Intracranial stereotactic positioning systems (ISPSs) are used to position patients prior to precise radiation treatment of localized lesions of the brain. Often, the lesion is located in close proximity to critical anatomic features whose functions should be maintained. Many types of ISPSs have been described in the literature and are commercially available. These are briefly reviewed. ISPS systems provide two critical functions. The first is to establish a coordinate system upon which a guided therapy can be applied. The second is to provide a method to reapply the coordinate system to the patient such that the coordinates assigned to the patient’s anatomy are identical from application to application. Without limiting this study to any particular approach to ISPSs, this report introduces nomenclature and suggests performance tests to quantify both the stability of the ISPS to map diagnostic data to a coordinate system, as well as the ISPS’s ability to be realigned to the patient’s anatomy. For users who desire to develop a new ISPS system, it may be necessary for the clinical team to establish the accuracy and precision of each of these functions. For commercially available systems that have demonstrated an acceptable level of accuracy and precision, the clinical team may need to demonstrate local ability to apply the system in a manner consistent with that employed during the published testing. The level of accuracy and precision required of an individual ISPS system is dependent upon the clinical protocol (e.g., fractionation, margin, pathology, etc.). Each clinical team should provide routine quality assurance procedures that are sufficient to support the assumptions of accuracy and precision used during the planning process. The testing of ISPS systems can be grouped into two broad categories, type testing, which occurs prior to general commercialization, and site testing, performed when a commercial system is installed at a clinic. Guidelines to help select the appropriate tests as well as recommendations to help establish the required frequency of testing are provided. Because of the broad scope of different systems, it is important that both the manufacturer and user rigorously critique the system and set QA tests appropriate to the particular device and its possible weaknesses. Major recommendations of the Task Group include: introduction of a new nomenclature for reporting repositioning accuracy; comprehensive analysis of patient characteristics that might adversely affect positioning accuracy; performance of testing immediately before each treatment to establish that there are no gross positioning errors; a general request to the Medical Physics community for improved QA tools; implementation of weekly portal imaging (perhaps cone beam CT in the future) as a method of tracking fractionated patients (as per TG 40); and periodic routine reviews of positioning accuracy.
The Task Group would like to thank the AAPM reviewers for their comments, and D. Langer for her editing. We would also like to express our appreciation to many members of the Medical Physics community, including various manufacturers, radiation therapists, radiation oncologists, and other medical physicists for sharing their insights into this technology.
II. REVIEW OF PRESENT TECHNOLOGY
II.A. The function of stereotactic imaging and positioning systems
II.B. Review of intracranial stereotactic positioning systems
II.B.1. Minimally invasive systems
II.B.2. Noninvasive systems
II.C. Measurement methods
II.C.1. Repeat CT scans
II.C.2. Repeat MRI scans
II.C.3. Anterior-posterior and lateral simulator films
II.C.4. Portal images
II.C.5. Anterior-posterior and lateral video images
II.C.6. Depth helmet
II.C.7. Cone beam
III. RECOMMENDATIONS OF TASK GROUP 68
III.B. Information required from manufacturers
III.B.1. Design review
III.B.2. Manufacturer’s type testing for relocation accuracy
III.B.3. Data for ISPSs in current clinical practice
III.C. Tasks before purchase
III.C.1. Technical validation
III.C.2. Economics of the ISPS
III.D. Installation, acceptance testing, and commissioning
III.E. Clinical use
III.F. Future developments
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