Incidental Radiation to Internal Mammary Nodes Drainage Area in Breast Cancer Treated With Modified Radical Mastectomy and Breast Conserving Surgery

Abstract

To analyze incidental radiation doses to the internal mammary nodes drainage area (IMN) after modified radical mastectomy (MRM) and breast conserving surgery (BCS). One hundred and thirty-eight patients treated with post mastectomy radiotherapy (PMRT) and 210 patients undergoing radiotherapy after BCS in our hospital were retrospectively analyzed. Patients were divided into two groups: patients undergoing MRM and matched control subjects with BCS. The IMN were contoured according to Radiation Therapy Oncology Group (RTOG) consensus, and were not include into the planning target volume (PTV). The prescription dose was 50 Gy in 25 fractions (2 Gy per fraction) to the PTV, five days per week for MRM group. And the whole breast and tumor bed were treated with 1.8 Gy and 2.15 Gy, respectively, in 28 fractions for BCS group. The mean doses (Dmean) to IMN, the first intercostal spaces of IMN levels (ICS1), the second intercostal spaces of IMN levels (ICS2), and the third intercostal spaces of IMN levels (ICS3) were valuated. The incidental radiation doses to IMN was 29.69 Gy and the dose delivered to IMN, ICS1, ICS2 showed a greater coverage in MRM group compared with BCS group (32.85 vs 27.1 Gy, 26.6 vs 12.5 Gy, 34.63 vs 30.42 Gy). The dose delivered to ICS3 showed no difference between MRM and BCS (37.41 vs 36.24 Gy). 37.64% of the patients received radiotherapy to the chest wall and ipsilateral supraclavicular fossa (SCF), while 62.36% of the patients only received irradiation to the chest wall or whole breast. The Dmean for IMN, ICS1, ICS were all greater in chest wall+ SCF radiotherapy group than chest wall (whole breast) radiotherapy group (32.87 vs 27.19 Gy, 26.8 vs 13.09 Gy, 34.65 vs 30.46 Gy). In univariate analysis, both the surgery form and SCF irradiation were the parameters affecting the incidental radiation Dmean of the IMN, ICS1, and ICS2. In multivariate analysis, surgery form was the only correlative factor that affected incidental radiation dose to IMN. Patients underwent BCS were accepted significantly lesser incidental radiation to IMN than MRM, especially for ICS1. And the real affecting factors of incidental dose to IMN was the surgery form rather than SCF irradiation’s accession.