Stereotactic Radiosurgery (SRS): What It Is and How Gamma Knife Fits

What Is Stereotactic Radiosurgery (SRS), and How Does It Differ From Gamma Knife?

Stereotactic radiosurgery (SRS) is a treatment that precisely focuses radiation from multiple directions on a limited area, such as a part of the brain. Although its name includes the word “surgery,” it is not a treatment in which the skull is opened and the lesion is cut out, as in conventional open brain surgery (craniotomy). Imaging tests are used to identify the location and shape of the lesion, and radiation is concentrated on the treatment target while keeping the effect on surrounding normal tissue as low as possible.

Gamma Knife is one of the main treatment systems used to perform SRS. In other words, SRS and Gamma Knife do not mean the same thing. SRS refers to the treatment concept and approach, while Gamma Knife is one of the devices and treatment methods used to deliver SRS. SRS may also be performed with other equipment, such as a linear accelerator (LINAC).

What Brain Tumors and Brain Conditions Is SRS Used For?

SRS may be considered for brain tumors such as brain metastases, meningiomas, vestibular schwannomas (acoustic neuromas), and pituitary tumors, as well as for conditions such as brain arteriovenous malformations (AVMs) and trigeminal neuralgia. However, a diagnosis alone does not determine whether SRS is appropriate. The treatment plan is decided through an overall assessment of factors such as the size, location, and number of lesions, their relationship to surrounding tissue, symptoms, previous treatment, and general health.

With Gamma Knife, MRI and other imaging are used for treatment planning, and the area to be treated and the radiation dose are designed individually. Changes after treatment do not necessarily appear right away, and depending on the lesion, changes are monitored over several months or a longer period. For this reason, follow-up with MRI or other imaging remains important after treatment.

If you are considering Gamma Knife treatment from outside Japan, the first step is likewise for a specialist to review your MRI images and medical information and determine whether SRS may be an appropriate option. Understanding SRS can make it easier to organize the basics when comparing Gamma Knife with open brain surgery, observation, and other types of radiation therapy.

When you look up SRS, you may come across several terms, such as “single-session,” “fractionated,” and “staged.” These terms reflect different ways of thinking about the number and spacing of treatments, so it is not appropriate to judge your own treatment method by its name alone. With Gamma Knife, a single treatment may be considered in some cases, while in others an approach that divides treatment into multiple sessions may be considered, depending on the characteristics of the lesion. Which approach is appropriate is decided with the characteristics of the lesion and safety in mind.

Also, while SRS is a “no-incision” treatment, that does not mean follow-up after treatment becomes unnecessary. Changes in the treated area are checked with MRI, and additional or different treatment is considered as needed. It is important to understand not only the name of the treatment method but also the plan for monitoring after treatment.