Partial breast irradiation: why and how

IORT implies delivery of a high, single dose of radiation to a limited intrasurgical anatomic area. In the case of post-tumorectomy early breast cancer, the target volume is the tumor bed, maintaining a safety margin in depth (thickness of tissue to be treated) and laterally. Dosimetrically, electrons and high dose rate brachytherapy are well suited to these requirements. Intrabeam (soft X-rays at 50 kV), mammosite 3DCRT and IMRT are alternative technologies that have been adopted into clinical radiotherapy practice and have theoretically favourable dose-gradient effects. Target size, normal tissues included in the radiation fields, and operative/treatment time are variables that differ for each individual patient. The optimal PBI dose is under investigation based upon radiobiological dose-effects models. An efficient therapeutic index in IORT trials has been identified, with boost doses in the range 10–12.5 Gy (maximum 15 Gy). For IORT single radiation component, clinical information is scarce [3,4].Limited institutional experience and pilot studies are available in the literature describing results with IORT as a boost, hypofractionated HDRB, or external irradiation. There are two ongoing randomized trials that have been recruiting patients since 2000 using Intrabeam system (active in UK, Europe, USA and Australia) and Novac-7 (electrons; Milan). Both trials are exploring single doses around 20 Gy. In 2005 a multi-institutional randomized trial including PBI HDR brachytherapy was initiated. Selection criteria for inclusion are strict in these trials, and a highly selected group of breast cancer patients with good prognosis are apparently being investigated. An extensive review of clinical research considerations, radiobiological implications, pathology and surgical methodological requirements, physics specifications, and summary of the available literature was recently published after a group expert meeting to define the state of the art and science of PBI, includ