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Development of a Phantom to Verify Targeting Accuracy of Single-Isocenter Multiple Lesion Stereotactic Radiosurgery

A Murray1*, H Kudrolli2 , L Tirpak3 , T Simon4 , V Mishra5 , (1) Sun Nuclear Corporation, Melbourne, FL, (2) Sun Nuclear Corporation, Melbourne, FL, (3) Sun Nuclear Corporation, Melbourne, FL, (4) Sun Nuclear Corporation, Melbourne, FL, (5) Baptist Hospital, Miami, FL


(Sunday, 7/14/2019) 3:30 PM - 4:00 PM

Room: Exhibit Hall | Forum 4

Purpose: We have developed a phantom and procedure to verify the targeting accuracy of treatment delivery systems (TDS) used for stereotactic radiosurgery (SRS) procedures to treat multiple lesions with a single isocenter. The phantom is designed to be compatible with the StereoPHANᵀᴹ, which is widely used for end-to-end commissioning and quality assurance testing for SRS.

Methods: The phantom is an 8.5 x 8.5 x 12.75 cm³ cuboid with 6 tungsten carbide spheres of 5 +/- 0.025 mm diameters placed on set locations within mechanical tolerance of +/- 0.05 mm. A CT of the phantom was acquired, and the DICOM images were used to cross-check the mechanical locations of the spheres. The phantom was tested on a Varian TrueBeam at a non-clinical facility using the CBCT for alignment. During data acquisition, the multileaf collimator (MLC) was set to 2 × 2 cm field size centered on the target. MV images were captured on an electronic portal imaging device (EPID) for various gantry, collimator, and couch angles. Eight images were acquired for the sphere at the isocenter, followed by the 5 off-center targets. A software analysis tool was developed to compute the offset between the target center and the radiation field center.

Results: Our results indicate a targeting accuracy within 1 mm for off-isocenter targets up to 7 cm of the linac isocenter. These results will be compared with a Varian Edge system at a clinical site. A mathematical matrix deconvolution model is being developed to isolate the source of TDS error.

Conclusion: This phantom is a readily useable off-the-shelf solution and a clinically useful tool for machine daily QA as it provides a simple method to verify targeting accuracy for multiple lesions with single isocenter. Its integration with the SteroPHANᵀᴹ makes it an effective supplemental tool for end-to-end testing for SRS.

Funding Support, Disclosures, and Conflict of Interest: Andy Murray, Haris Kudrolli, Lena Tirpak, and Thomas Simon are employees of Sun Nuclear Corp. Vivek Mishra has no disclosures or conflict of interest


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