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Improved Target Localization With 3D Cone Beam CT On-Board Imaging in Stereotactic Body Radiation Therapy
Proceedings of the 49th Annual ASTRO Meeting intensity maps. Overall, the dose distribution closely follows the ‘‘anatomy-of-the-day’’ in regions where SOIs’ position and shape changed, and highly resembles the original plan in regions where either SOIs remain unchanged or only normal tissues exist. The DVHs of the 3 plans is also shown in the figure. The D95 (min/max) doses to the GTV are 99.3% (90.0%/104.1%), 83% (57.6%/104.1%) and 98.3% (90.0%/103.8%), for the original, uncorrected and re-optimized plans, respectively. The DVH to the rectum appears better for the uncorrected plan, due to the gross under-dose to the nearby GTV regions. The D33 and median dose to the rectum are comparable between the original (55.4%, 14%) and re-optimized (61.0%, 16.0%) plans. The D20 (median dose) to the bladder are 49.1% (14%), 61% (18.8%), and 50% (16.4%) for the original, uncorrected and re-optimized plans, respectively. The re-optimization process took less than 1 min. on a desktop PC and the dMLC sequencing took another min. Conclusion: It is technically feasible to perform on-line re-optimization based on the ‘‘anatomy-of-the-day’’ and to achieve results similar to the original dose distribution. For clinical implementation, a quality assurance step is also needed.
Author Disclosure: D. Thongphiew, None; Q. Wu, None; Z. Wang, None; S. Yoo, None; W.R. Lee, None; Z. Vujaskovic, None; F. Yin, None.
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Improved Target Localization With 3D Cone Beam CT On-Board Imaging in Stereotactic Body Radiation Therapy
D. S. Yoo, Z. Wang, J. Nelson, J. Kirkpatrick, S. Yoo, J. Wu, J. Meyer, N. Larrier, L. Marks, F. Yin Duke University Medical Center, Durham, NC Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) delivers relatively high doses to a target, typically in a hypofractionated fashion. With large fraction sizes, ideal target margins must minimize normal tissue exposure while ensuring tumor
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I. J. Radiation Oncology d Biology d Physics
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Volume 69, Number 3, Supplement, 2007
coverage. Daily On-Board Imaging (OBI) for target localization facilitates reductions in margins. In this study, we qualitatively compared 2D orthogonal kV vs. 3D cone beam CT (CBCT) OBI techniques and their abilities to assess the degrees of interand intra-fractional variation in patients undergoing SBRT. Materials/Methods: 32 patients with 40 lesions received 123 fractions of SBRT. Customized alpha cradles were used for immobilization, and all patients had CT-based simulation. Patients with lung, liver, or adrenal masses underwent 4D CTs to evaluate respiratory effects on tumor motion. Based on tumor- and patient-specific factors, either gated or free breathing techniques were used. Patients were initially aligned with lasers to external marks drawn on skin and cradles. Then, 2D orthogonal images were taken and aligned to the planning DRR using bony landmarks. The treatment table was shifted based on 2D matching, and changes to the isocenter in the anterior-posterior (AP), cranial-caudal (CC), and medial-lateral (ML) planes were recorded. Pre-treatment CBCT images were acquired and matched to the planning CT based on soft tissue anatomy, clips, fiducial markers, and bone. Additional changes in isocenter position due to CBCT were recorded. Finally, post-treatment 2D kV or 3D CBCT images were taken and compared to pre-CBCT images to reflect any intra-fractional changes. Absolute averages, standard deviations, and root mean squares (RMS) were calculated and displayed. Results: Isocenter shifts recorded after 2D, pre-treatment CBCT, and post-treatment OBI are shown below. After initial set up to external marks with laser guidance, 2D kV images revealed set up deviations of 0.60 cm (RMS). CBCT detected additional isocenter shifts of 0.39 cm (RMS). Post-treatment OBI demonstrated intra-fractional variations of 0.14 cm (RMS). The individual shifts seen within the standard 3 orthogonal planes (AP, CC, ML) showed no obvious directional error bias. With regard to site-specific shifts, the deviations for liver lesions appeared to exceed those for lung and spine masses. Conclusions: For patients undergoing SBRT, CBCT allows further refinement of treatment set up and target localization beyond that provided by 2D bony registration. These advances in target tracking/immobilization during treatment allow for improved confidence in the accuracy and precision of treatment delivery in SBRT. Supported in part by Varian Medical Systems. Author Disclosure: D.S. Yoo, None; Z. Wang, None; J. Nelson, None; J. Kirkpatrick, None; S. Yoo, None; J. Wu, None; J. Meyer, None; N. Larrier, None; L. Marks, None; F. Yin, None.
