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Fiducial Properties of a 3-Dimensional Bioabsorbable Tissue Marker in Treatment Planning for Breast Cancer

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J Simpson

J Simpson1*, B Benjamin1, S Jones2, J Ross3, (1) Auckland Radiation Oncology, Auckland, New Zealand, (2) Northwest Arkansas Radiation, Fayetteville, AR, (4) Highlands Oncology Group, Fayetteville, AR

WE-G-WAB-8 Wednesday 4:30PM - 6:00PM Room: Wabash Ballroom

Purpose: Improvements in surgical techniques have increased the adoption of breast conservation. However, clearly defining the target volume as well as improving target positioning for the breast remains challenging, thus requiring large treatment margins to insure proper coverage of the target. To better define margin requirements, we evaluated the utility of a novel 3-D implantable, bioabsorbable tissue marker using multiple types of external beam treatment planning for breast cancer.

Methods: The BioZorbTM tissue marker (a 3-dimensional bioabsorbable carrier with embedded titanium markers) was implanted into the lumpectomy cavities of 28 breast cancer patients at the time of surgery. Multiple treatment plans (WBI + boost, IMRT, coplanar/non-coplanar VMAT, 3D-CRT) were prepared and compared.

Results: In all cases, the tissue marker was easily seen on all forms of clinical imaging including mammography, ultrasound, CT, 4D-CT, cone beam CT and MRI. Utilizing standard CT simulation software, the marker provided a clear region for target delineation/construction as well as positioning using EPID and CBCT. 3-D target excursions, due to respiration, were easily quantified on 4D-CT: superior-inferior, <4 mm; anterior-posterior, <3 mm; medial-lateral <1 mm (mean values). Fusion of beams-eye DRRs with EPID images allowed accurate positioning (uncertainty <1.5mm) for APBI (VMAT, 3D-CRT) and boost deliveries. When compared to conventional methods for determining treatment volumes, use of the marker significantly reduced PTVs, and in some cases made it possible to utilize accelerated protocols for treatment. On-board imaging (EPID, and MV/KV CBCT) provided reproducible patient positioning for both partial breast and boost techniques.

Conclusion: The utility of this 3-D, bioabsorbable tissue marker was confirmed when placed into the lumpectomy site during surgery. The marker was consistently visualized, improved the objectivity of target definition for treatment planning and provided unambiguous fiducials for use with IGRT techniques in the treatment of breast cancer.

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