Women aged 48-75 years with early breast cancer , a maximum tumour diameter of up to 25 cm , and suitable for breast-conserving surgery were randomly assigned in a 1:1 ratio ( using a random permuted block design , stratified for clinical tumour size [ < 10 cm vs 10-14 cm vs 15 cm ] ) to receive either whole-breast external radiotherapy or intraoperative radiotherapy with electrons .