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Are Pre and Post Imaging Sufficient to Assess Intrafraction Prostate Motion? 1
C. Noel , M. Roy1, P. J. Parikh1, P. Kupelian2, A. Mahadevan3, G. Weinstein4, C. Enke5, N. Flores6, D. Beyer6, L. Levine7 1 Washington University School of Medicine, St. Louis, MO, 2M.D. Anderson Cancer Center, Orlando, FL, 3Cleveland Clinic Foundation, Cleveland, OH, 4Sharp Memorial Hospital, San Diego, CA, 5Nebraska Medical Center, Omaha, NE, 6Arizona Oncology Services, Scottsdale, AZ, 7Calypso Medical Technologies, Seattle, WA
Purpose/Objective(s): Many publications have used pre and post imaging (x-ray localization of fiducials, cone-beam CT, ultrasound) to assess intrafraction prostate motion. The aim of this study is to determine if this method is a sufficient assessment of movement of the prostate during radiation delivery. Materials/Methods: The CalypsoÒ 4D Localization System was used to continuously track the prostate isocenter (at a rate of 10 Hz) of 35 patients over 1157 total fractions, representing 195 hours of tracking information. Pre and post static imaging was simulated by sampling the beginning and end of each tracking session data set and generating a linear model trajectory between the two points. This linear trajectory was used to predict whether the prostate exceeded radial margins of 3, 5, 7 and 10 mm for more than 30 seconds. This prediction was then compared with the data as measured by the Calypso System. The ability for the pre and post imaging technique to correctly identify if the tracked prostate isocenter deviated from the specified margins was assessed by calculating the sensitivity and specificity for each individual patient, as well as for the total number of fractions. Results: The sensitivity of pre and post imaging in determining motion greater than 3, 5, 7, or 10 mm for all fractions was 53%, 49%, 39% and 56%, respectively. The sensitivity was low, even for relatively large margins (7, 10 mm) and showed a considerably random distribution. The specificity of the pre and post imaging method in determining motion greater than 3, 5, 7, or 10 mm was 98%, 99%, 100% and 100%. There was large patient variability in the sensitivity, ranging from 12% to 100% in the 3 mm margin (Figure 1). Qualitatively, the poor sensitivity was secondary to the unpredictability of when a 30-second event occurred, and that the events often resolved by the end of the fraction. Conclusions: Pre and post imaging is not a sensitive test of intrafraction prostate motion. Because this method does not accurately reflect the intrafraction movement of the prostate throughout the duration of radiation delivery, caution should be used when relying on pre and post imaging for clinical interventions aimed at intrafraction prostate motion.
Author Disclosure: D. Thongphiew, None; Q. Wu, None; Z. Wang, None; S. Yoo, None; W.R. Lee, None; Z. Vujaskovic, None; F. Yin, None.
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Improved Target Localization With 3D Cone Beam CT On-Board Imaging in Stereotactic Body Radiation Therapy
D. S. Yoo, Z. Wang, J. Nelson, J. Kirkpatrick, S. Yoo, J. Wu, J. Meyer, N. Larrier, L. Marks, F. Yin Duke University Medical Center, Durham, NC Purpose/Objective(s): Stereotactic body radiation therapy (SBRT) delivers relatively high doses to a target, typically in a hypofractionated fashion. With large fraction sizes, ideal target margins must minimize normal tissue exposure while ensuring tumor
S21
I. J. Radiation Oncology d Biology d Physics
S22
Volume 69, Number 3, Supplement, 2007
coverage. Daily On-Board Imaging (OBI) for target localization facilitates reductions in margins. In this study, we qualitatively compared 2D orthogonal kV vs. 3D cone beam CT (CBCT) OBI techniques and their abilities to assess the degrees of interand intra-fractional variation in patients undergoing SBRT. Materials/Methods: 32 patients with 40 lesions received 123 fractions of SBRT. Customized alpha cradles were used for immobilization, and all patients had CT-based simulation. Patients with lung, liver, or adrenal masses underwent 4D CTs to evaluate respiratory effects on tumor motion. Based on tumor- and patient-specific factors, either gated or free breathing techniques were used. Patients were initially aligned with lasers to external marks drawn on skin and cradles. Then, 2D orthogonal images were taken and aligned to the planning DRR using bony landmarks. The treatment table was shifted based on 2D matching, and