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Stereotactic body radiotherapy (SBRT) is a method of external beam radiotherapy in which a high dose of radiation is delivered precisely to an extracranial target in one or a few treatment fractions. It is similar to brachytherapy (BT) in most respects, except that BT is not an external beam procedure. In this presentation, similarities and differences between BT and SBRT will be highlighted. An important issue is the comparison of physical doses, as both techniques can deliver high, often inhomogeneous doses to a small volume. Motion management is also important, as doses should be delivered with high dose gradients. Here, BT has an advantage because the applicators and radiation source are directly connected to the patient and movements do not have a major impact on the treatment.
Both techniques can be used adaptively, i.e., 3D imaging is performed immediately before irradiation, and the treatment plan is adjusted accordingly. Adaptive treatment of prostate cancer and cervical cancer has been used in BT for many years; for SBRT, this is still a challenge, but is already well possible with dedicated treatment devices for adaptive irradiation.
Another issue that should be considered is the integral dose. Due to the physical properties of high-energy photon beams, SBRT exposes a large volume of the patient to a low dose. This volume is lower with BT and therefore beneficial to the patient as secondary malignancies are likely to be reduced.