The commissioning and quality assurance of the Automatic Positioning System on the Leksell gamma knife.
OBJECTIVE
The authors describe a series of commissioning checks that were developed following the installation of the Automatic Positioning System (APS) on the model C gamma knife.


METHODS
System reliability was checked by performing a series of test treatments using the APS. A phantom was designed to enable the exposure of small pieces of Gaf Chromic film at 40 different predefined x, y, and z coordinates. The phantom consisted of a base plate with a series of film holders to facilitate the exposures using a 4-mm field, the center of which was marked. A spreadsheet calculation was performed to verify the conversion from Leksell coordinates to the APS coordinates when the treatment angle (gamma angle) is other than 90 degrees. A number of APS plans were prepared and the coordinate transformation verified. Precision measurements were performed to verify the correct positioning of the high bars when attached to the frame. The Gaf Chromic films were exposed, and the APS plans were used when confined to positions within the high bar range. A test tool to verify accurate location of the high bars on the frame was also designed.


CONCLUSIONS
The performance of APS was verified independently of the manufacturer by using specially designed tools, phantoms, and spread sheets. At all points tested, the positional accuracy was found to be within specification. Conversion to APS coordinates was verified as correct.
Soanes
Tracy
T
National Centre for Stereotactic Radiosurgery, Royal Hallamshire Hospital, Sheffield, England. tracy.soanes@sth.nhs.uk
Hampshire
Anna
A
Vaughan
Paul
P
Brownett
Christopher
C
Rowe
Jeremy
J
Radatz
Matthias
M
Kemeny
Andras
A
Walton
Lee
L
D004867:Equipment Design / Q000592:standards; D006801:Humans; D011786:Quality Control; D016634:Radiosurgery / Q000295:instrumentation* / Q000592:standards*; D015203:Reproducibility of Results; D013238:Stereotaxic Techniques / Q000295:instrumentation / Q000592:standards