Using Radiation in Cancer Treatment TYPES OF RADIOTHERAPY External beam radiotherapy Delivers radiation, usually photons (X-rays) or electrons, to the tumor from outside the body; it is the most common form of radiotherapy. There are several types of external beam radiotherapy: • Conventional external beam radiation therapy delivers a high-energy X-ray beam from one or more directions and is primarily used when high precision is not required. • Three-dimensional conformal radiotherapy (3DCRT) delivers high-energy X-rays via multiple beams that, with the help of computed tomography and/or magnetic resonance imaging, enable more precise planning to best target the shape and size of the tumor. • Intensity-modulated radiotherapy—a refinement of 3DCRT—delivers radiation by dividing each beam into many “beamlets,” each of which can have a different intensity, to achieve improved conformality. • Intraoperative radiation therapy delivers electron beam (superficial) radiation directly on tumors that have been exposed during surgical procedures, or to the tumor cavity immediately after cancer removal. • Stereotactic radiotherapy delivers radiation to very well-defined smaller tumors, typically using more than eight beams with the help of a highly sophisticated immobilization and imaging system. It is used in both stereotactic radiosurgery (to treat tumors of the brain and central nervous system) and stereotactic body radiotherapy (to treat small tumors within the rest of the body). Particle therapy Delivers radiation doses by protons or carbon ions, instead of X-rays, to the tumor with a dose distribution that better spares the exposure of surrounding tissue, because these particles deposit most of their energy in the target. Although of great interest, proton facilities are much more expensive than traditional facilities, and the overall benefit to patients remains to be defined. Brachytherapy Delivers radiation by placing small radioactive sources in or next to the tumor either temporarily or permanently. Radioisotope therapy Delivers radiation to the tumors via systemic ingestion or infusion of radioisotopes. USES OF RADIOTHERAPY Curative radiotherapy Used to eliminate cancers, often in combination with systemic therapy. Neoadjuvant radiotherapy Used to shrink a tumor so that it can be subsequently treated by a different method such as surgery. Adjuvant radiotherapy Used to eliminate any remaining cancer, often directed to the tumor cavity following prior surgical removal. Palliative radiotherapy Used to reduce or control symptoms of disease when cancer is considered incurable. Salvage radiotherapy Used to treat cancer after the cancer has not responded to other treatments but could be successfully controlled by radiotherapy. SIDEBAR 33 There are two major applications of ionizing radiation in cancer care: TREATMENT OF CANCER Radiotherapy, or radiation therapy, uses high-energy radiation to control and eliminate the disease. DETECTION OF CANCER Radiology largely uses lowenergy radiation to image tissues to diagnose the disease. HIGH LOW HIGH LOW Advancing the Frontiers of Cancer Science and Medicine AACR Cancer Progress Report 2023 81
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