Correlation between the respiratory waveform measured using a respiratory sensor and 3D tumor motion in gated radiotherapy.
OBJECTIVE
The purpose of this study is to investigate the correlation between the respiratory waveform measured using a respiratory sensor and three-dimensional (3D) tumor motion.


METHODS
A laser displacement sensor (LDS: KEYENCE LB-300) that measures distance using infrared light was used as the respiratory sensor. This was placed such that the focus was in an area around the patient's navel. When the distance from the LDS to the body surface changes as the patient breathes, the displacement is detected as a respiratory waveform. To obtain the 3D tumor motion, a biplane digital radiography unit was used. For the tumor in the lung, liver, and esophagus of 26 patients, the waveform was compared with the 3D tumor motion. The relationship between the respiratory waveform and the 3D tumor motion was analyzed by means of the Fourier transform and a cross-correlation function.


RESULTS
The respiratory waveform cycle agreed with that of the cranial-caudal and dorsal-ventral tumor motion. A phase shift observed between the respiratory waveform and the 3D tumor motion was principally in the range 0.0 to 0.3 s, regardless of the organ being measured, which means that the respiratory waveform does not always express the 3D tumor motion with fidelity. For this reason, the standard deviation of the tumor position in the expiration phase, as indicated by the respiratory waveform, was derived, which should be helpful in suggesting the internal margin required in the case of respiratory gated radiotherapy.


CONCLUSIONS
Although obtained from only a few breathing cycles for each patient, the correlation between the respiratory waveform and the 3D tumor motion was evident in this study. If this relationship is analyzed carefully and an internal margin is applied, the accuracy and convenience of respiratory gated radiotherapy could be improved by use of the respiratory sensor.Thus, it is expected that this procedure will come into wider use.
Proton Medical Research Center, University of Tsukuba, 1-1-1 Tennoudai Tsukuba, Ibaraki 305-8575, Japan. tsunashima@pmrc.tsukuba.ac.jp
Yoshikazu
Y
Tsunashima
Takeji
T
Sakae
Yoshiyuki
Y
Shioyama
Kenji
K
Kagei
Toshiyuki
T
Terunuma
Akihiro
A
Nohtomi
Yasuyuki
Y
Akine
D004938:Esophageal Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D005583:Fourier Analysis; D006801:Humans; D021621:Imaging, Three-Dimensional; D007834:Lasers; D008113:Liver Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009068:Movement; D011859:Radiography; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D012119:Respiration