Extracranial Stereotactic Radiosurgery Research Articles

Extracranial Stereotactic Radiosurgery: Applications for the Spine and Beyond

The role stereotactic radiosurgery has in the management of malformations of the spine is examined in this article. Specific problems in the application of stereotactic radiosurgery to the spine are discussed and the three techniques for spinal stereotaxis, bone screw fixation, contour mold fixation, and frameless stereotaxis, are reviewed.

Extracranial Stereotactic Radiosurgery of Localized Targets

A method for extracranial stereotactic radiosurgery (ESRS) is described. For this treatment method a stereotactic body frame was developed and is described here. The ESRS method uses a hypofractionation schedule with 2–3 fractions with 10–20 Gy/fraction to the periphery of the target volume, at the 65% isodose. The heterogeneous target dose is used as a means to increase the probability of killing the hypoxic tumor cells. It is argued from in vitro cell survival data that the dose increase used will give a reasonable probability to eradicate at least moderate concentrations of hypoxic cells. A high reproducibility of the target position with the ESRS method is based on the definition of the patient reference system to the stereotactic system and not to the bony anatomical reference points as used in conventional radiotherapy. Important to the ESRS method is that the target position is verified by computed tomography (CT) examinations. The positional accuracy of the target in the stereotactic system is 3.1 mm (mean deviation) in the transversal plane and 5.5 mm (mean deviation) in the longitudinal direction. The setup accuracy, i.e., the correct alignment of the stereotactic system to the isocenter of the treatment unit, is within 1 mm. Other aspects of the ESRS method that are discussed are the treatment technique including collimation methods and dose distributions used, as well as target margins. ESRS has been in clinical use for several years at Radiumhemmet, Karolinska Hospital.

1019 Extracranial stereotactic radiosurgery. Clinical results

1019 Extracranial stereotactic radiosurgery. Clinical results

Preliminary Clinical Experience with Linear Accelerator-based Spinal Stereotactic Radiosurgery

A prototype device called an extracranial stereotactic radiosurgery frame was used to deliver stereotactic radiosurgery, with a modified linear accelerator, to metastatic neoplasms in the cervical, thoracic, and lumbar regions in five patients. In all patients, the neoplasms had failed to respond to spinal cord tolerance doses delivered by standard external fractionated radiation therapy to a median dose of 45 Gy (range, 33-65 Gy/11-30 fractions). The tumors were treated with single-fraction stereotactic radiosurgery with the spinal stereotactic frame for immobilization, localization, and treatment. The median number of isocenters was one (range, one to five) with a median single fraction dose of 10 Gy (range, 8-10 Gy) with median normalization to 80% isodose contour (range, 80-160%). There has been a single complication of esophagitis to date from radiosurgery of a tumor involving the C6-T1 segments; the esophagitis resolved with medical therapy. Median follow-up in this group of patients has been 6 months (range, 1-12 mo). To date, there has been no radiographic or clinical progression of the treated tumor in any patient. Two patients have died from systemic metastatic disease. In the three surviving patients, there has been computed tomographic- or magnetic resonance-documented regression of the treated tumor with a decrease of thecal sac compression with a median follow-up of 6 months (range, 3-14 mo). These five patients represent the first clinical application of stereotactic radiosurgery in the spine. The results suggest that extracranial radiosurgery may be suitable for the treatment of paraspinal neoplasms after external fractionated radiation therapy, even in the face of spinal cord compression.

A prototype device for linear accelerator-based extracranial radiosurgery.

A prototype frame for accurate stereotactic localization and linear accelerator (LINAC)-based treatment of extracranial targets was developed. The ECRSF is designed to employ either spinal or skeletal osseous fixation to immobilize the area of interest and then encircle the targeted region with a traditional orthogonal, three-axis system. A series of experiments (n = 5) with semi-radiolucent calibration targets (n = 15) and computed tomography (CT) scanning using the EC showed that a mean localization error of 0.98 +/- 0.22 mm was obtainable in the last two and most accurate series of experiments with these targets (n = 8). Using the LINAC to irradiate these same targets demonstrated an overall radiation treatment accuracy ranging from 1.4 to 2.0 mm. This discrepancy between localization error and overall radiation treatment error can be explained by a lack of isocentricity of the LINAC treatment which is typically less than 1 mm and can be as low as 0.5 mm. These data demonstrate that extracranial stereotactic radiosurgery is now technically feasible and that the accuracy of such treatment would be acceptable for clinical treatment.