Radiation therapy is a common part of cancer treatment. Advances in both imaging technology and radiation delivery provide more a more specific attack on the cancer with less damage to surrounding tissue in the organs at risk.
Dr. S. A. Bhide and Dr. C. M. Nutting of the Institute of Cancer Research and Royal Marsden Hospital, London, UK, provided a review. X-rays and gamma rays are the most common types of radiation therapy, but charged particles are also used.
“The delivery of radiotherapy has changed significantly over the last few decades,” Bhide wrote. The therapeutic ratio is improved by techniques that deliver a higher radiation dose to the tumor with less irradiation of the organs at risk.
Depending on the type of cancer, the following techniques may be used:
1. IMRT: intensity modulated radiotherapy.
This is now standard for head and neck cancers, and for prostate cancer. When used for head and neck cancers, it minimizes damage to the salivary glands, upper aero-digestive tract mucosa, optic nerves, inner ear, swallowing muscles, brain stem, and spinal cord.
2. IGRT: image guided radiotherapy.
With highly “focused” radiation, it is critical to know the tumor's location, size, and shape accurately. Imaging techniques include computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET).
3. 3D-CRT: three-dimensional conformal radiotherapy.
This technique fits the shape of the radiation dose to the shape of the tumor.
4. Stereotactic radiotherapy.
The Cyberknife technique and similar linear accelerator systems are used for treating metastatic tumors in the head, and some cancers of the lung, kidneys, liver, spine, and prostate.
5. Particle therapy.
Charged particles, such as protons from an accelerator, deposit most of their energy in a small area called the Bragg peak at the end of their penetration range. This method is the closest to a “magic bullet” that can be aimed at just the cancer.
Dr. Silvia C. Formenti and Dr. Sandra Demaria of the New York University School of Medicine explained that radiation does much more than kill cancer cells directly.