M. Nakayama
Kobe University
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Featured researches published by M. Nakayama.
Medical Physics | 2016
M. Nakayama; Y Munetomo; T Ogata; Kazuyuki Uehara; S Tsudou; Hideki Nishimura; H Mayahara; Ryohei Sasaki
PURPOSEnTo evaluate the practicality use of ionization chambers with different volumes for delivery quality assurance of CyberKnife plans, METHODS: Dosimetric measurements with a spherical solid water phantom and three ionization chambers with volumes of 0.13, 0.04, and 0.01 cm3 (IBA CC13, CC04, and CC01, respectively) were performed for various CyberKnife clinical treatment plans including both isocentric and nonisocentric delivery. For each chamber, the ion recombination correction factors Ks were calculated using the Jaffe plot method and twovoltage method at a 10-cm depth for a 60-mm collimator field in a water phantom. The polarity correction factors Kpol were determined for 5-60-mm collimator fields in same experimental setup. The measured doses were compared to the doses for the detectors calculated using a treatment planning system.nnnRESULTSnThe differences in the Ks between the Jaffe plot method and two-voltage method were -0.12, -0.02, and 0.89% for CC13, CC04, and CC01, respectively. The changes in Kpol for the different field sizes were 0.2, 0.3, and 0.8% for CC13, CC04, and CC01, respectively. The measured doses for CC04 and CC01 were within 3% of the calculated doses for the clinical treatment plans with isocentric delivery with collimator fields greater than 12.5 mm. Those for CC13 had differences of over 3% for the plans with isocentric delivery with collimator fields less than 15 mm. The differences for the isocentric plans were similar to those for the single beam plans. The measured doses for each chamber were within 3% of the calculated doses for the non-isocentric plans except for that with a PTV volume less than 1.0 cm3 .nnnCONCLUSIONnAlthough there are some limitations, the ionization chamber with a smaller volume is a better detector for verification of the CyberKnife plans owing to the high spatial resolution.
Medical Physics | 2015
Kazuyuki Uehara; T Ogata; M. Nakayama; T Shinji; Hideki Nishimura; T Masutani; Takeaki Ishihara; Yasuo Ejima; Ryohei Sasaki
Purpose: In commissioning of volumetric modulated arc therapy (VMAT), it is necessary to evaluate the beam characteristics of various dose rate settings with potential to use. The aim of this study is to evaluate the beam characteristics of flattened and flattening filter free (FFF) including low dose rate setting. Methods: We used a Varian TrueBeam with Millennium 120 MLC. Both 6 and 10 MV beams with or without flattening filter were used for this study. To evaluate low-dose rate FFF beams, specially-designed leaf sequence files control out-of-field MLC leaf pair at constant dose rate ranging from 80 to 400 MU/min. For dose rate from 80 MU/min to the maximum usable value of all energies, beam output were measured using ionization chamber (CC04, IBA). The ionization chamber was inserted into water equivalent phantom (RT3000-New, R-tech), and the phantom was set with SAD of 100cm. The beam profiles were performed using the 2D diode array (Profiler2, Sun Nuclear). The SSD was set to 90cm and a combined 30cmx30cmx9cm phantom which consisted of solid water slabs was put on the device. All measurement were made using 100MU irradiation for 10cmx10cm jaw-defined field size with a gantry angle of 0°. Results: In all energies, the dose rate dependences with beam output and variation coefficient were within 0.2% and 0.07%, respectively. The flatness and symmetry exhibited small variations (flatness ≤0.1 point and symmetry≤0.3 point at absolute difference). Conclusion: We had studied the characteristics of flattened and FFF beam over the 80 MU/min. Our results indicated that the beam output and profiles of FFF of TrueBeam linac were highly stable at low dose rate setting.
International Journal of Radiation Oncology Biology Physics | 2014
M. Nakayama; N. Mukumoto; Hiroaki Akasaka; D. Miyawaki; Hideki Nishimura; Keiji Umetani; N. Nariyama; Takeshi Kondoh; Kunio Shinohara; Ryohei Sasaki
International Journal of Radiation Oncology Biology Physics | 2013
N. Mukumoto; D. Miyawaki; Hiroaki Akasaka; M. Nakayama; Yasushi Miura; Keiji Umetani; N. Nariyama; Kunio Shinohara; Takeshi Kondoh; Ryohei Sasaki
International Journal of Radiation Oncology Biology Physics | 2013
Hiroaki Akasaka; Ryohei Sasaki; N. Mukumoto; M. Nakayama; D. Miyawaki; K. Yoshida; Yasuo Ejima; Nor Shazrina Sulaiman; Yoshiyuki Mizushina
International Journal of Radiation Oncology Biology Physics | 2012
Hiroaki Akasaka; Ryohei Sasaki; Takumi Fukumoto; N. Mukumoto; M. Nakayama; Hideki Nishimura; K. Yoshida; D. Miyawaki; Shigeru Yamada; M. Murakami
International Journal of Radiation Oncology Biology Physics | 2012
M. Nakayama; Ryohei Sasaki; Chiaki Ogino; Tsutomu Tanaka; Mitsuo Umetsu; Satoshi Ohara; Zhenquan Tan; Kazuyoshi Sato; Chiya Numako; Akihiko Kondo
International Journal of Radiation Oncology Biology Physics | 2011
N. Mukumoto; Ryohei Sasaki; Hiroaki Akasaka; M. Nakayama; D. Miyawaki; Hideki Nishimura; Keiji Umetani; Takeshi Kondoh; Kunio Shinohara; Kazuro Sugimura
International Journal of Radiation Oncology Biology Physics | 2011
D. Miyawaki; Hideki Nishimura; K. Yoshida; O. Muraoka; M. Nakayama; Kazuyuki Uehara; S. Hasegawa; Ken-ichi Nibu; Kazuro Sugimura; Ryohei Sasaki
International Journal of Radiation Oncology Biology Physics | 2011
Kazuyuki Uehara; Ryohei Sasaki; D. Miyawaki; Hideki Nishimura; K. Yoshida; M. Nakayama; Toshinori Soejima; Osamu Fujii; Takashi Sasayama; Kazuro Sugimura