2738
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Results: CBCT scanning parameters have been optimized incorporating our initial experience and consideration for dose to the patient. Parameters will continue to be revisited at regular intervals. Our underlying strategy is that image quality need only to be good enough to ensure reliable patient alignment. We have found significant dose saving in the case of automatic alignment based on bony anatomy. Results of timing study showed that despite continuing therapist training during those cases, additional time per patient was only 5:21min on average (median 4:26 min). Total time from the end of room laser based manual patient setup to “beam on” was on average 12:15 min for CBCT based alignment versus 6:30 min for MV port films. Intervention limits for CBCT repositioning have been set similar to current port film based procedures: (1) no action is required for deviations 2 mm, (2) correction to be applied for deviation 2 - 10 mm, and (3) physician/physics to be called for larger deviations. Synergy CBCT system gives corrections for all 6 degrees of freedom (3 translations, 3 rotations); however, our procedures is to use only the three perpendicular translations, and not intervene if all angular deviations are below 2 degrees. DICOM transfer has been problematic. A key need identified is a robust RT PACS system. Physician review of CBCT image sets also is a challenge. Clinicians familiar with weekly planar MV port films need to adjust to the wealth of information available with CBCT. Adjustment process was handicapped by the fact that review of CBCT images is only possible from CBCT workstation at the treatment machine, while MV port films can be reviewed from any PC in the department through IMPAC. To reduce congestion at the treatment console, we developed a strategy to allow an additional monitor and input devices. QA emphasis has been on system safety, agreement of imaging (kV) and treatment (MV) isocenter, image quality, alignment algorithm capability, and dose to patient. Conclusions: The Elekta Synergy CBCT system is a robust first generation system. There is a clear need for improved DICOM transfer capability, integration with the IMPAC system, and the development of a robust RT PACS system. We expect that once therapists are familiar with the CBCT there will be no additional time needed for CBCT compared to current techniques. The optimum use of CBCT and the role and methods of physician image review remains an important area of investigation. Author Disclosure: J. Lehmann, None; J. Perks, None; S. Narayan, None; Z. Goldberg, None; J. Ryu, None; A. Chen, None; R. Harse, previously received speaker honorarium from Elekta, D. Speakers Bureau/Honoraria; S. Semon, None; S. Vijaya- kumar, None; J.A. Purdy, None. 2738 CT-Based Daily Localization of Prostate Patients: Anatomy vs. Implanted Markers K. Paskalev, S. Feigenberg, S. McNeeley, E. Horwitz, R. Price, A. Konski, M. Buyyounouski, C. Ma, P. Alan Fox Chase Cancer Center, Philadelphia, PA Purpose/Objective(s): The rapid advancement of image-guided radiation therapy (IGRT) opens the door for new localization techniques in the treatment of prostate cancer. Currently, the most reliable techniques involve insertion of radio-opaque markers in the prostate. These markers can be detected and aligned by using either 3D or 2D imaging. Another promising technique for prostate alignment utilizes high quality diagnostic CT images, acquired using a sliding CT gantry in the treatment room. The goal of this study was to compare anatomy-based alignments with implanted fiducial-based alignments for prostate parents who were localized daily with a CT-on-rails system. Materials/Methods: A total of 8 patients undergoing IMRT treatment for prostate cancer were included in the study. The prostate was localized daily with the Primatom CT-on-Rails system (Siemens, Concord, CA). All patients had four gold seeds (0.8 x 3 mm) inserted in the prostate prior to simulation. The seeds, prostate, bladder and rectum were contoured during simulation, and all contours as well as the planning isocenter were electronically transferred to the daily localization station. An in-room CT scan was acquired prior to each treatment. The seeds were aligned with the seed contours from simulation, the patient was shifted and the daily fraction of radiation was delivered. For the purpose of comparison, the seed contours were switched off at a separate time, and a second alignment was performed using only the anatomical contours. A total of 255 alignments were carried out using both techniques. The two sets of isocenter shifts generated were compared separately in anterior-posterior (AP), lateral and longitudinal directions, using