changes to the isocenter in the anterior-posterior (AP), cranial-caudal (CC), and medial-lateral (ML) planes were recorded. Pre-treatment CBCT images were acquired and matched to the planning CT based on soft tissue anatomy, clips, fiducial markers, and bone. Additional changes in isocenter position due to CBCT were recorded. Finally, post-treatment 2D kV or 3D CBCT images were taken and compared to pre-CBCT images to reflect any intra-fractional changes. Absolute averages, standard deviations, and root mean squares (RMS) were calculated and displayed. Results: Isocenter shifts recorded after 2D, pre-treatment CBCT, and post-treatment OBI are shown below. After initial set up to external marks with laser guidance, 2D kV images revealed set up deviations of 0.60 cm (RMS). CBCT detected additional isocenter shifts of 0.39 cm (RMS). Post-treatment OBI demonstrated intra-fractional variations of 0.14 cm (RMS). The individual shifts seen within the standard 3 orthogonal planes (AP, CC, ML) showed no obvious directional error bias. With regard to site-specific shifts, the deviations for liver lesions appeared to exceed those for lung and spine masses. Conclusions: For patients undergoing SBRT, CBCT allows further refinement of treatment set up and target localization beyond that provided by 2D bony registration. These advances in target tracking/immobilization during treatment allow for improved confidence in the accuracy and precision of treatment delivery in SBRT. Supported in part by Varian Medical Systems. Author Disclosure: D.S. Yoo, None; Z. Wang, None; J. Nelson, None; J. Kirkpatrick, None; S. Yoo, None; J. Wu, None; J. Meyer, None; N. Larrier, None; L. Marks, None; F. Yin, None.
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Are Pre and Post Imaging Sufficient to Assess Intrafraction Prostate Motion? 1
C. Noel , M. Roy1, P. J. Parikh1, P. Kupelian2, A. Mahadevan3, G. Weinstein4, C. Enke5, N. Flores6, D. Beyer6, L. Levine7 1 Washington University School of Medicine, St. Louis, MO, 2M.D. Anderson Cancer Center, Orlando, FL, 3Cleveland Clinic Foundation, Cleveland, OH, 4Sharp Memorial Hospital, San Diego, CA, 5Nebraska Medical Center, Omaha, NE, 6Arizona Oncology Services, Scottsdale, AZ, 7Calypso Medical Technologies, Seattle, WA
Purpose/Objective(s): Many publications have used pre and post imaging (x-ray localization of fiducials, cone-beam CT, ultrasound) to assess intrafraction prostate motion. The aim of this study is to determine if this method is a sufficient assessment of movement of the prostate during radiation delivery. Materials/Methods: The CalypsoÒ 4D Localization System was used to continuously track the prostate isocenter (at a rate of 10 Hz) of 35 patients over 1157 total fractions, representing 195 hours of tracking information. Pre and post static imaging was simulated by sampling the beginning and end of each tracking session data set and generating a linear model trajectory between the two points. This linear trajectory was used to predict whether the prostate exceeded radial margins of 3, 5, 7 and 10 mm for more than 30 seconds. This prediction was then compared with the data as measured by the Calypso System. The ability for the pre and post imaging technique to correctly identify if the tracked prostate isocenter deviated from the specified margins was assessed by calculating the sensitivity and specificity for each individual patient, as well as for the total number of fractions. Results: The sensitivity of pre and post imaging in determining motion greater than 3, 5, 7, or 10 mm for all fractions was 53%, 49%, 39% and 56%, respectively. The sensitivity was low, even for relatively large margins (7, 10 mm) and showed a considerably random distribution. The specificity of the pre and post imaging method in determining motion greater than 3, 5, 7, or 10 mm was 98%, 99%, 100% and 100%. There was large patient variability in the sensitivity, ranging from 12% to 100% in the 3 mm margin (Figure 1). Qualitatively, the poor sensitivity was secondary to the unpredictability of when a 30-second event occurred, and that the events often resolved by the end of the fraction. Conclusions: Pre and post imaging is not a sensitive test of intrafraction prostate motion. Because this method does not accurately reflect the intrafraction movement of the prostate throughout the duration of radiation delivery, caution should be used when relying on pre and post imaging for clinical interventions aimed at intrafraction prostate motion.