ADVANCES in radiotherapy have firmly established it as a viable alternative to radical cystectomy for the treatment of muscle-invasive bladder cancer (MIBC). By incorporating modern techniques such as chemosensitisation and hypofractionation, radiotherapy has shown cause-specific survival rates similar to surgery, while also offering the potential for an improved quality of life.
Despite these promising outcomes, bladder radiotherapy presents significant technical challenges, particularly due to the bladder’s shape and position, which can change throughout treatment. This variation necessitates large margins to ensure accurate targeting. However, this approach can lead to excessive toxicity, without reliably preventing geographical misses where parts of the tumour may be missed.
The introduction of image-guided radiotherapy (IGRT) has revolutionised targeting precision in bladder cancer treatment, allowing the development of adaptive strategies. These strategies not only reduce treatment volume but also maintain comprehensive tumour coverage. These improvements have led to target coverage exceeding 95% per fraction, with reductions in target volume by 25–40%. This precision has paved the way for dose escalation, enabling clinicians to focus full doses on the gross tumour volume, using smaller and more accurate margins. A phase 1/2 study demonstrated the feasibility of delivering a dose of 70 Gy in 32 fractions, and the RAIDER trial later confirmed the safety and efficacy of this approach across multiple centres.
In the RAIDER trial, 82% of patients received dose-escalated radiotherapy and experienced minimal late toxicity. Both adaptive radiotherapy groups reported less than 20% of patients experiencing grade ≥3 late radiotherapy-related toxicity. A significant portion of participants received either 60 Gy in 20 fractions or 70 Gy in 32 fractions, emphasising the role of adaptive planning in addressing bladder variability and optimising target coverage. Retraining and revised guidance improved treatment compliance, reinforcing the need for ongoing quality assurance.
Despite dose escalation, toxicity rates in RAIDER remained modest, with 2-year severe toxicity rates significantly lower than those in earlier bladder radiotherapy trials. These favourable outcomes can likely be attributed to modern techniques, such as intensity-modulated radiotherapy, alongside tumour-focused treatment. Furthermore, the promising tumour control rates in RAIDER were comparable to those in cystectomy patients, supporting the idea that adaptive radiotherapy can achieve similar survival outcomes without surgery.
Katie Wright, EMJ
Reference
Huddart R et al. Dose-escalated adaptive radiotherapy for bladder cancer: results of the Phase 2 RAIDER randomised controlled trial. Eur Urol. 2025;87(1):60-70.
