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.