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From Virginia Commonwealth University (DWA), Richmond, Virginia; and William Beaumont Hospital (FAV), Royal Oak, Michigan.
Correspondence: Address correspondence to: Douglas W. Arthur, MD, Department of Radiation Oncology, Virginia Commonwealth University Health System, 401 College Street, Richmond, Virginia 23298; Fax: (804) 828-6042; e-mail: dwarthur{at}hsc.vcu.edu
Several decades ago we experienced the initiation of a change in the local treatment paradigm for early stage breast cancer, from mastectomy to a breast-conservative approach comprising lumpectomy followed by whole-breast adjuvant radiotherapy. The treatment approach was not immediately accepted in 1990 when the National Cancer Institute Consensus stated breast conservation therapy to be the treatment of preference1 but rather was adopted at varying pace across the country. Breast conservation continues to be underutilized, in part because of logistical barriers of time and travel.2
Over the past decade, the use of accelerated partial breast irradiation (APBI) has been the focus of study as a possible treatment approach that may help overcome these barriers and provide an alternative method of treatment and a means of improving the rate of breast conservation. APBI now represents another change in the treatment paradigm, as we challenge the historical whole-breast treatment approach and suggest that partial-breast treatment is equivalent. In the United States, multicatheter interstitial brachytherapy was the original treatment method used for delivering APBI. Historically, multicatheter brachytherapy has been heavily dependent on operator experience, with significant variability in target coverage, homogeneity, and overall outcome. Although image-guided techniques have been developed, a learning curve and degree of variability remain.
The MammoSite Radiation Therapy System (RTS), developed by Proxima Therapeutics, Inc. (Alpharetta, Georgia), is a balloon treatment device that was designed to simplify the brachytherapy procedure, while improving the reproducibility of the radiation dosimetry. The research and development of this device have focused on the ability to reproduce the target coverage and dosimetry achieved with published multicatheter brachytherapy techniques.3 With an estimated 4000 devices placed since the time of U.S. Food and Drug Administration (FDA) approval in May 2002, the MammoSite RTS has quickly become the most prevalent method of delivering APBI in the United States.
In this issue of the Annals of Surgical Oncology, Richards et al. present their initial experience with the MammoSite RTS and evaluate the acute toxicities encountered.4 Applying conservative selection criteria, they selected 31 patients with 32 breast cancers for protocol treatment with the MammoSite RTS. Twenty-seven of the 31 patients had the device successfully placed and judged appropriate for treatment. Although actual treatment was tolerated well, with no acute toxicity, the authors report a subsequent 25% rate of bright erythema and patchy moist desquamation and a 7% rate (two patients) of confluent moist desquamation involving the skin immediately over the balloon.
Although the rate of skin toxicity appears high, they report that all skin toxicity resolved, and with a median follow-up of 11 months, cosmesis was rated as good to excellent in 86% of cases. They were unable to demonstrate a correlation between skin distance and skin toxicity, but acknowledging the obvious relationship between skin distance and skin dose, they have altered their protocol to maintain a distance of 
7 mm. An interesting finding was an unexpectedly high rate of infection (16%), and as a result they have initiated the use of intravenous antibiotics at the time of implantation and the use of prophylactic oral antibiotics during treatment.
As the enthusiasm for APBI continues to build, it is imperative that we continue to accurately and honestly report our treatment experiences, as these authors have done, so that we propagate a thorough understanding of this new treatment approach. Just as successful implantation of the MammoSite RTS and the subsequent safe delivery of treatment rely on coordination and communication between the surgeon, radiation oncologist, and physicist, it is also necessary to have a common knowledge of the basic physics and quality assurance aspects of treatment with this device so that we can appropriately evaluate these reported treatment experiences.
Albert Einstein said, "Everything should be made as simple as possible, but not simpler." Although the MammoSite RTS has simplified the process as compared with interstitial multicatheter brachytherapy, it is more complicated than inflating the balloon and having the computer insert the radioactive source. Without proper understanding of and respect for the intense doses delivered over a short time, significant complications could result.
There are four important principles that cannot be overlooked and should be discussed when presenting any treatment experience involving the MammoSite RTS. These parameters are important to determine appropriateness for treatment and to ensure that the treatment is delivered accurately. The initial three parameters are well known to those using the device. One must confirm conformance of the lumpectomy cavity with balloon surface, symmetry of the balloon and central catheter, and ensure the balloon surface to skin distance is at least 5 mm, preferably >7 mm. Computed tomographic evaluation of these parameters and dosimetric planning are the only reliable ways to ensure compliance with these requirements prior to treatment. The dose is then commonly delivered from a single central dwell position of the radioactive source and prescribed at a 1-cm radial distance from the balloon surface. This results in a dose delivery pattern that treats at least 90% of the intended target with at least 90% of the treatment dose and limits the amount of breast tissue on the surface of the balloon that receives doses that far exceed the prescribed dose.
When the patient’s anatomy and catheter placement are ideal, these guidelines yield appropriate target coverage and limited toxicity; however, if not ideal, then the application requires a more complicated planning approach. Multiple dwell positions may improve the shape of the isodose surface, leading to improved target coverage, and alteration of the catheter axis orientation as well as the location and number of dwell positions may provide the tools to decrease the skin dose in warranted situations.5 However, reporting of dose volume histogram analysis—a fourth important parameter—then becomes essential to the ability to evaluate the appropriateness of target coverage, dose homogeneity, and dose received by the skin in these situations. Additionally, it should be stated that the proper balloon inflation should be confirmed with fluoroscopy or ultrasound prior to each treatment and that the patient’s position for planning should be reproduced for each treatment to ensure that the intended dose distribution is delivered at each treatment session.
Presently, the American Society of Breast Surgeons is managing a registry study, as mentioned by the authors, and it is about to meet the accrual goal of 1500 patients treated by APBI with the MammoSite RTS as the sole method of adjuvant radiotherapy, following lumpectomy, for early stage breast cancer. This study will represent the largest group of patients treated with APBI to date, and both treatment and follow-up data have been collected for study. Until long-term follow-up data are available from projects such as the MammoSite registry study and the national phase III study, presently in joint development by the National Surgical Adjuvant Breast and Bowl Project and Radiation Therapy Oncology Group, it is important to continue to present treatment experiences with direct and objective assessments of the data, as exemplified in the article by Richards et al.
Received for publication June 9, 2004. Accepted for publication June 18, 2004.
REFERENCES
This article has been cited by other articles:
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  J. S. Jeruss, F. A. Vicini, P. D. Beitsch, B. G. Haffty, C. A. Quiet, V. J. Zannis, A. J. Keleher, D. M. Garcia, H. C. Snider, M. A. Gittleman, et al. Initial Outcomes for Patients Treated on the American Society of Breast Surgeons MammoSite Clinical Trial for Ductal Carcinoma-In-Situ of the Breast Ann. Surg. Oncol., July 1, 2006; 13(7): 967 - 976. [Abstract] [Full Text] [PDF]
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 D. W. Arthur and F. A. Vicini Accelerated Partial Breast Irradiation As a Part of Breast Conservation Therapy J. Clin. Oncol., March 10, 2005; 23(8): 1726 - 1735. [Full Text] [PDF]
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