ABSTRACT
The ZAP-X® is a newly designed, self-contained, and first-of-its-kind self-shielded therapeutic radiation therapy device dedicated to brain and head and neck stereotactic radiosurgery (SRS). By using an S-band linear accelerator (linac) and employing integrated minimal but sufficient shielding, the ZAP-X does not typically require a radiation bunker. At the same time, the self-shielded features of the ZAP-X are designed for more consistency of radiation protection, reducing the risk to radiation workers and others potentially exposed from a poorly designed or constructed radiotherapy vault. This study postulates that a radiosurgical system can be self-shielded, such that it produces radiation exposure levels deemed safe to the public while operating under a full clinical workload. The goal of self-shielding is achieved under all but the most exceptional clinical conditions. This work is intended to serve as guidance for the radiation safety evaluations of future ZAP-X treatment operations, following local or regional applicable regulatory requirements, and utilizing the unique provision of all or most of the required shielding material as an integral part of the device.
ABSTRACT
UNLABELLED: The NU 2-1994 standard document for PET performance measurements has recently been updated. The updated document, NU 2-2001, includes revised measurements for spatial resolution, intrinsic scatter fraction, sensitivity, counting rate performance, and accuracy of count loss and randoms corrections. The revised measurements are designed to allow testing of dedicated PET systems in both 2-dimensional and 3-dimensional modes as well as coincidence gamma cameras, conditions not considered in the original NU 2-1994 standard. In addition, the updated measurements strive toward being more representative of clinical studies, in particular, whole-body imaging. METHODS: Performance measurements following the NU 2-1994 and NU 2-2001 standards were performed on several different PET scanners. Differences between the procedures and resulting performance characteristics, as well as the rationale for these changes, were noted. RESULTS: Spatial resolution is measured with a point source in all 3 directions, rather than a line source, as specified previously. For the measurements of intrinsic scatter fraction, sensitivity, and counting rate performance, a 70-cm line source is now specified, instead of a 19-cm-long cylindric phantom. The longer configuration permits measurement of these performance characteristics over the entire axial field of view of all current PET scanners and incorporates the effects of activity outside the scanner. A measurement of image quality has been added in an effort to measure overall image quality under clinically realistic conditions. This measurement replaces the individual measurements of uniformity and of the accuracy of corrections for attenuation and scatter. CONCLUSION: The changes from the NU 2-1994 standard to the NU 2-2001 standard strive toward establishing relevance with clinical studies. The tests in the updated standard also are, in general, simpler and less time-consuming to perform than those in the NU 2-1994 standard.
