Breast Radiotherapy Guidelines

Introduction to Breast Radiotherapy

• The National Comprehensive Cancer Network recommends a dose of 45-50 Gy in 1.8-2.0 Gy fractions or 40-42.5 Gy in 15-16 fractions for whole breast irradiation, with a boost of 10-16 Gy for high-risk patients, while maintaining mean heart dose <2.5 Gy and mean left ventricle dose <3 Gy is not applicable due to missing reference, however, standard whole breast dose is 45-50 Gy in 23-25 fractions (1.8-2.0 Gy per fraction) or 40-42.5 Gy in 15-16 fractions (hypofractionation, which is preferred) 1, 2

Whole Breast Radiation Constraints

• Standard whole breast dose: 45-50 Gy in 23-25 fractions (1.8-2.0 Gy per fraction) or 40-42.5 Gy in 15-16 fractions (hypofractionation, which is preferred) 1, 2
• All dose schedules are given 5 days per week 3, 4
• A boost to the tumor bed is recommended for patients at higher risk for local recurrence (age <50 years, positive axillary nodes, lymphovascular invasion, high-grade disease, or close margins) 1, 3
• Typical boost doses: 10-16 Gy in 4-8 fractions 1, 5

Target Coverage

• Target should include the majority of breast tissue, defined through clinical assessment and CT-based treatment planning 1, 2
• Uniform dose distribution and minimal normal tissue toxicity are primary goals 1, 4

Chest Wall Radiation Constraints (Post-Mastectomy)

• Target includes ipsilateral chest wall, mastectomy scar, and drain sites 1, 4
• Dose: 46-50 Gy in 23-25 fractions 1, 6
• Consider scar boost at 2 Gy per fraction to a total dose of approximately 60 Gy 1, 5

Regional Nodal Radiation Constraints

• Dose: 46-50 Gy in 23-25 fractions to regional nodal fields 1, 5
• Target delineation best achieved through CT-based treatment planning 1, 4

Accelerated Partial Breast Irradiation (APBI) Constraints

• 34 Gy in 10 fractions delivered twice per day with brachytherapy 1, 2
• 38.5 Gy in 10 fractions delivered twice per day with external beam photon therapy 1, 2
• Suitable for select patients: women ≥60 years, not BRCA1/2 mutation carriers, with unifocal T1N0 ER-positive cancer 1, 2

Organ at Risk (OAR) Constraints

Lung

• For left-sided lesions, minimize the amount of heart in tangential fields 7, 8
• Not more than 3-3.5 cm of lung should be included in the treatment field 7, 8
• A minimum of 1-1.5 cm of lung is required in the treatment field 7, 8

Techniques to Minimize Normal Tissue Exposure

• CT-based treatment planning is encouraged to identify lung and heart volumes and minimize exposure 1, 2
• Weekly imaging is recommended for verification of daily setup consistency 1
• Routine use of daily imaging is not recommended 1

Common Pitfalls and Caveats

• Avoid overlap between adjacent fields to prevent hot spots 7, 8
• Techniques that result in cardiac irradiation should be minimized due to known increase in late cardiac mortality 7, 8