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

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Purpose: The American College of Surgeons Oncology Group Z0011 trial indicated no benefit from axillary lymph node (LN) dissection after a positive sentinel LN biopsy in patients receiving breast irradiation, suggesting that level I-II LNs were covered in tangential fields. Methods and materials: We evaluated 50 computed tomography–based tangential breast plans and contoured level I-III axillary LNs using the Radiation Therapy Oncology Group guidelines. The volumes of level I-III LN regions covered by 90% and 95% of the prescription dose (PD) were calculated and correlated with the V20 ipsilateral lung and mean heart dose. We calculated field length, distance from the humeral head, and separation. The Pearson correlation method and linear models were used in the correlative study. Results: Level I LN mean and median volume (MMV) covered by 90% of the PD were 46.8% and 47.2%, respectively. MMV covered by 95% of the PD was 30.8% and 29.62%. Mean and median dose to level I LNs were 29.03 Gy and 30.13 Gy, respectively. The MMV of level II LNs covered by 90% of the PD was 2.49% and 0%. The mean and median dose to level II LNs were 6.09 Gy and 2.12 Gy, respectively. The MMV of level III LNs was 0% with a mean and median dose of 1.04 Gy and 0.92 Gy, respectively. There was a moderate correlation between the 95% prescription coverage of level I LNs and V20 ipsilateral lung and a smaller correlation between 95% prescription coverage of level I LNs and mean heart dose. Distance from the humeral head was inversely correlated with coverage of level I and II LNs and positively correlated with V20 lung. Conclusion: In most patients, <50% of the level I LN volume was covered by 90% of the PD and <30% was covered by 95%; <5% of the level II nodes were covered by 90% of the PD; and coverage was 0% for level III LNs.