Indications for Radiation Boost in Breast Cancer
A radiation boost to the tumor bed after whole breast irradiation should be strongly considered for postmenopausal women with early-stage breast cancer who have any of the following high-risk features: positive or close surgical margins, positive axillary lymph nodes, lymphovascular invasion, or high-grade disease. 1
Mandatory Boost Indications
Positive surgical margins represent an absolute indication for tumor bed boost, with data demonstrating a dramatic reduction in 10-year local recurrence from 13% to 4% when boost is administered in this setting 2. If margins remain positive after re-excision and the patient declines mastectomy, a higher boost dose should be considered 2.
Strong Indications for Boost (High-Risk Features)
The following features warrant strong consideration of boost regardless of age 1:
Positive axillary lymph nodes: The relative reduction in local recurrence risk with boost is consistent across age groups, though absolute benefit varies 2
Lymphovascular invasion: Demonstrated benefit in reducing local recurrence 2
High-grade invasive ductal carcinoma: Boost reduces local relapse from 18.9% to 8.6% in this population 2
Close surgical margins: Even with negative margins, close margins benefit from boost 2, 1
Age-Related Considerations
While the relative reduction in local recurrence is similar across all age groups (from ≤40 to >60 years), the absolute gain in local control is highest in younger patients 2. For patients younger than 50 years, boost reduces local relapse from 19.4% to 11.4% 2. However, for postmenopausal women over 50 years with the high-risk features listed above, boost remains indicated 1.
When Boost May Be Omitted
In highly selected postmenopausal women ≥70 years with T1, ER-positive, clinically node-negative disease with negative margins, whole breast irradiation itself may be omitted if the patient receives endocrine therapy 2. In this low-risk subset, the 10-year locoregional recurrence difference is only 8% (90% vs 98%) 2.
For postmenopausal women with negative margins and no other high-risk features, the benefit of boost is less clear, as the EORTC trial showed boost did not significantly lower relapse rates in patients with truly negative margins 2.
Boost Delivery Techniques
Boost can be delivered using 1, 3:
- Electron beam (most common)
- Photon beam (enface technique)
- Brachytherapy (interstitial implant)
All three techniques provide equivalent local control 4. Typical boost doses are 10-16 Gy in 4-8 fractions, with 16 Gy used for higher-risk patients 2, 1, 5.
Important Caveats
Boost increases the risk of worse cosmetic outcome, particularly when photon technique is used, when boost volumes are large, or when higher doses (26 Gy vs 16 Gy) are employed 6. However, boost does not improve overall survival or disease-free survival—only local control 7. The decision must weigh the local control benefit against cosmetic considerations and patient preference, but in the presence of high-risk features, the local control benefit typically outweighs cosmetic concerns 7, 6.