Measurements of the Variation of RFKO Extracted Beam Current for Hitachi Proton Therapy and Carbon Therapy Synchrotrons and Implications for Particle Therapy

Abstract

Measurements of the extracted beam current (BC) for a Hitachi Carbon Therapy Synchrotron and a Hitachi Compact Proton Therapy Synchrotron are reported for the nominal extracted beam current (BC0) of 10mMUmsec , which was chosen since it is the magnitude of the clinical BC0, and a sample rate of 5 μsec (Carbon) and 8 μsec (Proton). A Noise Power Spectrum (NPS) analysis identifies the source of variation to be beam or power supply related. The rise time in the BC has been modeled and its effect on beam delivery time simulations have been estimated. The impact of the variation in BC from BC0 is shown to cause potentially significant dosimetric uncertainties in treatment delivery for modern particle therapy accelerators using fast Scanning Magnet (SCM) if plans are not simply beam current moderated or robustly optimized. The variation in beam current is shown to be inconsequential for medical physics quality assurance and commissioning measurements using properly biased ion chambers.