Axillary lymph node coverage with 3-dimensional tangential field irradiation and correlation with heart and lung dose

Area of Science:

• Radiation Oncology
• Medical Physics
• Surgical Oncology

Background:

• The Z0011 trial suggested axillary lymph node dissection is unnecessary after positive sentinel LN biopsy in irradiated breast cancer patients.
• This implies tangential breast irradiation fields adequately cover axillary lymph nodes (LNs).

Purpose of the Study:

• To quantitatively assess the coverage of axillary LNs (levels I-III) by tangential breast radiation fields.
• To correlate LN coverage with radiation dose to the lungs and heart.

Main Methods:

• Computed tomography (CT) based tangential breast plans from 50 patients were analyzed.
• Axillary LNs (levels I-III) were contoured using Radiation Therapy Oncology Group (RTOG) guidelines.
• The volume of LNs covered by 90% and 95% of the prescription dose (PD) was calculated and correlated with V20 ipsilateral lung and mean heart dose.

Main Results:

• Less than 50% of level I LN volume received 90% of the PD, and less than 30% received 95% PD.
• Coverage for level II LNs was minimal (<5% at 90% PD), and 0% for level III LNs.
• Moderate correlation found between level I LN coverage and ipsilateral lung dose (V20); smaller correlation with mean heart dose.

Conclusions:

• Standard tangential breast irradiation fields provide suboptimal coverage for axillary LNs, particularly levels II and III.
• The findings challenge the assumption that tangential fields adequately cover all relevant axillary lymph node levels.
• Further research may be needed to optimize radiation techniques for comprehensive axillary LN coverage.