Treatments and Technology

Linac Based Stereotactic Radiosurgery


Overview


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Stereotactic treatment can be delivered on an adapted standard linear accelerator, such as a Varian Trilogy and TruBeam, on a helical linear accelerator, called TomoTherapy, or on a robotic arm linear accelerator (CyberKnife). This approach delivers massive doses of radiation that are biologically much more effective than standard radiotherapy.

 

A linear accelerator can be adapted to deliver intracranial stereotactic radiation using a stereotactic frame or a very specialized non-invasive stereotactic mask.   Intracranial diagnoses conducive for stereotactic treatment include metastases, trigeminal neuralgia, acoustic neuroma, atriovenous malformation, and some recurrent gliomas.

 

 

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Stereotactic radiation therapy employs special equipment to deliver high doses of radiation while decreasing the normal tissue included in the treatment field. Using special equipment to position the patient and localize the tumor allows precise delivery of radiation therapy to the tumor. This has been used for many years for tumors in the brain for both benign and malignant tumors. Treatment in the brain is typically performed in one session, using rigid immobilization, and it is called stereotactic radiosurgery (SRS) since it is typically performed in one session.

 

 

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Rigid immobilization is not possible for tumors in the body and there is the added problem of daily variation in patient setup and positioning, organ changes between treatments (for example, variable filling of bladder or bowels), and organ motion during treatment (due to the natural motion of the heart and lungs). Recent advances in patient immobilization, in imaging, and daily tumor localization and tracking now allow treatment with nearly the same precision as those treatments for the brain.

These advances have also enabled the development of stereotactic body radiation therapy (SBRT). This technique allows the treatment from many different directions that allows for smaller total doses to normal tissue, and allows the delivery of much higher doses to the tumor during each treatment and increases the likelihood of tumor control.  SBRT is typically given in 2-5 radiotherapy sessions.

 

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SBRT is most useful in situations in which we can clearly identify the tumor, use imaging to localize the tumor before and during treatment, and in tumors that are not too close to the skin surface or involve critical normal structures. Tumors in the lung frequently meet these criteria, and that is where we have the most experience and most mature results with SBRT. Other treatment sites have included liver metastases, spinal metastases or paraspinal tumors, solitary bone metastases, and primary tumors of the prostate and pancreas.

 

 

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