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Patient Specific Verification System of IMRT/VMAT Using a CCD-Camera and Phosphor-Screen Based TG-142 QA Tool: Raven QA

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M Lee

M Lee*, K Ding**, J Wong**, B Yi* , * Univ. of Maryland School Of Medicine, Baltimore, MD ** Johns Hopkins University, Baltimore, MD


SU-I-GPD-T-224 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: The Raven QA (LAP Laser, Germany) is a device with a phosphor screen detector and CCD for QA’s of tasks of AAPM TG-142. This study reports the patient specific QA (PSQA) results using the Raven system for efficient PSQA.

Methods: Optical scatter component in the RavenQA box is corrected using deconvolution with the 2D spatial invariant, single optical scatter kernel (OSK). We assume that the OSK is a 2D isotropic point spread function with inverse-squared decrease as a function of radius from the center. An image of the maximum field size (25 x 25 cm) square field of the measurement day is used to correct the inhomogeneity of the fluorescent screen and CCD sensitivity. A graphical user interface (GUI) based software was developed to improve the practicality of this system in reading images, evaluating gamma passing rates and reporting the results.

Results: Twelve IMRT (4 head and neck, 4 pelvis, 3 lung, and 1 prostate) and three VMAT (Abdomen, head and neck, prostate) cases have been measured and analyzed. In VMAT test, static gantry setup is used when delivering the treatment beam for feasibility test purposes. Use of a spatially invariant single kernel for deconvolution enhances the computation speed for deriving the 2D dose distribution, less than 3 s. Detector resolution was 1 mm. All IMRT/VMAT cases have passed >95%, 3%/3mm criteria.

Conclusion: An algorithm for IMRT/VMAT verification using the RavenQA has been developed and tested. The single OSK works improves the calculation efficiency; 1 mm detector resolution is the finest resolution among the commercially available IMRT QA devices. It is proved that the RavenQA can be used for the patient specific verification of IMRT/VMAT.

Funding Support, Disclosures, and Conflict of Interest: Dr. John Wong is co-founder of JPLC Associates which licenses RavenQA from JHU This project is supported in part by Maryland Industrial Partnership Program

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