The Australian MRI-Linac Program: measuring profiles and PDD in a horizontal beam

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 degrees on a conventional linac. Results showed agreement to within 2.0% for PDD measured using both film and the water tank at gantry 90 degrees relative to PDD acquired using gantry 0 degrees. Profiles acquired using a water tank at both gantry 0 and 90 degrees showed agreement in FWHM to within 1 mm. The agreement for both PDD and profiles measured at gantry 90 degrees relative to gantry 0 degrees 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.