Intra Operative Radiation Therapy (IORT) is a combined treatment modality in which a large single dose of radiation is delivered concomitantly with tumor resection. The biological effects of chronic dose-rate irradiations have been traditionally well studied in radiation biology. However, the actual effectiveness of the extremely high dose per pulse and dose rates delivered by IORT, which can be 100-and 20-fold greater than those in conventional radiation therapy, is presently not taken into account in treatment planning. Early breast ...