Analysis of Treatment Efficacy, Cosmesis, and Toxicity Using the MammoSite Breast Brachytherapy Catheter to Deliver Accelerated Partial-Breast Irradiation: The William Beaumont Hospital Experience

Current status of accelerated partial breast irradiation

Accelerated partial breast irradiation (APBI) is a radiotherapy method used in breast-conserving therapy. In APBI, the tumor bed is topically irradiated over a short period after breast-conserving surgery. The fundamental concept underlying APBI is that more than 70% of ipsilateral breast tumor recurrence occurs in the neighborhood of the original tumor, and that hypofractionated radiotherapy can be applied safely when the irradiated volume is small enough. It is expected to reduce the time and cost required for conventional whole breast irradiation while maintaining equivalent local control. Several techniques including multicatheter interstitial brachytherapy, intracavitary brachytherapy, intraoperative radiation therapy, and 3D conformal external beam radiation therapy have been proposed, and each of them has its own advantages and drawbacks. Although APBI is increasingly used in the United States and Europe, and the short-term results are promising, its equivalence with whole breast radiation therapy is not fully established. In addition, because the average breast size in Japan is considerably smaller than in the West world, the application of APBI to Japanese patients is technically more challenging. At this point, APBI is still an investigational treatment in Japan, and the optimal method of radiation delivery as well as its long-term efficacy and safety should be clarified in clinical trials.

Characterisation of 6MV and 10MV superficial build up dosimetry in tangential beam radiography

Introduction: Although tangential radiotherapy is one of the major treatments for breast cancer, little has been done to address the skin toxicity and general dose inhomogeneity experienced in patients with larger breasts that are treated with 6MV photons. From our understanding of radiation in tissue at depth, it is proposed that 10MV photons could have a clear role in such patients through improved dose distribution. However, a greater build up depth with 10MV could mean that this energy is unacceptable.

Aims: To quantify and characterise superficial build up dosimetry in tangential breast irradiation for 6MV and 10MV photons.

Methods: Using Thermoluminescent Dosimeters (TLD’S), a comparative study was carried out investigating dose at a range of superficial depths in a phantom irradiated by tangential fields. Each delivering 2Gy for 6MV and 10MV photons.

Results: There was a 0.10Gy difference in maximum dose over a depth of 10.8 mm between 6MV and 10MV photons, along with an average difference of dose at depth of 0.09Gy.

Conclusion: Evidence has been obtained that eliminates comprise to superficial tissue if 10MV photons are used. Furthermore, reinforcement towards a more homogenous dose distribution with 10MV photons has been established.

Five-year results: the initial clinical trial of MammoSite balloon brachytherapy for partial breast irradiation in early-stage breast cancer

OBJECTIVE

Patients with early-stage invasive ductal breast cancer were prospectively evaluated using MammoSite RTS balloon brachytherapy (RTS Cytyc Corp, Marlborough, MA) as the sole modality for delivering accelerated partial breast irradiation to the lumpectomy bed with breast-conserving surgery. This report presents the 5-year results of the treated patients.

METHODS

From May 2000 to October 2001, 70 patients were enrolled in this prospective study. Forty-three patients completed accelerated partial breast irradiation with MammoSite brachytherapy following lumpectomy and axillary staging. Thirty-six patients have been followed for a median of 5.5 years (mean 65.2 months). Criteria for entry into the study were unifocal invasive ductal carcinoma, tumor size < or = 2 cm, age > or = 45 years, absence of extensive intraductal component, cavity size > or = 3 cm in 1 dimension, node-negative, and final margins negative per National Surgical Adjuvant Breast and Bowel Project definition. A minimum balloon-to-skin surface distance of 5 mm was required. A dose of 34 Gy was delivered in 10 fractions over 5 days prescribed to 1 cm from the applicator surface using iridium-192 high-dose-rate brachytherapy. Data on infection, seromas, cosmetic outcome, and toxicities were collected at 3 and 6 months and at yearly intervals. Local recurrences, both true recurrences in the lumpectomy bed and failures outside the initially treated target volume (elsewhere failures), were recorded. Contralateral breast failure rates were noted.

RESULTS

The catheter was not implanted in 16 of the 70 enrolled patients due to cavity size not amenable to balloon placement (n = 10), ineligible by criteria (n = 4), and skin spacing (n = 2). Fifty-four patients were implanted and 43 were successfully treated with MammoSite balloon brachytherapy. Reasons for catheter explantation in 11 patients were poor cavity conformance in 7, inadequate skin spacing in 2, positive node in 1 and age less than 45 years in 1. Of the 43 patients who completed treatment, the infection rate was 9.3%. Seroma formation occurred in 32.6% of patients, of which 12% were symptomatic requiring aspiration. Asymptomatic fat necrosis was identified in 4 of the 43 patients, noted from time of catheter removal at 11, 14, 42, and 63 months. Good-excellent cosmetic outcomes were achieved in 83.3% of the 36 patients with more than 5 years of follow-up. Cosmetic outcomes were improved, with increased skin spacing having statistical significance at skin spacing > or = 7 mm. The only serious adverse events were 2 infections: mastitis and abscess. Seven of the 43 treated patients have been discontinued from follow-up. None had a local recurrence recorded at last visit. Reasons for exit from the study were death from metastatic disease (n = 3), lost to follow-up (n = 2), and placed in hospice for other medical conditions (n = 2). No local recurrences (either at the tumor bed or elsewhere in the breast) or regional recurrences have occurred in the 36 patients who have been followed for a median of 5.5 years. No contralateral cancers have developed.

CONCLUSIONS

MammoSite balloon brachytherapy as a sole modality for delivering radiation to the tumor bed has been successful in achieving excellent local control in this initial clinical study of patients with early-stage invasive ductal breast cancer. This has been achieved with minimal toxicities and good-excellent cosmetic outcomes in 83.3%. Accelerated partial breast irradiation using the MammoSite balloon in a carefully selected group of patients has demonstrated 5-year local recurrence results comparable to those achieved with conventional whole breast radiation therapy and interstitial catheter brachytherapy as reported at 5-year data points in studies of these treatment modalities. Poor cavity conformance and inadequate skin distance were the main factors limiting use of the MammoSite device. Extended follow-up will be required to determine the long-term efficacy of this treatment modality.