Four-dimensional lung treatment planning in layer-stacking carbon ion beam treatment: comparison of layer-stacking and conventional ungated/gated irradiation.
OBJECTIVE
We compared four-dimensional (4D) layer-stacking and conventional carbon ion beam distribution in the treatment of lung cancer between ungated and gated respiratory strategies using 4DCT data sets.


METHODS
Twenty lung patients underwent 4DCT imaging under free-breathing conditions. Using planning target volumes (PTVs) at respective respiratory phases, two types of compensating bolus were designed, a full single respiratory cycle for the ungated strategy and an approximately 30% duty cycle for the exhalation-gated strategy. Beams were delivered to the PTVs for the ungated and gated strategies, PTV(ungated) and PTV(gated), respectively, which were calculated by combining the respective PTV(Tn)s by layer-stacking and conventional irradiation. Carbon ion beam dose distribution was calculated as a function of respiratory phase by applying a compensating bolus to 4DCT. Accumulated dose distributions were calculated by applying deformable registration.


RESULTS
With the ungated strategy, accumulated dose distributions were satisfactorily provided to the PTV, with D95 values for layer-stacking and conventional irradiation of 94.0% and 96.2%, respectively. V20 for the lung and Dmax for the spinal cord were lower with layer-stacking than with conventional irradiation, whereas Dmax for the skin (14.1 GyE) was significantly lower (21.9 GyE). In addition, dose conformation to the GTV/PTV with layer-stacking irradiation was better with the gated than with the ungated strategy.


CONCLUSIONS
Gated layer-stacking irradiation allows the delivery of a carbon ion beam to a moving target without significant degradation of dose conformity or the development of hot spots.
Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan. shinshin@nirs.go.jp
Shinichiro
S
Mori
Nobuyuki
N
Kanematsu
Hiroshi
H
Asakura
Gregory C
GC
Sharp
Motoki
M
Kumagai
Suguru
S
Dobashi
Mio
M
Nakajima
Naoyoshi
N
Yamamoto
Susumu
S
Kandatsu
Masayuki
M
Baba
D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002244:Carbon / Q000627:therapeutic use*; D045853:Exhalation; D056973:Four-Dimensional Computed Tomography / Q000379:methods*; D006801:Humans; D001239:Inhalation; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects; D008175:Lung Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D008875:Middle Aged; D009068:Movement; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000528:radiation effects; D047368:Tumor Burden
D002244:Carbon