Room: ePoster Forums
Purpose: Due to the neurocognitive side effects associated with whole brain radiotherapy (WBRT), stereotactic radiosurgery (SRS) is increasingly being used for patients with multiple (>4) brain metastases. Gamma Knife (GK) is considered by many the gold standard; however, advances in linac-based delivery have enabled this technology to evolve as a potential alternative to lengthy GK treatments. Still, there are questions as to which technology is optimal, both in terms of quality and the tradeoff with efficiency. This study is a continuation of previous work by our group to assess the plan quality of linac-based SRS versus GK in the treatment of multiple brain metastases.
Methods: Thirty volumetric-modulated arc therapy (VMAT) and 30 GK treatments were planned on a CT/MRI dataset from a patient previously treated with WBRT. Thirty brain metastases were identified on a T1-weighted MR image. The metastases were randomly ordered, and plans were created for 5, 10, 15, 20, 25, and 30 metastases. Additionally, uniform volume expansions of 0-4mm were applied to the targets. Total target volume ranged from 0.33-46.92cc. Treatments were planned using Eclipse(v11), standardized to 4 arcs, and GammaPlan. Plan quality was assessed based on Paddick conformity, V5Gy, V12Gy, and integral dose to the brain.
Results: V5Gy is lower in GK due to the rapid dose falloff inherent to the modality; conformity is superior using VMAT across all plans. While GK is superior to VMAT for small/few target volumes, this superiority diminishes as the number/volume of targets increases. For larger/many target volumes, V12Gy and integral dose becomes comparable in the two modalities.
Conclusion: VMAT should be considered as an appropriate treatment option depending on both the number of brain metastases and the total target volume. This study hopes to aid the physician and physicist in their determination of a balance between plan quality and treatment efficiency.