Purpose: Hippocampal sparing WBRT has proven to mitigate neurocognitive deficit and improve patient quality-of-life (QoL). Herein, we demonstrate the feasibility study of HyperArc VMAT for sparing hippocampi, while delivering WBRT with SIB dose to multiple brain metastases (m-BM).
Methods: Seven patient plans with 2-7 brain lesions were selected and retrospectively re-planned via fully-automated HyperArc module using Encompass support, Q-fix mask, Acuros-based dose engine, and 6MV-FFF (1000MU/min) beam. Brain lesions, hippocampi, and other critical organs were delineated on T1-weighted MRI images and co-registered with planning CT images. Hippocampus avoidance zones (HAZ) were defined as hippocampi plus 5 mm margin and whole brain-PTV defined as whole brain parenchyma minus HAZ and m-BM PTVs. Prescribed dose was 30 Gy to whole brain and 45 Gy to each lesion in 10 fractions. Dose delivery accuracy and efficiency were evaluated.
Results: HyperArc plans demonstrated an average maximum dose to hippocampi of 14.5 Gy; <16 Gy as suggested by NRG-CC001. An average D98% and D2% of 26.7 Gy and 36.5 Gy, respectively, evidenced adequate whole brain-PTV coverage. Average total MUs of 1090 and beam-on time of 3.5 min indicated quick treatment delivery times of <15 min. Average BED10 to m-BM was >71 Gy suggesting a higher BED dose to each m-BM than a therapeutic stereotactic dose of 20 Gy in 1 fraction (60 GyBED10). Portal dosimetry QA yielded pass rates of 99.4% for 2%/2mm gamma index criteria, and within 1% agreement of Monte Carlo calculations independent to planning system, demonstrating accurate treatment delivery.
Conclusion: More accurate patient setup via frameless HyperArc for WBRT with SIB dose to m-BM have shown a fast, safe, and accurate treatment modality by sparing hippocampi and reducing normal tissue toxicity, while escalating BED10 to m-BM in the same RT course–reducing intrafraction motion error, improving patient comfort and compliance, and clinic workflow.
Stereotactic Radiosurgery, Immobilization