MAINTAINING ACCURACY IN STEREOTAXIC RADIOSURGERY

Purpose: To provide the manufacture's specification for the base phant om of a commercially available stereotactic radiosurgery system so tha t its accuracy can be confirmed, and to describe a calibration device that allows the accuracy of the base phantom to be verified quickly an d on a routine basis, Modifications to the target pointer system that make matching the pointer tips easier and less likely to damage the po inter tips are also described. Methods and Materials: In stereotactic radiosurgery, spatial accuracy is the key factor for successful dose d elivery, With some commercially available systems, this accuracy depen ds on the accuracy of the base phantom coordinate system, how closely the tip of the target pointer can be matched to the tip of the base ph antom pointer, and how accurately the coordinates set on the isocentri c subsystem match those set on the base phantom, Two major problems, u sually overlooked when evaluating system accuracy are, first, the base phantom, which establishes the stereotactic coordinate system, is ass umed to be completely accurate. This is a dangerous assumption because the base phantom is used frequently for routine patient treatments an d for standard quality assurance tests, To exacerbate the problem, no independent device is provided with stereotactic systems to check the accuracy of the base phantom, Second, the accuracy of the isocenter co ordinates set on the head support stand depends upon how closely the t arget pointer and the base phantom pointer can be aligned, The hardwar e provided with the system is difficult to use and easily leads to dam age of the pointer tips. Results: In this work, we provide the manufac turer's specifications for a popular stereotactic system, describe a d evice that can be used to check quickly and easily the accuracy of the base phantom, and describe a modification to the transfer pointer sys tem that allows the pointer tips to be more easily aligned with reduce d possibility of damage to the pointer tips. Conclusion: The methods a nd apparatus described in this paper should be useful to anyone using a base phantom for testing radiosurgery accuracy.