Open AccessAnalysis of the optimum internal margin for respiratory‐gated radiotherapy using end‐exhalation phase assessments using a motion phantom
Author(s) -
Yaegashi Yuji,
Tateoka Kunihiko,
Nakazawa Takuya,
Fujimoto Kazunori,
Shima Katsumi,
Suzuki Junji,
Nakata Akihiro,
Saito Yuichi,
Abe Tadanori,
Sakata Koichi,
Hareyama Masato
Publication year - 2012
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1120/jacmp.v13i2.3715
Subject(s) - imaging phantom , exhalation , scanner , nuclear medicine , physics , artifact (error) , biomedical engineering , optics , materials science , medicine , computer science , radiology , computer vision
We aimed to optimize internal margin (IM) determination for respiratory‐gated radiotherapy using end‐expiratory phase assessments using a motion phantom. Four‐dimensional computed tomography (4D CT) data were acquired using a GE LightSpeed RT CT scanner, a respiratory‐gating system, and a motion phantom designed to move sinusoidally. To analyze the accuracy of 4D CT temporal resolution, a 25.4 mm diameter sphere was inserted into the motion phantom, and we measured the differences in sphere diameters between static and end‐exhalation phase images. In addition, the IM obtained from the maximum intensity projection within the gating window ( MIP GW ) image was compared to theoretical value. Cranial–caudal motion displacement ranged from 5.0 to 30.0 mm, and the respiratory period ranged from 2.0 to 6.0 sec. Differences in sphere diameters between static and end‐exhalation phase images ranged from 0.37 to 4.6 mm, with 5.0 ‐mm and 30 mm target displacements, respectively. Differences between the IM obtained from the MIP GW and the theoretical values ranged from 1.12 to 6.23 mm with 5.0 mm and 30 mm target displacements, respectively. These differences increased in proportion to the target velocity due to a motion artifact generated during tube rotation. In this study, the IMs obtained using the MIP GW image were overestimated in all cases. We therefore propose that the internal target volume (ITV) for respiratory‐gated radiotherapy should be determined by adding the calculated value to the end‐exhalation phase image. We also demonstrate a methodology for subtracting motion artifacts from the ITV using a motion phantom. PACS numbers: 87.53.Kn, 87.55.Gh, 87.56.jk