AbstractID: 6972 Title: Implementation of the Siemens HDI technique on a 3D Treatment Planning System
Stepped leaf edges are the major limitation of conforming to the prescribed treatment
field contour using the conventional multileaf collimator (MLC), which produces a
scalloped dose pattern. The Siemens HDI MLC technique provides a software solution to
achieve well defined, smooth edges, and optimal penumbra of the MLC shaped field. We
implemented the HDI technique on a 3D treatment planning system and modeled the
dosimetric effects. The HDI delivery is accomplished by dividing the prescribed MLC
field into segments. By equally dividing the 1 cm leaf width at isocenter, the HDI
planning creates a number of field segments, which is determined by the resolution
chosen. Each segment has a shifted isocenter and adjusted leaf positions to maintain
conformal blocking to the treatment volume. The isocenter of each segment is calculated
by the HDI geometric algorithm, which moves the table perpendicular to the MLC leaf
plane. The table shift is three-dimensional and varies depending upon the gantry,
collimator, and table angles, and the source to target volume distance (usually 100 cm).
The dosimetric effect of the HDI delivery was simulated for the maximum stepping
configuration (leaf displacement equals leaf width) of the MLC leaves. The delivery of
radiation by the original field shows obvious scalloped dose pattern. In contrast, the result
of the HDI delivery gives a smoothed MLC field edge with the reduced effective
penumbra and isodose undulation when the total dose delivered to the prescribed field is
measured. This project is supported by Siemens Medical Systems, Inc.