Moving target irradiation with fast rescanning and gating in particle therapy.
OBJECTIVE
In moving target irradiation with pencil beam scanning, the interplay effect between the target motion and the scanned beam is a problem because this effect causes over or under dosage in the target volume. To overcome this, we have studied rescanning using a gating technique.


METHODS
A simulation and experimental study was carried out. In the experiment, we used the fast scanning system developed at the HIMAC to verify the validity of phase controlled rescanning method, in which the time for rescanning irradiation of each slice is matched to the gating duration.


RESULTS
Simulation and experimental results showed that controlling the scan speed to match the respiration cycle with rescans can deliver the blurred dose distribution. In the comparison between the static measurements and the moving measurements with the phase controlled rescanning method, the dose difference was less than 2% for pinpoint chambers in the target volume.


CONCLUSIONS
The simulation and experimental results demonstrated that the phase controlled rescanning method makes it possible to deliver the dose distribution close to the expected one. As an experimental result for 3D irradiation, it was estimated that blurring by the probability density function was not only for a lateral distribution, but also for a distal distribution, even in the lateral rescanning.
Medical Physics Research Group, Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263-8555, Japan. t_furu@nirs.go.jp
Takuji
T
Furukawa
Taku
T
Inaniwa
Shinji
S
Sato
Toshiyuki
T
Shirai
Shinichiro
S
Mori
Eri
E
Takeshita
Kota
K
Mizushima
Takeshi
T
Himukai
Koji
K
Noda
D063193:Heavy Ion Radiotherapy; D009068:Movement; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D013997:Time Factors