While whole breast irradiation is currently the standard approach in women undergoing breast conserving therapy (BCT), increasing attention is being focused on an alternative approach known as Partial Breast Irradiation (PBI).

As the name implies, PBI involves treatment of only a portion of the breast (the lumpectomy cavity plus a limited amount of surrounding tissues).  Since a smaller volume of breast tissue is irradiated, treatment times are significantly shorter than conventional treatment.

PBI series (view paper 1, paper 2 and paper 3) from a number of institutions have demonstrated that local recurrences rates are low and are comparable to those reported following whole breast irradiation.  Moreover, good-to-excellent cosmetic results have been achieved in the majority of patients.

Although promising, patients need to be carefully selected for PBI to minimize the risk of tumor recurrence.  The best candidates appear to be women with small (≤ 2 cm) tumors, negative resection margins, and without involvement of the regional lymph nodes.  Moreover, patients should be preferably over the age of menopause (post-menopausal).

Ask your Radiation Oncologist whether PBI is appropriate for you. 

PBI Techniques                                                                                

Various PBI approaches have been used over the years.  Initially, PBI was performed with a technique known as interstitial brachytherapy, whereby hollow catheters are inserted into the breast and loaded with radioactive Iridium (192Ir). 

More recently, 3D Conformal Radiation Therapy (3DCRT) approaches have been used consisting of multiple shaped radiation beams focused on the lumpectomy site and surrounding tissues.

3DCRT Plan in a patient undergoing partial breast irradiation (PBI). Treatment consisted of 5 shaped photon fields.

Mammosite                                                                                       

An alternative PBI approach commonly used today is Mammosite.  Mammosite is is a form of intracavitary brachytherapy in which a high-dose-rate (HDR) source inserted into a specially-designed balloon catheter placed within the lumpectomy cavity.  

A total dose of 34 Gy is delivered twice daily over 5 days. If used solely as a boost following whole breast irradiation, a lower dose is delivered, typically over 1-2 days.

Schematic of Mammosite Treatment

Strut Assisted Volume Implant (SAVI)                                                      

SAVI (www.biolucent.com) is a novel intracavitary brachytherapy approach designed to deliver PBI in women with early stage breast cancer treated with breast conserving surgery.

Unlike Mammosite, SAVI consists of a multi-channel catheter system.  Each individual channel can be loaded with a brachytherapy source for varying lengths of time to better conform the dose to the shape of the lumpectomy cavity.  Moreover, lower doses can be delivered to the overlying skin and chest wall.

SAVI device

Treatment is delivered using the same number of treatments and total dose as the Mammosite device.  Once completed, the catheter is collapsed and withdrawn from the patient.

UCSD is the 2nd center in the world to offer SAVI to patients.

Clinical Trials                                                                       

To determine whether PBI is equivalent to whole breast irradiation, UCSD and other institutions are participating in a large clinical trial (NSABP B-39).  In this study, patients eligible for breast conserving therapy are randomized following lumpectomy to either whole breast irradiation or PBI.

Results of this important trial will help determine the care of breast cancer patients in the future.