Analysis of discontinued radiotherapy trials registered on ClinicalTrials.gov between 2014 and 2024

Premature terminated clinical trials waste resources, burden patients, and hinder scientific progress. The extent of discontinuation of radiotherapy trials is largely unknown. This study analyzed the reasons, prevalence, and characteristics of discontinued radiotherapy trials registered on ClinicalTrials.gov.

Oncology trials registered between June 1, 2014, and June 1, 2024, were categorized as radiotherapy or other oncology trials. Discontinuation rates and reasons were compared. Multivariable logistic regression was fitted to identify predictors of radiotherapy trial discontinuation.

Of 35,402 trials, 1799 (5.1 %) were radiotherapy trials. Radiotherapy trials had a lower termination/withdrawal rate than other oncology trials (8.6 % vs. 12.8 %; p < 0.001). An analysis of reported reasons for trial discontinuation showed that radiotherapy trials were more prone to termination because of insufficient enrollment (58.7 % [95 % CI, 50.8 %-66.2 %] vs. 27.1 % [95 % CI, 25.8 %-28.5 %]; p < 0.001) and less likely to end because of business/sponsor decisions (1.9 % [95 % CI, 0.5 %-5.5 %] vs. 20.0 %[95 % CI, 18.8 %-21.2 %]; p < 0.001) compared to other oncology trials. Predictors of radiotherapy trial discontinuation included parallel groups (odds ratio [OR], 4.06; p < 0.001), National Institutes of Health sponsorship (OR, 3.85; p = 0.008), and academic institution sponsorship (OR, 3.17; p = 0.003). Trials conducted at multiple sites (OR, 0.49; p = 0.010), in Asia (OR, 0.16; p < 0.001), and in Europe (OR, 0.51; p = 0.019) were more likely to be completed.

Nearly 60 % of the radiotherapy trials terminated due to poor accrual. Radiotherapy trials failure was associated with funding, location, and study design. Targeted efforts are needed to promote trial completion and strengthen evidence-based radiation oncology.