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The axillary region is considered problematic; as it is an organ at risk (OAR), a predictive dosimetric parameter of long term lymphedema, and a residual-disease site in case of breast cancer radiotherapy. The purpose of our study is to determine the dose received by the axillary area in adjuvant radiotherapy for breast cancer and to assess its clinical impact on long term lymphedema.

A retrospective dosimetric study was carried out in the Radiotherapy Department of Farhat Hached Hospital of Sousse. It included 50 female patients treated with three-dimensional adjuvant radiotherapy for breast cancer between 2018 and 2019. The axillary area was delineated according to the European Organization for Research and Treatment of Cancer (EORTC) guidelines.

The average age was 52 [30-80]. Sixty-four percent of our patients had a mastectomy with ipsilateral axillary lymph node dissection (IALND), while 36% had a lumpectomy with a IALND. 17 patients among the 50 had lymph node metastasis (N+).Thirty-five patients (70%) received regional radiotherapy and 15 patients (30%)  had only local radiotherapy with two tangential fields.All the patients were treated with normofractionated radiotherapy dose of 50Gy. Patients with conservative surgical treatment or with a T4 classified tumors, received additional boost up to 66Gy (21 patients) and up to 70Gy for tumoral surgical limits (1 patient). The mean axillary volume was 77.9 cm3 [9.4-181]. The average mean dose, the maximal dose and the minimal dosereceived by the axillary region were respectively 28.49Gy [3.19-53.7Gy], 54.18Gy [33.96-72.63Gy] and 2.61Gy [0.32-10.74].Late complications of lymphedema and radio induced dermatitis (GI and II according to the CTCAE V5.0 scale) were observed respectively in 6(12%)and 17(34%) patients.

Based on the results of our study, we have observed that the axillary area received unintentional yet significant doses during breast irradiation either by the tangential fields or by the additional supraclavicular field. Some authors consider that the axillary-lateral thoracic vessel junction (ALTJ), which is just above level I Berg, can be regarded as an OAR for long-term lymphedema, and the dose for which can be minimized especially for clinically node-negative patients. Therefore, further validation of lymphedema OAR dosimetric parameters by prospective studies is justified.