Trial Comparing Prone and Supine Intensity-modulated Radiotherapy (IMRT) After Breast-conserving Surgery in Patients With Large Breast Volume at High Risk for Skin Toxicity and Fibrosis

Inclusion Criteria: * female patients * multidisciplinary decision of adjuvant whole-breast irradiation (WBI) after lumpectomy for breast cancer * minimum 18 years * informed consent obtained, signed and dated before specific protocol procedures Exclusion Criteria: * mastectomy * need for axillary irradiation * bilateral breast irradiation * previous irradiation at the same time * mental condition rendering the patient unable to understand the nature, scope and possible consequences of the study * patient unlikely to comply with the protocol; i.e. uncooperative attitude, inability to return for follow-up visits, and unlikely to complete the study.