Clinical trials evaluating partial breast irradiation

Single-institution trials have shown that in highly selected patients, partial breast irradiation (PBI) to the area from which the tumor was removed appears to provide good results in terms of tumor control. Patients have generally been treated with brachytherapy techniques, but we also have limited experience with external beam radiation. In those investigators' hands, PBI appears to be a very promising technique for treating select patients.

However, the trials have been conducted at a limited number of institutions and in limited numbers of highly selected patients. For that reason, a large trial is being planned that will randomly assign women to either whole breast radiation therapy (WBT) or PBI. I strongly support that trial; otherwise we'll never know which patients will benefit from this type of technique.

Proposed NSABP/RTOG randomized trial comparing PBI to WBT

A proposed NSABP/RTOG trial will include women with DCIS or Stage I/II breast cancer and up to three positive nodes. The patients can have either invasive or noninvasive cancers, and their margins must be negative. At one time, it was discussed that only patients with infiltrating ductal carcinoma (not lobular carcinoma) would be included because many of the pilot studies did not include patients with lobular carcinoma. The NSABP wanted to include all patients, so those with lobular carcinoma and DCIS will also be enrolled.

The PBI techniques allowed in the proposed randomized trial include external beam radiation therapy and brachytherapy with either an implant or MammoSite®, which is an easier way to deliver brachytherapy. Although outcome data with MammoSite® are not yet available, the data demonstrate it to be a safe procedure.

When the trial opens for accrual, I predict external beam radiation will be used most frequently because most radiation oncologists use that technique. Few radiation oncologists in this country have continued using brachytherapy in the treatment of patients with breast cancer. As we gather more data about the use of external beam PBI, most radiation oncologists will probably gravitate toward that technique.

Techniques for delivering PBI

Brachytherapy is delivered through a catheter either with a template that guides the radioactive sources or by freehand. Doctors who are experienced in brachy-therapy can do it freehand, but using a template is the kinder, simpler method because it forces the catheters in a certain direction. However, the template method may not provide as thorough coverage as the freehand method.

Placement of catheters is extremely important. Catheters placed too close to the chest wall may cause rib, localized lung or heart complications. Catheters placed in the deep part of the breast where the heart is close to the chest wall may cause cardiac problems. Catheters placed too close to the skin may cause severe fibrosis, telangiectasia and an adverse cosmetic result.

MammoSite® is like a glorified Foley catheter with high dose rate radiation. The balloon treats a spherical target area inside the breast. The FDA approved MammoSite® based on safety. We still need efficacy data, and studies are currently underway. MammoSite® has caught on dramatically with the radiation oncology community and surgeons. Radiation oncologists do the dosimetry, but surgeons are involved in the actual placement.

External beam radiation is the most "user friendly" of the three techniques. With external beam radiation, however, in order to treat the target area, a larger portion of the breast may be exposed to radiation than with brachytherapy. We don't want the external beam radiation technique for PBI to end up treating nearly the whole breast. To do PBI, we want to limit the doses administered and the area exposed to a high dose of radiation.

Select publications

Dr Pierce is an Associate Professor in the Department of Radiation Oncology at the Michigan in Ann Arbor, Michigan.

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