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Comparison of 1.5T vs. 3T MRI of Brain for Target Delineation in Glioblastoma Multiforme (GBM) Patients
Proceedings of the 49th Annual ASTRO Meeting
2816
S653
Can MVCT be Used for Adaptive Radiotherapy? A Feasibility Study
S. R. Thomas, H. Jaradat, D. T. Vonk, M. P. Mehta, W. A. Tome´, P. E. Galavis, D. Khuntia University of Wisconsin, Madison, WI Purpose/Objective(s): Pretreatment megavoltage (MV) CT offers verification of patient position during radiation therapy with considerably more anatomic detail than conventional port films. Often, changes in tumor characteristics can be visualized and the potential exists where one may be able to replan off of the MVCT. The purpose of this study is to determine whether critical structures, including gross tumor, can be adequately visualized on MVCT for the purpose of replanning. Materials/Methods: Six patient plans (2 prostate cancer, 2 lung cancer, and 2 head and neck cancer) were selected and structures contoured on initial kilovoltage (KV) CT were recontoured on the first MVCT taken prior to initiation of radiation therapy by physicians with expertise in these disease sites. The KV and MV regions of interest (ROI) were analyzed for percentage of ROI volume incorrectly identified by MVCT (false identification [FI]), and percentage of ROI correctly identified by MVCT (positive identification [PI]). FI was calculated by (MV ROI–KV ROI)/KV ROI and PI was calculated by (MV ROI overlapping KV ROI)/KV ROI. Results: PI and FI values are shown in Table 1 for a sample of the ROI’s. For most structures, MVCT significantly underestimated the size of region of interest. The exception are the rectum and bladder, which may have significant changes based on day to day variations. Significant discrepencies were seen in the identification of GTV’s on KVCT versus MVCT’s with PI’s of GTV’s for prostate, H&N, and lung of 64.7%, 74.0%, and 74.1%, respectively. Structures where bone is used as a landmark for contouring (femoral heads and CTV’s from head and neck cancer) showed much higher positive identification rates. Conclusions: MVCT is an excellent modality for verification of patient position. It also offers good imaging data for tumor response during therapy, but the resolution and contrast with the current system is not ideal for the purpose of replanning off of the MVCT alone. For patients in whom anatomical and tumor changes are significant, replanning with a KVCT imaging is recommended. Table 1 ROI
Avg Pos ID (%)
Avg False ID (%)
Prostate GTV Femoral Heads SV H&N GTV Parotid Cervical Cord Lung GTV Esophagus Residual Lung
64.7 87.5 41.6 74 60.5 42.8 74.1 68.4 86.9
4.1 7.8 11.6 21.5 7.6 9.8 3.9 20.3 10.1
Author Disclosure: S.R. Thomas, None; H. Jaradat, None; D.T. Vonk, None; M.P. Mehta, None; W.A. Tome´, None; P.E. Galavis, None; D. Khuntia, None.
2817
Comparison of 1.5T vs. 3T MRI of Brain for Target Delineation in Glioblastoma Multiforme (GBM) Patients
N. Al-Dhaibani, N. Pervez, T. Stanescu, G. Fallone Cross Cancer Institute, Edmonton, AB, Canada Introduction: Due to a higher signal-to-noise ratio, 3T MRI shows a higher contrast and hence is expected to have an improved image quality compared to 1.5T MRI. There is a scant literature comparing 1.5T vs. 3T MRI in clinical set-up. To our knowledge, there is no comparison of these scans has been reported in GBM patients. Purpose/Objective(s): This study aims to compare target delineation between 1.5T and 3T MRI in GBM patients. Materials/Methods: Nine patients were prospectively enrolled in a currently open GBM study at Cross Cancer Institute. Each patient had a 1.5T and 3T MRI after contrast injection. Type of images (1.5T vs. 3T) and patient identity were blinded from the Radiation Oncologist prior to the target delineation process. Image quality was assessed, and tumor and/or surgical cavity was delineated on each image by the same Radiation Oncologist. The contours drawn on both 1.5T and 3T MR images were evaluated in terms of target volumes. Results: In all nine cases, the Radiation Oncologist found that it was easier to delineate the tumor bed on the 3T images due to an increased contrast. For two patients, the target volume delineated on the 1.5T images was up to 60% larger than on the corresponding 3T images. For other two patients, the volumes delineated on the 3T data sets were about 3 times larger than the ones drawn on the 1.5T data sets. Conclusions: The target volume contours obtained from 3T images were different in size and shape compared to the ones delineated on 1.5T images. It was easier to delineate the tumor bed on the 3T images due to higer contrast. A larger study is required to assess the clinical impact of this target delineation difference. Author Disclosure: N. Al-Dhaibani, None; N. Pervez, None; T. Stanescu, None; G. Fallone, None.
