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Breast Imaging

E2761. Imaging of a 3D Bioabsorbable Implant for Radiation Therapy Planning in Breast Lumpectomy Cavities

Horst K1,  Patel A1,  Ikeda D1,  Weiss K2,  Dirbas F.1 1. Stanford University Medical Center, Stanford, CA; 2. Rhode Island Hospital, Brown University, Providence, RI

Address correspondence to A. Patel (Aleema@stanford.edu)

Objective: Lumpectomy followed by radiotherapy is a standard treatment option for women with early-stage breast cancer. Radiotherapy is often delivered to the whole breast followed by a boost to the lumpectomy cavity or, in selected patients suitable for accelerated partial breast irradiation, delivered to the lumpectomy cavity alone plus margin. However, identifying the lumpectomy cavity on CT treatment planning scans can be difficult given that CT may not provide optimal imaging of the cavity in relation to surrounding breast tissue. To facilitate identification of the true lumpectomy cavity margins on CT, a 3D device was developed that can be sutured in the postlumpectomy resection bed to guide radiation therapy planning. The device consists of titanium clips interspaced in a fixed pattern over a helical, spiral, and bioabsorbable scaffolding, which is absorbed by the body over 12 months or more. As there is little information regarding the imaging characteristics of the device in the radiology literature, we report imaging findings on mammography, CT, MRI, and ultrasound in the postoperative period.

Materials and Methods: We reviewed the records of 20 patients undergoing lumpectomy for breast cancer who also underwent surgical suturing of the device in the biopsy cavity for radiotherapy planning. The CT (n = 16), mammograms (n = 5), ultrasounds (n = 4), and MRI (n = 1) studies were reviewed for visibility of clips and the spiral scaffolding, obscuration of diagnostic findings, artifacts, and seromas.

Results: On CT, the device appeared as six bright metallic markers displayed along the spirals of the helical scaffolding either seen en face as bright specks or in a tubular spiral structure within a fluid cavity that was either equal to or larger than the sphere. In each case there was fluid within the sphere. On mammography, the titanium markers were equally spaced in a cross pattern, the helical scaffolding was invisible, and the biopsy site was well visualized for appropriate assessment of residual calcifications or evolving tissue changes. On ultrasound, the clips were echogenic. The bioabsorbable material was seen as either tubular structures along their axis, given moderate seroma surrounding them, or en face, simulating calcifications unless the tubing could be followed on cine ultrasound videos. On MRI, there was a moderate signal void that somewhat obscured the biopsy site.

Conclusion: The 3D device had a unique and typical appearance on CT, mammography, and ultrasound. On mammography, the device did not obscure the biopsy site or evaluation for calcifications. On ultrasound, the helical scaffolding could be mistaken for calcifications unless seen on cine videos or at real-time scanning. On MRI, there was a moderate signal void. Radiologists should be aware of the unique appearances of this new device.