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Lessons From Ongoing Clinical Experience With MammoSite Breast Brachytherapy

Lessons From Ongoing Clinical Experience With MammoSite Breast Brachytherapy

DENVER—Accumulating clinical experience with MammoSite breast brachytherapy is supporting its safety, efficacy, and good cosmetic outcomes, while also providing lessons to improve its use, according to a pair of studies presented at the 47th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (ASTRO).

Martin Keisch, MD, medical director of radiation oncology, Cedars Medical Center, Miami, presented updated data from the original cohort trial conducted to obtain Food and Drug Administration approval for the MammoSite device (abstract 10). To be eligible for the trial, patients had to be at least 45 years old; have T1N0 cancers, a lumpectomy cavity size of 3 cm, and no tumor on inked margins; and have undergone their final surgery no more than 10 weeks earlier.

"The critical criteria from a technical perspective included skin-to-balloon distance, balloon-cavity conformance (that is, the surface of the balloon was in contact with the lumpectomy margin), and that the balloon was symmetrical," Dr. Keisch said.

In the trial, 43 patients received brachytherapy (34 Gy given in 10 fractions over 5 treatment days). The balloon was placed at the time of lumpectomy in 25 of these patients and after lumpectomy, as a closed procedure, in 18 patients.

A total of 40 patients agreed to follow-up, and the updated data were obtained at a median follow-up of 48 months (range, 28 to 62 months), Dr. Keisch said. None of the patients have experienced a recurrence. "There is no question that these patients are still within a window where we could anticipate a local recurrence," he acknowledged. "The plan is to follow them out to 10 years."

Cosmetic outcomes have been stable over time, Dr. Keisch said, with excellent to good results noted in 88% of patients in 2004, 84% in 2005, and 80% at this most recent follow-up. "The median skin spacing continues to be significantly different in those patients having a good to excellent cosmetic outcome vs a fair cosmetic outcome. It's really a surrogate for dose," he noted. The proportion of patients with good or excellent cosmesis was significantly higher among those whose skin spacing was 8 mm or greater than among those with skin spacing of 5 to 7 mm (89% vs 58%). In contrast, a variety of other factors (timing of implantation, balloon volume, breast size, receipt of chemotherapy, and age) were not associated with cosmetic outcome.

There have not been any adverse events requiring intervention, Dr. Keisch said. Moreover, none of the patients have developed symptomatic fat necrosis, and only 8% have developed asymptomatic fat necrosis. Moderate proportions of patients have experienced cosmetic complications: focal telangiectasias (40%), localized fibrosis (35%), and localized breast tissue retraction (12%).

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