This is a pre-and post intervention study on the effect and implementation of an personalized decision aid for woman with breast cancer who face a decision on their radiation treatment.

Rationale: Guidelines on breast cancer treatment show grey areas for some radiotherapy (RT) indications. In some recommendations the uncertainty is marked and deferred to sharing the final decision on the treatment of choice with the patient. Other recommendations are straightforward, but the multidisciplinary team may decide, based on the latest literature, that different options should be discussed with the patient. In these so called "preference sensitive decisions" there is not one best option. The best option depends on the individual patients' preferences based on neutral and complete information tailored to her own situation. Decision aids support clinicians as well as patients in Shared Decision Making (SDM). Decision aids reduce the patient's decisional conflict after making their decision, increase their knowledge on their illness and the treatment options, and their perceived level of involvement in the decision making process. Although extensive research has been carried out on the effect of decision aids in clinical trials, less is known of the effect of a decision aid in daily clinical practice. The implementation of SDM is challenged by many barriers. The investigators hypothesize that adapting the decision aid to individual patient characteristics may enhance both personalised medicine and SDM.

Objective: To investigate whether SDM using a personalised decision aid, results in improved outcomes of decisional quality, measured by the Decisional Conflict Scale after 3 months and one year, and improved outcomes of the decisional process, measured with the SDMQ9 and collaboRATE directly after the last consultation, compared to the standard clinical practices in breast cancer patients facing a decision on their radiation treatment.

Study design: This is a multicenter clustered , pre- and post-intervention study. Before the intervention 164 patients will be included. After introducing the decision aid, at the beginning of the intervention period, clinicians will be trained in using the decision aid and the other 164 patients will be recruited.

Study population: Breast cancer patients facing a decision in their adjuvant radiation treatment.

Intervention: The intervention group will receive the instructions and the online decision aid.

Main study parameters/endpoints: Primary endpoint: Decisional conflict 3 months after the decision has been made. Secondary endpoint(s): The perceived level of shared decision making, patient knowledge, , and decisional conflict 1 year after decision has been made. A process evaluation will also be perform.

Inclusion Criteria:

• 18 years or older

• Female

• Doubtful indication of:

  • Whole breast irradiation after lumpectomy for DCIS
  • Whole breast irradiation after lumpectomy for low risk invasive BC (TOP-1 study)
  • Boost dose in case of Breast Conserving Therapy
  • Thoracic wall irradiation post mastectomy

Exclusion Criteria:

• Metastasis
• Inability to speak and read Dutch. Inability to use internet access, either in the home or at a hospital facility.

Female

first 164 patients will not receive the decision aid, they will only fill out the questionnaires.

The next 164 patients will receive the decision aid and will be asked to fill out the same questionnaires.