Comparative efficacy of intraoperative radiotherapy and external boost irradiation in early-stage breast cancer: a systematic review and meta-analysis

External boost radiotherapy (EBRT) and intraoperative radiotherapy (IORT) are shown to be effective in patients with early-stage breast cancer. However, the difference between IORT and EBRT for patients' prognosis remains to be elucidated. The purpose of this meta-analysis is to investigate differences in local recurrence (LR), distant metastases, disease free survival (DFS), and overall survival (OS) between these two therapies. We searched the Cochrane Library, PubMed, Web of Science and Embase, from inception to Jan 10th, 2022. We used The Cochrane risk-of-bias assessment tool to assess the risk of bias of the included studies, and the STATA15.0 tool was used for the meta-analyses. Eight studies were ultimately included. Meta-analysis demonstrated that there was an inconsistent finding in the long-term risk of LR between the two radiotherapies, and there was no significant difference in short-term risk of LR, the metastasis rate, DFS, and OS IORT would be more convenient, less time-consuming, less costly, and more effective at reducing side effects and toxicity. However, these benefits must be balanced against the potential for increased risk of LR in the long term.

Global adoption of single-shot targeted intraoperative radiotherapy (TARGIT-IORT) for breast cancer—better for patients, better for healthcare systems

Micro abstract

Targeted intraoperative radiotherapy (TARGIT-IORT) is delivered immediately after lumpectomy for breast cancer. We estimated its impact. At least 44,752 patients with breast cancer were treated with TARGIT-IORT in 260 centres in 35 countries, saving >20 million miles of travel and preventing ~2,000 non–breast cancer deaths. The TARGIT-IORT website (https://targit.org.uk/travel) provides maps and tools to find the nearest centre offering TARGIT-IORT and travel savings.

Background

Targeted intraoperative radiotherapy (TARGIT-IORT) delivers radiotherapy targeted to the fresh tumour bed exposed immediately after lumpectomy for breast cancer. TARGIT-A trial found TARGIT-IORT to be as effective as whole-breast radiotherapy, with significantly fewer deaths from non–breast cancer causes. This paper documents its worldwide impact and provides interactive tools for clinicians and patients.

Method

Centres using TARGIT-IORT provided the date of the first case and the total number of patients. We plotted these data on a customised Google Map. An interactive web-based tool provided directions to the closest centre. Using the data from the TARGIT-A trial, we estimated the total savings in travel miles, carbon footprint, and the number of non–breast cancer deaths that might be prevented.

Results

Data from 242 (93%) of the 260 centres treating patients from 35 countries were available. From the first patient treated in 1998 to early 2020, at least 44,752 women with breast cancer have been treated with TARGIT-IORT. The TARGIT-IORT website (https://targit.org.uk/travel) displays the Google Map of centres with number of cases and an interactive tool for patients to find the nearest centre offering TARGIT-IORT and their travel savings. Scaling up to the already treated patients, >20 million miles of travel would have been saved and about 2,000 deaths prevented.

Conclusion

One can ascertain the number of patients treated with a novel treatment. These data show how widely TARGIT-IORT has now been adopted and gives an indication of its beneficial worldwide impact on a large number of women with breast cancer.

Impact assessment of breast glandularity on relative biological effectiveness of low energy IORT X-rays through Monte Carlo simulation

INTRODUCTION

Intraoperative radiotherapy (IORT) by low energy X-rays is a single fraction treatment modality for tumor bed irradiation after breast-conserving surgery. It has been shown that the variations of breast tissue composition can affect the absorbed dose in this method. Apart from physical quantities such as absorbed dose value, radiobiological quantities including relative biological effectiveness (RBE) may also change with the variations of breast tissue composition. Accordingly, the current study aims to quantify both single and double-strand break RBE values (RBE_SSB and RBE_DSB) of low energy X-rays at different breast glandular fractions using a hybrid Monte Carlo (MC) simulation approach.

MATERIALS AND METHODS

Produced low-energy X-rays by a validated MC model of INTRABEAM machine with 50 kV nominal voltage were considered as the radiation source. The secondary electron energy spectra at various depths inside the breast tissue with different glandular fractions were scored through GEANT4 MC Toolkit. Calculated spectra were then imported to MCDS MC code for DNA strand break calculation and RBE assessment. Both RBE_SSB and RBE_DSB were calculated for various breast glandular fractions.

RESULTS

Changing the breast glandularity can affect both the trend of secondary electron spectra and relevant RBE values at different depths inside the breast volume. In this regard, RBE_SSB increments by about 1% with increasing the breast glandular fraction from 0% to 100%. On the other hand, RBE_DSB decrements by about 3.3% with increasing the glandular fraction in the range of 0% to 100%. Variations of the depth within the breast tissue can also influence the RBE value so that RBE_SSB reduces by about 1% with increasing the depth from 2 mm to 10 mm one, while RBE_DSB increases about 3.4%. The relevant RBE_SSB and RBE_DSB values to the entire target volume (breast PTV) respectively increment and decrement by about 0.8% and 3.2% with increasing the breast glandularity from 0% to 100%.

CONCLUSION

From the results, it can be concluded that the breast tissue composition has a measurable effect on RBE values of employed low energy X-rays during breast IORT which can cause variations of prescribed dose for patients with distinct breast glandularity fractions.