Accelerated partial-breast irradiation (APBI)--ready for prime time?

Comparison of two radiation techniques for the breast boost in patients undergoing neoadjuvant treatment for breast cancer

OBJECTIVE

After breast conservative surgery (BCS) and whole-breast radiotherapy (WBRT), the use of boost irradiation is recommended especially in patients at high risk. However, the standard technique and the definition of the boost volume have not been well defined.

METHODS

We retrospectively compared an anticipated pre-operative photon boost on the tumour, administered with low-dose fractionated radiotherapy, and neoadjuvant chemotherapy with two different sequential boost techniques, administered after BCS and standard adjuvant WBRT: (1) a standard photon beam (2) and an electron beam technique on the tumour bed of the same patients. The plans were analyzed for the dosimetric coverage of the CT-delineated irradiated volume. The minimal dose received by 95% of the target volume (D95), the minimal dose received by 90% of the target volume (D90) and geographic misses were evaluated.

RESULTS

15 patients were evaluated. The sequential photon and electron boost techniques resulted in inferior target volume coverage compared with the anticipated boost technique, with a median D95 of 96.3% (range 94.7-99.6%) and 0.8% (range 0-30%) and a median D90 of 99.1% (range 90.2-100%) and 54.7% (range 0-84.8%), respectively. We observed a geographic miss in 26.6% of sequential electron plans. The results of the anticipated boost technique were better: 99.4% (range 96.5-100%) and 97.1% (range 86.2-99%) for median D90 and median D95, respectively, and no geographic miss was observed. We observed a dose reduction to the heart, with left-sided breast irradiation, using the anticipated pre-operative boost technique, when analyzed for all dose-volume parameters. When compared with the sequential electron plans, the pre-operative photon technique showed a higher median ipsilateral lung Dmax.

CONCLUSION

Our data show that an anticipated pre-operative photon boost results in a better coverage with respect to the standard sequential boost while also saving the organs at risk and consequently fewer side effects.

ADVANCES IN KNOWLEDGE

This is the first dosimetric study that evaluated the association between an anticipated boost and neoadjuvant chemotherapy treatment.

Accelerated partial breast irradiation: advances and controversies

The management of localized breast cancer has changed dramatically over the past three to four decades. Breast-conserving therapy, which involved lumpectomy followed by adjuvant irradiation, is now widely considered the standard of care in women with early-stage breast cancer. Accelerated partial breast irradiation (APBI), which involves focal irradiation of the lumpectomy cavity over a short period of time, has developed over the past two decades as an alternative to whole breast irradiation (WBI). Multiple APBI modalities have been developed including brachytherapy, external beam irradiation, and intraoperative irradiation. These new techniques have provided early-stage breast cancer patients with shorter treatment duration and more focused irradiation, delivering very high biological doses to the region at a high risk of failures over a much shorter treatment course as compared with conventional radiotherapy. However, the advantages of APBI over conventional radiotherapy are controversial, including a higher risk of complications reported in retrospective literature and shorter follow-up duration in the intraoperative APBI trials. Nevertheless, APBI presents a valuable alternative to WBI for a selected population of women with early-stage breast cancer.

Intraoperative radiotherapy during breast-conserving surgery using a miniature x-ray generator (Intrabeam®): theoretical and experimental background and clinical experience

Breast cancer is currently the most frequent indication for intraoperative radiotherapy with increasing numbers worldwide. Intraoperative radiotherapy can be used as a tumor bed boost followed by whole breast radiotherapy, or as a distinct form of accelerated partial breast irradiation in selected patients. This article summarizes the theoretical background including pattern of recurrence and distribution of tumor cell foci in the breast and discusses the rationale for intraoperative radiotherapy, especially using a miniature x-ray generator (Intrabeam(®)). The concepts of how to avoid geographic and temporal miss by giving radiotherapy during surgery to the open wound cavity are described. Experimental and clinical experience is presented based on in vitro experiments and more than 300 treated patients in a single department with mature follow-up.

Adjuvant therapy for women over age 65 with breast cancer

BACKGROUND

Women over age 65 with breast cancer are often not treated in accordance with current guidelines as far as adjuvant therapy is concerned, because of the lack of adequate scientific evidence.

METHODS

This article is based on a selective review of pertinent literature retrieved by a PubMed search, as well as on the German S3 guidelines for the diagnosis, treatment, and follow-up care of breast cancer, the treatment recommendations of the German Working Group on Gynecological Oncology (Arbeitsgemeinschaft Gynäkologische Onkologie, AGO) and the German Society of Radiation Oncology (Deutsche Gesellschaft für Radioonkologie), US National Comprehensive Cancer Network, and the Cochrane database.

