This study will test the impact of a short video intervention for people who are receiving radioiodine treatment for thyroid conditions (such as hyperthyroidism or thyroid cancer). After their single-dose treatment, patients need to follow safety instructions to protect others and manage side effects during recovery. Some people find these instructions hard to remember, and side effects (or anticipation of side effects) can feel worrying or disruptive. The video aims to present the treatment information in a more accessible patient-friendly way, so that patients feel less distressed, find their side effects easier to cope with, and better engage with safety precautions. All patients will first have a pre-treatment consultation with their doctor and receive the standard treatment information currently provided. Before this consultation patients will be randomly assigned to view one of two videos. The control group will see a neutral video that details standard health information that is not specific to radioiodine, while the intervention group will see a video that explains side effects, safety requirements and recovery period in a more adaptive way. Comparing these two groups will allow us to assess whether this new approach improves coping, reduces distress, and enhances adherence to safety instructions in the post-dose recovery phase of radioiodine treatment.

This study is a two-arm randomised controlled trial. Prior to treatment, participants will be randomly assigned to one of two arms. The control group will view a neutral video that discusses general health advice unrelated to the radioiodine treatment, while the intervention group will view a video that reframes side effects and safety instructions in a more adaptive way. All participants will receive a standard pre-treatment consultation with their doctor and the usual written information. Outcomes will then be compared between the two groups in terms of side effects, disability and understanding of treatment precautions. To control for expectation effects both groups will be told that we are testing different videos to assist patients with the radioiodine treatment. This study aims to find out whether a short video intervention (1) helps patients cope better with side effects and get back to normal activities more quickly, (2) improves how well patients remember and understand the safety instructions they need to follow after their dose, (3) reduces disability related to the treatment and its side effects. By examining whether a brief video intervention improves coping with side effects, understanding of safety instructions, and post-treatment recovery, the research will provide new knowledge on how information about radioiodine can be delivered more effectively.

Inclusion Criteria:

• Adults aged 18 years or older
• Clinical diagnosis of hyperthyroidism or thyroid cancer
• Scheduled to receive radioiodine therapy at Auckland City Hospital Radiation Oncology Clinic
• Able to understand and communicate in English
• Access to an internet-connected device to complete study questionnaires

Exclusion Criteria:

• Completed previous radioiodine treatment
• Self-reported difficulty completing questionnaires

De-identified individual participant data (IPD) will be shared, including item-level questionnaire responses and derived summary scores collected at each study time point (e.g., symptom attribution scores, functional interference scores, and adherence scores), as well as basic demographic variables necessary to reproduce the primary analyses.

Data that could directly or indirectly identify individual participants (e.g., names, contact details, dates of birth) will not be shared.

The start date will be after publication of the primary results or completion of the thesis, whichever occurs first. IPD will be available upon reasonable request for up to 5 years following study completion.

De-identified IPD and supporting information will be available to qualified researchers upon reasonable request. Requests must include a brief proposal outlining the intended use of the data and will be reviewed by the study investigators. Approved requestors will be granted access to de-identified datasets and supporting documentation via secure data transfer. Data sharing will be conducted in accordance with institutional ethics approval and data governance requirements.

To control for expectation effects both groups will be told that we are testing different videos to assist patients with the radioiodine treatment.