AbstractID: 9499 Title: A Quality Assurance Program for Stereotactic Radiosurgery
Using a Miniature Multileaf Collimator
High precision mMLC beam shaping has made it possible to deliver conformal dose
distributions to targets using limited number of non-coplanar beams in stereotactic
radiosurgery (SRS). A quality assurance program is essential to guarantee a high quality
standard for the delivery of a high single dose of radiation to a small target within the
sensitive brain. Our QA program for SRS includes routine check for LINAC, mMLC run
in auto cycle, Winston-Lutz test for isocenter and laser verification, independent MU
check, and treatment procedure review before treatment. Relative output and mechanical
check follows the routine LINAC QA schedule. mMLC run in autocycle is done on the
treatment day. Winston-Lutz test is performed with at least three couch rotations, 0, 90,
and 270 degrees, with various gantry rotations. For three months period, mechanical
isocenter was stable within 1.1 mm for all combinations of table-gantry rotations. An
independent MU calculation is done with a custom-made chart check program with
Clarkson dose algorithm. Two different approaches are agreed within +/-3.0 % for all
fields and cases. The position of the PTV projected to the target positioner overlays and
their relations to the isocenters are checked. The planned gantry and table angles based
on the table of ‘forbidden’ angles are checked visually to avoid possible collisions
between the gantry and the couch. Before starting treatment, patient file and all QA
procedure is reviewed. The QA program is being used routinely for a single stereotactic
treatment in our cancer center.