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A Comparison Between Cyberknife-Based and LINAC-Based Fiducial-Less Stereotactic Body Radiotherapy of Lung Lesions Without Respiratory Gating Or Tracking

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Z Wang

M Monterroso, Z Wang*, D Arsenault, W Amestoy, Univ Miami, Miami, FL

SU-E-T-434 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To benchmark the tracking accuracy of Accuray Cyberknife (CK) newly released Lung Optimized Treatment (LOT) tracking algorithm in 0-View mode and investigate the dosimetric differences of lung Stereotactic Body Radiotherapy (SBRT) based on internal target volume (ITV) using Cyberknife and LINAC.

Methods: CT scans at normal inspiration and normal expiration of CIRIS thorax motion phantom were fused and an ITV was created. A 5mm expansion around the ITV resulted in the planning target volume (PTV). Two individual plans were generated in Accuray MultiPlan using LOT 0-View technique, with two tracking distances (3.9cm and 7.1cm) from the target. Kodak EBT Gafchromic film, carefully marked to identify the target volume, was inserted in the moving target of the phantom during delivery. H-D calibration of the film was performed for absolute dosimetry purposes. An in-house program processed the scanned films after delivery to perform a dosimetric comparison between plan and treatment and verify tracking accuracy. Also, a LINAC-based plan (Eclipse) and CK-based plan (Multiplan) for the same PTV were generated to compare the two systems in the planning stage.

Results: The film dosimetric results indicate that LOT algorithm in 0-View mode is accurate. Good target coverage was achieved in both CK-based and LINAC-based plans: 96% and 98%, respectively. Critical structure doses for CK-based and LINAC-based plans, respectively, were: total lung V20/V5 9.2%/37.3% and 7.5%/21.1%, and maximum cord dose 9.8Gy and 11.14Gy.

Conclusion: Current results show LINAC-based plans are superior to CK-based plans, achieving lower lung integral dose with minor differences in cord dose and target coverage, and having added advantages of faster delivery and confidence during setup with lesion visualization using cone beam CT (CBCT). More work will be done to examine if CK-based plans are advantageous when treating more complex cases, when no fiducial placement and no respiratory tracking is desired.

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