Entrance dose

In external-beam radiotherapy, the beam enters from the outside into the patient’s body. As the beam enters the body and makes its way to the tumour, it inevitably harms some cells along its way. We call this the entrance dose. As opposed to external-beam radiotherapy delivered by a linear accelerator, brachytherapy is a modality where the radiation beams from the inside out. Yes, from within the body. This is made possible via insertion of radioactive seeds into body cavities (the most common being the vagina). The dose to surrounding healthy tissues is thus lowered. Brachytherapy may be administered via different modes: remote-afterloading exposes staff to less dose; high dose-rate allows the treatment to be delivered in an outpatient basis.