ESTRO 2025 - Abstract Book

S148

Invited Speaker

ESTRO 2025

4913

Speaker Abstracts Hypofractionation as the new kid on the block: When, how and why? Rick Haas Radiotherapy, The Netherlands Cancer Institute, Amsterdam, Netherlands. Radiotherapy, Leiden University Medical Center, Leiden, Netherlands

Abstract: Hypofractionation as the new kid on the block: When, how and why?

Introduction Sarcomas are rare mesenchymal neoplasms of various origins (fibroblasts, fat cells, blood vessels, muscles, neurons, cartilage, bone etc.). Although for most tumors, surgery is the cornerstone of management, additional radiotherapy may reduce the local failure rate, roughly with a factor of 3. Historically, this radiation is conventionally fractionated in 1.8-2 Gy once-daily fractions. When? Lessons on hypofractionation, taking response evaluation into account, can only be learned with the sarcoma mass still in situ, meaning only in the preoperative phase. Postoperative radiotherapy, although still mentioned as an option in several Transatlantic Clinical Practice Guidelines, is not a good platform to in-depth learn the value of hypofractionation. How? Carefully designed prospective clinical studies and even registries should be the basis to investigate preoperative hypofractionation. As recently stated in the Journal of Clinical Oncology, the time has not yet arrived to exploit this routinely in daily practice. Why? First, hypofractionation helps in reducing the treatment burden for patients. Second, preclinical studies (on cells) and recent clinical phase II trials have suggested that sarcomas exhibit α/β ratios substantially below 10 Gy. These observations form the rationale for exploiting hypofractionation in the clinic. Third, the recent COVID-19 pandemic has urged care givers to simplify cancer management. Sarcomas were no exception. Fourth, in areas of the world with a relatively low density in radiotherapy facilities, hypofractionation reduces the pressure on hospitals.

4915

Speaker Abstracts How to best integrate systemic treatment and local approaches Michiel Strijbos Medical Oncology, ZAS, Antwerp, Belgium

Abstract:

Integrating Systemic and Local Therapies in Kidney Cancer: Lessons from Randomized Trials

Renal cell carcinoma (RCC) is increasingly treated with both targeted and immunotherapeutic agents, yet durable control in advanced disease remains a major clinical challenge. Stereotactic body radiotherapy (SBRT) has emerged as a powerful local treatment option, offering high rates of local control in both primary and metastatic sites. Evidence from phase II studies in RCC demonstrates that combining SBRT with systemic therapy is not only feasible