Background: Level 1 evidence exists for the use of both neoadjuvant chemotherapy (NAC) and concomitant radiosensitization (CRS) to improve outcomes in patients receiving radical radiotherapy (RT) for muscle invasive bladder cancer, but uptake has been patchy. We report here the current patterns of usage in an ongoing trial of adaptive radiotherapy. Methods: RAIDER is an international randomized phase II trial recruiting patients with unifocal T2-T4a urothelial carcinoma of the bladder suitable for RT (ISCRTN:26779187). Patients are randomized in a 1:1:2 ratio to one of 3 arms: Standard whole bladder RT (control); Standard dose adaptive tumour focused RT; Dose escalated (DE) adaptive tumour boost RT. Standard dose patients are treated to either 64Gy/32f or 55Gy/20f and DE patients to 70Gy in 32f or 60Gy in 20f. Patients are encouraged to receive NAC and CRS. The primary endpoint is the rate of late toxicity 6-18 months post treatment in arm 3, with secondary endpoints of patient reported and disease related outcomes. Results: To August 2019, 285 patients had been recruited. Median age is 72 years (IQR 67-79). Stage of disease is T2 79%, T3 19%, T4 2%; 19% have hydronephrosis. Patients receiving NAC were more likely to be PS 0 at trial entry (70% v 45%). Variation in frequency of CRS use is seen across sites, with some offering to >90% of participants and some <50%. Data on NAC and CRS use is available for 249 patients recruited to date is shown in table. Conclusions: In this ongoing clinical trial the majority of patients are receiving NAC and/or CRS. However, uptake is not universal with ~30% of patients not receiving low dose CRS, including some who have received NAC. Clinical trial information: 26779187.