Is Medical Linac Suitable for High-precision Stereotactic Irradiation? Investigations in geometrical accuracies of gantry and couch

Etsuo Kunieda, Masayuki Kitamura, Osamu Kawaguchi, Takayuki Ohira, Naoyuki Shigematsu, Takenori Tonai, Yutaka Ando, Atsushi Kubo, Takeshi Kawase

Research output: Contribution to journalArticle


Linac-based radiosurgery has many advantages over the gamma knife, including low initial cost and no need of source replacement. On the other hand, most of the medical linacs currently in use were not originally designed to be applied for radiosurgery, and, therefore, careful quality assurance programs are required. In the gantry-head of a linac, a small CCD video camera is mounted in a position optically identical to that of the x-ray source. The video signal from the camera was digitalized to be evaluated for gemetrical errors. A metal ball fixed to the stereotactic base frame via XYZ-sliding rods was used as a simulated target. Displacements of the target from the isocenter were measured during rotation of the gantry. Displacements in the gantry-rotation plane were satisfactorily small, while those perpendicular to it were maximal at gantry position angles of 0° and 180°. This error night be caused by gravitational vending of the heavy gantry head. Although other major errors of the linac were within one millimeter, the center of coach rotation around the isocenter did not coincide with the center of gantry rotation, probably owing to gravitational vending. Special care should be taken when very small collimators are employed.

Original languageEnglish
Pages (from-to)86-90
Number of pages5
JournalNippon Acta Radiologica
Issue number3
Publication statusPublished - 1998 Dec 1



  • Accuracy
  • Linac
  • Quality
  • Radiosurgery

ASJC Scopus subject areas

  • Radiology Nuclear Medicine and imaging
  • Oncology

Cite this