ESTRO 2022 - Abstract Book

S852

Abstract book

ESTRO 2022

Abstract Text Tumor heterogeneity and habitats are not mostly taken into account in current radiotherapy (RT) planning procedures. The extraction of quantitative imaging biomarkers allow for the voxelwise characterisation of lesions, ensuring spatial coherence across different imaging series by the use of optimized registration algorithms. Further development in the field of dose painting and formats for the integration of parametric maps (i.e. parametric DICOM) with RT planning software needs to be explored. Beyond planning, the assessment of RT treatment response as well as early detection of recurrence are key applications of the spatial biology capabilities that bring imaging biomarkers. In this presentation I will review the process for the extraction of accurate imaging biomarkers, accounting for sources of variability, and how to use them for RT planning as well as treatment response evaluation and prediction of recurrence.

Joint Symposium: ESTRO-ESGO: Joint guidelines on the management of vaginal cancer

SP-0973 Diagnosis, staging and role of surgery

C. Fotopolou UK Abstract not available

SP-0974 Role of external beam radiotherapy

R. Nout The Netherlands Abstract not available

SP-0975 Role of brachytherapy

D. Chargari France Abstract not available

SP-0976 Management in children and adolescents

D. Orbach France

Abstract not available

Symposium: Fractionation for external beam radiation therapy in early breast cancer: State-of-the-art

SP-0977 Whole breast irradiation: How fast can we go?

P. Poortmans 1

1 Iridium Netwerk & University of Antwerp, Radiation Oncology, Wilrijk - Antwerpen, Belgium

Abstract Text Decades ago, the concept of 50 Gy/25 fractions to eradicate residual microscopical disease was calculated based on a 50% cell survival rate after 2 Gy. Moderately hypofractionated RT became introduced as the new standard based on solid data more than 10 years ago, but its broad adoption remains slowed down a.o. due to improper considerations such as inappropriate reimbursement based on the number of fractions. Nowadays, the only patients that might benefit from more protracted schedules are those for whom we combine it with systemic or other concomitant therapies to obtain radio- sensitisation. Since the publication of the results of the FAST-Forward trial, with a median follow-up of 71.5 months, ultra- hypofractionated radiation therapy should be considered the new standard for whole breast irradiation. Whereas the COVID- related “pandemisery” facilitated rapid introduction in clinical practice, it should indeed not be considered as a “crisis- related schedule”. Quite like for the adaptation of moderate hypofractionation, considerable reluctance exists regarding the clinical introduction of ultra-hypofractionation, even for whole breast irradiation which formed the vast majority of the trial population of in total 4096 patients. We saw that, similar to moderate hypofractionation studies in breast and prostate cancer, small differences in fractionation exert a measurable impact on endpoints, as seen in the 27 Gy in 5 fractions regimen. Noteworthy, with 40 Gy/15 fractions being more gentle for normal tissues compared to 50 Gy/25 fractions, we now see that the 26 Gy/5 fractions is iso-effective for normal tissue effects with 40 Gy/15 fractions, while 27 Gy/5 fractions equates the side effects seen with 50 Gy/25 fractions. Several large trials that evaluated e.g., the value of a boost to the primary tumourbed, clearly showed that the difference in development of fibrosis and the impact on cosmetic outcome with a (higher) boost dose is present after 3 to 5 years, with thereafter only little further changes in frequency and severity of side effects. Therefore, the follow-up of nearly 6 years of the FAST-Forward trial reliably provides evidence for long-term evolution of fibrosis and cosmesis. Moreover, the prevalence of moderate/marked late effects was low in all FAST-Forward schedules, the most frequent being