Breast-conservation therapy (BCT), consisting of lumpectomy followed by whole-breast irradiation (WBI), is the standard of care for women with early-stage breast cancer. However, many women who are candidates for BCT either choose mastectomy or lumpectomy alone for myriad reasons. Accelerated partial-breast irradiation (APBI) is a collection of radiotherapy techniques that deliver higher daily doses of radiation to the surgical cavity with margin over a shorter time than WBI, reducing total treatment time from 6-6.5 weeks to 1-2 weeks. Advocates of APBI state that early results of this approach demonstrate excellent local control, minimal acute toxicity, and are associated with more convenience for the patient. Phase III randomized clinical trials are currently underway to assess local control, acute and chronic toxicities, and quality of life associated with APBI compared to WBI. In this review, we hope to clarify the rationale behind APBI and discuss in depth data concerning various partial-breast irradiation techniques that are being used throughout the United States and around the world.
The theme in breast cancer treatment over the past few decades has been toward less invasive techniques with equivalent or more effective results. This has been seen with the evolution from radical mastectomy to modified radical mastectomy to lumpectomy, and with the adoption of sentinel lymph node biopsy instead of axillary dissection for most breast cancer patients.
The concept of limiting radiation therapy from the whole breast to the partial breast is consistent with this evolution. There is sound justification for this movement to irradiate only the area surrounding the tumor, as highlighted in this review. Most breast cancer local recurrences occur within the same quadrant as the original cancer. The incidence of new primaries in different quadrants of the ipsilateral breast is similar to the incidence of new cancers in the contralateral breast. We certainly do not advocate radiation therapy for the contralateral breast, so it does seem inconsistent and illogical that we recommend this for the remaining quadrants of the ipsilateral breast. Hence, the concept of partial-breast radiation therapy is based on data regarding recurrence patterns.
Variety of Techniques
As stated in this review, several types of accelerated partial-breast irradiation (APBI) are currently available. These include multicatheter interstitial brachytherapy, MammoSite balloon catheter brachytherapy, three-dimensional (3D) conformal external-beam radiotherapy, and intraoperative radiotherapy (IORT). Each technique has advantages and disadvantages. All of the ABPI options offer patients a shorter course of radiation therapy that is more convenient for the patient and may allow increased compliance and acceptance of radiation therapy for those patients who must travel some distance from their home for treatment.
The multicatheter approach is an involved technique and may be perceived from the patient's perspective as rather invasive as well as requiring the inconvenience of an inpatient hospital stay. The MammoSite catheter technique has been received well by both patients and physicians given the ease of catheter placement. This technique offers the option of intra-operative or postoperative catheter placement depending upon the preference of the treating physicians. Some surgeons may place a temporary "space-holder" Foley catheter at the time of lumpectomy, with an anticipated office exchange for the treatment catheter after final pathology reports are available. The MammoSite catheter may not be suitable in patients with small breasts or for tumors located in the upper-inner quadrant because of the requirement for skin-to-cavity distances.
The 3D conformal external-beam radiation therapy offers patients the advantage of avoiding any implanted device. IORT involves the shortest treatment time but may be complicated in patients who are determined to have positive surgical margins and need reexcision. This may not have been a significant issue in the Versonesi studies, as all patients received generous resections with quadrantectomies.
The longest reported follow-up in APBI is with multicatheter interstitial brachytherapy. As per this review, Vicini et al have shown local recurrence rates of 3.6% at 10 years. The other techniques have shorter follow-up, with local recurrence rates of 1% at 2 years follow-up for MammoSite irradiation, no reported recurrences in 10 to 28 months with single-institution studies of 3D conformal radiation, and 1.3% at 19 months in a single-institution study of IORT.
We await the results of ongoing trials for more data on long-term effectiveness of these therapies. Several current clinical trials are evaluating the clinical efficacy of these APBI techniques. These studies include the National Surgical Adjuvant Breast and Bowel Project (NSABP) B-39/Radiation Therapy Oncology Group (RTOG) 0413 trial, in which patients are randomized to either whole-breast irradiation or APBI. All types of APBI are included in this trial.
In addition, the American Society of Breast Surgeons has established a registry for patients undergoing radiation therapy with the MammoSite catheter. Although not derived from a randomized clinical trial, the long-term data regarding local recurrence, toxicity, infection, and cosmesis will be informative.
Rache M. Simmons, MD
The author has no significant financial interest or other relationship with the manufacturers of any products or providers of any service mentioned in this article
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