Perturbation Analysis Of Relationship Of Conebeam Ct And Stereoscopic Optical Localization System In Frameless Stereotactic Radiosurgery

Purpose/Objective(s)Treatment targets under frameless stereotactic radiosurgery (SRS) can be localized by optical guidance platform (OGP) using a stereoscopic camera. The registration of the target to isocenter is by IR markers on a patient bite block. The rigidity of the bite block and treatment target will determine the accuracy of the treatment. However, the offset between the biteblock and target cannot be visually detected; therefore conebeam CT(CBCT) is used to verify the accuracy of target localization based on information of anatomy volume. In this study, the relationship between these two localization methods was investigated by sequential perturbations of the setup.Materials/MethodsA Lucy phantom was treated as a patient model. A biteblock with markers was attached to the frame on the Lucy phantom. The Lucy phantom was scanned in a GE simulation CT (1.25 mm slices), and a treatment plan was done in the Varian Eclipse TPS. Then the plan was sent to the Optical Guidance Platform (OGP) and scheduled in the 4DTC with ARIA system. Vector with zero magnitude was reached by delicately setting up the patient model and camera system. Then, several magnitudes of perturbations were applied to simulate different possible misalignments of the frameless system. The perturbations were generated by displacement in y, x, z, couch rotation, tilt and spin. Then, CBCT was used to detect these perturbations. By automatically applying the detected shifts into the patient alignment system, system correlation information between the two localization systems was attained.ResultsWhile keeping other degrees of freedom at zero magnitude, the patient model was displaced along y, x, z, couch rotation, tilt and spin with units (mm or degrees) of 1.0, 2.0, 3.0, 2.0, 1.0, and 1.0 individually. The CBCT automatic matching algorithm was able to catch the corresponding displacements with suggested couch vertical, longitudinal, lateral and rotational movement. In this study, as the shift was applied to the automatic couch motion, it also generated average displacements in y, x, z direction, couch rotation, and vector with magnitude 0.92, 0.03, 1.40,-0.12 and 1.92 unit, with SD at 1.00, 0.33,0.23,0.10, and 0.25 (tilt and spin displacement was not adjustable with this table).ConclusionsPerturbation can be employed to test functional accurate stability for correlated location localization systems, CBCT and OGP. Using the 0.1 mm tracking ability of OGP, when correlated by couch motion, the discrepancy between CBCT and OGP is at the level of 2.0 mm for target localization of frameless SRS. In practice, It suggests that the OGP system is used for patient setup and intrafraction monitoring, while CBCT was used as second check for anatomy alignment and IR marker to target rigidity. Purpose/Objective(s)Treatment targets under frameless stereotactic radiosurgery (SRS) can be localized by optical guidance platform (OGP) using a stereoscopic camera. The registration of the target to isocenter is by IR markers on a patient bite block. The rigidity of the bite block and treatment target will determine the accuracy of the treatment. However, the offset between the biteblock and target cannot be visually detected; therefore conebeam CT(CBCT) is used to verify the accuracy of target localization based on information of anatomy volume. In this study, the relationship between these two localization methods was investigated by sequential perturbations of the setup. Treatment targets under frameless stereotactic radiosurgery (SRS) can be localized by optical guidance platform (OGP) using a stereoscopic camera. The registration of the target to isocenter is by IR markers on a patient bite block. The rigidity of the bite block and treatment target will determine the accuracy of the treatment. However, the offset between the biteblock and target cannot be visually detected; therefore conebeam CT(CBCT) is used to verify the accuracy of target localization based on information of anatomy volume. In this study, the relationship between these two localization methods was investigated by sequential perturbations of the setup. Materials/MethodsA Lucy phantom was treated as a patient model. A biteblock with markers was attached to the frame on the Lucy phantom. The Lucy phantom was scanned in a GE simulation CT (1.25 mm slices), and a treatment plan was done in the Varian Eclipse TPS. Then the plan was sent to the Optical Guidance Platform (OGP) and scheduled in the 4DTC with ARIA system. Vector with zero magnitude was reached by delicately setting up the patient model and camera system. Then, several magnitudes of perturbations were applied to simulate different possible misalignments of the frameless system. The perturbations were generated by displacement in y, x, z, couch rotation, tilt and spin. Then, CBCT was used to detect these perturbations. By automatically applying the detected shifts into the patient alignment system, system correlation information between the two localization systems was attained. A Lucy phantom was treated as a patient model. A biteblock with markers was attached to the frame on the Lucy phantom. The Lucy phantom was scanned in a GE simulation CT (1.25 mm slices), and a treatment plan was done in the Varian Eclipse TPS. Then the plan was sent to the Optical Guidance Platform (OGP) and scheduled in the 4DTC with ARIA system. Vector with zero magnitude was reached by delicately setting up the patient model and camera system. Then, several magnitudes of perturbations were applied to simulate different possible misalignments of the frameless system. The perturbations were generated by displacement in y, x, z, couch rotation, tilt and spin. Then, CBCT was used to detect these perturbations. By automatically applying the detected shifts into the patient alignment system, system correlation information between the two localization systems was attained. ResultsWhile keeping other degrees of freedom at zero magnitude, the patient model was displaced along y, x, z, couch rotation, tilt and spin with units (mm or degrees) of 1.0, 2.0, 3.0, 2.0, 1.0, and 1.0 individually. The CBCT automatic matching algorithm was able to catch the corresponding displacements with suggested couch vertical, longitudinal, lateral and rotational movement. In this study, as the shift was applied to the automatic couch motion, it also generated average displacements in y, x, z direction, couch rotation, and vector with magnitude 0.92, 0.03, 1.40,-0.12 and 1.92 unit, with SD at 1.00, 0.33,0.23,0.10, and 0.25 (tilt and spin displacement was not adjustable with this table). While keeping other degrees of freedom at zero magnitude, the patient model was displaced along y, x, z, couch rotation, tilt and spin with units (mm or degrees) of 1.0, 2.0, 3.0, 2.0, 1.0, and 1.0 individually. The CBCT automatic matching algorithm was able to catch the corresponding displacements with suggested couch vertical, longitudinal, lateral and rotational movement. In this study, as the shift was applied to the automatic couch motion, it also generated average displacements in y, x, z direction, couch rotation, and vector with magnitude 0.92, 0.03, 1.40,-0.12 and 1.92 unit, with SD at 1.00, 0.33,0.23,0.10, and 0.25 (tilt and spin displacement was not adjustable with this table). ConclusionsPerturbation can be employed to test functional accurate stability for correlated location localization systems, CBCT and OGP. Using the 0.1 mm tracking ability of OGP, when correlated by couch motion, the discrepancy between CBCT and OGP is at the level of 2.0 mm for target localization of frameless SRS. In practice, It suggests that the OGP system is used for patient setup and intrafraction monitoring, while CBCT was used as second check for anatomy alignment and IR marker to target rigidity. Perturbation can be employed to test functional accurate stability for correlated location localization systems, CBCT and OGP. Using the 0.1 mm tracking ability of OGP, when correlated by couch motion, the discrepancy between CBCT and OGP is at the level of 2.0 mm for target localization of frameless SRS. In practice, It suggests that the OGP system is used for patient setup and intrafraction monitoring, while CBCT was used as second check for anatomy alignment and IR marker to target rigidity.