L Ma¹*, W Hu², T Nano¹, L Wang³, C Chuang³, (1) University of California, San Francisco, San Francisco, CA, (2) Department of Radiation Oncology, Fudan University Shanghai Cancer Center, Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China (3) Stanford University, Stanford, CA

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  L Ma

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PO-GePV-T-350 (Sunday, 7/25/2021)   [Eastern Time (GMT-4)]

Purpose: Image-guided stereotactic radiosurgery (SRS) is rapidly disseminating worldwide. A robust low-cost and universally accessible QA method is critically needed for its safe implementation and global collaborations. In this study, we developed a low-cost, universal, end-to-end Winton-Lutz method to address such a need.

Methods: After surveying the state-of-the-art SRS phantoms and QA strategies on the market, a simple two-piece detachable plastic film slab was created and specifically implemented for isocentric and off-center Winston-Lutz measurements. The phantom is constructed similar to the OSLD slabs shipped from IROC for Gamma Knife units. To conduct off-center Winston-Lutz testing, the user was instructed to cut a 0.3-mm solder wire into small bits (~ 0.5 mm). These fiducial bits were then randomly taped onto a radiochromic film (~250 cm²). The film was then needle-pricked on its back side at central positions of the taped fiducial bits. The film was then sandwich pressed between the two slabs. Treatment plan was created to deliver a near-spherical dose toward individual fiducials via online imaging guidance. The film and RTDose file were collected and analyzed centrally, a process similar to IROC workflow.

Results: The initial measurements with the method yielded excellent results, showing submillimeter matching in mechanical-vs-radiological isocenters and peripheral isodose lines. Most excitingly, the technique for CBCT-guided trigeminal neuralgia treatments yielded < 0.5 mm isocenter deviation that cemented clinical workflow. Additional benefits of our technique is its low cost and ease of implementation with the consumable cost estimated to be $10.20. Since final dose distribution associated with different phantom constructs was embedded into the DICOM RTDose file, no special restrictions were placed for the film slabs if made locally.

Conclusion: A low-cost, high-functional, end-to-end test procedure is developed and demonstrated for the first time. Implementations of the technique across modalities including carbon machines are underway with results forthcoming.

Keywords

Not Applicable / None Entered.

Taxonomy

TH- Radiation Dose Measurement Devices: Development (new technology and techniques)

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