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Dosimetric Comparison Between a Single Isocenter Dynamic Conformal Arc Treatment Technique and the CyberKnife System for Multiple Brain Metastases SRS

J Liu*, L Wang, X Chen, T Lin, C Ma, Fox Chase Cancer Center, Philadelphia, PA

Presentations

PO-GePV-T-399 (Sunday, 7/10/2022)   [Eastern Time (GMT-4)]

ePoster Forums

Purpose: The latest Elements Multiple Brain Mets (MBM) SRS 3.0 (Brainlab, Munich, Germany) supports fast automatic optimization of single-isocenter dynamic conformal arc plans for MBM treatment. This study aimed to conduct dosimetric comparison between the Elements 3.0 and the existing CyberKnife system for MBM SRS treatment planning.

Methods: Five patients previously treated with CyberKnife (Multiplan 5.2) with 24Gy in 3 fractions were replanned with the Elements 3.0. The patients have 3 to 7 PTVs with the target volume ranging from 0.3cc to 14.0cc. Four to seven half arcs with 6MV FFF photon beam (Elekta Versa HD) were used to generate the plans. The collimator angle, couch angle and number of arcs were automatically selected by the optimizer. The plan quality was evaluated based on the inverse Paddick conformity index (CI) and gradient index (GI) per target, as well as the volume of normal brain receiving dose higher than 12Gy (V12), 10Gy (V10), 8Gy (V8) and 6Gy (V6). For CyberKnife plans, the CI and GI per target were recalculated by evaluating the dose in an expansion volume of each target. The size of the expansion was selected between 10mm to 20mm depending on the target size and proximity to other targets.

Results: Among the 19 targets included in CI/GI analysis, the average CI was increased from 1.22 (Multiplan 5.2) to 1.35 (Elements 3.0), while the average GI per target was decreased from 5.25 (Multiplan 5.2) to 3.63 (Elements 3.0). The high dose spillage to normal brain was decreased by Elements 3.0 compared to Multiplan 5.2, with percent change of V12 in (-32.2%, -7.6%), V10 in (-32.3%, -5.5%), V8 in (-35.1%, -3.1%) and V6 in (-35.4%, -6.2%).

Conclusion: This preliminary evaluation study found the Elements 3.0 generated unfavorable target conformity but favorable dose fall-off and dose spillage compared to the CyberKnife Multiplan.

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