The precision of respiratory-gated delivery of synchrotron-based pulsed beam proton therapy.
A synchrotron-based proton therapy system operates in a low repetition rate pulsed beam delivery mode. Unlike cyclotron-based beam delivery, there is no guarantee that a synchrotron beam can be delivered effectively or precisely under the respiratory-gated mode. To evaluate the performance of gated synchrotron treatment, we simulated proton beam delivery in the synchrotron-based respiratory-gated mode using realistic patient breathing signals. Parameters used in the simulation were respiratory motion traces (70 traces from 24 patients), respiratory gate levels (10%, 20% and 30% duty cycles at the exhalation phase) and synchrotron magnet excitation cycles (T(cyc)) (fixed T(cyc) mode: 2.7, 3.0-6.0 s and each patient breathing cycle, and variable T(cyc) mode). The simulations were computed according to the breathing trace in which the proton beams were delivered. In the shorter fixed T(cyc) (<4 s), most of the proton beams were delivered uniformly to the target during the entire expiration phase of the respiratory cycle. In the longer fixed T(cyc) (>4 s) and the variable T(cyc) mode, the proton beams were not consistently delivered during the end-expiration phase of the respiratory cycle. However we found that the longer and variable T(cyc) operation modes delivered proton beams more precisely during irregular breathing.
Department of Radiation Physics, Unit 94, The University of Texas M D Anderson Cancer Center, 1515 Holcombe Blvd, Houston, TX 77030, USA. ytsunash@mdanderson.org
Yoshikazu
Y
Tsunashima
Sastry
S
Vedam
Lei
L
Dong
Masumi
M
Umezawa
Peter
P
Balter
Radhe
R
Mohan
D006801:Humans; D009068:Movement; D061766:Proton Therapy; D011881:Radiotherapy, Computer-Assisted / Q000379:methods*; D012119:Respiration; D017356:Synchrotrons; D013997:Time Factors; D011522:Protons
D011522:Protons