Room: Exhibit Hall
Purpose: Dosimetric impact from daily patient setup variations may be less forgiving in intensity modulated proton therapy treatments compared with other types of external beam treatments. Daily cone beam CT (CBCT) registration with the reference CT is dependent on CBCT image fidelity and user selected region of interest (ROI). Commonly, image artifacts may be present in the CBCT acquisition and could negatively influence the registration. In light of this, the purpose of this study was to quantify the accuracy of registrations when varying degrees of artifacts are present in the CBCT.
Methods: VelocityAIâ„¢ software was utilized to evaluate the effect of variable image artifacts from daily CBCT based localization for cranial IMPT treatments. CBCTs acquired pre-treatment were registered with the reference CT in VelocityAI. To determine influences, for each CBCT/CT registration, three registrations were performed: 1) automatic registration with entire head as ROI 2) automatic registration with a target specific ROI and 3) manual registration. Differences were quantified against the manual registration which served as the gold standard validated by bony landmarks.
Results: Thirty CBCTs of 5 cranial patients were studied. Mean deviations in translational (lateral, longitudinal, vertical) and rotational (roll, pitch, yaw) shifts were: 0.38 Â± 0.64 mm, 0.11 Â± 0.73 mm, -0.02 Â± 0.76 mm, -0.01Â° Â± 0.83Â°, -0.20Â° Â± 0.48Â°, -0.14Â° Â± 0.52Â° for automatic registration using the entire head as ROI vs manual registration and were: 0.31 Â± 0.59 mm, 0.26 Â± 0.90 mm, 0.08 Â± 0.97 mm, 0.20Â° Â± 0.62Â°, 0.03Â° Â± 0.45Â°, -0.03Â° Â± 0.57Â° for automatic registration using target specific ROI vs manual registration, respectively.
Conclusion: Deviations in registration using different ROIs against the manual registration showed minimal differences for the majority of cases. It appears cranial registrations are not significantly influenced by the various CBCT image artifacts investigated in this study.