Purpose: To develop a respiration‐phase‐matched DTS technique to monitor moving targets, and to evaluate its accuracy for various imaging parameters and anatomical characteristics Methods: Conventional methods, registering on‐board DTS(OB‐DTS, reconstructed from on‐board projections) to reference DTS(R‐DTS, reconstructed from DRRs of 3D‐planning‐CT), are inadequate to monitor moving targets. Our proposed technique registers OB‐DTS to R‐DTS reconstructed from DRRs generated by the same phase images of 4D‐planning‐CT as the corresponding on‐board projections. To evaluate the improved accuracy of our technique, we performed thoracic phantom studies using (1)simulation with the 4D Digital Extended‐cardiac‐torso(XCAT) phantom, and (2)experiments with an anthropomorphic motion phantom. The studies were performed for various: respiratory‐cycle(RC), scan angle and fraction of RC contained therein. Also, we assessed the accuracy of our technique relative to target size/location, and respiration changes from the planning‐CT scan to on‐board volume. Results: In both simulation and experimental studies the respiration‐phase‐matched DTS technique is significantly more accurate in determining moving target positions. For 324 different scenarios simulated by XCAT, the respiration‐phase‐matched DTS technique localizes the 3D target position to within 1.07±0.57mm(mean±S.D.), as compared to (a)2.58±1.37mm and (b)7.37±4.18mm, for traditional DTS using 3D‐planning‐CT of (a)average‐intensity‐projection(AIP) and (b)free‐breathing‐CT(FB‐CT). For the 60 scenarios evaluated through experimental study, the uncertainties corresponding to those above are 1.24±0.87mm, 2.42±1.80mm, and 5.77±6.45mm, respectively. For a given scan angle, the accuracy of respiration‐phase‐matched DTS technique is less dependent on RC and the fraction of RC included in the scan. Increasing scan angle improves its accuracy. Its accuracy is also minimally dependent on different tumor size/location combinations, or different respiratory cycle changes from planning‐CT to on‐board volume. Increasing the respiratory amplitude change will decrease its accuracy. Conclusion: The respiration‐phase‐matched DTS is more accurate and robust in determining moving target positions than traditional DTS. It has potential application in pre‐treatment setup, post‐treatment analysis and intra‐fractional target verification. Research partially supported by grant from Varian Medical Systems.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging