Optical high-precision three-dimensional position measurement system suitable for head motion tracking in frameless...

Head motion is a significant source of therapy-effect degradation in frameless stereotactic radiosurgery (SRS). In this study, a three-dimensional (3-D) optical head motion measurement system and a coordinate transformation algorithm were used to track patient head motion. With this system, head motion in frameless SRS was carefully investigated with a precision of < 0.1 mm. Head motions without any restraint (three cases) and with a Laitinen adapter (four cases) were measured with a data sampling rate of once per second for 30 min. Positions of IR light emission diode markers attached to the head were analyzed by two statistical methods. From these data, mathematically simulated head motions were obtained in each of the three coordinate directions for nonrestraint and Laitinen-adapter SRS. The results show that segmenting a frameless SRS procedure into a sequence of short intervals and repeating registration of the target position for each interval is a good strategy for better therapy precision. This optical 3-D position measurement system is suitable for high-precision head motion tracking in frameless SRS.