RESULTS

Women over age 65 are underrepresented in randomized trials of treatments for breast cancer. Geriatric assessment is essential for therapeutic decision-making. Endocrine treatment is feasible for nearly all patients with hormone-sensitive tumors. In selected patients over age 65, chemotherapy significantly improves overall survival. The best evidence regarding toxicity is available for anthracycline monotherapy and for combined therapy with doxorubicin/cyclophosphamide or taxane/doxorubicin. Women without cardiac disease can be given trastuzumab, which may lead to reversible cardiotoxicity. Adjuvant radiotherapy significantly improves local tumor control and survival. Adjuvant radiotherapy that is carried out with modern treatment planning, as recommended by the current guidelines, is no more toxic to older patients than to younger ones; thus, it should always be given, unless there is a special reason not to.

CONCLUSION

Women with breast cancer over age 65 whose life expectancy is greater than 5 years, and who are not otherwise too ill, should be given chemotherapy, trastuzumab, and radiotherapy as standard adjuvant treatment. Adjuvant therapy can be reduced or omitted in frail patients. Patients over age 65 should be given the opportunity to enroll in clinical trials.

Intraoperative radiotherapy as accelerated partial breast irradiation for early breast cancer : beware of one-stop shops?

Intraoperative radiotherapy (IORT) was originally introduced in breast cancer treatment as an "anticipated boost" during the procedure of breast conserving surgery (BCS). In addition to whole breast irradiation (WBI), it has yielded excellent long-term results [31, 38]. Under the assumption that the majority of in-breast tumor recurrences (IBTR) occur in the originally affected site, accelerated partial breast irradiation (APBI) as the sole treatment modality was initiated in several studies and with different techniques, one of which was IORT first with electrons, later also with conventional x-rays [29]. The question whether and for whom the gold standard of WBI may be replaced by APBI - especially IORT - alone has recently been one of the most controversial issues of adjuvant therapy for breast cancer. Two recently published studies by Veronesi et al. [36] and Vaidya et al. [35] presenting shortterm results of single shot IORT with electrons (ELIOT) and with an orthovoltage system (TARGIT), respectively, have further invigorated this discussion as illustrated by several letters to the editor commenting on the TARGIT study. While Vaidya et al. [35] indicate their results of IORT alone as "an alternative to WBI for selected patients" and one editorial even proclaims it as standard [6], all the authors of the respective letters [10, 16, 27, 33] strongly disagree with this conclusion. The present editorial comments on the two publications and, furthermore, provides respective statements of the breast cancer expert panel of the German Society of Radiation Oncology (DEGRO).

Radiobiological comparison of hypofractionated accelerated partial-breast irradiation (APBI) and single-dose intraoperative radiotherapy (IORT) with 50-kV X-rays

BACKGROUND AND PURPOSE

Intraoperative radiotherapy (IORT) of the tumor bed in early breast cancer is presently performed with a single dose of 50-kV X-rays from a miniaturized X-ray machine using spherical applicators. The purpose was to model the biological effect of hypofractionated accelerated partial-breast irradiation (APBI) with ten fractions.

MATERIAL AND METHODS

The relative biologic effectiveness (RBE) was estimated from the linear-quadratic (L-Q) formalism including repair of sublethal damage or assuming a constant RBE = 1.2-1.5. The radial distribution of biological effect was assessed from clinical dose-response curves. In accordance with clinical convention, the dose for APBI was prescribed at 1 cm depth in the tumor bed, whereas for IORT it was prescribed at the applicator surface.

RESULTS

The fraction size was fitted to give the same risk of late normal-tissue reaction (fibrosis) as single-dose IORT with a maximum dose of 20 Gy. The isoeffective fraction size at 1 cm depth varied between 1.01 Gy for RBE estimated from the L-Q model and 1.64 Gy for constant RBE. The applicator size and dose prescription point influenced the radial dose distribution. The "sphere of equivalence" within which the risk for local recurrence is the same for whole-breast radiotherapy was predicted to extend to 11-15 mm distance from the applicator for alpha/beta = 10 Gy and 9-13 mm for alpha/beta = 4 Gy for hypofractionated APBI, representing an increase of the sphere of equivalence by 2.5-6 mm relative to single-dose IORT.

CONCLUSION

An increase of the therapeutic window with hypofractionated APBI relative to single-dose IORT should be feasible.