Room: Exhibit Hall
Purpose: Develop a robust optimization method for efficient dose delivery with high conformity dedicated to a new generation of the rotating gamma system. This novel design is an integrated, multi-modality guided (real time IGRT and SRS/SBRT) radiotherapy system.
Methods: We used an EGS4/PRESTA user code MCSIM for accurate Monte Carlo dose calculations and the input sources are phase space data of â?¶â?°Co beams for different cone sizes. The tumor volume is divided into subvolumes and painted with different cones to achieve optimal dose distributions. To ensure good conformity, the outer edge (defined at half maximum) of the radiation focus is always kept tangent to the periphery of the layer. Radiation dose is delivered with simultaneous rotation of the treatment gantry and movement of the couch. In this study, the irregularly-shaped tumor is selected for generality and total number of beams is set as 60 for each arc with incident angles equally spaced by 6Â°.
Results: Preliminary results for irregular tumor targets showed that prescription doses could be given to 50-80% isodose lines to achieve superior target coverage with steep dose fall-off in surrounding normal tissues. The target conformity (CI: < 1.2) was comparable to other SRS/SBRT systems.
Conclusion: This pilot study demonstrates the feasibility and great potential of the subvolume revolving dose painting delivery method for the new rotating gamma system. Future in-depth investigations will focus on the optimal selection of the total number, sites and weights of radiation focuses and their association with the subvolume definition. In addition, critical structures will be added in our optimization.