ESTRO 2022 - Abstract Book

S854

Abstract book

ESTRO 2022

a single-centre trial of postmastectomy radiotherapy in 810 women with primary T3–4 tumours or at least four positive axillary nodes randomised to 43.5 Gy in 15 fractions or 50 Gy in 25 fractions, both to the chest wall and level 3–4 axillary nodal regions. At around 5 years of median follow-up, the risk of locoregional recurrence was similar between treatment groups, and no significant increase in late normal tissue effects was observed. The only significant difference described was the reduced severity of acute skin toxicity in patients treated with hypofractionation, which is reassuringly consistent with recent observations from the past decade. Further evidence is awaited from other groups, which are conducting clinical trials to investigate this clinical setting across Europe. Mastectomies are increasing worldwide, due to genetic testing, women’s choice, and the improvements in modern reconstruction techniques. Indeed, breast reconstruction has transformed a mastectomy in a much less demolitive procedure. It is possible either as a delayed step (delayed breast reconstruction) or simultaneously to the oncological procedure (immediate breast reconstruction). Thanks to modern “conservative mastectomies” (skin-sparing, nipple- sparing, and skin-reducing), immediate breast reconstruction has become a very common option and it is preferred to both delayed breast reconstruction and no reconstruction at all. Implants have been by far preferred in Europe for many years and lately this is frequent in the US as well. An immediate implant-based breast reconstruction (IBBR) can be either performed in two stages, using tissue expanders (TE), to be exchanged with permanent implants, or in one stage, with an immediate permanent implant positioning (direct-to-implant, DTI). The choice of TE or DTI is based on oncological, anthropometric, and comorbidity factors. More recently, a paradigm shift has been introduced in the IBBR scenario, namely the prepectoral approach. There are no large, randomized trials testing moderate hypofractionation after mastectomy radiotherapy in the setting of breast reconstruction. Small, non-randomised series suggest that late normal tissue effects and capsular contracture rates are like those obtained with 2 Gy daily fractionation. The lower equivalent dose in 2 Gy fractions with 40 Gy in 15 fractions compared with 50 Gy in 25 fractions would, in fact, favour moderately hypofractionated radiotherapy because it results in less side-effects. This dose and fractionation have been a standard of care for all types of breast reconstruction for several years in many countries. Relative mastectomy proportions within the FAST-Forward trial were as follows: 6.7% in the 40 Gy group, 6.5% in the 27 Gy group, and 6.1% in the 26 Gy group. One local recurrence was observed in the 40 Gy group and none in the 173 patients in the five fraction groups. The 2021 UK Royal College of Radiologists’ Consensus Statements Programme reached a consensus on offering 26 Gy in five fractions over 1 week for chest wall irradiation without reconstruction. Immediate reconstruction rates within the FAST-Forward trial were less than 1% across all groups with only ten patients receiving immediate implant- based reconstruction. An overview on recent advances on fractionation for external beam radiation therapy chest wall irradiation with or without breast reconstruction, including the recently published ESTRO-ACROP consensus recommendations on patient selection and dose and fractionation for external beam radiotherapy in early breast cancer, is hereby presented.

Symposium: Medical physicists should be directly involved in the design, execution and interpretation of clinical trials

SP-0980 NTCP modelling: A tool for designing clinical trials

I.R. Vogelius

Denmark Abstract not available

SP-0981 How to design clinical trials which assess the advantage of new technologies

G. Price 1

1 The University of Manchester, Manchester Cancer Research Centre, Manchester, United Kingdom

Abstract Text Much of the improvement in radiotherapy care witnessed seen over the last few decades has been driven by the clinical adoption of technical innovations. However, the well-known phase I-III randomised controlled trial framework used to assess new drug treatments is often not well suited to the evaluation of such innovations. As a result, many technical changes in radiotherapy practice are implemented without robust evidence of their impact on clinical outcome. In this presentation we use historic and contemporary examples to explore the need for such evidence, the reasons conventional clinical trials can be inappropriate for the evaluation of new techniques and technologies, and some of the approaches used and proposed to address this unmet need in clinical oncology. The talk will cover novel trial designs that are finding use in radiotherapy centres, the potential of pragmatic evaluations, and the advantages and disadvantages of observational studies, including prospective registries (e.g. MOMENTUM). We will introduce frameworks developed by investigators and regulatory bodies to draw on data from different study types when introducing and evaluating new technologies (e.g. R-IDEAL), and the impact that newly emerging analytical techniques such as causal inference and in-silico trials may have on these approaches in the future. Lastly, we will discuss whether the Leaning Healthcare System concept, that combines digital healthcare initiatives and clinical studies with the continuous improvement approaches used in Quality Improvement, might have a role in the introduction, evaluation, and potential optimisation of technical changes in radiotherapy practice.

SP-0982 Benchmarking for contouring and treatment planning for accreditation of clinical trials

E. Clementel

Belgium