Stereotactic Radiosurgery (SRS) is a medical procedure, which is non-invasive surgery to destroy tumors. High dose of ionizing radiation is precisely delivered into a specific area of an organ to kill tumor cells. The beam of radiation is the surgical knife in radiosurgery. The most common forms of ionizing radiation are: proton beams, X-rays and photons.
Unlike conventional surgery that removes tumors by bulk dissection, SRS only distorts the DNA of the tumor cells. Those cells then lose their ability to divide. Tumor shrinkage can be seen often over several months.
Currently there are three basic forms of stereotactic radiosurgery: Cobalt-60 (photon), Linear accelerator (linac) and Particle beam (proton). Each one is different from the other in both the equipment used and the radiation emitted. One type may be more effective than the other depending on the location of the tumor.
1. Cobalt-60 (photon) – also called a Gamma Knife® is an extremely accurate instrument used to treat brain tumors. The Gamma Knife® allows noninvasive brain surgery, sparing tissues adjacent to the target. The beams of gamma radiation are programmed to target the tumor at the point where they intersect. In a single treatment session, 201 beams of gamma radiation focus precisely on the tumor. Over time, most lesions slowly shrink in size and dissolve. The exposure is brief and only the tissue being treated receives a significant radiation dose, while the surrounding tissue remains unharmed. The Gamma Knife® technology is used for tumors which are small, less than 3.5 cm, or in patients who have limited symptoms from the tumor. When Gamma Knife® cannot be utilized or is not available to the patient, radiosurgery with linear accelerator technology can usually be utilized.
Click here to read more about Gamma Knife® at the university of Pittsburg, at the Johns Hopkins, at the University of Virginia.
2. Linear accelerator (linac)
Linac is short for the term “linear accelerator”. The Linear accelerator instruments produce high-energy X-ray radiation. Conventional X-rays are a form of electromagnetic radiation with short wavelength, without charge or mass. The most improved linac technology is based on Intensity – Modulated Radiation Therapy (IMRT). It takes into account the three-dimensional shape of the tumor. This is done through the use of a CT scanner that is incorporated into the IMRT. The CT scans identify the exact tumor location and its shape. The radiation beams in varying intensities are delivered to the tumor with increased accuracy, reducing the harmful effects of the X-rays on normal tissue.
This treatment is very beneficial for large tumor (up to 2.5 cm) in one-session, and tumors greater in size (over 3.5 cm) in several treatment sessions. When several treatments are required this is called fractionated stereotactic radiotherapy. Linear accelerator based machines can be used to treat tumors throughout the body, as well as in the head and neck.
Read more about Cyberknife:
Cyberknife to treat tumors anywhere in the body
Cyberknife, frequently asked questions
Cyberknife at Stanford
Compare: Gamma Knife versus Cyberknife to treat brain tumors
3. Particle beam (proton) – Also known as Proton beam, is radiation of positively charged particles that impact the tumor cells by way of their mass. The side effects of the treatment with Proton beam are less than those that are caused by X-ray treatment. X-rays affect cells as they travel through the body in a straight line, delivering injury both at the surface of the body where they enter, and in tissues behind the cancer. Proton beams do not travel all the way through the body and can be used very accurately to kill cancer cells without the collateral damage seen with traditional radiation: Proton beams can be controlled to deposit the bulk of their energy at the EXACT tumor location. The Proton beam machines are very expensive and therefore exist only in six centers in the United States: M.D. Anderson in Houston; Loma Linda University Medical Center in California AND Proton treatment at Loma Linda; The Midwest Proton Radiotherapy Institute in Bloomington, Indiana; Massachusetts General Hospital, Boston; The University of Florida Proton Therapy Institute in Jacksonville; and the University of California, Davis Cancer Center in Sacramento.
Click here to Read more about Proton Beam
*This summary aims to introduce you into SRS. Please be aware that we mentioned only some of the centers, which practice SRS. While some centers treat cancer in only few organs, other centers may use the same technique to treat tumors in more locations.
Yosef Landesman, Ph.D.
President & Cancer Research Director
Cure Alveolar Soft Part Sarcoma International (iCureASPS)