Breast cancer is the most common malignancy among women worldwide. For early stage breast cancer, adjuvant radiotherapy is essential to minimize loco-regional disease recurrence. However, significant portions of the heart and the lungs are exposed to low dose radiation during radiotherapy, which result in stochastic side effects among breast cancer survivors. Inspired by 3D printing technology, we approached this issue with an in-house made PERSonalized BReAst holder system (PERSBRA). PERSBRA is composed of a 3D-printed plastic holder covering the whole breast and an air-filled interface. Its main function is to reproducibly adjust the breast position to decrease heart and lung radiation exposure in tangential fields. Here we propose to measure the performance of PERSBR in terms of radiation dosimetry in 50 patients receiving scheduled whole breast irradiation. For customized PERSBRA, body shape of the patient with or without a bustier corset will be captured with a handheld 3D scanner and input into a 3D printer for PERSBRA design and manufacturing. A participant will receive two more CT scans in addition to the simulation scan with PERSBRA in place before the first and the sixth fractions of irradiation. These images will be analyzed for dosimetric parameters in the presence/absence of PERSBRA as well as position reproducibility. The data will provide proof-of-principle evidence for the clinical utility of PERSBRA and will facilitate its further refinement.

1. Patients with early breast cancer or ductal carcinoma in situ treated with breast conservation surgery.
2. Adjuvant radiotherapy to the breast is part of the patient's initial treatment plan.
3. Non-contrast CT scan is a routine procedure for the patient's radiotherapy treatment planning.

Inclusion Criteria:

• Patients with early breast cancer or carcinoma in situ after partial mastectomy have decided to receive adjuvant radiation therapy for the breast on the affected side, and use non-contrast computed tomography to obtain localized images is part of the original treatment plan.

Exclusion Criteria:

• Clinical diagnosis or pathological diagnosis has lymph node metastasis, lymph node micrometastasis, or lymph node tumor cells.
• The clinical diagnosis is likely to have metastatic cancer.
• Pregnant women.
• Be younger than 20 years old.
• The subject was unable to read and understand the subject consent form written in Chinese and complete the informed consent procedure.