What are the recommended dose constraints for breast radiotherapy?

Recommended Dose Constraints for Breast Radiotherapy

For breast radiotherapy, the recommended dose constraints include 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. 1, 2

Whole Breast Radiation Constraints

Dose and Fractionation

• 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
• All dose schedules are given 5 days per week 1
• 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
• Typical boost doses: 10-16 Gy in 4-8 fractions 1

Target Coverage

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

Chest Wall Radiation Constraints (Post-Mastectomy)

• Target includes ipsilateral chest wall, mastectomy scar, and drain sites 1
• Dose: 46-50 Gy in 23-25 fractions 1
• Consider scar boost at 2 Gy per fraction to a total dose of approximately 60 Gy 1
• Special consideration for bolus material to ensure adequate skin dose 1

Regional Nodal Radiation Constraints

• Dose: 46-50 Gy in 23-25 fractions to regional nodal fields 1
• Target delineation best achieved through CT-based treatment planning 1
• For internal mammary node identification, use internal mammary artery and vein as surrogate for nodal locations 1

Accelerated Partial Breast Irradiation (APBI) Constraints

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

Organ at Risk (OAR) Constraints

Heart

• Mean heart dose <2.5 Gy 2
• Mean dose to left ventricle (LV) <3 Gy 2
• V5LV (volume of LV receiving ≥5 Gy) <17% 2
• V23LV (volume of LV receiving ≥23 Gy) <5% 2
• Mean dose to left anterior descending artery (LAD) <10 Gy 2
• V30LAD (volume of LAD receiving ≥30 Gy) <2% 2
• V40LAD (volume of LAD receiving ≥40 Gy) <1% 2

Lung

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

Techniques to Minimize Normal Tissue Exposure

• CT-based treatment planning is encouraged to identify lung and heart volumes and minimize exposure 1
• Compensators such as wedges, forward planning using segments, and IMRT can improve dose homogeneity 1, 3
• Respiratory control techniques including deep inspiration breath-hold and prone positioning can reduce dose to heart and lung 1, 4
• Field-in-Field technique has been shown to reduce mean doses to organs at risk compared to VMAT 3

Common Pitfalls and Caveats

• Avoid overlap between adjacent fields to prevent hot spots 1
• Techniques that result in cardiac irradiation should be minimized due to known increase in late cardiac mortality 1
• For left-sided breast cancers, breath-holding techniques are recommended to minimize cardiac exposure 4
• Weekly imaging is recommended for verification of daily setup consistency 1
• Routine use of daily imaging is not recommended 1