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viewing voxels as the cost function. As a comparison, mutual information is applied for patient image registration. To test the accuracy of the 3D volumetric image registration technique, three head phantoms were used to acquire CT, MR and PET/CT images with lateral shifts of 0.0, 5.0, 10.0 and 15.0 mm on the scanner couches and compared with the image registration shifts. For patient head movement studies, 14 patient cranial MR (T1/T2/FLAIR) images acquired from the same scanner and 18 patient cranial PET/CT images acquired in the hybrid scanner were used and compared with the 3D volumetric registration results. Results: Based on the head phantom studies, 0.1 mm accuracy is achieved for anatomic (CT/CT and MR/MR) images and 0.5 mm accuracy is achieved for PET/CT images. Based on the 14 patient MR/MR image registration results, the average patient movements during two consecutive scans are 0.40.4 mm in translation and 0.2°0.4° in rotation. Based on the 18 patient PET/CT image registration results, the average patient movements are 0.70.4 mm in translation and 0.4°0.5° in rotation. One patient example is shown in Figure 1. In the patient studies, the largest misalignment observed is 1.6 mm in translation and 1.5° in rotation, which is similar to the setup error in stereotactic radiotherapy/radiosurgery. Conclusions: The 3D volumetric image registration method is useful in detecting and correcting small misalignment error in cranial PET/CT images, and should be used for quality assurance, especially for stereotactic radiation treatment. Figure 1: The color homogeneity of PET/CT cranial images is improved from (A) to (B) and (C), where the PET image is in red, and CT image is in green, light blue and yellow, respectively. (A) The original PET/CT images, (B) the registered images using mutual information and (C) the registered images using 3D volumetric views. The color inhomogeneity in the orbital/nose region is due to the low-resolution artifact at high curvature area of the PET image. Also, some bone facial bone structures are shown where little PET signal is available. Author Disclosure: G. Li, None; H. Xie, None; H. Ning, None; D. Citrin, None; J. Capala, None; P. Guion, None; B. Arora, None; K. Camphausen, None; N. Coleman, None; R. Miller, None. 2776 Automated Registration and Correction of Patient Positioning for IGRT and Body Radiosurgery Using the Novalis “ExacTrac” System R. M. Macklis, C. Robinson, T. Djemil Cleveland Clinic Foundation, Cleveland, OH Purpose/Objective(s): Radiation Medicine is now incorporating more sophisticated degrees of automation in its technologic progression towards an Image-Guided Radiation Therapy (IGRT) treatment paradigm. This is especially true for stereotactic body radiosurgery (SBR) and similar focal approaches to beam targeting. As the IGRT/SBR paradigm evolves, we are relying less on skin marks in daily patient set-up. Instead, internal fiducials such as radioopaque anatomic structures or implanted markers are used as proxies for positional target registration. Phantom studies have shown that the combination of trackable skin markers and internal fiducials produce targeting accuracies on the order of /- 1 mm. However, real-world usability data for such systems are sparse. We are currently utilizing the BrainLab “ExacTrac” IGRT system for SBR and extracranial stereotactic radiotherapy. Patients are set up in treatment position based on traditional skin marks correlated to a planning CT. These skin mark positions are tracked daily using 5–7 removable infrared reflector markers affixed to the most informative and stable skin sites. The initial set-up is made using these reflector markers followed by correction to a final position based on orthogonal high resolution X-ray images of internal fiducials or bony anatomy acquired prior to treatment and used to validate final treatment coordinates. Final targeting coordinates are based on near-real-time X-ray images of informative markers. We have analyzed a representative clinical dataset indicating the magnitude of the positional discordances between original skin mark target position vs. the final internal fiducial position and analyzed patterns seen in a representative set of over 100 measurements obtained in 13 extracranial IGRT patients. These data are of interest because they give some indication of daily radiotherapy set-up reproducibility and the degree of positional modification necessary when final treatment coordinates are corrected based on internal markers in a real-world situation. Materials/Methods: Patients were divided into tumor groups: Head/Neck (N 4) Lung (N 3) Trunk (N 3) and Spine (N 3). H/N immobilization was accomplished using an ORFIT mask, while body immobilization was accomplished using the BODYFIX system. The center of mass was calculated for each target prior to treatment based on the x,y,z positional information obtained from the internal markers. The ExacTrac system was used to calculate and automatically adjust patient positioning. Data presented here represent the absolute magnitude of the shifts (mean /- SD) for the center of mass for the target. Results: For H/N sites, correction shifts were within 1–2 (/- 1) mm of original skin mark set-up. For Spine sites, shifts were much larger (approx. 2–9 (/- 8) mm. For Trunk and Lung cases, shifts were intermediate (in the range of 2–7 (/- 2) mm. The automated system typically added less than 5 minutes to daily clinical treatment times. Conclusions: This real-world usability analysis confirmed the utility and applicability of the ExacTrac IGRT positioning system for extracranial SBR cases for a broad range of target sites. The combination of trackable infrared skin markers and in-room high-resolution orthogonal X-ray imagers represents a facile and robust automated solution to set-up challenges in clinical IGRT and body radiosurgery. Author Disclosure: R.M. Macklis, Brainlab, D. Speakers Bureau/Honoraria; C. Robinson, None; T. Djemil, None. S644 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
Transcript of 2776
viewing voxels as the cost function. As a comparison, mutual information is applied for patient image registration. To test theaccuracy of the 3D volumetric image registration technique, three head phantoms were used to acquire CT, MR and PET/CTimages with lateral shifts of 0.0, 5.0, 10.0 and 15.0 mm on the scanner couches and compared with the image registration shifts.For patient head movement studies, 14 patient cranial MR (T1/T2/FLAIR) images acquired from the same scanner and 18patient cranial PET/CT images acquired in the hybrid scanner were used and compared with the 3D volumetric registrationresults.
