Mariken Stegmann

short instructional video is available. As the OPT is very easy to use, as shown in earlier  research,  9,21  we believe that more training will be unnecessary.  When a GP will be unable to participate in the study temporarily, another GP from the  project group will perform the OPT conversation. When a GP will not want to participate  at all, patients will complete their questionnaires as if they had been randomised to the  control group. Analysis in the intervention group will be on an intention‐to‐treat basis,  while analysis in the control‐group will be on a per‐protocol basis.  Care as usual  Patients in the care as usual group will not be asked to contact their GP, but will be  allowed to seek the care of their GP at their own discretion without being subject to the  OPT‐based consultation. These contacts will be recorded to study potential bias.  Outcomes  Baseline characteristics  Patients will be asked to provide their age, gender, education, living situation, social  network, and dependency in activities of daily living. Furthermore, information about  tumour type, tumour size, tumour location, tumour stage, performance score,  comorbidities, and treatments will be extracted from hospital and GP records.  Primary outcome  The primary outcome is patient empowerment, as measured by the decision self‐efcacy  (D‐SE) scale directly after consultations with oncologists when treatment choices have  been made. Decision self‐efcacy is described as self‐condence or belief in one’s ability  to make decisions, including participating in SDM. The scale was originally developed in  Ottawa, Canada, in 1996, 22,23  and has been validated in patients with cancer in  Denmark. 23  It consists of 11 items that can be scored on 0–4 point scales. Prior to the  study, the questionnaire was translated into Dutch, and the translation was validated by  back‐translation into English.  Secondary outcomes  The presence of anxiety and depression symptoms will be measured using the Hospital  Anxiety and Depression Scale (HADS). 24  The HADS is used in research for patients with  cancer, and has shown adequate psychometric properties in this specic group. 25 Fatigue will be measured by the multidimensional fatigue inventory (MFI‐20). 26  This self‐ report scale consists of 20 items in ve dimensions: general fatigue, physical fatigue,  mental fatigue, reduced motivation, and reduced activity. It was developed in Dutch in  1995 and has been validated in patients with cancer. 27  In patients with cancer, a subscale  difference of two points is usually considered the minimally clinically important  difference in change over time. 28 During the study, scores for both secondary outcomes (HADS and MFI‐20) will be made  available to the oncologists and GPs of all participants.  2 23 Protocol for the OPTion study