correlation coefficients and correlated t-tests. The differences between the shifts were analyzed using their standard deviations, and average values. Results: The systematic differences between the two sets of shifts were 0.1 mm (lateral), 0.3 mm (AP) and 0.3 mm (longitudinal). The lateral difference was not statistically significant (p value of 0.237). The other two differences were statistically significant (p 0.02), but their clinical significance was minimal. The two sets of shifts had a very high level of correlation (correlation coefficients from 0.90 in the longitudinal direction to 0.98 in the lateral direction). The random differences (one standard deviation) between the anatomy-based and the seed-based alignments were 1.3 mm (lateral), 1.9 mm (AP), and 2.0 mm (longitudinal). Previously, we estimated that random uncertainties (one standard deviation) of the anatomy-based alignments were in the range of 1.0 to 1.5 mm. Therefore the random uncertainties of the seed-based alignments, calculated using quadratic subtraction were in the same range. Conclusions: The results of this study showed that there was a strong correlation between anatomy-based and seed-based alignments of the prostate, when diagnostic quality CT scans were used for localization. The two techniques were similar in terms of uncertainties and the systematic discrepancies were minimal. Author Disclosure: K. Paskalev, None; S. Feigenberg, None; S. McNeeley, None; E. Horwitz, None; R. Price, None; A. Konski, None; M. Buyyounouski, None; C. Ma, None; P. Alan, None. 2739 Inter-Fractional Variations in Patient Setup and Anatomic Change Assessed by Daily CT From Helical Tomotherapy X. A. Li, X. Qi, K. Mueller, P. A. Jursinic, B. A. Erickson, D. Wang, C. J. Schultz, S. Y. Firat, J. F. Wilson Medical College of Wisconsin, Milwaukee, WI Background: Inter-fractional variations in patient setup and anatomic changes are significant and site specific, which can negatively impact treatment effectiveness. Purpose/Objective(s): To report our initial experience on using a MVCT to systematically quantify and to account for inter-fractional variations in patient setup and anatomic changes at various anatomic sites throughout the patient body. S621 Proceedings of the 48th Annual ASTRO Meeting
Transcript of 2738
Results: CBCT scanning parameters have been optimized incorporating our initial experience and consideration for dose to thepatient. Parameters will continue to be revisited at regular intervals. Our underlying strategy is that image quality need only tobe good enough to ensure reliable patient alignment. We have found significant dose saving in the case of automatic alignmentbased on bony anatomy. Results of timing study showed that despite continuing therapist training during those cases, additionaltime per patient was only 5:21min on average (median 4:26 min). Total time from the end of room laser based manual patientsetup to “beam on” was on average 12:15 min for CBCT based alignment versus 6:30 min for MV port films. Intervention limitsfor CBCT repositioning have been set similar to current port film based procedures: (1) no action is required for deviations �2mm, (2) correction to be applied for deviation 2 - 10 mm, and (3) physician/physics to be called for larger deviations. SynergyCBCT system gives corrections for all 6 degrees of freedom (3 translations, 3 rotations); however, our procedures is to use onlythe three perpendicular translations, and not intervene if all angular deviations are below 2 degrees. DICOM transfer has beenproblematic. A key need identified is a robust RT PACS system. Physician review of CBCT image sets also is a challenge.Clinicians familiar with weekly planar MV port films need to adjust to the wealth of information available with CBCT.Adjustment process was handicapped by the fact that review of CBCT images is only possible from CBCT workstation at thetreatment machine, while MV port films can be reviewed from any PC in the department through IMPAC. To reduce congestionat the treatment console, we developed a strategy to allow an additional monitor and input devices. QA emphasis has been onsystem safety, agreement of imaging (kV) and treatment (MV) isocenter, image quality, alignment algorithm capability, anddose to patient.
Conclusions: The Elekta Synergy CBCT system is a robust first generation system. There is a clear need for improved DICOMtransfer capability, integration with the IMPAC system, and the development of a robust RT PACS system. We expect that oncetherapists are familiar with the CBCT there will be no additional time needed for CBCT compared to current techniques. Theoptimum use of CBCT and the role and methods of physician image review remains an important area of investigation.
