What are the indications for breast radiotherapy?

Indications for Breast Radiotherapy

Radiotherapy after breast-conserving surgery is mandatory for invasive breast cancer, reducing local recurrence by two-thirds and improving survival, while post-mastectomy radiotherapy is clearly indicated for patients with ≥4 positive nodes or T3-T4 tumors. 1

After Breast-Conserving Surgery (BCS)

Invasive Breast Cancer

• Whole breast radiotherapy should always be performed after BCS for invasive cancer, using a minimum dose of 45-50 Gy in 25-28 fractions (standard fractionation) or 15-16 fractions with 2.5-2.67 Gy per fraction (hypofractionation). 2, 1
• Radiotherapy reduces the 10-year risk of any first recurrence from 35% to 19.3% (absolute reduction 15.7%) and reduces 15-year breast cancer death from 25.2% to 21.4% (absolute reduction 3.8%). 3
• A boost dose of 10-16 Gy to the tumor bed provides an additional 50% reduction in local recurrence risk and should be routinely administered, particularly in patients under 50 years old, those with grade 3 tumors, vascular/lymphovascular invasion, or close/focally positive margins. 2, 1, 4

Limited Exceptions to Radiotherapy After BCS

• In highly selected patients ≥70 years with stage I (T1N0), hormone receptor-positive tumors with clear margins, radiotherapy may potentially be omitted if the patient receives endocrine therapy. 2, 5
• This exception requires careful consideration as the absolute benefit is minimal (0.1% reduction in 15-year breast cancer death) only in this very low-risk group. 3

DCIS (Ductal Carcinoma In Situ)

• Whole breast radiotherapy after BCS for DCIS decreases local recurrence risk by 50-60% but has no effect on survival. 2, 5
• Standard dose is 4,500-5,000 cGy at 180-200 cGy per fraction. 6
• A boost to the tumor bed can be considered for patients at higher risk for local failure (young age, high-grade DCIS). 2
• Selected patients with low-risk DCIS (low/intermediate grade, small size <1 cm, wide margins ≥10 mm) may be considered for excision alone without radiotherapy, though this remains controversial and 5-year recurrence rates still reach 6.1%. 2

After Mastectomy

Clear Indications for Post-Mastectomy Radiotherapy (PMRT)

• PMRT is always recommended for patients with ≥4 positive axillary lymph nodes (reduces 10-year recurrence from 63.7% to 42.5% and 15-year breast cancer death from 51.3% to 42.8%). 2, 1, 3
• PMRT is indicated for T3-T4 tumors (>5 cm or chest wall/skin involvement) independent of nodal status. 2, 1

Conditional Indications for PMRT

• PMRT should be considered for patients with 1-3 positive axillary lymph nodes when additional risk factors are present: 2, 1
  • Young age (<40-45 years)
  • Vascular or lymphovascular invasion
  • Low number of examined axillary lymph nodes (<10)
  • High tumor grade
  • Close or positive margins

Regional Nodal Irradiation

Supraclavicular and Apical Nodes

• Irradiation of the supraclavicular and apical lymph nodes is indicated when there is extensive axillary involvement (≥4 positive nodes or N≥2). 2, 1

Internal Mammary Nodes

• Internal mammary node irradiation is indicated when the tumor is medial or central with axillary node involvement, or when there is documented metastatic spread to this region. 2, 1

Axillary Irradiation

• After complete axillary dissection (Levels I-III), axillary irradiation should be avoided due to increased risk of lymphedema and other complications. 2

Absolute Contraindications to Breast-Conserving Therapy with Radiotherapy

• Prior radiation therapy to the breast or chest wall 2
• Radiation therapy during pregnancy 2
• Diffuse suspicious or malignant-appearing microcalcifications that cannot be completely excised 2
• Widespread disease that cannot be incorporated by local excision through a single incision with negative margins and satisfactory cosmetic result 2
• Positive pathologic margins after reasonable surgical attempts 2

Relative Contraindications

• Active connective tissue disease involving the skin, especially scleroderma and systemic lupus erythematosus 2, 7
• Tumors >5 cm (though not absolute) 2
• Focally positive margins (may be acceptable in selected cases with higher boost dose) 2

Technical Considerations and Common Pitfalls

Timing

• Radiotherapy should begin within 2-4 weeks after uncomplicated breast-conserving surgery, as soon as adequate healing has occurred, and not later than 12 weeks after surgery. 2, 6, 7
• When chemotherapy is indicated, most centers favor administering chemotherapy before radiotherapy, though optimal sequencing is not clearly defined. 7

Cardiac Protection

• For left-sided breast cancer, minimize cardiac irradiation using CT simulation and appropriate techniques to avoid late cardiac mortality. 2
• Not more than 3-3.5 cm of lung should be treated to minimize radiation pneumonitis risk. 2, 6

Hypofractionation

• Hypofractionated regimens (e.g., 15-16 fractions with 2.5-2.67 Gy per fraction) show similar effectiveness and comparable side effects to conventional fractionation and are generally recommended. 2, 1
• Exercise caution in young patients, those receiving post-mastectomy radiotherapy, or those requiring regional nodal irradiation, as these groups were underrepresented in hypofractionation trials. 2

Partial Breast Irradiation

• Partial breast irradiation (PBI) should only be used in carefully selected patients ≥50 years with unicentric, unifocal, node-negative, non-lobular cancer ≤3 cm without extensive intraductal component or lymphovascular invasion, preferably within clinical trials. 2, 1