ABSTRACT
External radiation therapy (sometimes called teletherapy) delivers high-energy X-rays, electron beams, or proton beams to a tumour from a radioactive cobalt-60 (60Co) source or linear accelerator, often under imaging guidance. Worldwide, over 30,000 patients with benign and malignant brain tumours are treated annually with an external radiation procedure known as gamma knife radiosurgery, which involves focusing gamma radiation from over 200 60Co sources on brain lesions. A total of one million stem cell transplants (from bone marrow, peripheral blood, or umbilical cord blood) have been performed worldwide for haematological malignancies, which may seem surprising given that stem cell transplantation was regarded as an uncommon procedure until the end of the 20th century. Total body irradiation with doses ranging from 10 to 12 Gy (4.5 Gy is fatal in 50% of exposed individuals without aggressive medical care) is used as part of the preparation for haematopoietic stem cell (or bone marrow) transplantation. In July 2013, researchers from Harvard Medical School [3] announced that two patients with longstanding HIV infection appeared to be virus free after undergoing bone marrow transplants using total body irradiation. Unfortunately, after a few months with no HIV detected, sign of the virus remerged, suggesting that there may be an important long-lived HIV reservoir outside the blood compartment. This finding is scientifically significant.