Author Disclosure: J. Lehmann, None; J. Perks, None; S. Narayan, None; Z. Goldberg, None; J. Ryu, None; A. Chen, None;R. Harse, previously received speaker honorarium from Elekta, D. Speakers Bureau/Honoraria; S. Semon, None; S. Vijaya-kumar, None; J.A. Purdy, None.
2738 CT-Based Daily Localization of Prostate Patients: Anatomy vs. Implanted Markers
K. Paskalev, S. Feigenberg, S. McNeeley, E. Horwitz, R. Price, A. Konski, M. Buyyounouski, C. Ma, P. Alan
Fox Chase Cancer Center, Philadelphia, PA
Purpose/Objective(s): The rapid advancement of image-guided radiation therapy (IGRT) opens the door for new localizationtechniques in the treatment of prostate cancer. Currently, the most reliable techniques involve insertion of radio-opaque markersin the prostate. These markers can be detected and aligned by using either 3D or 2D imaging. Another promising technique forprostate alignment utilizes high quality diagnostic CT images, acquired using a sliding CT gantry in the treatment room. Thegoal of this study was to compare anatomy-based alignments with implanted fiducial-based alignments for prostate parents whowere localized daily with a CT-on-rails system.
Materials/Methods: A total of 8 patients undergoing IMRT treatment for prostate cancer were included in the study. Theprostate was localized daily with the Primatom CT-on-Rails system (Siemens, Concord, CA). All patients had four gold seeds(0.8 x 3 mm) inserted in the prostate prior to simulation. The seeds, prostate, bladder and rectum were contoured duringsimulation, and all contours as well as the planning isocenter were electronically transferred to the daily localization station.An in-room CT scan was acquired prior to each treatment. The seeds were aligned with the seed contours from simulation, thepatient was shifted and the daily fraction of radiation was delivered. For the purpose of comparison, the seed contours wereswitched off at a separate time, and a second alignment was performed using only the anatomical contours. A total of 255alignments were carried out using both techniques. The two sets of isocenter shifts generated were compared separately inanterior-posterior (AP), lateral and longitudinal directions, using correlation coefficients and correlated t-tests. The differencesbetween the shifts were analyzed using their standard deviations, and average values.
Results: The systematic differences between the two sets of shifts were 0.1 mm (lateral), 0.3 mm (AP) and 0.3 mm(longitudinal). The lateral difference was not statistically significant (p value of 0.237). The other two differences werestatistically significant (p� 0.02), but their clinical significance was minimal. The two sets of shifts had a very high level ofcorrelation (correlation coefficients from 0.90 in the longitudinal direction to 0.98 in the lateral direction). The randomdifferences (one standard deviation) between the anatomy-based and the seed-based alignments were 1.3 mm (lateral), 1.9 mm(AP), and 2.0 mm (longitudinal). Previously, we estimated that random uncertainties (one standard deviation) of theanatomy-based alignments were in the range of 1.0 to 1.5 mm. Therefore the random uncertainties of the seed-based alignments,calculated using quadratic subtraction were in the same range.
Conclusions: The results of this study showed that there was a strong correlation between anatomy-based and seed-basedalignments of the prostate, when diagnostic quality CT scans were used for localization. The two techniques were similar interms of uncertainties and the systematic discrepancies were minimal.
Author Disclosure: K. Paskalev, None; S. Feigenberg, None; S. McNeeley, None; E. Horwitz, None; R. Price, None; A. Konski,None; M. Buyyounouski, None; C. Ma, None; P. Alan, None.
2739 Inter-Fractional Variations in Patient Setup and Anatomic Change Assessed by Daily CT From HelicalTomotherapy
X. A. Li, X. Qi, K. Mueller, P. A. Jursinic, B. A. Erickson, D. Wang, C. J. Schultz, S. Y. Firat, J. F. Wilson
Medical College of Wisconsin, Milwaukee, WI
Background: Inter-fractional variations in patient setup and anatomic changes are significant and site specific, which cannegatively impact treatment effectiveness.
Purpose/Objective(s): To report our initial experience on using a MVCT to systematically quantify and to account forinter-fractional variations in patient setup and anatomic changes at various anatomic sites throughout the patient body.
S621Proceedings of the 48th Annual ASTRO Meeting
