The trials within cohorts design facilitated efficient patient enrolment and generalisability in oncology setting

Abstract Objective The trials within cohorts (TwiCs)-design aims to improve recruitment efficiency. We conducted the first TwiCs in radiation oncology and described efficiency of the design and generalisability of the results. Study design and setting In two radiotherapy centres, patients with rectal cancer were asked to participate in a prospective cohort, and to provide broad consent for randomisation and patient-reported outcomes (PROs). Consenting patients who met the trial criteria were randomised directly after cohort enrolment. The intervention arm was offered a radiotherapy boost. We evaluated acceptance rate, its impact on sample size and compared clinical characteristics with those of the Dutch national cancer registry. Results 128 of the 200 eligible patients (64%) were randomised. Sixty-two patients did not consent (in time) to cohort participation, to broad randomisation or to PROs. Of the 64 patients in the intervention arm, 52 (81%) accepted the intervention. During the trial, the acceptance rate dropped temporarily, after which sample size was adapted. Trial patients were comparable in age, comorbidity and disease stage to the national rectal cancer population. Conclusions The TwiCs design is feasible, allows enrolment of a high proportion of randomizable patients, with positive impact on trial efficiency and generalisability of results in a clinical oncology setting.