hematology and oncology
Radiation Therapy for Cancer
Introduction
Radiation therapy can cure many cancers (see also Overview of Cancer Therapy ), particularly those that are localized or that can be completely encompassed within a radiation field. Radiation therapy plus surgery (for head and neck, laryngeal, or uterine cancer) or combined with chemotherapy and surgery (for sarcomas or breast, esophageal, lung, or rectal cancers) improves cure rates and allows for more limited surgery. Radiation therapy may be given before surgery or chemotherapy ( Radiation therapy can provide palliation even when cure is not possible: For brain tumors: Prolongs patient functioning and prevents neurologic complications For cancers that compress the spinal cord: Prevents progression of neurologic deficits For superior vena cava syndromes: Relieves obstruction For painful bone lesions: Usually relieves symptoms Radiation cannot destroy cancer cells without destroying some adjacent normal cells. Consequently, the risk of damage to normal tissue must be weighed against potential gain. The final outcome of a dose of radiation depends on numerous factors, including Type of radiation (eg, photons, electrons, protons, alpha particles, type of radionuclide) Dose, schedule, fractionation (ie, how dose is divided over time) Sensitivity of the cancer to killing by radiation In general, cancer cells are selectively damaged because of their high metabolic and proliferative rates. Normal tissue repairs itself more efficiently. Important considerations in the use of radiation therapy include the following: Dose and schedule Fractionation Ability to accurately target the cancer Target volume Configuration of radiation beams Dose distribution Treatment is tailored to take advantage of the cellular kinetics of the cancer to maximize damage to the cancer and minimize damage to normal tissues. Radiation therapy sessions begin with the precise positioning of the patient. Foam casts or plastic masks are often constructed to ensure exact repositioning for serial treatments. Laser-guided sensors are used. Typical courses consist of large daily doses given over several weeks for palliative treatment or smaller doses given once a day 5 days/week for 6 to 8 weeks for curative treatment. 