Dosimetric Evaluation of Axillary Dose during Irradiation with Standard Breast Tangent Technique: An Observational Study

Abstract

Introduction: Axillary irradiation is a part of adjuvant radiotherapy for breast cancer. During chest wall or breast irradiation, axilla often receives some amount of dose which may help control micrometastasis or isolated tumour cells but is not sufficient to treat axilla as a target volume. This study aimed to evaluate the dose received by axillary levels I, II, and III and the volume receiving 95% of the prescribed dose using standard breast tangents.

Methods: A cross-sectional study was conducted at Bhaktapur Cancer Hospital after ethical approval from the Institutional Review Board (IRB), National Academy of Medical Science (NAMS) Ethical approval number:135/2078/79. Seventy patients with early breast cancer who had undergone breast-conserving surgery (BCS) or modified radical mastectomy (MRM) with sentinel lymph node biopsy (SLNB) or axillary lymph node dissection (ALND) with indication for adjuvant radiotherapy were included. All patients received three-dimensional conformal radiotherapy (3DCRT) to the whole breast or chest wall with or without supraclavicular lymph node region. Axillary levels on the ipsilateral side were delineated using Radiation Therapy Oncology Group (RTOG) guidelines, and incidental doses to levels I–III were calculated.

Results: Axillary level I received a mean dose of 35 Gy, level II 27.3 Gy, and level III 26.4 Gy. The mean volume receiving 95% of the prescribed dose was 20.5 cc for level I, 10.6 cc for level II, and 10.7 cc for level III.

Conclusions: Standard tangential radiation fields deliver adequate dose to breast or chest wall but underdose the axilla. For patients at risk of microscopic metastasis to regional lymph nodes careful radiation planning to include axilla as a target volume is recommended for better regional control of disease.