Results: Based on the head phantom studies, 0.1 mm accuracy is achieved for anatomic (CT/CT and MR/MR) images and 0.5mm accuracy is achieved for PET/CT images. Based on the 14 patient MR/MR image registration results, the average patientmovements during two consecutive scans are 0.4�0.4 mm in translation and 0.2°�0.4° in rotation. Based on the 18 patientPET/CT image registration results, the average patient movements are 0.7�0.4 mm in translation and 0.4°�0.5° in rotation.One patient example is shown in Figure 1. In the patient studies, the largest misalignment observed is 1.6 mm in translationand 1.5° in rotation, which is similar to the setup error in stereotactic radiotherapy/radiosurgery.
Conclusions: The 3D volumetric image registration method is useful in detecting and correcting small misalignment error incranial PET/CT images, and should be used for quality assurance, especially for stereotactic radiation treatment.
Figure 1: The color homogeneity of PET/CT cranial images is improved from (A) to (B) and (C), where the PET image isin red, and CT image is in green, light blue and yellow, respectively. (A) The original PET/CT images, (B) the registered imagesusing mutual information and (C) the registered images using 3D volumetric views. The color inhomogeneity in the orbital/noseregion is due to the low-resolution artifact at high curvature area of the PET image. Also, some bone facial bone structures areshown where little PET signal is available.
Author Disclosure: G. Li, None; H. Xie, None; H. Ning, None; D. Citrin, None; J. Capala, None; P. Guion, None; B. Arora,None; K. Camphausen, None; N. Coleman, None; R. Miller, None.
2776 Automated Registration and Correction of Patient Positioning for IGRT and Body Radiosurgery Usingthe Novalis “ExacTrac” System
R. M. Macklis, C. Robinson, T. Djemil
Cleveland Clinic Foundation, Cleveland, OH
Purpose/Objective(s): Radiation Medicine is now incorporating more sophisticated degrees of automation in its technologicprogression towards an Image-Guided Radiation Therapy (IGRT) treatment paradigm. This is especially true for stereotacticbody radiosurgery (SBR) and similar focal approaches to beam targeting. As the IGRT/SBR paradigm evolves, we are relyingless on skin marks in daily patient set-up. Instead, internal fiducials such as radioopaque anatomic structures or implantedmarkers are used as proxies for positional target registration. Phantom studies have shown that the combination of trackable skinmarkers and internal fiducials produce targeting accuracies on the order of �/- 1 mm. However, real-world usability data forsuch systems are sparse.
We are currently utilizing the BrainLab “ExacTrac” IGRT system for SBR and extracranial stereotactic radiotherapy. Patientsare set up in treatment position based on traditional skin marks correlated to a planning CT. These skin mark positions aretracked daily using 5–7 removable infrared reflector markers affixed to the most informative and stable skin sites. The initialset-up is made using these reflector markers followed by correction to a final position based on orthogonal high resolution X-rayimages of internal fiducials or bony anatomy acquired prior to treatment and used to validate final treatment coordinates. Finaltargeting coordinates are based on near-real-time X-ray images of informative markers. We have analyzed a representativeclinical dataset indicating the magnitude of the positional discordances between original skin mark target position vs. the finalinternal fiducial position and analyzed patterns seen in a representative set of over 100 measurements obtained in 13 extracranialIGRT patients. These data are of interest because they give some indication of daily radiotherapy set-up reproducibility and thedegree of positional modification necessary when final treatment coordinates are corrected based on internal markers in areal-world situation.
Materials/Methods: Patients were divided into tumor groups: Head/Neck (N � 4) Lung (N � 3) Trunk (N � 3) and Spine(N � 3). H/N immobilization was accomplished using an ORFIT mask, while body immobilization was accomplished usingthe BODYFIX system. The center of mass was calculated for each target prior to treatment based on the x,y,z positionalinformation obtained from the internal markers. The ExacTrac system was used to calculate and automatically adjust patientpositioning. Data presented here represent the absolute magnitude of the shifts (mean �/- SD) for the center of mass for thetarget.
Results: For H/N sites, correction shifts were within 1–2 (�/- 1) mm of original skin mark set-up. For Spine sites, shifts weremuch larger (approx. 2–9 (�/- 8) mm. For Trunk and Lung cases, shifts were intermediate (in the range of 2–7 (�/- 2) mm.The automated system typically added less than 5 minutes to daily clinical treatment times.
Conclusions: This real-world usability analysis confirmed the utility and applicability of the ExacTrac IGRT positioningsystem for extracranial SBR cases for a broad range of target sites. The combination of trackable infrared skin markers andin-room high-resolution orthogonal X-ray imagers represents a facile and robust automated solution to set-up challenges inclinical IGRT and body radiosurgery.
Author Disclosure: R.M. Macklis, Brainlab, D. Speakers Bureau/Honoraria; C. Robinson, None; T. Djemil, None.
S644 I. J. Radiation Oncology ● Biology ● Physics Volume 66, Number 3, Supplement, 2006
