AbstractID: 6943 Title: Beam arc setup dependence of dose distribution in Multi-arc Stereotactic
Radiosurgery
Three types of Multi-arc collimations are currently used in stereotactic radiosurgery: the
fixed circular collimator, the fixed conformal shape, and the dynamic conformal shape.
The dose distribution of these Multi-arc collimations is influenced by the beam arc setup
including the isocenter position, the beam arc length and locations, the collimator size,
and the arc weighting factor. The dependence of dose distribution on the beam arc
setup for these three collimations has been systematically investigated. Both the
conformity index and the dose avoidance to the critical organs are used to evaluate the
dose distribution. For fixed circular collimator, the collimator size directly affects the
treatment volume. The isocenter position affects the treatment location. The shape of
the treatment volume highly depends on the arc locations and weighting factors. For
conformal arc with fixed shape, since each beam arc has an individual conformal MLC
opening, the treatment volume is automatically adjusted to fit the target. Isocenter
position has little influence on the treatment volume location. Beam arc locations and
weighting factors still affect the shape of treatment volume, but their influence is
significantly decreased. For dynamic shaped arc, the conformal treatment volume is
achieved by shaping the beam at each couch and gantry position. Beam arc locations,
weights, or isocenter position do not affect treatment volume significantly. For all three
collimations, the dose avoidance to the critical organ mainly depends on the beam arc
locations. This study provides guidelines for optimizing the dose distribution in Multi-arc
stereotactic radiosurgery.