Permanent breast seed implants were successfully used as the sole adjuvant radiation technique for early-stage breast cancer, according to Canadian researchers. They reported the first use of the technique, in a series of patients, in the January issue of the International Journal of Radiation Oncology, Biology, Physics.
Current breast radiation methods are time-consuming -- three to seven weeks' worth of treatment -- and also carry significant side effects, such as acute skin reactions. Permanent breast seed implants would be implanted just once, and would deliver a therapeutic radiation dose to the tumor site, with the radiation levels declining to harmless levels over time.
"Therefore, simpler effective treatment delivered over a shorter period of time is required to improve the care of these women," wrote Dr. Jean-Philippe Pignol, Ph.D., and colleagues from Sunnybrook and Women's College Health Sciences Centre at the University of Toronto. "We have developed a permanent breast 103-Pd seed implant (PBSI) technique administered under neuroleptanalgesia in a single one-hour session" (IJROBP, January 2006, Vol. 64:1, pp. 176-181).
For this study 16 women over the age of 40 were enrolled. All were diagnosed with an infiltrating ductal carcinoma of less than 3 cm with surgical margins of 2 mm or more. The treatment plan included breast ultrasound to localize and measure the size of the surgical bed, as well as measure the distance to the skin surface.
CT simulation helped determine clinical target volume (CTV) and planned target volume (PTV). A dose of 90 Gy was the minimal peripheral dose to cover PTV. A 17-gauge fiducial brachytherapy needle was used for seed implantation. This device facilitates accurate seed placement, according to the authors.
A CT scan was done two months after the procedure to evaluate end-of-treatment dose distributions. Patients recorded their pain levels before and after the procedure, and answered a satisfaction questionnaire.
According to the results, the average CTV was 8.0 cc and the average PTV was 31.7 cc. The latter "is much smaller compared to PTV volumes in other partial breast irradiation series," the authors stated.
On average, 70 seeds were used per patient, with a seed strength ranging from 1.59 U to 2.59 U. The V100 (relative volume receiving 100% of the prescribed dose) significantly improved over time, coming in at 74% for the first eight patients and climbing to 87% for the remainder. The authors stated that this demonstrated an operator learning curve phenomenon. In addition, the V100 and the V200 (relative volume receiving 200% of the prescribed dose) increased between CT scans, indicating that the seeds came closer together with time.
So far, none of the patients have evidence of their cancer returning, and the researchers report that acute skin irritation is six times less frequent when compared to external beam radiation.
In terms of pain, 56% of the patients reported pain during the procedure. One week later, 37% claimed minimal pain while 31.5% experienced moderate to significant pain. Asymptomatic hardening of the implantation site occurred in 62.5% of the women, although complete healing occurred at two months.
The authors acknowledged that pain may be a limiting factor with PBSI, but pointed out that 57% of the patients reported being very satisfied with the procedure. Also, women with larger seromas (where seeds could float freely inside the cavity) and larger tumor size (exceeding the template grid) may not be eligible for PBSI.
However, "this technique represents an ultimate step in reducing radiation treatment burden (and) in reducing dose delivered to the skin," the authors wrote. Another major advantage is that patients are discharged the same day as the procedure, returning to a relatively normal life.
By Shalmali Pal
AuntMinnie.com staff writer
January 5, 2006
Related Reading
Distance from radiation therapy facility affects breast cancer treatment, November 29, 2005
Breast MR helps refine partial-breast irradiation, October 19, 2005
Gamma detector proves less invasive, more accurate for seed migration, June 15, 2005
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