2816
S653
Can MVCT be Used for Adaptive Radiotherapy? A Feasibility Study
S. R. Thomas, H. Jaradat, D. T. Vonk, M. P. Mehta, W. A. Tome´, P. E. Galavis, D. Khuntia University of Wisconsin, Madison, WI Purpose/Objective(s): Pretreatment megavoltage (MV) CT offers verification of patient position during radiation therapy with considerably more anatomic detail than conventional port films. Often, changes in tumor characteristics can be visualized and the potential exists where one may be able to replan off of the MVCT. The purpose of this study is to determine whether critical structures, including gross tumor, can be adequately visualized on MVCT for the purpose of replanning. Materials/Methods: Six patient plans (2 prostate cancer, 2 lung cancer, and 2 head and neck cancer) were selected and structures contoured on initial kilovoltage (KV) CT were recontoured on the first MVCT taken prior to initiation of radiation therapy by physicians with expertise in these disease sites. The KV and MV regions of interest (ROI) were analyzed for percentage of ROI volume incorrectly identified by MVCT (false identification [FI]), and percentage of ROI correctly identified by MVCT (positive identification [PI]). FI was calculated by (MV ROI–KV ROI)/KV ROI and PI was calculated by (MV ROI overlapping KV ROI)/KV ROI. Results: PI and FI values are shown in Table 1 for a sample of the ROI’s. For most structures, MVCT significantly underestimated the size of region of interest. The exception are the rectum and bladder, which may have significant changes based on day to day variations. Significant discrepencies were seen in the identification of GTV’s on KVCT versus MVCT’s with PI’s of GTV’s for prostate, H&N, and lung of 64.7%, 74.0%, and 74.1%, respectively. Structures where bone is used as a landmark for contouring (femoral heads and CTV’s from head and neck cancer) showed much higher positive identification rates. Conclusions: MVCT is an excellent modality for verification of patient position. It also offers good imaging data for tumor response during therapy, but the resolution and contrast with the current system is not ideal for the purpose of replanning off of the MVCT alone. For patients in whom anatomical and tumor changes are significant, replanning with a KVCT imaging is recommended. Table 1 ROI
Avg Pos ID (%)
Avg False ID (%)
Prostate GTV Femoral Heads SV H&N GTV Parotid Cervical Cord Lung GTV Esophagus Residual Lung
64.7 87.5 41.6 74 60.5 42.8 74.1 68.4 86.9
4.1 7.8 11.6 21.5 7.6 9.8 3.9 20.3 10.1
Author Disclosure: S.R. Thomas, None; H. Jaradat, None; D.T. Vonk, None; M.P. Mehta, None; W.A. Tome´, None; P.E. Galavis, None; D. Khuntia, None.
2817
Comparison of 1.5T vs. 3T MRI of Brain for Target Delineation in Glioblastoma Multiforme (GBM) Patients
N. Al-Dhaibani, N. Pervez, T. Stanescu, G. Fallone Cross Cancer Institute, Edmonton, AB, Canada Introduction: Due to a higher signal-to-noise ratio, 3T MRI shows a higher contrast and hence is expected to have an improved image quality compared to 1.5T MRI. There is a scant literature comparing 1.5T vs. 3T MRI in clinical set-up. To our knowledge, there is no comparison of these scans has been reported in GBM patients. Purpose/Objective(s): This study aims to compare target delineation between 1.5T and 3T MRI in GBM patients. Materials/Methods: Nine patients were prospectively enrolled in a currently open GBM study at Cross Cancer Institute. Each patient had a 1.5T and 3T MRI after contrast injection. Type of images (1.5T vs. 3T) and patient identity were blinded from the Radiation Oncologist prior to the target delineation process. Image quality was assessed, and tumor and/or surgical cavity was delineated on each image by the same Radiation Oncologist. The contours drawn on both 1.5T and 3T MR images were evaluated in terms of target volumes. Results: In all nine cases, the Radiation Oncologist found that it was easier to delineate the tumor bed on the 3T images due to an increased contrast. For two patients, the target volume delineated on the 1.5T images was up to 60% larger than on the corresponding 3T images. For other two patients, the volumes delineated on the 3T data sets were about 3 times larger than the ones drawn on the 1.5T data sets. Conclusions: The target volume contours obtained from 3T images were different in size and shape compared to the ones delineated on 1.5T images. It was easier to delineate the tumor bed on the 3T images due to higer contrast. A larger study is required to assess the clinical impact of this target delineation difference. Author Disclosure: N. Al-Dhaibani, None; N. Pervez, None; T. Stanescu, None; G. Fallone, None.