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Dosimetric Comparison Between Single Isocenter Brain Metastases Treatment Using Dynamic Conformal Arcs (Elements) and VMAT (RapidARC)

C Venencia

C Venencia1*, R Morais Cardozo2 , M Almada1 , G Rivelli1 , E Garrigo1 , P Castro Pena1 , (1) Instituto de Radioterapia - Fundacion Marie Curie, Cordoba, ARGENTINA ,(2) Brainlab, Sao Pablo, BRAZIL


SU-I-GPD-T-614 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: Several studies indicate that SRS is an effective treatment option for patients with numerous metastases. Single-isocenter dynamic conformal arcs (Elements, BrainLAB) and volumetric modulated arc therapy (RapidARC, VARIAN) are proven techniques where high conformal dose distribution could be obtained and treatment time could be within 20min. The objective of this study was to make a dosimetric comparison between Elements and RapidARC using 3D calculated and experimental dose distribution.

Methods: A patient with 10 brain metastases was selected. A 6MV beam from a Novalis TX equipped with a HDMLC was used. Using Element a plan was created using 5 non-coplanar incidences. RapidARC plan was generated using 4-arcs according to published technique. Dose plans were identically normalized. Plans were compared in Eclipse v13.6 using MU, delivery time (DT), conformity index (RCI and PCI), homogeneity index (HI), fall-off (GI) and peripheral dose (V100%, V50%, V25% and V10%). Patient specific quality controls were performed using DELTA4 (ScandiDos) without couch rotation (2%/2mm) and absolute dose measurement. The CT of the patient was sent to RTSafe and two identical copies of the patient were created with a 3D printer and filled with a polymer gel dosimeter material. Phantoms were irradiated using both treatment modalities and MRI scans were acquired. DICOM doses, plans, structures and MRI studies were sent to RTSafe for comparison.

Results: The average volume of the PTVs was 0.5cc [0.11, 1.16]. The Elements (RapidARC) plan achieved total MU=4534 (5749), DT=15’40’’ (13’54’’), average RCI=1.45 (1.69), average PCI=0.64 (0.56), average HI=1.21 (1.43), GI=5.53 (11.3), V100%=7.2 (8.9), V50%=39.6 (100.5), V25%=272.8 (601.8) and V10%=1103 (1925). QA plans were within tolerance. Comparison of calculated dose with gel dosimetry by 1D and 2D gamma analysis (2mm/5%) showed perfect agreement.

Conclusion: Plan’s quality and delivery time are comparable. Elements produced a simpler plan with lower peripheral dose spread.

Funding Support, Disclosures, and Conflict of Interest: Brainlab

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