In summary, breast conserving therapy (BCT) is an effective, save and widely used treatment technique for early breast cancer. Radiotherapy has shown to give better local control and survival benefit and is an integrated part of BCT. The simultaneous integrated boost (SIB) technique is a new treatment technique in breast irradiation. In this technique the whole breast is irradiated simultaneous with boosting the tumour bed, as part of BCT. Late radiation-induced toxicity has not been investigated in patients treated with radiotherapy using this technique. Proposed study will study the late radiation-induced toxicity, describe patients-rated complaints, quality of life, survival and local control curves in patients treated for early breast cancer with breast-conserving surgery in combination with radiotherapy with the SIB technique as compared to sequential radiotherapy treatment.

Inclusion Criteria:

• WHO performance status 0-2.
• Invasive breast cancer or ductal carcinoma in situ (DCIS).
• Stage I-III breast cancer or DCIS.
• Treated with curative radiotherapy of the breast (as part of breast conserving therapy) with simultaneous integrated boost technique, with or without irradiation of the regional (including internal mammary) lymph nodes.

Exclusion Criteria:

• Previous thoracic radiotherapy.
• Previous history of malignancy, except adequately treated carcinoma in situ of the cervix or basal cell carcinoma of the skin.
• Bilateral (synchrone) invasive breast cancer.
• Treatment prior to surgery (i.e. neoadjuvant chemotherapy, neoadjuvant hormonal therapy, pre-operative radiotherapy).
• Distant metastases at diagnosis (M1).
• Unsufficient knowledge of Dutch language.

Patients with breast cancer treated with curative intent.