@misc{oai:repo.qst.go.jp:00069898,
 author = {Okada, Tohru and Tsuji, Hiroshi and Sugahara, Shinji and Kamada, Tadashi and 岡田 徹 and 辻 比呂志 and 菅原 信二 and 鎌田 正},
 month = {Oct},
 note = {Intrafractional and interfractional motions of the prostate during Carbon ion therapy: quantification by four-dimensional CT
\nResearch center for charged particle therapy, National institute of radiological sciences
Tohru Okada, Hiroshi Tsuji, Shinji Sugahara, Motohisa Suzuki, Motoki Kumagai, Shinichiro Mori, Shinichi Minohara, Tadashi Kamada, Hirohiko Tsujii
\nPurpose: Carbon ion radiotherapy (C-ion RT) for the prostate cancer has been performed with hypofractionated regimen at our institute for 14 years. The results so far has been quite satisfactory both in the toxicity and tumor control, and even better results might be expected with more precise and more hypofractionated C-ion RT. It is essential to know how the prostate can move with our immobilization method to realize more precise C-ion RT with smaller PTV margins. In this study, four-dimensional CT (4DCT) was used to measure the intrafractional and interfractional prostate motion to determine the validity of our immobilization method of C-ion RT for the prostate cancer.
Methods and Materials : Twenty patients undergoing our treatment between April and August 2008 were enrolled to the study with the written informed consent. The median age was 66.7 years. Of those, 7 high and 11 intermediate risk patients underwent neo-adjuvant androgen deprivation therapy with C-ion RT, and 2 low risk patients received C-ion RT alone. Every patient received C-ion RT in supine position with rigid body cast for the pelvis and under free breathing. The 4DCT images were acquired after the first 5 fractions out of the 16 fractions. All scans were carried out in supine position with the customized body cast as routinely used in actual treatment. To evaluate the influence of respiration on intrafractional motion, scans under both free and gated breathing conditions were performed. The movement of center-of-mass (COM) and edges of prostate were measured. Also interfractional movement of prostate COM was measured from peak exhalation 4DCT images relative to the initial planning CT images.
Results: Under free breathing, the maximum movement of prostate COM was 0.7mm with the mean value of 0.2mm, and the maximum movement of edges was 1.6mm with the mean of 0.2mm. Under gated breathing, the maximum movement of COM was 0.5mm with the mean of 0.1mm, and the maximum movement of edges was 1.6mm with the mean of 0.1mm. Interfractional displacement of prostate COM was also small enough to perform C-ion RT with the current PTV margins.
Conclusions: The intrafractional and interfractional prostate motions were both sufficiently small to perform the current C-ion RT with our immobilization method. Further, particularly small intrafractional motion will enable us to apply dynamic irradiation using scanning beam with this immobilization method under free breathing only by verification of initial position of the prostate., PTCOG 48},
 title = {Intrafractional and interfractional motions of the prostate during carbon ion therapy: quantification by four-dimensional CT},
 year = {2009}
}