Four-dimensional lung treatment planning in layer-stacking carbon ion beam treatment: comparison of layer-stacking and conventional ungated/gated irradiation.

Authors:
Shinichiro Mori
Shinichiro Mori
National Institute of Radiological Sciences
Japan
Nobuyuki Kanematsu
Nobuyuki Kanematsu
Research Center for Charged Particle Therapy
Hiroshi Asakura
Hiroshi Asakura
National Institute of Health Sciences
Japan
Gregory C Sharp
Gregory C Sharp
Massachusetts General Hospital
United States
Motoki Kumagai
Motoki Kumagai
Research Center for Charged Particle Therapy
Suguru Dobashi
Suguru Dobashi
School of Health Sciences
Japan
Mio Nakajima
Mio Nakajima
Research Center Hospital for Charged Particle Therapy
Naoyoshi Yamamoto
Naoyoshi Yamamoto
Research Center Hospital for Charged Particle Therapy

Int J Radiat Oncol Biol Phys 2011 Jun 23;80(2):597-607. Epub 2010 Oct 23.

Research Center for Charged Particle Therapy, National Institute of Radiological Sciences, Chiba, Japan.

Purpose: 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 And Materials: 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.
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June 2011
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