Accelerated partial breast irradiation trials: diversity in rationale and design.

Seven randomised trials are currently testing accelerated partial breast irradiation against whole breast radiotherapy after breast conservation surgery. The trials are varied in the techniques used to deliver partial breast radiotherapy, reflecting the range of opportunities offered by advanced brachytherapy and teletherapy modalities. Dose schedules also vary between trials, but the most important point of difference between them reflects alternative concepts of clinical and planning target volumes. These are based mainly on the spatial pattern of relapse in retrospective and prospective studies, which report the majority of first local relapses close to the primary tumour site, and on the assumption that radiotherapy does not prevent the development of new primary tumours developing elsewhere in the breast. However, the pattern of ipsilateral breast tumour relapse is not accurately defined in the clinical literature and does not correspond closely to pathological findings. In addition, published data are consistent with a significant reduction in the rate of other quadrant relapse after whole breast radiotherapy. Regardless of the biological model of local tumour relapse and responsiveness to radiation, the ongoing trials will generate level I evidence for or against accelerated partial breast irradiation, provided patients are followed up long enough before the first reporting of results.