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Title: SU-E-J-46: Evaluation of the Accuracy of a Six Degree of Freedom Robotic Couch Using ConeBeam CT Images of the Isocal Phantom

Abstract

Purpose The accuracy of Varian PerfectPitch six degree of freedom (DOF) robotic couch was examined using Varian Isocal phantom and cone-beam CT (CBCT) system. Methods CBCT images of the Isocal phantom were taken at different pitch and roll angles. The pitch and roll angles were varied from 357 to 3 degrees in one degree increments by input from service console, generating a total of 49 combinations with couch angle (yaw) zero. The center positions of the 16 tungsten carbide BBs contained in the Isocal were determined with in-house image processing software. Expected BBs positions at different rotation angles were determined mathematically by applying a combined translation/rotation operator to BB positions at zero pitch and roll values. A least square method was used to minimize the difference between the expected BB positions and their measured positions. In this way rotation angles were obtained and compared with input values from the console. Results A total of 49 CBCT images with voxel sizes 0.51 mm × 0.51 mm × 1 mm were used in analysis. Among the 49 calculations, the maximum rotation angle differences were 0.1 degree, 0.15 degree, and 0.09 degree, for pitch, roll, and couch rotation, respectively. The mean ± standard-deviationmore » angle differences were 0.028±0.001 degree, −0.043±0.003 degree, and −0.009±0.001 degree, for pitch, roll, and couch rotation, respectively. The maximum isocenter shifts were 0.3 mm, 0.5 mm, 0.4 mm in x, y, z direction respectively following IEC6127 convention. The mean isocenter shifts were 0.07±0.02 mm, −0.05±0.06 mm, and −0.12±0.02 mm in x, y and z directions. Conclusion The accuracy of the Varian PerfectPitch six DOF couch was studied with CBCTs of the Isocal phantom. The rotational errors were less than 0.15 degree and isocenter shifts were less than 0.5 mm in any direction. This accuracy is sufficient for stereotactic radiotherapy clinical applications.« less

Authors:
; ; ; ; ; ; ; ; ; ; ;  [1]
  1. University of Nebraska Medical Center, Omaha, NE (United States)
Publication Date:
OSTI Identifier:
22494069
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; ACCURACY; COMPUTERIZED TOMOGRAPHY; DEGREES OF FREEDOM; IMAGE PROCESSING; IMAGES; PHANTOMS; PITCHES; RADIOTHERAPY

