and profiles measured at gantry 90° relative to gantry 0° curves indicates that the methodology described can be used to acquire the necessary beam data for horizontal beam lines and in particular, commissioning the Australian MRI-linac
Summary
The Australian MRI-Linac Program [1] is developing a 1 T split-bore MRI/6 MV linac using a Varian Linatron-MP (Palo Alto, USA) horizontal 6 MV beam. This work presents the methodology used to measure large field profiles and PDDs for a horizontal beam. 2. Method To validate measurements made in a horizontal geometry, a CC13 ionisation chamber was used to compare PDD and profiles measured at gantry 0 and 90°. For gantry 90° measurements, the water tank was aligned to the origin markings using lateral room lasers and the level of the tank and rails adjusted until level. Corrections for the wall thickness, central axis offset from the inside of the window and effective point of measurement in the chamber (peff = 1.8 mm) were applied post acquisition. A PDD was acquired from the film scan and appended to water tank data to show the build up region. Scanning Accuracy Accuracy of movement - assessed by moving tank to known positions over large travel distances and reading out position in software (< 0.5 mm)
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