OVERVIEW
Radiation therapy, one of the three established cancer treatment modalities, is used to treat most types of solid tumors and selected hematologic malignancies. It is used almost entirely to treat malignant disease, although it has a small role in preventing proliferation in benign disease. Radiation therapy is routinely combined with surgery, chemotherapy, or both to improve therapeutic results. It is often used with surgery to destroy microscopic regions of tumor extension and with chemotherapy to more effectively destroy the primary tumor. An understanding of the therapeutic use of ionizing radiation requires a basic comprehension of both the physics of radiation therapy delivery and the biological effects of the interaction of radiation with matter.
APPLICATION
Above threshold energy, a photon can be absorbed into an atomic nucleus and cause one of the nucleons (a proton or a neutron) to be ejected. This process is called photodisintegration. Photodisintegration is more probable in high-Z materials (such as metals), and thus is more likely to happen during photon generation in a linear particle accelerator (linac) than in tissue. Neutrons produced in this manner can contribute a significant background radiation dose to patients receiving radiotherapy from very high-energy machines. However, photodisintegration is negligible for accelerators operating below 10 MV.
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