Factors affecting the accuracy of respiratory tracking of the image-guided robotic radiosurgery system.

PURPOSE: To analyze the factors affecting the tracking accuracy of the CyberKnife Synchrony Respiratory Tracking System (SRTS). MATERIALS AND METHODS: A dynamic motion phantom (motion phantom) reproduced the respiratory motions of each patient treated with the SRTS using a ball as the target. CyberKnife tracked the ball using the SRTS, and this process was recorded by a video camera mounted on the linear accelerator head. The tracking error was evaluated from the images captured by the video camera. Multiple regression analysis was used to identify factors affecting tracking accuracy from 91 cases. RESULTS: The median tracking error was 1.9 mm (range 0.9-5.3 mm). Four factors affected the tracking accuracy: the average absolute amplitude of the tumor motion in the cranio-caudal (CC) direction (p = 0.007), average position gap due to the phase shift between the internal tumor and external marker positions in the CC direction (p < 0.001), and average velocity of the tumor in the CC (p < 0.001) and anterior-posterior directions (p = 0.033). CONCLUSION: We identified factors that affected tracking accuracy. This information may assist the identification of suitable margins that should be added to each patient's clinical target volume.

[Evaluation of the Effect of Adiabatic Pulse and B1 Shim to the Radio Frequency Homogeneity in Chemical Shift Imaging].

It is considered that the enhancement of chemical shift and the elevation of signal-to-noise ratio (SNR) induced by high magnetic fields are useful for the evaluation of metabolism using magnetic resonance spectroscopy (MRS). However, the reduction of the localization in MRS seems to be caused by the decreased homogeneity of radio frequency (RF) pulses, especially in chemical shift imaging (CSI). To search the influence of B1 shim mode and the significance of adiabatic pulses, we have examined the changes of RF homogeneity using 3 T magnetic resonance imaging (MRI) with the water phantom and the metabolites phantom (containing acetate and lactate) in CSI. The RF homogeneity and chemical shift artifact were obviously improved using the adiabatic pulses. Improvement of the homogeneity of RF pulses was observed when B1 shim was used. These results suggest the usefulness of CSI using adiabatic pulses and B1 shim when small amount of metabolites of target is measured in MRS.

[Examination of the orbitomeatal basal line-anthropological basal line crossing angle and acanthiomeatal line-anthropological basal line crossing angle].

Orbitomeatal basal line-anthropological basal line (OML-ABL), and the acanthiomeatal line (AML)-ABL crossing angles were measured using profile pictures. There were 219 volunteers in total: 42 people four years old, 44 people nine years old, 45 people 14 years old, 43 people 19 years old, and 45 people 40 years or older (48±7.4 years). The average OML-ABL crossing angle was 14.3 degrees in the 4-year-old group, while that of the 40-year or older group was 11.1 degrees. The deviation width of the 4-year-old group was 4.8 degrees, and that of the 40-year or older group was 2.4 degrees. The average AML-ABL crossing angle was 12.3 degrees in the 4-year-old group, while that of the 40-year or older group was 15.7 degrees. There were differences between males and females. The deviation width of the 4-year group was 5.4 degrees, and that of the 40-year or older group was 2.7 degrees. The results showed that 14.0 degrees for around 4-year-old, and 12.0 degrees for around 9- to 14-year-olds, could be used as OML-ABL crossing angles as a practical proposition.