Stereotactic radiosurgery (SRS) is a form of radiation therapy that focuses high-power energy (X-rays) on a small area of the body. The term radiosurgery is truly a misnomer .It is not a surgical procedure and is rather a technique of radiation therapy.Some patients receive more than one treatment session, but usually no more than five sessions then the process is termed as stereotactic radiotherapy (SRT).and when it is performed for tumours outside skull it is called Stereotactic body radiation therapy (SBRT).
SRS targets and treats an abnormal area without damaging nearby healthy tissue. SRS is more likely to be recommended for patients who are too high risk for surgery. This may be due to age or other comorbidities. The aim of stereotactic radiosurgery is to destroy target tissue while preserving adjacent normal tissue, where fractionated radiotherapy relies on a different sensitivity of the target and the surrounding normal tissue to the total accumulated radiation dose.
SRS is often used to impede the growth of small, deep seated brain tumors that are not amenable to surgery. These includespinal cord tumors,pituitary tumors, acoustic neuromaand brain metastasis. There are many noncancerous conditions which can also be treated with SRS like such as arteriovenous malformations ,Parkinson disease, trigeminal neuralgia and epilepsy.
There are many types of radiation therapy machines which can be used to perform radiosurgery namelylinear accelerator, Gamma knife,and Cyberknife. Not all Linear accelerators are competent to perform SRS.The prerequisite is to havemicro multileaf collimators which has a submilimetric precision capability. Inaddition there should be an inbuilt online imaging system to guide the treatment.
Modern stereotactic planning systems are computer based.The stereotactic method has continued to evolve ever since it was first started by Prof Leksell in 1949. At present an elaborate amalgam of image-guided surgery that uses computed tomography, magnetic resonance imaging and stereotactic localization is employed.Stereotaxy makes use of a three-dimensional coordinate system to locate small targets inside the body and to performa procedure, a stereotactic planning system, including atlas, multimodality image matching tools, coordinates calculator, a stereotactic device or apparatus and stereotactic localization and placement procedure.
During treatment the patient is on the treatment table with an appropriate immobilisation. The immobilisation includes masks and cushions.The treatment table slides into a machine that delivers radiation: The patient is under constant supervision by means of real time cameras. Patient can also communicate on microphones in case of any discomfort. If need arises then treatment can be interrupted and later resumed.
SRS/SRT where it stands in Indian Scenario: It providesasafe, and minimal invasive and efficacious treatment alternative for patients diagnosed with malignant, benign and functional indications in the brain and spine.Indications include not only to primary and secondary brain tumours but also meningiomas, schwannomas, pituitary adenomas, arteriovenous malformations, and trigeminal neuralgia.More recent evolution extrapolates the original concept of stereotactic radiosurgery to extra-cranial targets, most notably in the lung, liver, pancreas, and prostate.
If the effectiveness is valued in Indian context Stereotactic radiation therapy techniques are very cost effective as theyensure shortened treatment time and lesser number of visits to the hospital. Since it is an outpatient treatment the cost of hospitalisation further decreases.
Since the availability of state of the art radiation therapy facility is very sparse and mainly confined to metropolitan cities patients have to travel from far flung areas and spend at times many months for availing these facilities. Hypo-fractionation as achieved by SRS and SRT decreases the patient and family members stay for the treatment .The results are rewarding in terms of outcome of the carefully selected patients as all patients may not be the suitable candidates for this form of therapy.