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Basic Performance Comparison Between Two Types of Proton Beam Modulated Scanning Systems

J Farr

J Farr1,2*, F Dessy3, O DeWilde3, O Bietzer3, D Schoenenberg4, M Stuschke1, (1) University Hospital of Essen, Germany, (2) St. Jude Children's Research Hospital, Memphis, TN, (3) Ion Beam Applications, Louvain-la-neuve, Belgium, (4) Westdeutsches Protonentherapiezentrum Essen, Germany

SU-E-T-405 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: The purpose of this investigation was to compare and contrast the fundamental properties of two new types of modulated proton scanning systems. A secondary purpose was to develop and apply new characterization approaches where necessary to do so.

Methods: The following performances of the proton scanning systems were investigated: beamlet alignment, static in-air beamlet size and shape, scanned in-air penumbra, scanned fluence map accuracy, geometric alignment of scanning system to iso-center, maximum field size, lateral and longitudinal field uniformity of a one liter cubic uniform field, output stability over time, gantry angle invariance, monitoring system linearity and reproducibility. A range of detectors was used: film, ionization chambers, multi-ionization chamber lateral and longitudinal detectors, and a scintillation screen combined with a digital video camera. Characterization of the scanned fluence maps was performed with a software analysis tool.

Results: The resulting measurements and analysis indicated that the two types of delivery systems performed within specification for those aspects investigated. The significant differences observed between the two type of scanning systems where: One type exhibits a smaller spot size and associated penumbra than the other. The differential is minimum at maximum energy and increases inversely with decreasing energy. Additionally, the large spot system showed an increase in dose precision to a static target with layer re-scanning whereas the small spot system did not.

Conclusion: The measured results from the two types of modulated scanning types of systems were consistent with their designs. The most significant difference between the types of systems was their proton spot size and associated resolution, factors of magnetic optics and vacuum length. The need and benefit of muti-element detectors and high-resolution sensors was also shown. The use of a fluence map analytical software tool was particularly effective in characterizing the dynamic proton energy-layer scans.

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