Room: ePoster Forums
Purpose: The current gamma knife radiosurgery is planned based on a sphere-packing method and the dose delivery is inefficient. In this work, we propose a scanning beam method instead of packing spherical shots for efficient dose delivery with improved target dose conformity, dedicated to the new generation of rotating gamma systems (RGS).
Methods: We used an EGS4/PRESTA user code MCSIM for accurate dose calculation for the â?¶â?°Co beams of different cone sizes. Each beam consists of 16 focusing â?¶â?°Co sources arranged on a 35áµ’ arc. In our method, the tumor volume is divided into layers in the S-I direction and the layer thickness is based on the axial dimensions of the tumor and equal to the diameter of an available cone. A scanning pattern is developed with the beam edge following the tumor periphery for optimal conformity and dose fall-off. Tumors of various shapes (e.g., circular, elliptical, racetrack-shaped) have been investigated. For a racetrack-shaped tumor with its adjustable length in any direction on the axial plane, coplanar beams scan along the tumor periphery with beam axis equidistant from the periphery by a cone radius.
Results: Preliminary results showed that prescription doses could be given to 50-70% isodose lines to achieve good target coverage with steep dose fall-off in surrounding normal tissues. As expected, dose falls off most rapidly along the S-I direction. In the transverse plane, dose falls off nearly isotropically with the fall-off distance from 100% to 50% prescription dose ~1.2-1.6cm. The target conformity was comparable to other SRS/SBRT systems and dependent on the tumor size.
Conclusion: This pilot study demonstrates the feasibility and great potential of the beam-based dose-painting delivery method for the new RGS. Further investigations are being carried out of realistic patient plans to quantify the improvement of target dose conformity and delivery efficiency.
Gamma Knife, Optimization, Stereotactic Radiosurgery