Program Information
Technical Commissioning of a Proton Treatment Room Converted From Double Scattering to Pencil Beam Scanning
H Oesten1,2,3*, E Cascio1 , S Bradley1 , R Brett1 , L O'Brien1 , B Clasie1 and J Flanz1 , (1) Massachusetts General Hospital, Boston, USA. (2) OncoRay - National Center for Radiation Research in Oncology, Dresden, Germany. (3) Helmholtz-Zentrum Dresden-Rossendorf, Institute of Radiooncology, Dresden, Germany.
Presentations
SU-I-GPD-T-186 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: It is advantageous for Proton Therapy Centers with multiple Treatment Rooms (TR) that the rooms have matched treatment beam characteristics. This allows patient treatment to be interchangeable among the rooms. At the Burr Proton Center of the Massachusetts General Hospital in Boston, MA, we are currently converting one of two TRs from Double Scattering (TR1) to the Pencil Beam Scanning (PBS) treatment modality. Our aim is to ensure that the beam characteristics in the converted TR1 match those in the current TR2 which employs PBS.
Methods: In order to match the beam properties a number of considerations are necessary. The Beam Optics Characteristics in TR1 are commissioned to be nearly identical to the current characteristics in TR2, including such parameters as the beam size. Therefore, spot size measurements were performed with the 2D ion chamber array MatriXX (IBA dosimetry, Schwarzenbrueck, Germany). We then adjusted the beam optics settings to bring the measurements into agreement with those in TR2. The beam position is also an important parameter and was checked at five different locations along the beamline, at six energies and four gantry angles (120 single adjustments). The data was fitted with a third order polynomial fit. These characteristics were then used together with an automated procedure to adjust the beam trajectory in the final section of the beamline.
Results: Beam size measurements in TR1 are within +/-7.9% from the currently used clinical spot sizes of TR2, but >95% of the measurements are within <5%. The polynomial fit is used to set the magnetic elements for the beam position. The last beamline section tuning enables a beam trajectory which has a maximum deviation from the center of <0.5mm for all gantry angles.
Conclusion: The current work is ongoing and additional parameters will be validated including output, dose rate, and range.
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