Citation Formats

Zhang, Q, Driewer, J, Wang, S, Li, S, Zheng, D, Zhu, X, Zhen, W, Wahl, A, Lin, C, Thompson, R, Zhou, S, and Enke, C. SU-E-J-46: Evaluation of the Accuracy of a Six Degree of Freedom Robotic Couch Using ConeBeam CT Images of the Isocal Phantom. United States: N. p., 2015. Web. doi:10.1118/1.4924133.
Zhang, Q, Driewer, J, Wang, S, Li, S, Zheng, D, Zhu, X, Zhen, W, Wahl, A, Lin, C, Thompson, R, Zhou, S, & Enke, C. SU-E-J-46: Evaluation of the Accuracy of a Six Degree of Freedom Robotic Couch Using ConeBeam CT Images of the Isocal Phantom. United States. doi:10.1118/1.4924133.
Zhang, Q, Driewer, J, Wang, S, Li, S, Zheng, D, Zhu, X, Zhen, W, Wahl, A, Lin, C, Thompson, R, Zhou, S, and Enke, C. Mon . "SU-E-J-46: Evaluation of the Accuracy of a Six Degree of Freedom Robotic Couch Using ConeBeam CT Images of the Isocal Phantom". United States. doi:10.1118/1.4924133.
@article{osti_22494069,
title = {SU-E-J-46: Evaluation of the Accuracy of a Six Degree of Freedom Robotic Couch Using ConeBeam CT Images of the Isocal Phantom},
author = {Zhang, Q and Driewer, J and Wang, S and Li, S and Zheng, D and Zhu, X and Zhen, W and Wahl, A and Lin, C and Thompson, R and Zhou, S and Enke, C},
abstractNote = {Purpose The accuracy of Varian PerfectPitch six degree of freedom (DOF) robotic couch was examined using Varian Isocal phantom and cone-beam CT (CBCT) system. Methods CBCT images of the Isocal phantom were taken at different pitch and roll angles. The pitch and roll angles were varied from 357 to 3 degrees in one degree increments by input from service console, generating a total of 49 combinations with couch angle (yaw) zero. The center positions of the 16 tungsten carbide BBs contained in the Isocal were determined with in-house image processing software. Expected BBs positions at different rotation angles were determined mathematically by applying a combined translation/rotation operator to BB positions at zero pitch and roll values. A least square method was used to minimize the difference between the expected BB positions and their measured positions. In this way rotation angles were obtained and compared with input values from the console. Results A total of 49 CBCT images with voxel sizes 0.51 mm × 0.51 mm × 1 mm were used in analysis. Among the 49 calculations, the maximum rotation angle differences were 0.1 degree, 0.15 degree, and 0.09 degree, for pitch, roll, and couch rotation, respectively. The mean ± standard-deviation angle differences were 0.028±0.001 degree, −0.043±0.003 degree, and −0.009±0.001 degree, for pitch, roll, and couch rotation, respectively. The maximum isocenter shifts were 0.3 mm, 0.5 mm, 0.4 mm in x, y, z direction respectively following IEC6127 convention. The mean isocenter shifts were 0.07±0.02 mm, −0.05±0.06 mm, and −0.12±0.02 mm in x, y and z directions. Conclusion The accuracy of the Varian PerfectPitch six DOF couch was studied with CBCTs of the Isocal phantom. The rotational errors were less than 0.15 degree and isocenter shifts were less than 0.5 mm in any direction. This accuracy is sufficient for stereotactic radiotherapy clinical applications.},
doi = {10.1118/1.4924133},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Purpose: To test the accuracy and reproducibility of both translational and rotational movements for a couch with six degrees of freedom (6DoF) using a novel phantom design Methods: An end-to-end test was carried out using two different phantoms. A 6 cm3 cube with a central fiducial BB (WL-QA Sun Nuclear) and a custom fabricated rectangular prism (31 cm x 8 cm x 8 cm), placed on a baseplate with known angular offsets for pitch, roll and yaw with a central fiducial BB and unique surface structures for registration purposes, were used. The end-to-end test included an initial CT simulation formore » a reference study, setup to an offset mark on each phantom, registration of the reference CT to the acquired cone-beam CT, and final Winston-Lutz delivery at four cardinal gantry angles. Results for both translational and rotational movements were recorded and compared for both phantoms. Results: Translational and rotational measurements were performed with a PerfectPitch (Varian) couch for 10 trials for both phantoms. Distinct translational shifts were [−5.372±0.384mm, −10.183±0.137mm, 14.028±0.155mm] for the cube and [7.520±0.159mm, −9.117±0.101mm, 16.273±0.115mm] for the prototype phantom for lateral, longitudinal, and vertical shifts, respectively. Distinct rotational adjustments were [1.121±0.102o, −1.067±0.235o, −2.662±0.380o] for the cube and [2.534±0.059o, 1.994±0.025o, 2.094±0.076o] for the prototype for pitch, roll, and yaw, respectively. Winston-Lutz test results performed after 6DoF couch correction from each cardinal gantry angle ranged from 0.26–0.72mm for the cube and 0.55–0.86mm for the prototype. Conclusion: The prototype phantom is more precise for both translational and rotational adjustments compared to a commercial phantom. The design of the prototype phantom allows for a more discernible visual confirmation of correct translational and rotational adjustments with the prototype phantom. Winston-Lutz results are more accurate for the commercial phantom but are still within tolerance for the prototype phantom.« less
  • Purpose: To determine the 6 degree of freedom systematic deviations between 2D/3D and CBCT image registration with various imaging setups and fusion algorithms on the Varian Edge Linac. Methods: An anthropomorphic head phantom with radio opaque targets embedded was scanned with CT slice thicknesses of 0.8, 1, 2, and 3mm. The 6 DOF systematic errors were assessed by comparing 2D/3D (kV/MV with CT) with 3D/3D (CBCT with CT) image registrations with different offset positions, similarity measures, image filters, and CBCT slice thicknesses (1 and 2 mm). The 2D/3D registration accuracy of 51 fractions for 26 cranial SRS patients was alsomore » evaluated by analyzing 2D/3D pre-treatment verification taken after 3D/3D image registrations. Results: The systematic deviations of 2D/3D image registration using kV- kV, MV-kV and MV-MV image pairs were within ±0.3mm and ±0.3° for translations and rotations with 95% confidence interval (CI) for a reference CT with 0.8 mm slice thickness. No significant difference (P>0.05) on target localization was observed between 0.8mm, 1mm, and 2mm CT slice thicknesses with CBCT slice thicknesses of 1mm and 2mm. With 3mm CT slice thickness, both 2D/3D and 3D/3D registrations performed less accurately in longitudinal direction than thinner CT slice thickness (0.60±0.12mm and 0.63±0.07mm off, respectively). Using content filter and using similarity measure of pattern intensity instead of mutual information, improved the 2D/3D registration accuracy significantly (P=0.02 and P=0.01, respectively). For the patient study, means and standard deviations of residual errors were 0.09±0.32mm, −0.22±0.51mm and −0.07±0.32mm in VRT, LNG and LAT directions, respectively, and 0.12°±0.46°, −0.12°±0.39° and 0.06°±0.28° in RTN, PITCH, and ROLL directions, respectively. 95% CI of translational and rotational deviations were comparable to those in phantom study. Conclusion: 2D/3D image registration provided on the Varian Edge radiosurgery, 6 DOF-based system provides accurate target positioning for frameless image-guided cranial stereotactic radiosurgery.« less
