Program Information
Evaluation of Plan Metrics Between Cyberknife and Volumetric Arc Therapy (Rapid-Arc) for Multiple Cranial Metastases Radiosurgery
A Koletowo*, R Selvaraj , S Kirkpatrick , S Oliveira , 21st Century Oncology, Deerfield Beach, FL
Presentations
PO-BPC-Exhibit Hall-3 (Saturday, March 18, 2017) Room: Exhibit Hall
Purpose: The purpose of the study is to evaluate treatment planning metrics for multiple brain metastases between Accuray Cyberknife (CK) and Volumetric Arc Therapy (implemented by Varian as Rapid-Arc, RA).
Methods: Twenty one multiple brain metastases patients who were previously planned on our Cyberknife Multiplan TPS v4.6 were selected for this study. These plans were re-optimized using a 4-Arc RA single isocenter technique in Eclipse TPS v11. All target prescriptions were normalized to 18Gy. Each plan was normalized for 100% prescription dose to 95% of the individual target volumes. Dosimetric parameters investigated included target conformity (Radiation Therapy Oncology Group and Paddick conformity indices (CIs), Cyberknife index, Homogeneity Index, Coverage and gradient dose index), dose fall-off (area under the dose-volume histogram curve), as well as normal brain V12Gy, V9Gy, V18Gy volumes. Other parameters analyzed included total monitor units, beam-on and treatment time.
Results: RA has improved plan conformity compared to CK (RTOG Conformity Index RA=1.15, CK=1.19; p=0.004, individual PADDICK Conformity Index RA=0.73, CK=0.79; p=0.002).In addition, RA illustrated significant reduction in median brain dose fall-off (p = 0.006) and normal brain 12Gy isodose volume (p = 0.002).RA and CK were comparable in median body dose falloff (p = 0.065), 9 Gy isodose volume (p =0.070) and gradient dose index (p= 0.257).
Conclusion: RA radiosurgical metrics can be optimized to mimic Cyberknife dose distributions. However, RA with single isocenter 4-Arc plans produced clinically superior conformity, dose fall-off and 12Gy normal brain volume. RA plans produced lower monitor units and significantly reduced beam-on times compared with CK. Based on the improved planning metrics, single-isocenter RA is a suitable alternative to Cyberknife for treating multiple brain metastases.
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