Whole breast irradiation with high tangents in the prone position

Objective Extending the superior border of the breast tangent fields to include the low axilla is a technique employed to target the axillary lymph node (LN) without adding additional fields. This technique, commonly referred to as high tangents, is typically done in the supine position. The feasibility of delivering high tangents in the prone position has never been reported. Methods Patients from 2012 to 2018 at a single institution who were prescribed treatment with high tangents using two tangentially opposed beams in the prone position were identified. The levels I–III axillary LNs were retrospectively contoured. The dose delivered to the LN, breast, and organs at risk was calculated using the original treatment plan. For LN, coverage was defined as > 90% of the prescribed dose. Results Forty-one patients treated with high tangents were identified. The median age was 62. Most patients underwent sentinel LN biopsy (88%), of which 59% had macroscopic disease and 30% had micrometastatic disease. Four patients had no axillary staging. Most patients (76%) were treated with hypofractionated radiation. The median distance from the superior border of the anterior oblique field to the humeral head was 0.6 cm (range: 0–1.5 cm). The mean coverage of the level I and level II axilla was 88.7% and 40.0% respectively. Axillary level I coverage for distance from the humeral head < 1 cm was 95.1%, whereas distance > 1 cm was 76.4% ( p = 0.017). Conclusions This series demonstrates the feasibility of high tangents in the prone position, offering good coverage of level I LN, particularly with < 1 cm distance from the humeral head.