No_intervention: Pre-Delphi patient focus group

During this focus group, we aim to achieve various goals:~* To gain insight into the bowel symptoms and the consequences patients experienced after treating rectal cancer~* To understand the expectations of the patients regarding an electronic bowel diary~* To determine whether the questions/items derived from the literature study for the bowel diary are clear and understandable for the patients~* To explore other relevant questions/items that should be added to the bowel diary~We will include 8-12 patients in this focus group.

No_intervention: Delphi survey

In this Delphi survey, a multidisciplinary group of experts and patients will score each item of the long list on a 1-9-point Likert scale from 'Not relevant' (1) to 'Essential' (9) for inclusion in the bowel diary. Finally, a patient consultation meeting and a consensus meeting will be held for the participants who completed the Delphi survey.~We will recruit 10-18 Delphi panelists per area of expertise. These panelists are experts with international expert recognition in treating bowel symptoms in the following health care categories (abdominal surgeons, digestive/radiation oncologists, specialized pelvic floor muscle physiotherapists, nursing specialists). In addition, we will include one group comprising 10-18 patients in the Delphi survey, ensuring a comprehensive and holistic perspective on treating bowel symptoms across various healthcare categories.

No_intervention: Post-Delphi patient focus group

During this focus group, our objective is to ensure that both the questions and answers are meaningful.~We will include 8-12 patients in this focus group.

Experimental: Usability of e-diary

The participants will be asked to use the newly developed electronic bowel diary for 7 consecutive days.~To evaluate the usability of the e-diary, a group of 10 patients will participate in the assessment using the System Usability Scale (SUS).~Furthermore we will have conversations with these patients regarding the use of the application: complexity, need for additional support, coherence of the application, user-friendliness, and the need for prior knowledge.

Experimental: Psychometric properties of e-diary

To evaluate the validity of the e-diary, encompassing test-retest reliability, construct validity and responsiveness, participants will be instructed to use the e-diary for two separate 7-day periods.