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Consideration to Treatment Planning when Beams Pass Through Hip Prosthesis
Proceedings of the 50th Annual ASTRO Meeting Conclusions: The surrounding critical structures receive relatively lesser dose with better target conformity for high energy as compared to lower energy beams. The beam energy and the number of beams do not have an appreciable impact on the dose to the target volume and critical structures due to setup error. Author Disclosure: R. Prabhakar, None; K.P. Haresh, None; G.K. Rath, None; J. Nikhil, None; P.K. Julka, None.
2919
Metal Artifact Reduction Technique for Accurate Seeds Localization using Limited EPID Projections and Deformable Registration
J. Chang1, T. Suh1, W. Jung1, H. Jang2, S. Park3 1 Dept. of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea, 2Dept. of Radiation Oncology, Kangnam St. Mary’s Hospital, The Catholic University of Korea, Seoul, Republic of Korea, 3Dept. of Radiation Oncology, Asan Medical Center, University of Ulsan, Korea, Seoul, Republic of Korea
Purpose/Objective(s): Scatter radiation can degrade the quality of a kilovoltage cone-beam CT (KV CBCT) image due to the use of a larger flat-panel detector. Especially, if KV CBCT is employed for seed localization, the effect of streak metal artifacts of the seeds can be magnified in CBCT images. In this study, we describe the preliminary application of MV cone-beam reconstruction (CBR) image from EPID projections and deformable registration for metal artifact reduction in a test phantom. Materials/Methods: To perform the CBR and deformable registration based technique, the following three steps were used. (1) Extract a seeds only image and an image of seeds with bright metal streak regions by using a user-defined threshold value in the CBR image and KV CBCT images. (2) A derived intensity based 3D ‘demon’ deformable registration algorithm was applied to both seeds images, and the use of the algorithm generated the deformation field. (3) Resample the original CT image according to the deformation field. Results: The intensities of the metal artifact region were decreased with the use of the deformation grid, as the seeds in KV CBCT images were deformed as compared to the original seeds in CBR images. Although image quality was not dramatically enhanced, the metal artifact removed volume which causes the dose calculation error was 2.795 mm3 over 61 CT slices of the test phantom. Conclusions: Preliminary results with a test phantom demonstrated a bright streak metal artifact reduction effect. We believe that if dose calculation associated with KV CBCT yields reliable results, our study could provide an efficient method for post-implant dosimetry. This research sponsored by the Mid- and Long-Term Nuclear R&D Program of the Ministry of Science and Technology (M20709005474-07B0900 and M20706000007-07M0600-00710). Author Disclosure: J. Chang, None; T. Suh, None; W. Jung, None; H. Jang, None; S. Park, None.
2920
Consideration to Treatment Planning when Beams Pass Through Hip Prosthesis
T. Furuya1, H. Saito2, K. Karasawa1 1
Juntendo University, Tokyo, Japan, 2Tokyo Metropolitan University, Tokyo, Japan
Purpose/Objective(s): Because of metallic artifacts on CT images and the limit of conversion of CT value into relative electron density (ED), the accuracy of a CT-based dose calculation on a treatment planning system for a radiotherapy patient with metal implant such as HIP prosthesis is not sufficient. For treatment planning when beams pass through HIP prosthesis, we compared dose profile calculated by RTPS with measurement. The objective of this study is to evaluate the accuracy of dose calculation in this situation, and propose better way to improve them. Materials/Methods: Most common type HIP prosthesis is Co-Cr-Mo and Ti. In our first study, we use simple phantom which consist with Cu, Al, and water equivalent phantom, because relative ED of these metal are similar to Co-Cr-Mo and Ti, respectively. For simple phantom, we adopted two dose calculation models, one is CT images with metallic artifacts, another is numerical model which represent this phantom shape and relative ED. We compared measured dose profile with calculations of RTPS in three respects, (1) inhomogeneity correction which use modified CT value - relative ED table, (2) selection dose calculate algorithm, PBC or AAA, (3) effect of metallic artifacts. We made some suggestions for improve dose calculation accuracy based on above results. We measured dose profile under HIP prosthesis to make sure these suggestions are effective for HIP prosthesis phantom. Results: Appropriate relative ED for metallic materials improve calculation dose. We selected AAA, dose calculation was within 5% for Cu and Al. For copper, dose calculation overestimated the beam attenuation by about 20%, because metallic artifacts are remarkable on CT images. Although we adopted modified CT value - relative ED table, selected AAA, and replace CT value on artifacts by water equivalent to reduce metallic artifacts, beam attenuation under Co-Cr-Mo material is overestimated about 30% in maximum for HIP prosthesis. This is due to inaccuracy to contour for HIP prosthesis on kV CT images. Conclusions: To improve dose calculation when beam pass through HIP prosthesis, (1) Modify CT value - relative ED table, (2) Select algorithm which can calculate more accurate, (3) Reduce metallic artifacts on CT images, and (4) Contouring for metallic materials, and input appropriated ED on RTPS. In these, accuracy of metallic materials contour has most influence on dose calculation result. Author Disclosure: T. Furuya, None; H. Saito, None; K. Karasawa, None.
