title: Dosimetry of a linear accelerator under respiratory gating.
abstract: In the present study, the impact of respiratory gating on the beam characteristics of a linear accelerator is investigated. The main focus is put on the influence of the duty cycle. Measurements were performed on a linear accelerator type Oncor (Siemens) with photon energies 6 MV and 15 MV, equipped with the Anzai gating system AZ-733V. Depth dose curves and beam profiles were found not to be significantly altered by gating even for duty cycles down to 5% for realistic respiration frequencies (dose variations all <2.5%). However, for very small duty cycles, the absolute dosimetry changes significantly (dose deviations > 10%), leading to clinically relevant underdoses. The crucial parameter for the dosimetry is the number of monitor units per gate. Our results imply that treatment planning for respiratory gating can be performed on the basis of data obtained under ungated operation if and only if the absolute gates sizes during treatment are sufficiently large. The limiting values for the gate sizes have to be determined individually for each accelerator.
authors.affiliation: Klinik für Strahlentherapie und Radioonkologie, Universitätsklinikum Jena, Germany. kirsten.weibert@med.uni-jena.de
authors.forename: Kirsten
authors.initials: K
authors.lastname: Weibert
authors.forename: Sebastian
authors.initials: S
authors.lastname: Biller
authors.forename: Thomas Georg
authors.initials: TG
authors.lastname: Wendt
authors.forename: Tilo
authors.initials: T
authors.lastname: Wiezorek
mesh_terms: D006801:Humans; D010315:Particle Accelerators; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D020266:Radiotherapy, Conformal / Q000379:methods; D055425:Respiratory-Gated Imaging Techniques / Q000379:methods*