Brachytherapy is a general term for many similar techniques such as post-mounted therapy and particle therapy, which means that the radiation source is placed inside or next to the tumor tissue for irradiation. The closer the distance to the radiation source, the stronger the intensity of its radiation, and the distance increases, the intensity can decrease rapidly, and the dose distribution is in accordance with the inverse square law. The radiation sources often used are cobalt-60, iridium-192 and iodine-125, and the radiation therapy for cervical cancer requires a high curative dose.