ESTRO 2024 - Abstract Book

S15 ESTRO 2024 (HDR) MIBT delivering a total dose of 32 Gy or 30.3 Gy over 4 days. Based on these excellent clinical results, can breast brachytherapy match EBRT hypofractionation? This question appears clearly relevant for early breast cancers defined as low-risk for GEC-ESTRO APBI Classification with Luminal A/B molecular status. However, for more aggressive tumours, and because a whole breast irradiation (WBI) will be mandatory, MIBT will be not proposed being by definition a partial breast irradiation. Focusing on low-risk breast cancer, STRAT B Phase 3 trial confirmed that 25 d versus 15 d of breast irradiation were non-inferior in terms of local control. FAST-Forward Trail continues by showing that 15 d were non inferior to 5 d. While GEC-ESTRO phase 3 trial reported non inferior local control between 25 d and 5 d by using MIBT, we could hypothesis by transitivity that MIBT is non inferior to EBRT 5 d regimen. If oncological appears equivalent between whole breast EBRT and MIBT PBI for low-risk breast cancer, what about toxicity? Due to its own and particular dose distribution, MIBT represents an elective irradiation technique allowing decreasing the dose to organs at risk (OARs: non-CTV remaining breast tissue, contralateral breast, lung, heart/coronary arteries, chest-wall). The potential deleterious effect of “old” adjuvant EBRT techniques on overall survival was initially reported by the EBCTCG in 2011, while in 2014, it appears that EBRT technique was a key factor for avoiding deleterious side effects impacting on non-breast cancer death rates. In 2013, Darby et al. confirmed that the dose delivered to the heart was a strong prognostic factor for ischemic heart disease after breast cancer irradiation. Using MIBT allows protecting coronary arteries from late side effects and subsequent heart late complications for patients with long life expectancy. Radiation-induced carcinogenesis represents another late and rare but deleterious potential consequence of irradiation of the breast. After WBI, the excess risk of secondary cancer (mainly lung cancer) for a patient treated at age 50 years could be about 4 to 5%. Hoekstra et al. reported that for a typical early stage patient irradiated at 50, the excess risks of secondary lung cancer were 1.1% after MIBT, between 2.2% and 2.5% with 3D-CRT/CK, 3.5% for VMAT APBI, and 3.8% for WBI. MIBT allows delivering a high-dose (efficacy) in a small volume (toxicity) in a short time (treatment convenient). This irradiation profile appears to be more attractive/relevant in case of breast re-irradiation for ipsilateral breast cancer recurrence (or in a pre-irradiated area i.d. lymphoma, lung or esophagus cancers). Indeed, in this particular clinical situation, compared to EBRT, MIBT will reduce the dose delivered to the OARs which have already been irradiated. Invited Speaker

Last but not least, in terms of patient comfort and radiation therapy department organization, very APBI based on single fraction can easily be performed with MIBT.

In conclusion, EBRT and MIBT should be used in specific indications, by playing their own key role for achieving excellent results.

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Breath regularisation during stereotactic cardiac radioablation

Irma W.E.M. van Dijk 1 , Brian V. Balgobind 1 , Edith M.T. Dieleman 1 , Wiert F. Hoeksema 2 , Rianne (M.)A.J. de Jong 1 , Zdenko van Kesteren 1 , Michael J. Parkes 1 , Pieter G. Postema 2 , Markus F. Stevens 3 , Johannes K. Veldman 1 , Joost J.C. Verhoeff 1 , Jorrit Visser 1 , Thomas Weststrate 1 , Niek van Wieringen 1 , Arjan Bel 1