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Dose Sharpening Via Packing and Optimizing Hundreds of Isocenters for Intracranial Radiosurgery of Large Brain Lesions

L Ma1*, J Chiu2 , S Luan3 , (1) UCSF School of Medicine, San Francisco, CA, (2) University of Arizona School of Medicine, Tucson, AZ, (3) University of New Mexico, Alburquerque, NM


(Tuesday, 7/16/2019) 4:30 PM - 5:30 PM

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 9.4±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%±1%) and conformity (0.80±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 2.72±0.15 (conventional) versus 2.55±0.12 (HIP) (p< 0.04, two-tailed t-test). The beam-on time was slightly higher (3.1%±5.2%) but < 10 min for the HIP treatments but such delivery also produced 5.8±1.2% enhancement in the biological effective dose to the target (assuming α/β=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.


Radiosurgery, Treatment Planning, Gamma Knife


TH- External beam- photons: intracranial stereotactic/SBRT

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