Intraoperative Radiotherapy (IORT) with 50-kV X-Ray Machines as Boost in Breast Cancer – More Questions than Answers

Accessible online at: www.karger.com/onk Fax +49 761 4 52 07 14 E-mail Information@Karger.de www.karger.com ies [11–15] we reach our goal – if we want to compare intraoperative radiotherapy (IORT) using a 50-kV x-ray machine with other techniques for boost irradiation, first of all we have to know is the size of our target volume, second the form of our target volume, also in respect to the distances (relations) to the skin, and third we need to know if this technique is able to give a sufficient dose to the target. Regarding the first question, it is a well known fact that the risk of remaining microscopic disease depends on the resection margins. The larger the resection margins, the less likely are tumour foci in the remaining breast tissue and the smaller can be the ‘safety margin’ which has to be irradiated. Data from Holland [11, 12] suggest that margins of 2–3 cm from the tumour borders should be covered by the surgical resection margin and the ‘radiotherapeutic safety margin’. In the EORTC boost trial, a safety margin of 1.5 cm breast tissue after complete and 3 cm after incomplete resection was used. Regarding the second and third question it is obvious that only in rare cases it is possible for the surgeon to guarantee the same resection margins in all directions. Therefore, most often the radiation oncologist has to resolve the situation: for example in the direction ‘skin’ the resection margin is >10 mm, in the direction ‘thoracic wall’ it is <2 mm (and also the intact fascia was resected), cranial 5 mm, lateral >10 mm, medial only 1 mm and caudal 2 mm. The job of the radiation oncologist in a such situations is to choose an appropriate boost technique, which allows to give a sufficient dose of 20 Gy (or in case of resection margins >2 mm 16 Gy) in appropriate distances from the tumour bed (addition of ‘radiotherapeutic safety margins’ and of surgical resection margins must be in all directions 2 cm at least, better 3 cm) and simultaneously respecting that the skin (at least 5 mm thickness) and the thoracic wall are not part of the clinical target volume. In principle the radiation oncologist has 3 techniques for the delivery of the boost dose: electron beams, interstitial multiIn the treatment of breast cancer in early stages breast conserving therapy is a generally accepted treatment philosophy. Local control and survival data are the same as after mastectomy. The additional aim of breast conserving therapy is to treat patients with breast cancer without mutilation and simultaneously with optimal cosmetic results, as far as possible. Radiation therapy to the whole breast after breast conserving surgery is the standard treatment in the conservative approach and its value has been established in many retrospective studies as well as prospective randomised trials. The hazard ratio calculated according to the largest studies indicates a reduction of local failures after radiation therapy by a factor of 4 in comparison to not irradiated cohorts [1–6]. Randomised trials have recently confirmed older data, showing that a clear doseresponse relationship for local control exists. A dose increase of 15 Gy as boost (after 50 Gy postoperative whole breast irradiation) reduces the local recurrence rates by about one half [7]. On the other hand, cosmetic outcome is inversely related to radiation dose and volume of reference isodose. It is indisputable that incomplete tumour resection results in a very high risk of local recurrence and is undoubtedly an indication for a boost with 20 Gy. In patients with complete resection the indication for boost irradiation is more complex. Recently 3 randomized trials using boost irradiation [8–10] reported about increased local control rates in some subgroups of breast cancer patients. The published EORTC data deal with results on patients with negative margins only. A 16 Gy boost in addition to 50 Gy whole breast radiotherapy significantly reduced the annual odds of local recurrence by 41%; the benefit was verifiable only in patients aged 50 years and younger [8]. The main prognostic parameters in Romestaign’s data [9] are the positive resection margins, presence of an EIC (extensive intraductal component), tumour size and age. Based on these facts and data from further pathological studIntraoperative Radiotherapy (IORT) with 50-kV X-Ray Machines as Boost in Breast Cancer – More Questions than Answers