Accelerated Partial Breast Irradiation in Clinical Practice

Abstract

Accelerated partial breast irradiation (APBI) has been under clinical investigation for more than 15 years. There are several technical approaches that are clinically established, e.g. brachytherapy, intraoperative radiotherapy (IORT), or external-beam radiotherapy. The understanding of the underlying biology, optimal technical procedures, patient selection criteria, and imaging changes during follow-up has increased enormously. After completion of several phase III trials using brachytherapy or IORT, APBI is currently increasingly used either in phase IV studies, registries, or in selected patients outside of clinical studies. Consensus statements about suitable patients are available from several international and national societies like ASTRO, ESTRO, and DEGRO. One may expect that 15-25% of patients undergoing breast-conserving surgery may qualify for APBI, i.e. patients with small invasive ductal breast cancer without clinical lymph node involvement.

Biology of high single doses of IORT: RBE, 5 R’s, and other biological aspects

“…Technological advances in mobile radiotherapy (RT) units have greatly increased the clinical application of intraoperative radiotherapy (IORT) [1–4] by providing highly localized beams of low-energy X-rays (LEX) or high-energy (MeV) electrons. The physical radiation qualities of these sources may differ to some extent from that of high-energy photons (MeV X- or γ-rays) used in conventional external beam RT, and thus potentially influence the relative biologic effectiveness (RBE).…”

“…For both modalities, very high local control rates have been reported in non-randomised series [124–127] suggesting a clinical benefit of eliminating time for repopulation (‘temporal miss’) and reducing geographic miss. However, conclusions regarding potential superiority of an IORT boost over a conventional postoperative boost must await long-term follow-up of randomized trials [4]. …”

Recent Developments in Radiation Oncology: An Overview of Individualised Treatment Strategies in Breast Cancer

“…Overall, recurrence rates in the APBI studies are very low. Most trials have demonstrated increased rates of local recurrences, but no difference in OS [24]. The rationale for this approach is based on the knowledge that most local in-breast recurrences are located very close to the initial tumour site (within a 1- to 2-cm radius), and the rate of relapses outside the tumour bed area seems to be the same as the recurrence rate in the contralateral breast [25].…”

“…The rationale for this approach is based on the knowledge that most local in-breast recurrences are located very close to the initial tumour site (within a 1- to 2-cm radius), and the rate of relapses outside the tumour bed area seems to be the same as the recurrence rate in the contralateral breast [25]. APBI has been administered using different techniques (brachytherapy, IORT/IOERT, EBRT), applying different doses and fractionation schedules, and using various target volume definitions [24]. A summary of results and patient characteristics of the recent randomized trials of APBI versus WBI has been recently published in a review by Krug et al [26].…”

Current controversies in radiotherapy for breast cancer

“…Moreover, APBI has been administered as sole RT modality applying different dose and fractionation schemes using various target volume definitions [12]. Summarizing results of these trials, equieffectiveness of the various techniques is unclear and the differences in patient characteristics as well as dosimetric characteristics render the optimal selection of the treatment regimen as well as technique for individual patients difficult.…”