NEW ORLEANSTemplate-based interstitial brachytherapy is an effective method for treating breast cancer, according to a study presented at the 44th Annual Meeting of the American Society for Therapeutic Radiology and Oncology (abstract 147). The study is one of the first to use a template to position interstitial implants in its entire study population as part of its protocol.
"In properly selected patients, accelerated partial breast irradiation via interstitial techniques offers 5-year results comparable to contemporary standard breast conservation therapy with whole breast external beam radiation therapy," said lead investigator Peter Y. Chen, MD, associate director of education, Radiation Oncology, William Beaumont Hospital, Royal Oak, Michigan.
Brachytherapy involves placing multiple catheters or needles into and around the site of the lumpectomy. For low-dose-rate brachytherapy, a number of radioactive sources are then manually afterloaded into the catheters. In contrast, for high-dose rate brachy-therapy, one high-activity iridium-192 source is remotely afterloaded sequentially into each of the needles in a specified amount of time at designated dwell positions to deliver precise doses of radiation.
Conventional placement of the catheters or needles has been freehand guided. A template allows exact geometric placement of the catheters/needles, which improves the physician’s ability to target and control the delivery of radiation to the tumor site. The template holds the breast physically in place and, in conjunction with diagnostic imaging, provides a navigational aid in placing the catheters/needles in the tumor bed. For women receiving high-dose-rate outpatient therapy, the needles remain in place for the 4 to 5 days of twice-daily treatment.
In the study, 199 women with early-stage breast cancer were treated according to one of three protocols of tumor bed irradiation alone: low-dose-rate implant with I-125 as the radiation source treated continuously as an inpatient (50 Gy over 96 hours) (n = 122) or high-dose-rate implant with Ir-192 as the radiation source treated as an outpatient (32 Gy in eight twice-daily fractions or 34 Gy in 10 twice-daily fractions) (n = 77). Every implant was designed to irradiate the lumpectomy cavity plus a 1- to 2-cm margin.
Patients ranged in age from 40 to 90 years (median, 65). Median follow-up on all patients was 5 years (6.3 years for the low-dose-rate patients and 3.1 years for the high-dose-rate patients). A total of 129 patients (65%) have been followed for 4 or more years, 95 (48%) for 5 or more years, and 70 (35%) for 6 or more years.
The study originally included patients with up to three positive lymph nodes, but was revised in 1997 to exclude patients with any positive nodes. Other exclusion criteria included pure ductal carcinoma-in-situ, infiltrating lobular histology, an extensive intraductal component, and significant lobular carcinoma- in-situ, as well as breasts that were technically not suitable for the implant.