title: Improved delivery efficiency for step and shoot intensity modulated radiotherapy using a fast-tuning magnetron.
abstract: The delivery efficiency of step and shoot intensity modulated radiotherapy (IMRT) has been improved by the installation of fast-tuning magnetrons into three travelling wave linear accelerators. The IMRT delivery efficiency and the beam start-up performance have been compared before and after installation. Start-up and inter sub-field times were reduced by an average of 3.0 s. A typical start-up time from depression of the start button to beam on is now around 4 s. Delivery efficiency for a variety of clinical and quality control prescriptions was improved by an average of 30.7% (range 7.4-60.9%), depending on a complex combination of the number of sub-fields, distance moved by leaves and dose rate. For the oldest accelerator (7 years old), dosimetric accuracy was significantly improved for low dose sub-fields. The dose output was within 2% for a 1 monitor unit (MU) sub-field and 1% for a 2 MU sub-field. The two newer accelerators displayed similar or better dose characteristics even before fast-tuning magnetron installation. Beam symmetries and flatnesses were acceptable at all energies and dose rates, and showed no obvious degradation in low dose sub-fields. It is recommended that fast-tuning magnetrons are adopted for accelerators of this design performing step and shoot IMRT.
authors.affiliation: North Western Medical Physics, Christie Hospital NHS Trust, Manchester, UK. Geoff.Budgell@physics.cr.man.ac.uk
authors.forename: G J
authors.initials: GJ
authors.lastname: Budgell
authors.forename: C
authors.initials: C
authors.lastname: Martens
authors.forename: F
authors.initials: F
authors.lastname: Claus
mesh_terms: D008280:Magnetics; D010315:Particle Accelerators; D011874:Radiometry; D020266:Radiotherapy, Conformal / Q000295:instrumentation* / Q000379:methods*; D015203:Reproducibility of Results; D013997:Time Factors