Dosimetric Comparison of Gamma Knife ICON and Linac VMAT SRS Treatment Plans for Single Brain Metastasis
Abstract
Purpose
Our center has two options for stereotactic-radiation-surgery (SRS) for brain metastasis, namely Gamma Knife ICON (GK-ICON) and VMAT on Versa-HD LINACs. In this study, we aim to conduct a dosimetric comparison of the GK-ICON plans generated with inverse-plan-optimization (IPO) in GammaPlan V11 with the LINAC-based VMAT plans.
Methods
10 cases that have been treated with GK were selected. The target volumes range from 0.41 cc to 16.76 cc (on average 7.79+/-2.1cc). The VMAT plans were generated using Eclipse V16.1 TPS for 6MV flattening-filter-free beams and were normalized so that the target coverages are the same as the corresponding GK plans. Target dose heterogeneity, Conformity index (CI), Paddick conformity index (PCI), gradient index (GI), and beam-on time (BOT) were compared for the GK and VMAT plans.
Results
The prescription doses are on average 53%+/-2% and 72%+/-2% of the maximum dose for the GK and VMAT plans, respectively. The VMAT plan CI (1.14+/-0.02) is slightly better than that of the GK plans (1.18+/-0.03). PCI is overall comparable between the VMAT (0.86+/-0.01) and GK plans (0.84+/-0.02). GI of the GK plans (2.64+/-0.04) is less sensitive to the tumor size and is significantly better than that of the VMAT plans (3.75+/-0.34). In general, VMAT plan GI deteriorates with decrease of tumor size. The GK plans, however, have significantly longer BOT (51.1+/-7.8 min) than the VMAT plans (4.7+/-0.3 min). No significant difference was found in the brain stem or the optical nerve/chiasm maximum dose for the cases in which they were close to the target.
Conclusion
GK plans have “hotter” hotspots but longer treatment times than VMAT plans. For large brain metastasis, the plan quality is comparable between the inversely optimized GK and VMAT plans. For smaller lesions, the sharper dose falloff of the GK plans becomes more advantageous than the VMAT plans.