RADIOTHERAPY PROCEDURES
Treatment Of Patients With Solitary Brain Metastasis Or Oligometastatic Brain Disease (Up To Four Metastasis)
Stereotactic Radiosurgery
The most appropriate treatment for patients with solitary brain metastases has been a source of controversy for nearly two decades, and still needs to be defined. Recently, stereotactic radiosurgery, an elegant, sophisticated and non-invasive modality, has provided local intensification of dosage for well-defined intracranial targets with relative sparing of the surrounding normal brain. Stereotactic radiosurgery delivers a high dose of radiation to a relatively small volume of disease, secondary to the sharp dose gradients. Brain metastasis are considered ideal targets for stereotactic radiosurgery since they 1) take up the iodized contrast or the gadolinium so they can be easily identified on contrast enhanced CT or MRI; 2) are almost always spherical in shape, and 3) grow with minimal or no infiltration into the adjacent brain parenchyma. Also, with modern technology, they can be detected earlier, when the volume of the metastatic deposit is still relatively small. This has represented an attractive alternative to surgical resection, and possibly Whole Brain Radiotherapy for patients with oligometastatic brain disease. Stereotactic radiosurgery appears to offer several advantages over surgery, such as the treatment of surgically inaccessible lesions and decreased acute morbidity, as well as the decreased cost of the procedure.
Description Of The Stereotactic Radiosurgery Procedure
Prior to the procedure, informed consent is obtained from all patients. All patients are placed on steroids prior to and following the procedure. On the day of the stereotactic radiosurgery, the Brown-Robert-Wells Stereotactic frame (Radionics. Inc., Burlington. Mass.) Is placed by the neurosurgeon. After frame placement, 5 millimeter thick cuts at 5 millimeter intervals are taken throughout the cranium. After delineation of the tumor volume and administration of Intravenous contrast, 2-3 millemeter cuts at 2-3 millimeter intervals were taken throughout the tumor. These images are transferred to the radiation oncology department via Intranet, with a DICOM-RT format. The tumor volume and treatment plans are performed by the radiation physicist, neurosurgeon and radiation oncologist, using the radiosurgical planning system by Scandiplan (Scanditronix, Ann Arbor, MI). Consideration is given to proximity of critical structures (i.e., brain stem and optic apparatus), previous radiotherapy, size and volume of lesion. At the end of the regularly scheduled treatment day, the linear accelerator is modified to accommodate the base plate and the floor stand. Appropriate quality assurance checks are performed to verify isocentricity and accuracy of set-up prior to beginning treatment. Once all the verifications have been done successfully, the patient is transferred to the treatment suite and placed on the treatment table that has been modified to have the stereotactic frame attached to it. The treatment machine will describe arcs around the patient while delivering a high dose of radiation specifically focused on the tumor. The procedure takes less than 20 minutes. The frame is then removed and the patient can be sent home soon afterward.