  • Purpose: The proper operation of a six degree of freedom couch (6DOFC) to position a patient for treatment requires that a number systems on the treatment unit work together correctly. Commissioning a 6DOFC requires not only the commissioning of each separate system but also commissioning the interactions between the systems. Methods: To commission a 6DOFC, we tested the resolvers that readout the linear and angular positions; the orthogonality of the axes of the laser positioning system, the imaging system, the gantry and the couch as well as their relationship to each other. An automated Winston-Lutz test was used verify themore » coincidence of the origins of the laser system, imaging system and treatment unit. The IsoCal phantom was used to verify the consistency of axes orientations between systems. The operation of the couch and imaging system was verified under simulated load conditions and an end to end test was performed to verify correct operation of the system. Results: The tests on the couch resolvers, orthogonality and coincidence of the axes of each system were successfully completed and showed excellent agreement. The automated Winston-Lutz test showed that the maximum displacement of the center of the radiation field with respect to the isocenter was <0.6 mm (radius) at isocenter. The analysis of the IsoCal phantom showed that the maximum variation of the radiation field with respect to known locations in the phantom was ∼0.9 mm for all the BBs in the phantom. Load tests showed maximum errors of 1 mm. Conclusion: We tested all system associated with the 6DOFC and found the uncertainty due to imaging was <.9mm and the uncertainty due to loading ∼1 mm, resulting in a total error of ∼1.4 mm.« less
  • Purpose: To assess the accuracy of internal target volume (ITV) segmentation of lung tumors for treatment planning of simultaneous integrated boost (SIB) radiotherapy as seen in 4D PET/CT images, using a novel 3D-printed phantom. Methods: The insert mimics high PET tracer uptake in the core and 50% uptake in the periphery, by using a porous design at the periphery. A lung phantom with the insert was placed on a programmable moving platform. Seven breathing waveforms of ideal and patient-specific respiratory motion patterns were fed to the platform, and 4D PET/CT scans were acquired of each of them. CT images weremore » binned into 10 phases, and PET images were binned into 5 phases following the clinical protocol. Two scenarios were investigated for segmentation: a gate 30–70 window, and no gating. The radiation oncologist contoured the outer ITV of the porous insert with on CT images, while the internal void volume with 100% uptake was contoured on PET images for being indistinguishable from the outer volume in CT images. Segmented ITVs were compared to the expected volumes based on known target size and motion. Results: 3 ideal breathing patterns, 2 regular-breathing patient waveforms, and 2 irregular-breathing patient waveforms were used for this study. 18F-FDG was used as the PET tracer. The segmented ITVs from CT closely matched the expected motion for both no gating and gate 30–70 window, with disagreement of contoured ITV with respect to the expected volume not exceeding 13%. PET contours were seen to overestimate volumes in all the cases, up to more than 40%. Conclusion: 4DPET images of a novel 3D printed phantom designed to mimic different uptake values were obtained. 4DPET contours overestimated ITV volumes in all cases, while 4DCT contours matched expected ITV volume values. Investigation of the cause and effects of the discrepancies is undergoing.« less
  • Purpose: To evaluate the residual setup error and intrafraction motion following kilovoltage cone-beam CT (CBCT) image guidance, for immobilized spine stereotactic body radiotherapy (SBRT) patients, with positioning corrected for in all six degrees of freedom. Methods and Materials: Analysis is based on 42 consecutive patients (48 thoracic and/or lumbar metastases) treated with a total of 106 fractions and 307 image registrations. Following initial setup, a CBCT was acquired for patient alignment and a pretreatment CBCT taken to verify shifts and determine the residual setup error, followed by a midtreatment and posttreatment CBCT image. For 13 single-fraction SBRT patients, two midtreatmentmore » CBCT images were obtained. Initially, a 1.5-mm and 1 Degree-Sign tolerance was used to reposition the patient following couch shifts which was subsequently reduced to 1 mm and 1 Degree-Sign degree after the first 10 patients. Results: Small positioning errors after the initial CBCT setup were observed, with 90% occurring within 1 mm and 97% within 1 Degree-Sign . In analyzing the impact of the time interval for verification imaging (10 {+-} 3 min) and subsequent image acquisitions (17 {+-} 4 min), the residual setup error was not significantly different (p > 0.05). A significant difference (p = 0.04) in the average three-dimensional intrafraction positional deviations favoring a more strict tolerance in translation (1 mm vs. 1.5 mm) was observed. The absolute intrafraction motion averaged over all patients and all directions along x, y, and z axis ({+-} SD) were 0.7 {+-} 0.5 mm and 0.5 {+-} 0.4 mm for the 1.5 mm and 1 mm tolerance, respectively. Based on a 1-mm and 1 Degree-Sign correction threshold, the target was localized to within 1.2 mm and 0.9 Degree-Sign with 95% confidence. Conclusion: Near-rigid body immobilization, intrafraction CBCT imaging approximately every 15-20 min, and strict repositioning thresholds in six degrees of freedom yields minimal intrafraction motion allowing for safe spine SBRT delivery.« less