2921
Daily Megavoltage CT Registration on Adaptive Radiotherapy with Helical Tomotherapy
A. N. Gutierrez1, P. Mavroidis2, F. Su1, D. Giantsoudi1, S. Stathakis1, G. Komisopoulos3, C. Shi1, G. Swanson1, C. Ha1, N. Papanikolaou1 1 2
Cancer Therapy & Research Center at The University of Texas Health Science Center San Antonio, San Antonio, TX, Karolinska Institutet and Stockholm University, Stockholm, Sweden, 3University Hospital of Larissa, Larissa, Greece
Purpose/Objective(s): MVCT image sets have to be acquired for reducing setup uncertainties by accounting for daily changes in the patient internal anatomy and setup position. The kVCT study used for treatment planning is compared with the MVCT images
S581
2919
Metal Artifact Reduction Technique for Accurate Seeds Localization using Limited EPID Projections and Deformable Registration
J. Chang1, T. Suh1, W. Jung1, H. Jang2, S. Park3 1 Dept. of Biomedical Engineering, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea, 2Dept. of Radiation Oncology, Kangnam St. Mary’s Hospital, The Catholic University of Korea, Seoul, Republic of Korea, 3Dept. of Radiation Oncology, Asan Medical Center, University of Ulsan, Korea, Seoul, Republic of Korea
Purpose/Objective(s): Scatter radiation can degrade the quality of a kilovoltage cone-beam CT (KV CBCT) image due to the use of a larger flat-panel detector. Especially, if KV CBCT is employed for seed localization, the effect of streak metal artifacts of the seeds can be magnified in CBCT images. In this study, we describe the preliminary application of MV cone-beam reconstruction (CBR) image from EPID projections and deformable registration for metal artifact reduction in a test phantom. Materials/Methods: To perform the CBR and deformable registration based technique, the following three steps were used. (1) Extract a seeds only image and an image of seeds with bright metal streak regions by using a user-defined threshold value in the CBR image and KV CBCT images. (2) A derived intensity based 3D ‘demon’ deformable registration algorithm was applied to both seeds images, and the use of the algorithm generated the deformation field. (3) Resample the original CT image according to the deformation field. Results: The intensities of the metal artifact region were decreased with the use of the deformation grid, as the seeds in KV CBCT images were deformed as compared to the original seeds in CBR images. Although image quality was not dramatically enhanced, the metal artifact removed volume which causes the dose calculation error was 2.795 mm3 over 61 CT slices of the test phantom. Conclusions: Preliminary results with a test phantom demonstrated a bright streak metal artifact reduction effect. We believe that if dose calculation associated with KV CBCT yields reliable results, our study could provide an efficient method for post-implant dosimetry. This research sponsored by the Mid- and Long-Term Nuclear R&D Program of the Ministry of Science and Technology (M20709005474-07B0900 and M20706000007-07M0600-00710). Author Disclosure: J. Chang, None; T. Suh, None; W. Jung, None; H. Jang, None; S. Park, None.
2920
Consideration to Treatment Planning when Beams Pass Through Hip Prosthesis
T. Furuya1, H. Saito2, K. Karasawa1 1
Juntendo University, Tokyo, Japan, 2Tokyo Metropolitan University, Tokyo, Japan
Purpose/Objective(s): Because of metallic artifacts on CT images and the limit of conversion of CT value into relative electron density (ED), the accuracy of a CT-based dose calculation on a treatment planning system for a radiotherapy patient with metal implant such as HIP prosthesis is not sufficient. For treatment planning when beams pass through HIP prosthesis, we compared dose profile calculated by RTPS with measurement. The objective of this study is to evaluate the accuracy of dose calculation in this situation, and propose better way to improve them. Materials/Methods: Most common type HIP prosthesis is Co-Cr-Mo and Ti. In our first study, we use simple phantom which consist with Cu, Al, and water equivalent phantom, because relative ED of these metal are similar to Co-Cr-Mo and Ti, respectively. For simple phantom, we adopted two dose calculation models, one is CT images with metallic artifacts, another is numerical model which represent this phantom shape and relative ED. We compared measured dose profile with calculations of RTPS in three respects, (1) inhomogeneity correction which use modified CT value - relative ED table, (2) selection dose calculate algorithm, PBC or AAA, (3) effect of metallic artifacts. We made some suggestions for improve dose calculation accuracy based on above results. We measured dose profile under HIP prosthesis to make sure these suggestions are effective for HIP prosthesis phantom. Results: Appropriate relative ED for metallic materials improve calculation dose. We selected AAA, dose calculation was within 5% for Cu and Al. For copper, dose calculation overestimated the beam attenuation by about 20%, because metallic artifacts are remarkable on CT images. Although we adopted modified CT value - relative ED table, selected AAA, and replace CT value on artifacts by water equivalent to reduce metallic artifacts, beam attenuation under Co-Cr-Mo material is overestimated about 30% in maximum for HIP prosthesis. This is due to inaccuracy to contour for HIP prosthesis on kV CT images. Conclusions: To improve dose calculation when beam pass through HIP prosthesis, (1) Modify CT value - relative ED table, (2) Select algorithm which can calculate more accurate, (3) Reduce metallic artifacts on CT images, and (4) Contouring for metallic materials, and input appropriated ED on RTPS. In these, accuracy of metallic materials contour has most influence on dose calculation result. Author Disclosure: T. Furuya, None; H. Saito, None; K. Karasawa, None.
2921
Daily Megavoltage CT Registration on Adaptive Radiotherapy with Helical Tomotherapy
A. N. Gutierrez1, P. Mavroidis2, F. Su1, D. Giantsoudi1, S. Stathakis1, G. Komisopoulos3, C. Shi1, G. Swanson1, C. Ha1, N. Papanikolaou1 1 2
Cancer Therapy & Research Center at The University of Texas Health Science Center San Antonio, San Antonio, TX, Karolinska Institutet and Stockholm University, Stockholm, Sweden, 3University Hospital of Larissa, Larissa, Greece
Purpose/Objective(s): MVCT image sets have to be acquired for reducing setup uncertainties by accounting for daily changes in the patient internal anatomy and setup position. The kVCT study used for treatment planning is compared with the MVCT images
S581