Program Information
Commissioning of An IntraOp Mobetron
S Grzetic*, J Hessler , M Carlson , Arthur G. James Cancer Hospital, Columbus, OH
Presentations
SU-E-T-193 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: This study will describe the commissioning process of an Intra-Op Mobetron following the guidance of TG72 and includes a detailed method for measuring gap factors.
Methods: Beam data was collected for 6, 9, and 12MeV electrons on the Mobetron using a PTW water tank and a Markus chamber. Commissioning data was collected for 3 sets of cones (0°, 15°, and 30° with respect to the water surface) that ranged in size from 3cm to 10cm diameter in half centimeter increments. Profiles were collected at six depths for all integer cones. PDI’s were taken for all cones in a path perpendicular to the water surface and then converted to dose using MEPHYSTO’s internal algorithm. The depth of maximum dose was determined from the PDD’s and used for measurement of output factors. Output factors were normalized to the 10cm flat cone. Gap factors were measured for all flat cones by raising the cone away from the water surface in defined gaps. These gap factors were measured at dmax for gaps of 1cm to 5cm in 1cm increments Gap factors and effective SSD values were calculated.
Results: Output factors measured for all cones were within 3% of the representative beam data for flat cones. There is no published data on beveled cones, but the angled cone output factors agreed with the flat cones within 5%. Gap factors follow a linear pattern with the output decreasing 3-7% per centimeter gap depending on the size of the cone and energy. Effective SSD values calculated and fit a 3rd order polynomial curve with R2>0.98 for all energies.
Conclusion: Commissioning of an Intra-Op Mobetron was completed with general agreement to published data. New data was published for beveled cones and a method for determining gap factors was established.
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