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Localization Accuracy of a Novel Prone Breast Stereotactic Immobilization and Localization System

Y Mutaf

Y Mutaf1*, C Yu1,2, E Nichols1, B Yi1, K Prado1, W D'Souza1, W Regine1, S Feigenberg1, (1) University of Maryland School of Medicine, Baltimore, MD, (2) Xcision Medical Systems Inc, Columbia, MD

SU-C-103-2 Sunday 1:00PM - 1:55PM Room: 103

Purpose: The GammaPodTM stereotactic radiotherapy device incorporates a novel stereotactic immobilization system and a fiducial based localization frame for the breast. We present the localization accuracy achieved with this stereotactic system through an IRB approved prospective protocol.

Methods: GammaPodTM target localization is achieved using a dual layered immobilization breast cup under a negative pressure which has a built-in stereotactic frame. Patient CT scans were attained using a pivoted patient loader which automatically lowers the patient from a vertical position to a horizontal prone-lying position. We then performed two CT scans 30 minutes apart, simulating the pre-treatment imaging and treatment sessions. The patient is disconnected from the patient loader after the first scan, but the immobilization cup remains on the breast under 150 mmHg of negative pressure until the end of the second scan. Evaluation of target localization was carried out via previously implanted surgical clips (two to five) and superficially positioned markers (three to seven). Scans were performed with 1 mm CT slice thickness.

Results: The first 9 patients' results are presented with a total of 25 patients expected. Two patients were excluded due to improper fitting of the breast cup and patient comfort; one patient was excluded due to loss of breast cup pressure between the two scans. In the remaining six patients, the spatial reproducibility of internal markers was found to be 1.2 ± 1.0 mm (range 0.3-3.7) in between the two scans while the external marker positions differed by 0.9 ± 0.9 mm (range 0.1-3.9). The intrinsic accuracy of the stereotactic localization system found to be 0.1 ± 0.1 mm.

Conclusion: The GammaPodTM target localization system is a unique approach to breast immobilization employing stereotactic principles. Preliminary results of this study suggest that the overall localization uncertainty of this system is 2.8 mm (95% CL).

Funding Support, Disclosures, and Conflict of Interest: C. Yu and W. Regine have financial interests in Xcision Medical Systems.

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