Evaluation of breast sentinel lymph node coverage by standard radiation therapy fields

Area of Science:

• Oncology
• Radiotherapy
• Surgical Oncology

Background:

• Sentinel lymph node (SLN) biopsy is a standard staging procedure for early-stage invasive breast cancer.
• The anatomical location of breast SLNs and their relation to radiation fields are not well-described.

Purpose of the Study:

• To describe the anatomical location of breast sentinel lymph nodes (SLNs) relative to standard radiotherapy fields.
• To assess the coverage of SLNs by standard whole-breast and axillary radiation fields in breast cancer patients.

Main Methods:

• Retrospective review of radiotherapy treatment planning data for 106 breast cancer patients who underwent SLN biopsy.
• Evaluation of SLN clip location relative to vertebral body level, whole-breast tangential fields, and standard axillary fields.

Main Results:

• Breast SLNs were most commonly located opposite the T4 vertebral body level (range T2-T7).
• 90% of SLN clips were below the clavicle, excluding them from standard axillary fields.
• 78% of SLN clips were within whole-breast tangent fields, but 10% were outside.

Conclusions:

• Standard axillary radiotherapy fields do not adequately cover the highest-risk lymph nodes in breast cancer patients.
• Modifying tangent field design to exclude superior-posterior multileaf collimators could include SLNs in 90% of patients.