II. Therapeutic radiology

Therapeutic radiology, also referred to as radiation oncology, is based on the use of ionizing radiation in the treatment of cancer. Normal tissues have a greater ability to recover from the effects of radiation than tumors and tumor cells. A radiation dose sufficient to destroy cancerous cells only temporarily injures adjacent normal cells. When the ability of normal tissues to recover from a given amount of radiation is the same as or less than that of the cancerous tissue, the tumor is described as radioresistant. In such cases radiation therapy is usually not considered an appropriate form of treatment.

Treatment with ionizing radiation is often described in terms of the energy of the beam used: superficial (less than 120 kilovolts, or kv); orthovoltage (120 to 1000 kv); and megavoltage (greater than 1000 kv). Superficial radiation therapy is used in treating malignant diseases involving the skin, the eye, or other body surfaces. Orthovoltage therapy has been largely replaced by megavoltage (cobalt, linear accelerator, and betatron) therapy. Megavoltage therapy provides more efficient and effective delivery of the intended radiation dose to tumors deep inside the body and, at the same time, spares the healthy skin and surrounding normal tissue from excess radiation.

Radiation therapy may be used alone as the treatment of choice in most cancers of the skin; in certain stages of cancers involving the cervix, uterus, breast, and prostate gland; and in some types of leukemia and lymphoma, particularly Hodgkin’s disease. In such instances, radiation therapy is intended to effect a cure. When radiation therapy is used in conjunction with cancer-treatment drugs (known as combined modality therapy), however, it may be intended for either cure or palliation (the relief of symptoms). Radiation therapy is commonly employed either before or shortly after surgical removal of certain tumors to destroy tumor cells that could (or may already have) spread beyond the surgical margins. Radiation therapy is also frequently employed in controlling local tumor recurrence after surgery. Radiation therapy can also treat noncancerous tumors and growths. Future therapies may use targeted radiation to help control brain-related movement disorders such as tremor, epilepsy and Parkinson disease.

III. Interventional radiology

Interventional radiology is the nonsurgical treatment of a growing number of diseases using radiologic imaging to guide catheters (hollow, flexible tubes), balloons, filters, and other tiny instruments through the body’s blood vessels and other organs.

Common interventional radiologic procedures include: balloon angioplasty, the use of a balloon to open blocked or narrowed arteries; chemoembolization, the delivery of anticancer drugs directly to a tumor; fallopian tube catherization, which opens blocked fallopian tubes, a common cause of infertility in women; and thrombolysis, which dissolves blood clots.