Program Information

Patient-Specific Quality Control Workflow for Dedicated SBRT Vero System

M Mamalui-Hunter*, J Wu, H Chen, Z Su, University of Florida, Jacksonville, FL

SU-E-P-19 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose/Objectives: To set up patient specific quality control (QC) process that ensures the integrity, deliverability and accurate dose for the SBRT lung plan.
Materials/Methods: In 11/2012, SBRT Vero system (C-band 6MV linac on gimbals, mounted on a rotating (+/- 60 degree) ring) was commissioned at our facility. The gimbals allow pan/tilt of the linac to mechanically account for gantry sag during gantry rotation, and track the motion of the target by moving the axis of the treatment beam. The linac is equipped with 0.5 mm (at isocenter) MLC. The treatment planning system (BrainLab iPlanTM) has the following algorithms available: Pencil Beam, Monte-Carlo (Dose-to-water and Dose-to-Medium options). For the treated 37 targets (15 patients), 24 were located in lung. Monte-Carlo (dose-to-water) algorithm was used, as it best corresponded to the film/ion chamber commissioning dosimetry. Quality assurance (QA) for lung targets utilizes 0.01cc ion chamber measurements in CIRSTM heterogeneous lung motion phantom with a range of small targets available. Per institutional policy, point dose from the patient plan mapped onto the phantom is compared to measured dose in the same heterogeneous phantom in static configuration. Additionally, the same QC process was repeated using 3D sinusoidally moving target with the amplitudes similar or exceeding the results of patient-specific target motion evaluation performed for each 4DCT patient at UFPTI.
A range of planning geometries was used and QC-verified: ring angles within ±15degrees and fields 2.5-5.0cm diameter.
Results and Conclusions: The measured dose was within 2.5% from the Monte Carlo calculation, with 1.2 % average difference between plan and measurement in the static case, and within 3% with average 1.6% and 1% SD for dynamic case.
The agreement was satisfactory and ensured the integrity of the treatment planning and delivery process

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