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A Study of the Magnetic Field in the Treatment Room of a IBA ProteusONE Proton Therapy System

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Y Liu

Y Liu*, J Dugas , K Chen , H Wu , Willis-Knighton Medical Center, Shreveport, LA


SU-I-GPD-T-210 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: During proton therapy, both the magnetic field and the neutron dose present potential hazards to patients with cardiovascular implantable electronic devices (CIEDs) such as pacemakers and defibrillators. The ProteusOne proton system utilizes pencil beam scanning technique which delivers much smaller neutron dose to patients. However, due to its compact design with the last bending magnet located much closer to the treatment isocenter, a relatively stronger magnetic field exists during beam delivery. To evaluate the feasibility of treating patients with CIEDs safely, this work aimed to establish a baseline of the magnetic field in the treatment room.

Methods: A NIST traceable vector/magnitude gauss meter (model: VGM, AlphaLab Inc.) was used to measure the magnetic field. The bending magnetic current was set as 700A for all measurements. The gantry was positioned at 0°, 90° and 180° angle. At each gantry angle, the magnitude and the vectors of magnetic field at various distances (0 to 100cm with 10cm increment along the X, Y and Z direction) from the isocenter were measured.

Results: The magnitude was used as a conservative estimation of the magnetic field strength. The field strength was independent of gantry angle. The average strength at isocenter was 1.9±0.4 Gauss (G). Field strength decreased little as a function of distance away from the isocenter on the plane perpendicular to beam direction. On the contrary, the magnetic field magnitude changed swiftly along the beam direction. The average value was 5.14±0.36G at 20cm away from the isocenter.

Conclusion: A preliminary mapping of the magnetic field in the treatment room was established. In the most conservative scenario, which the CIEDs are located at 20cm away from the isocenter, the magnetic strength is around 5G. This suggests that the magnetic field of the ProteusONE presents a minimal concern for the routine isocentric patient setup treatment.

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