Stereotactic radiotherapy and radiosurgery are techniques that use highly conformal and high dose therapies to treat small areas of the body. It has use in brain, lung and liver therapy (and possible other sites). This topic will cover the hardware that can deliver stereotactic therapy, the software that runs this, planning stereotactic treatment, quality assurance, and other features of stereotactic plans.
Stereotactic radiosurgery delivers high doses using stereotactic (ie. localised with 3D co-ordinate system) techniques. Radiotherapy doses are high and multiple beams are used to spare normal tissues outside the treatment volume. Radiotherapy doses are no comparable using the linear-quadratic model as it becomes unreliable after doses of 6-8 Gy per fraction. Stereotactic radiosurgery is also used outside the brain.
Stereotactic radiotherapy uses multiple fractions to deliver a dose, also using a conventional technique. Fractions range from normal fractionation to very hypofractionated. Stereotactic radiotherapy keeps the benefits of stereotactic radiosurgery (sharp dose falloff) together with increased normal tissue tolerance, allowing for its use near critical structures such as the optic chiasm or brainstem.
A critical component of stereotactic radiotherapy is the immobilisation technique. The most accurate method is to use a stereotactic frame upon which the patient's skull is attached. This limits movement to < 1 mm but is uncomfortable. Frameless stereotactic techniques (eg. thermoplastic masks) are used but are slightly less accurate.
Common CNS sites treated with stereotactic treatment:
- Benign CNS disease
- Arteriovenous malformations (20 Gy in 1 fraction)
- Meningioma (15 Gy in 1 fraction)
- Vestibular Schwannoma (13 Gy in 1 fraction, 50.4 Gy in 28 fractions (FRST))
- Pituitary adenomas (15 Gy for non-secretory, 25 Gy for secretory tumours)
- Malignant CNS disease
- Brain oligometastases
- Glioma (expiremental)
- Functional disorders
- Trigeminal neuropathy (treat intracranial portion of the trigeminal nerve to 80 Gy)
Stereotactic body radiotherapy is a newer technique. Treatment relies heavily on image guidance techniques as the patient's body can not be immobilised in the same way as the scalp. It is predominately used for early stage lung cancer in otherwise surgically unfit patients, where it shows excellent results (eg. 3 year local control 90%) with high doses (60 Gy in 3 #). It can also be used in other body sites (eg. liver). Evidence related to other sites is limited to case series.
Stereotactic treatment is available at major metropolitan centres but is being rolled out throughout Australia.
- 15.1.2: Stereotactic Radiosurgery
- 15.5.1 - Stereotactic Hardware