The accuracy of frameless stereotactic intracranial radiosurgery.
OBJECTIVE
To determine the accuracy of frameless stereotactic radiosurgery using the BrainLAB ExacTrac system and robotic couch by measuring the individual contributions such as the accuracy of the imaging and couch correction system, the linkage between this system and the linac isocenter and the possible intrafraction motion of the patient in the frameless mask.


METHODS
An Alderson head phantom with hidden marker was randomly positioned 31 times. Automated 6D couch shifts were performed according to ExacTrac and the deviation with respect to the linac isocenter was measured using the hidden marker. ExacTrac-based set-up was performed for 46 patients undergoing hypofractionated stereotactic radiotherapy for 135 fractions, followed by verification X-rays. Forty-three of these patients received post-treatment X-ray verification for 79 fractions to determine the intrafraction motion.


RESULTS
The hidden target test revealed a systematic error of 1.5 mm in one direction, which was corrected after replacement of the system calibration phantom. The accuracy of the ExacTrac positioning is approximately 0.3 mm in each direction, 1 standard deviation. The intrafraction motion was 0.35±0.21 mm, maximum 1.15 mm.


CONCLUSIONS
Intrafraction motion in the BrainLAB frameless mask is very small. Users are strongly advised to perform an independent verification of the ExacTrac isocenter in order to avoid systematic deviations.
Department of Radiation Oncology, VU University Medical Center, Amsterdam, The Netherlands. w.verbakel@vumc.nl
Wilko F A R
WF
Verbakel
Frank J
FJ
Lagerwaard
Arjan J E
AJ
Verduin
Stan
S
Heukelom
Ben J
BJ
Slotman
Johan P
JP
Cuijpers
D001921:Brain / Q000601:surgery*; D001932:Brain Neoplasms / Q000556:secondary / Q000601:surgery; D006801:Humans; D002538:Intracranial Arteriovenous Malformations / Q000601:surgery; D009464:Neuroma, Acoustic / Q000601:surgery; D019047:Phantoms, Imaging; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods; D014277:Trigeminal Neuralgia / Q000601:surgery