ESTRO 2026 Congress Report

By the ESTRO SBRT Focus Group

The ESTRO 2026 congress highlighted the growing role of stereotactic ablative radiotherapy (SABR) in the management of localised renal cell carcinoma (RCC). Across oral presentations and posters, the focus was not only on long-term tumour control and side effects outcomes, but also on the bigger question facing the field: we now have the evidence, but how do we move towards broader implementation and potential practice change?

One of the main presentations came from Prof. Shankar Siva (Peter MacCallum Cancer Centre, Australia) with the TROG 15.03 FASTRACK II trial, presenting final long-term outcomes for SABR in primary RCC. RCC incidence is rising worldwide, particularly in patients over 70 years old, many of whom are medically unfit for surgery or have significant comorbidities. While surgery remains the standard of care, many older patients still undergo radical nephrectomy rather than nephron-sparing approaches, while others are managed with surveillance or non-surgical options.

SABR was presented as a potential treatment that ‘ticks all the boxes’, completely non-invasive, no requirement for general anaesthetic, and suitable even for larger or peri-hilar tumours that may not be ideal for thermal ablation. FASTRACK II was the first multicentre phase II trial investigating non-surgical treatment for primary RCC, recruiting 70 patients across Australia and the Netherlands between 2016 and 2020. Most patients were elderly, comorbid, and had tumours that had already demonstrated growth during active surveillance before enrolment.

Patients received either 26Gy in a single fraction for tumours under 4cm, or 42Gy in three fractions for larger lesions. Importantly, many of these tumours were larger and cases more complex than would traditionally be considered suitable for thermal ablation.

The long-term outcomes presented were impressive. Local control remained at 100% throughout follow-up, with cancer-specific survival also reaching 100%. Freedom from distant failure was 88% at five years. Kidney function declined mainly within the first two years before stabilising, and only one patient required dialysis. Seven grade 3 adverse events were reported, and no grade 4 or 5 adverse events were observed. Notably, all grade 3 side effects occurred within the first nine months, with no significant late adverse events seen with extended follow-up.

We then had Dr Ajay Aggarwal (Guy’s and St Thomas’ NHS Foundation Trust, UK) discuss how, as a profession, we move from strong evidence to actually delivering renal SABR routinely to patients. His message was that the evidence is now difficult to ignore. Recent meta-analyses and prospective studies have demonstrated clear efficacy, and the field has moved beyond asking whether SABR works. The real question now is implementation.

Several barriers to adoption were discussed, including a lack of referrals from urologists, limited SABR expertise, and unequal access to technology and multidisciplinary pathways. He also highlighted emerging competitors such as histotripsy and robotic surgery, both of which continue to evolve and may challenge the perceived equipoise between surgery and SABR. As he noted, many surgeons are enthusiastic about the data but remain cautious about offering SABR to younger operable patients.

Another major discussion point was the difficulty of conducting randomised trials comparing surgery and radiotherapy in RCC, a challenge that has been encountered across many SABR disease sites. Traditional trial designs often struggle because of recruitment challenges and strong treatment preferences. Alternative methods of evidence generation, including registry-based studies, target trial emulation, and newer trial designs using prioritised endpoints such as side effects, quality of life, and distant metastases, were proposed as potential ways forward.

Additional real-world evidence came from a poster presentation by Dr Vivian Tan (Western University, Canada), who evaluated outcomes in medically operable and inoperable patients treated with renal SABR between 2012 and 2024. Despite larger tumours and greater comorbidity burden in the inoperable cohort, outcomes remained excellent in both groups. Local control reached 100% in operable patients and 95% in medically inoperable patients, while cancer-specific survival at two years was 100% in both cohorts. Severe side effects remained uncommon, with no grade 4 or 5 adverse events reported.

Overall, the RCC sessions reflected a field with growing confidence and momentum. Long-term prospective data now support SABR as a safe and effective treatment option for medically inoperable RCC, while emerging real-world evidence suggests its role may continue to expand. Moving forward, ensuring equitable access to renal SABR will depend not only on continued evidence generation but also on the development of clinical expertise, multidisciplinary collaboration, and the infrastructure required to deliver these increasingly specialised treatments safely.

Harley Stephens
University Hospitals Bristol and Weston
UK
Member of the ESTRO SBRT Focus Group