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Accelerated Partial Breast Irradiation: A Promising Adjuvant to LumpectomyBy Maude Veech Lumpectomy offers patients with localized breast cancers a potentially curative option that spares most of their healthy breast tissue. The surgery is usually followed by adjuvant whole-breast radiation therapy for up to 6 weeks, which minimizes the risk of recurrence but increases the inconvenience and physical toll of treatment. Increasingly, however, researchers are starting to imagine a world in which selected lumpectomy patients do not have to undergo 6 weeks of radiation therapy. Accelerated partial breast irradiation (APBI) is a relatively new therapeutic approach gaining fans among patients and (cautiously) radiation oncologists. At The University of Texas M. D. Anderson Cancer Center, APBI is performed via brachytherapy, in which the radiation source is placed using a catheter, or with radiation beams conformally shaped around the tumor bed. In addition to lasting just 5 days, APBI treatments may prove to have fewer treatment side effects. Exposing less of the healthy breast, lung, and rib cage to radiation is the ultimate goal, and ongoing studies are seeking to determine if decreasing the irradiated volume does decrease the risk and severity of radiation toxicity. Still, the question remains: Does APBI brachytherapy prevent recurrence as effectively as whole-breast irradiation (WBI), which has a success rate of approximately 95%? Elizabeth Bloom, M.D., an associate professor in the Division of Radiation Oncology, is among the M. D. Anderson oncologists trying to answer that question. She has been offering patients APBI brachytherapy at the institution’s Bellaire Radiation Treatment Center since August 2008. “We show patients videos explaining both WBI and APBI, and we go through the data with them,” Dr. Bloom said. “We are very up-front about the fact that no 15- to 20-year efficacy data are available for APBI, as there are for WBI.” Yet, she finds many patients jump at the opportunity to try a procedure that is less lengthy than WBI and exposes them to less radiation. “To me, it is surprising that, even though we are quite clear on the lack of long-term data compared to WBI, it does not faze them. But so far, the data look good,” said Dr. Bloom, noting that APBI brachytherapy data gleaned over the past 10 years on outcomes and toxicity profiles are encouraging. Different methods of administration Brachytherapy requires great skill and more time of the radiation oncologist than does WBI. According to National Research Council guidelines, patients have to have brachytherapy treatments twice a day. “My office is right down the hallway from the machine,” said Dr. Bloom, noting that this allows her to efficiently treat several patients with brachytherapy on any given day. Patients who wish to receive APBI at the main M. D. Anderson campus can also explore the possibility with any of the seven breast cancer radiation oncology faculty who practice there. Though APBI brachytherapy is relatively new, the catheters used in the procedure are already in their third generation. Originally, in a procedure known as interstitial brachytherapy, multiple catheters were inserted separately to surround the tumor cavity. “This is the type of brachytherapy about which we have the most data,” said Dr. Bloom. “It requires a very skilled radiation oncologist and involves 15 to 20 catheters.” However, interstitial brachytherapy for breast cancer has largely been superseded by the less-invasive MammoSite (Cytyc, Marlborough, MA), which is the method offered at M. D. Anderson’s Bellaire clinic. MammoSite uses only one catheter with a collapsible balloon on the end. Once inside the breast, the balloon is expanded inside the lumpectomy cavity with a saline-contrast mixture. A central catheter within the balloon serves as a conduit for the targeted radiation source, an iridium-192 high-dose-rate seed. Sophisticated computer planning using imaging allows specialists to define the seed positions and treatment times, which are calculated to deliver the prescribed dose to the lumpectomy cavity and margin while minimizing exposure to normal structures. Treatment is generally delivered over 5 to 10 minutes twice a day. While the balloon catheter remains in place for the duration of the treatment sessions, the iridium seed is removed from the catheter after each session.
This single-catheter technique for APBI brachytherapy does have limitations. Sometimes the balloon is too close to the skin (it needs to be at least 5 mm away) or conforms poorly to the lumpectomy cavity. Newer “hybrid” catheters (which essentially combine the single- and multiple-catheter approaches) may allow more patients to be candidates for APBI brachytherapy by addressing those limitations. “Even though we currently offer only MammoSite, hybrid catheters open even more options for APBI, and we hope to use them as indicated in the future,” Dr. Bloom said. Clinical studies available Many of Dr. Bloom’s brachytherapy patients are participating in DR08-0535, a prospective data collection study that aims to assess acute and late normal tissue sequelae in patients who receive APBI. To qualify, patients must be at least 50 years old, have invasive ductal carcinoma or ductal carcinoma in situ, have disease-free surgical margins after lumpectomy, and have no lymph node involvement. Information is collected about long-term cosmesis and acute and late toxicities following APBI delivered via various techniques—in part to compare MammoSite with hybrid catheters. Most of the women enrolled so far have tumors that are estrogen receptor (ER) positive, which means they are more likely to be treated with hormonal therapy than chemotherapy and generally have a better prognosis. Also available is the Radiation Therapy Oncology Group study RTOG 0413, which randomly assigns patients to receive either WBI or APBI after lumpectomy and surgical axillary evaluation. The trial is currently open to higher-risk patients (those younger than 50 years old or those who have node-positive disease or invasive breast cancer that is ER and progesterone receptor negative). Promising data lead to further investigation Nonrandomized, single-center studies over the past 5 to 8 years appear to have shown a low rate of in-breast cancer recurrence in lumpectomy patients after APBI brachytherapy. “A lot of women like that it is a targeted, shorter treatment with the potential for less long-term toxicity,” Dr. Bloom said. Higher-risk patients usually receive chemotherapy after a lumpectomy. “One advantage of brachytherapy is that, unlike WBI, it can be done before chemotherapy, so we don’t have to delay radiation therapy 4 to 6 months for chemotherapy,” added Dr. Bloom. As the randomized Radiation Therapy Oncology Group study is no longer available to low-risk patients, some patients may be offered APBI brachytherapy off-protocol. Many oncologists believe it is safe to offer APBI off-protocol to patients who meet certain criteria. The American Society of Breast Surgeons and the American Brachytherapy Society guidelines define differently those patients who can be offered APBI in lieu of WBI. “At M. D. Anderson, we are using a composite of the two societies’ guidelines and being conservative,” said Dr. Bloom. “One set of guidelines allows the patient to be as young as 45 years old—but we prefer the patient to be postmenopausal. We will offer APBI to treat invasive ductal carcinoma or ductal carcinoma in situ, as long as there is no lymphovascular space invasion.” APBI is appropriate in such cases because the cancer is confined to a small area. Dr. Bloom stressed the need for more data on the risks and benefits of all forms of APBI, but she finds that patients appreciate having options. “So far, APBI looks very promising for the appropriately selected patient.”For more information, contact Dr. Bloom at 713-745-6123. Other articles in OncoLog, February 2009 issue:
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