Abstract
Volumetric repainting is considered as one of the techniques for motion mitigation in proton therapy. Faster layer switching time to deliver a volumetric repainting proton plan is very critical to reduce the overall treatment time. Recently, IBA (proton therapy vendor at the Miami Cancer Institute) has implemented a “field regulation” – a new feature to reduce the switching time between layers by applying a magnetic field setpoint to specific groups of magnets. In order to investigate the impact of field regulation and volumetric repainting technique on the spot size, several spot maps were generated. The spot sizes were measured at the isocenter and four off-axis points using the Lynx 2D scintillation detector. The average difference in spot size between two delivery sequences (“down” vs. “up” directions) for given energy at all five locations was 0.6±0.5%. The measurement results from the current study demonstrated that the impact of field regulation on the spot size was very minimal, and this was true for both the volumetric and non-volumetric techniques on a ProteusPLUS proton system with a PBS dedicated nozzle.
Highlights
In recent years, pencil beam scanning (PBS) is becoming a preferred technique in proton therapy in comparison to the passive scattering techniques such as double-scattering and uniform scanning
We focused on the spot size and sought to understand how the combination of field regulation” (FR) and volumetric repainting technique affects the spot sizes of various energies on a ProtusPLUS proton therapy system with a PBS dedicated nozzle
In this study, we investigated variations in spot size as a result of FR feature on a ProteusPLUS proton system with a PBS dedicated nozzle
Summary
Pencil beam scanning (PBS) is becoming a preferred technique in proton therapy in comparison to the passive scattering techniques such as double-scattering and uniform scanning. For the current clinical treatment delivery, different types of magnets are employed in order to transport the proton beam from the cyclotron to the treatment room. The clinical commissioning of the system was done for the beam delivery in the “down” direction only with a site configuration that has all magnets being regulated in the current (CR). The fluctuations of current to the quadrupoles and variations in the magnetic field in B1234E, B1Gx, and B2Gx during “down” and “up” directions can potentially change the spot size of a given energy, adding to the beam delivery uncertainty that can affect the quality of the delivered volumetric repainting plan. We focused on the spot size and sought to understand how the combination of FR and volumetric repainting technique affects the spot sizes of various energies on a ProtusPLUS proton therapy system with a PBS dedicated nozzle. The difference in spot sizes measured in CR and FR modes is expected to be minimal, and this hypothesis needs to be validated in a clinical environment
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