External Beam Treatment Using IGRT-IMRT
Radiation therapy (RT) is a type of cancer treatment that uses high energy x-rays or particles to kill cancer cells. Radiation kills cancer cells by destroying the genetic material that controls how cells divide and grow. There are two main types of radiation therapy; external beam radiation and brachytherapy.
External beam radiation therapy (EBRT) remains one of the primary treatment modalities for patients with localized or locally advanced prostate cancer. During external beam radiation therapy (EBRT), beams of radiation are generated with a machine called a linear accelerator, these beams are directed through the skin to the cancer and the immediate surrounding areas to destroy tumors and any nearby cancer cells. In order to minimize side effects, treatments are typically given five days a week, for a number of weeks. The process of dividing a dose of radiation into multiple "fractions" is called fractionation. Fractionation allows enough radiation to get into the body to kill the cancer while giving healthy cells time to recover. There are several specific types of external beam radiation therapy used for specific types of cancer.
Image guided radiation therapy (IGRT) is the use of imaging during radiation therapy to improve the precision and accuracy of treatment delivery. IGRT is used to treat tumors in areas of the body that move, i.e. lungs, liver, prostate gland. Linear accelerators are equipped with imaging technology which allows the radiation therapist to image the tumor before and during treatment. Images taken before or during treatment are compared to reference images taken during the simulation process. The patient's position can then be adjusted to more precisely target the radiation dose to the tumor. IGRT can use cone-beam computed tomography (CBCT), magnetic resonance imaging (MRI), ultrasound (US) or x-ray imaging to precisely target the treatment area. IGRT is often used in conjunction with IMRT or 3-D CRT.
IMRT (intensity modulated radiation therapy) is a mode of high-precision radiation therapy that allows radiation dose intensity to be modulated within the given radiation field. It often involves a sophisticated treatment planning system to optimize treatment delivery by adjusting two radiation beam properties: beam shape and dose delivered. IMRT treatments create highly conformal fields by treating the patient with multiple static portals or dynamic fields. Multileaf collimators (MLCs) allow for these dynamic fields by reshaping themselves many times as the machine performs a series of rotations around the target.