CT-targeted irradiation of the breast and internal mammary lymph nodes using a 5-field technique

Abstract 

Purpose: To develop an effective and resource-efficient radiotherapy technique to treat the breast and regional nodes, including the ipsilateral internal mammary nodes.

Methods and Materials: Eighty female patients who underwent MRI scans for a variety of indications had coronal, T1-weighted images of the chest performed to determine the position of the internal mammary chain (IMC). Based on these results, a 5-field treatment technique was developed that would include the breast, supraclavicular fossa, and ipsilateral IMC, while maintaining a low dose to the heart, lungs, and contralateral breast. This technique was implemented in a cohort of 13 patients.

Results: The lateral position of the right and left IMC were measured in three cephalo-caudad positions: at the clavicular heads, upper manubrium, and midsternum (at the 2nd/3rd rib interspace). The mean lateral separation between the right and left IMC chains at each level (and 95% confidence interval) at each level were 5.8 cm (4.67–7.00), 5.6 cm (4.49–6.73), and 5.9 cm (4.66–7.19), respectively. Treatment was delivered to 13 patients using a 5-field technique, with tangential photon fields for the breast, anterior and posterior supraclavicular/axillary field, and a matching anterior electron field. Three-dimensional treatment planning of a representative case confirmed adequate coverage of the planning target volume (PTV). The median dose to the whole heart was 10 Gy, and 20% of the ipsilateral lung received more than 20 Gy. Seven of the 13 patients treated experienced moist desquamation at the junction of the electron field and breast tangents, and 1 patient had persistent ulceration at 3 months’ follow-up.

Conclusion: The 5-field technique described in this paper provides good coverage to the breast and regional nodes with acceptable toxicity, and without requiring three-dimensional treatment planning or intensity-modulated radiotherapy techniques.

Keywords:  Breast cancer, Radiation therapy, Internal mammary lymph nodes