With improved cure rates and prolonged patient survival after breast-cancer radiotherapy, radiation-induced second cancers and heart diseases become increasingly important. The heart, lungs and contralateral breast are the most critical organs for these long-term effects. Doses to these organs and hence the risks differ between radiotherapy techniques and especially among patients. To address this variability, treatment plans were generated for 128 early-stage breast-cancer patients using intensity-modulated, 3D-conformal and hybrid radiotherapy. Twenty dedicated anatomic measures were assessed from CT data, such as the width and thickness of the treated breast or its distance from the heart. Their impact on doses to critical nearby organs was analysed. The majority of inter-patient variability can be covered with a few anatomic parameters. Patients can thus be stratified according to long-term risks already before treatment planning, and guidance can be provided towards a personalised selection of technique associated with the lowest risk.