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Towards Dosimetrically Equivalent Proton Facilities: Golden Beam Data for Proton Pencil Beam Scanning

Y Zhang

Y Zhang1*, Z Xiao2 , E Lee3 , A Mascia4 , L Dong5 , (1) University of Cincinnati Medical Center, Liberty Township,, OH, (2) Cincinnati Children's/UC Health, Liberty Campus, OH, (3) Cincinnati Children's/UC Health, Liberty Campus, OH, (4) University of Cincinnati Medical Center, Cincinnati, OH, (5) University of Pennsylvania, Philadelphia, PA


SU-I-GPD-T-189 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Establishing adequate beam-matching across proton facilities with pencil beam scanning (PBS) delivery allows the use of golden beam data set for dose calculations, and thus offers greater advantage of reducing commissioning time and improving operational efficiency. The purpose of this study is to investigate and validate critical dosimetric parameters for beam matching across proton centers with the same type of PBS system.

Methods: This study has been conducted in two multiple-gantry proton centers equipped with the same PBS delivery and treatment planning system. The dose monitors in both centers were configured with identical counts per MU. Critical beam-matching specifications were reviewed at these two centers: 1) Ranges of Bragg peaks of all of the available energies. 2) Absolute dose per MU relationship. 3) In-air spot size variations across multiple gantry angles at two centers. By matching those parameters, a universal beam model was created in the treatment planning system using beam data set acquired at one of the centers for dose calculations. At the time of writing, over thirty fields from real patients planned at one center, were delivered and measured by ion chambers at treatment rooms in both centers to validate the beam matching accuracy.

Results: The range difference of Bragg peaks was adjusted as close as 0.2±0.1(mm) between two centers. The absolute doses per MU deviated at an average of 0.7±0.7% over all energies in two centers, and the average in-air spot size variations was achieved as low as 4±4.4%. With such specifications, the average dose difference between centers was -0.5±1.2% for thirty patient fields within target region. Planar dose measurements at both centers also matched well with the universal beam model with 94±3.9% passing rate at 3%/3mm.

Conclusion: Dosimetrically equivalent facilities can be achieved for the same type of PBS systems with standard beam data.

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