Definition of Chest Wall in Breast Carcinoma
In the context of breast carcinoma, the chest wall refers to the ipsilateral musculoskeletal structures underlying the breast, including the ribs, intercostal muscles, and serratus anterior muscle, which serves as the target for postmastectomy radiation therapy (PMRT) along with clinically relevant mastectomy scars and drain sites 1.
Clinical Definition for Treatment Planning
The chest wall target in breast cancer treatment encompasses:
- Ipsilateral chest wall structures (ribs, intercostal muscles, serratus anterior)
- Clinically relevant mastectomy scar
- Drain sites when indicated 1
This definition is critical for radiation oncologists when contouring treatment volumes for PMRT. Modern treatment planning requires volumetric delineation using CT-based contouring guidelines, such as those from RADCOMP (Radiotherapy Comparative Effectiveness) and RTOG atlases, to accurately define the chest wall target while minimizing dose to adjacent organs at risk 2.
Anatomical Context
From an anatomical perspective, the breast attaches to the chest wall along its entire perimeter through both periosteal and fascial connections, requiring sharp dissection for removal 3. However, for oncologic purposes in breast carcinoma, the clinical definition focuses on the structures that remain after mastectomy and require radiation coverage to prevent locoregional recurrence.
Treatment Implications
The chest wall is treated with radiation doses of either:
- Conventional fractionation: 45-50.4 Gy in 25-28 fractions
- Moderate hypofractionation: 40-42.5 Gy in 15-16 fractions 1
For high-risk patients (T4 disease, positive margins), a chest wall scar boost of approximately 10 Gy in 4-5 fractions may be considered 1. The routine use of bolus is not recommended except for inflammatory breast cancer or situations where skin dose adequacy is a concern 1.
Important Caveats
The chest wall definition excludes the breast parenchyma itself (which is removed during mastectomy) and should not be confused with the broader anatomical chest wall that includes the sternum, clavicles, and deeper structures. These deeper structures are only relevant when there is direct tumor invasion requiring en bloc resection 4, 5.