Room: Exhibit Hall
Purpose: Due to the neurocognitive side effects associated with whole brain radiotherapy (WBRT), stereotactic radiotherapy (SRT) is increasingly being used for patients with multiple (>4) brain metastases. Gamma Knife (GK) is considered the reference standard; however, advances in linac-based delivery have enabled this technology to evolve as a potential alternative to lengthy GK treatments. More recently, volumetric-modulated arc therapy and flattening filter-free designs have resulted in fast delivery while maintaining radiosurgical precision. Still, there are major questions as to which technology is optimal, both in terms of quality and the tradeoff with efficiency. Thus, we conducted this study to assess the limits and quality of linac-based SRS with multiple arcs vs. GK in treating a variable number of brain metastases.
Methods: A patient initially referred to GK, later identified with 30 brain metastases, and ultimately treated with WBRT, was used for this work. All metastases were identified and contoured on a T1 weighted MR image and registered to the planning CT. Volumes ranged from <0.1cmÂ³ to 0.8cmÂ³. Six plans (5, 10, 15, 20, 25, and 30 metastases) were generated using Gamma Plan and Eclipse (3-5 arcs). Plan quality was assessed using Paddick and RTOG conformity indices, V5, V12, and integral dose to the whole brain.
Results: Despite similar target dose coverage, the dose to normal brain was strongly dependent on modality. The integral dose to the whole brain and V12 were substantially lower in GK plans, especially when treating a larger number of lesions. A nonlinear increase in dose to normal brain volumes with increasing number of targets was also observed.
Conclusion: Normal brain dose is strongly dependent on the stereotactic radiotherapy platform utilized. Future work designed to assess the dependence on the number of lesions, size of lesions, and planning techniques (such as multiple isocenters) are under investigation.