Influence of absorbed dose and field size on the geometry of the radiation-surgical brain lesion

Inception of a national multidisciplinary registry for stereotactic radiosurgery

Stereotactic radiosurgery (SRS) represents a multidisciplinary approach to the delivery of ionizing high-dose radiation to treat a wide variety of disorders. Much of the radiosurgical literature is based upon retrospective single-center studies along with a few randomized controlled clinical trials. More timely and effective evidence is needed to enhance the consistency and quality of and clinical outcomes achieved with SRS. The authors summarize the creation and implementation of a national SRS registry. The American Association of Neurological Surgeons (AANS) through NeuroPoint Alliance, Inc., started a successful registry effort with its lumbar spine initiative. Following a similar approach, the AANS and NeuroPoint Alliance collaborated with corporate partners and the American Society for Radiation Oncology to devise a data dictionary for an SRS registry. Through administrative and financial support from professional societies and corporate partners, a framework for implementation of the registry was created. Initial plans were devised for a 3-year effort encompassing 30 high-volume SRS centers across the country. Device-specific web-based data-extraction platforms were built by the corporate partners. Data uploaders were then used to port the data to a common repository managed by Quintiles, a national and international health care trials company. Audits of the data for completeness and veracity will be undertaken by Quintiles to ensure data fidelity. Data governance and analysis are overseen by an SRS board comprising equal numbers of representatives from the AANS and NeuroPoint Alliance. Over time, quality outcome assessments and post hoc research can be performed to advance the field of SRS. Stereotactic radiosurgery offers a high-technology approach to treating complex intracranial disorders. Improvements in the consistency and quality of care delivered to patients who undergo SRS should be afforded by the national registry effort that is underway.

The earliest gamma unit patients

The inventors were very excited and drove the first patient from Stockholm over 100 km for the first treatment. The treatment was a technical success. The new machine was transported to Sophiahemmet (a private Stockholm hospital) and installed. A further eight patients were treated and assessed. At the start, there was no computerized treatment planning program, but this was soon developed and named KULA after the Swedish word for a sphere, since the actual treatment unit was spherical. The term Gamma Knife was first used later by the Pittsburgh group.

Gamma knife radiosurgery for thalamotomy in parkinsonian tremor: a five-year experience

OBJECT

Certain patients, for example, elderly high-risk surgical patients, may be unfit for radiofrequency thalamotomy to treat parkinsonian tremor. Some patients, when given the opportunity, may choose to avoid an invasive surgical procedure. The authors retrospectively reviewed their experience using gamma knife radiosurgery for thalamotomies in this patient subpopulation: 1) to determine the efficacy of the procedure; 2) to see if there is a dose-response relationship; 3) to review radiological findings of radiosurgical lesioning; and 4) to assess the risks of complications.

METHODS

Radiosurgical nucleus ventralis intermedius thalamotomy using the gamma knife unit was performed to make 38 lesions in 24 men and 10 women (median age 73 years, range 58-87 years) over a 5-year period. A median radiation dose of 130 Gy (range 100-165 Gy) was delivered to 38 nuclei (four patients underwent bilateral thalamotomy) using a single 4-mm collimator following classic anatomical landmarks. Twenty-nine lesions were made in the left nucleus ventralis intermedius thalamus for right-sided tremor. Patients were followed for a median of 28 months (range 6-58 months). Independent neurological evaluation of tremor based on the change in the Unified Parkinson's Disease Rating Scale tremor score was correlated with subjective patient evaluation. Comparison was made between a subgroup of patients in whom "low-dose" lesions were made (range 110-135 Gy, mean 120 Gy) and those in whom "high-dose" lesions were made (range 140-165 Gy, mean 160 Gy) for purposes of dose-response information. Four thalamotomies (10.5%) failed, four (10.5%) produced mild improvement, 11 (29%) produced good improvement, and 10 (26%) produced excellent relief of tremor. In nine thalamotomies (24%) the tremor was eliminated completely. The median time to onset of improvement was 2 months (range 1 week-8 months). Concordance between an independent neurologist's evaluation and that of the patient was statistically significant (p < 0.001). Two patients who underwent unilateral thalamotomy experienced bilateral improvement in their tremor. There were no neurological complications. There was better tremor reduction in the high-dose group than in the low-dose group (p < 0.04).

CONCLUSIONS

Although less effective than other stereotactic techniques, gamma knife radiosurgery for thalamotomy offers tremor control with minimal risk to patients unsuited for open surgery.

A new stereotactic X-ray knife

For many years, the irradiation of small volumes of tissue in the brain to necrotizing doses has been investigated as a "non-invasive" alternative to neurosurgery. We propose a new system in which a precisely machined helmet serves as a multi-port focussed X-ray collimator when it is itself irradiated by a conventional medical linear accelerator run in the electron mode. When the collimator is attached to a stereotactic frame, the geometric accuracy of delivering small radiation fields to the brain is limited primarily by the accuracy of the stereotactic localization, and is relatively independent of the positional stability of the accelerator. Field sizes as small as two millimeters are readily achievable. The problem of low dose rate associated with these small fields is overcome by the use of high electron beam currents.

Dosimetric considerations on multiple arc stereotaxic radiotherapy

The aim of this paper is to present the physical and dosimetrical features of the stereotaxic radiosurgical method already published by the authors. This method concentrates the dose into the stereotaxic target volume, placed at the isocenter of a 4 MV X-ray beam. Computer calculations showed that: 9-17 arcs provide almost spherical dose distributions; the optimal photon beam quality is about 4-6 MV. The angle between adjacent rotation planes is 20-40 degrees and the arcs are 100-160 degrees wide. In this way the dose to healthy tissue is minimized. The dose distribution was experimentally verified both by ionometric and photodensitometric methods. The procedure for dose calculation at isocenter of fields as small as required by the radiotherapist, has been investigated.