Is there a tradeoff in using modified high tangent field radiation for treating an undissected node-positive axilla?

Recent data are changing axillary management in patients with 1 to 2 positive sentinel nodes. The proposed omission of completion axillary node dissection calls into question the need for axillary nodal irradiation. This study evaluates the difference in dose to the lung and heart and risk of radiation pneumonitis (RP) for patients treated with standard tangent fields (STF) compared with modified high tangent fields (MHTF).

Plans of 30 patients treated with STF were evaluated. A second plan (MHTF) was developed to include axillary levels I (Ax1) and II (Ax2). Ax1 and Ax2 volumes were contoured based on the RTOG (Radiation Therapy Oncology Group) Atlas guidelines. Dose-volume histograms of the 2 plans were used to compare doses received by Ax1, Ax2, lung, and heart volumes. The risk of RP was calculated using normal tissue complication probability (NTCP) modeling.

The D95 (dose to 95% of volume) received by Ax1 and Ax2 volumes increased from 16.38 Gy and 5.71 Gy for STF to 49.38 Gy and 48.08 Gy for MHTF, respectively. Mean lung dose increased from 5.40 Gy for STF to 9.47 Gy for MHTF. Mean ipsilateral lung V5, V10, and V20 values increased from 19%, 14%, and 10%, respectively, for STF, to 32%, 24%, and 18%, respectively, for MHTF. Mean heart dose increased from 1.98 Gy for STF to 3.93 Gy for MHTF. Mean heart V25 and V30 values increased from 2% and 1%, respectively, for STF, to 4% and 3%, respectively, for MHTF. NTCP for RP increased from near 0% for STF to 1% for MHTF.

Modified high tangent fields are necessary for definitive coverage of Ax1 and Ax2. This technique increases mean ipsilateral lung and heart doses as well as the V5, V10, and V20 of ipsilateral lung and the V25 and V30 of the heart. Risk of RP remains low by use of MHTF.