When patients receive radiation therapy for breast cancer, they need to take off their underwear to avoid build-up effects. However, it is a mental burden for female patients to take off their underwear at every fraction of radiation therapy. The purpose of this study was to investigate whether commercially available thin underwear can be worn during radiation therapy for breast cancer.

In this phantom study, we investigated whether commercially available underwear can be worn during radiation therapy for breast cancer using six thin non-disposable brassieres and one disposable paper brassiere. The dose increase rate (ΔD) was calculated by measuring skin doses with or without each brassiere.

The mean ΔD values of six non-disposable brassieres were 13.5% (9.0–21.8%), whereas that of disposable ones was 2.0%.

Due to the risk of excessive radiation to the skin, wearing commercially available underwear is not recommended during radiation therapy for breast cancer, but a thin disposable paper brassiere may be safe to be used.