Radiotherapy of breast cancer after breast-conserving surgery:: an improved technique using mixed electron-photon beams with a multileaf collimator

Background and purpose: Loco-regional radiotherapy after breast cancer surgery significantly reduces the risk of recurrences. An increase of cardiac deaths for irradiated breast cancer patients has been reported in some studies, especially for women with tumours in the left breast. The aim of this study was to compare retrospectively the conventionally used technique using two opposed tangential photon beams with a modified technique using a combination of photon and electron beams to find an optimal technique with respect to dose homogeneity in the breast and surrounding regional lymph nodes and a minimal dose in the organs at risk. Materials and methods: Thirty patients with stage II breast cancer who received different types of adjuvant systemic therapy were included in the investigation. Comparative dose planning of two techniques was performed, i.e. an isocentric technique with two photon beams with coplanar medial beam edges and a technique with one electron and three photon beams with a common isocentre for all beams aided by a multileaf collimator. Results: The mixed technique was selected for eight of 12 patients with left-sided breast cancers because of significantly lower doses to the heart. However, the decision-making was influenced by many factors such as dose coverage of the target volume combined with minimizing of the doses to the organs at risk and the contralateral breast. Conclusion: The use of the mixed technique will optimize the loco-regional radiotherapy after breast-conserving surgery for many left-sided breast cancers. (C) 1998 Elsevier Science Ireland Ltd.