Room: Exhibit Hall | Forum 3
Purpose: Creating a sharp dose fall-off is important in stereotactic radiosurgery of large brain lesions (> 8 cc in volume), where normal brain tissue surrounding the target is substantial and must be carefully spared to avoid treatment-related complications. In this study, we investigated a new approach of sharpening the dose fall-off via packing and optimizing hundreds of isocenters inside a target.
Methods: Packing and optimizing hundreds of isocenters was implemented on the Gamma Knife Icon system. In this approach, 200-400 isocenters were initially traced and discretized on a dynamic dose-painting path by solving a modified lawn-mowing problem. Once optimized, a high isocenter packed (HIP) treatment plan was reconstructed in the clinical treatment planning system for final dose calculations. As a proof of concept, HIP was tested for eight cases (mean target volume 9.4Â±2.3 mL) and the resulting HIP dose distribution were compared with those of conventional treatment planning using less than 30 isocenters.
Results: Compared to the conventional treatment approach, HIP produced identical target volume coverage (99%Â±1%) and conformity (0.80Â±0.096 in Paddick Conformity Index) for all the cases. However, the dose fall-off was significantly sharper for the HIP treatment plans: the gradient index was 2.72Â±0.15 (conventional) versus 2.55Â±0.12 (HIP) (p< 0.04, two-tailed t-test). The beam-on time was slightly higher (3.1%Â±5.2%) but < 10 min for the HIP treatments but such delivery also produced 5.8Â±1.2% enhancement in the biological effective dose to the target (assuming Î±/Î²=10 Gy) due to favorable dose hot spot distribution and sequencing.
Conclusion: High isocenter packing is clinically feasible and sharpens dose fall-off while enhancing the biological effective dose for treating of large brain lesions.