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Interior Landmarks Improve Deformable Image Registration Spatial Accuracy in the Lung
I. J. Radiation Oncology d Biology d Physics
S452
2632
Volume 72, Number 1, Supplement, 2008
Early and Late Lung Injury Following Stereotactic Radiation Therapy
1
M. Trovo , A. Linda2, I. El Naqa3, J. D. Bradley3 1
University of Milan, Milan, Italy, 2Department of Radiology, University of Udine, Udine, Italy, 3Washington University in St. Louis, St. Louis, MO Purpose/Objective(s): To describe the early and late radiographic pattern of lung injury after hypofractionated stereotactic body radiation therapy (SBRT) for primary and metastatic lung cancer, and to correlate the radiological findings to patient and treatment characteristics. Materials/Methods: The follow-up CT scans of 68 patients with 70 lung tumors were reviewed. All patients were enrolled with an IRB-approved consent form. The typical fractionation was 54 Gy in 3 fractions using 9-12 beams. The follow-up was divided into 4 study periods: (1) 6 weeks; (2) 2-6 months; (3) 7-12 months and (4) 13-18 months after the completion of SBRT. Early (within 6 months) and late radiological injuries were evaluated according to Ikezoe and Koening, respectively. Baseline images were used for comparison and for pulmonary emphysema assessment according to Satoh grades: grade 0, no low-attenuation areas (LLAs); Grade 1, sparse, scattered small LLAs up to 5 mm in diameter; Grade 2, adjacent LLAs up to 10 mm in diameter; Grade 3, LLAs .10 mm that were adjacent to or indistinguishable from each other; and Grade 4, absence of normal lung parenchyma. Results: In the first 6 weeks the radiological findings were: (1) Linear consolidation 1.5%, (2) Diffuse consolidation 1.5%, (3) Patchy consolidation and ground-glass opacity (GGO) 13.2%, (4) Diffuse GGO 13.2%, (5) Patchy GGO 16.2%, and (6) no findings 54.4%. From 2-6 months the findings were: (1) Diffuse consolidation 27%, (2) Patchy consolidation and GGO 33%, (3) Diffuse GGO 21%, (4) Patchy GGO 6%, and (5) no findings 21%. The late injuries between 7-12 months were: (1) Modified conventional pattern (consolidation, volume loss, bronchiectasis) 54%, (2) Mass-like 20%, (3) Scar-like 14% and (4) no findings 20%. In the fourth period (13-18 months): (1) Modified conventional pattern 44%, (2) Mass-like 28%, (3) Scar-like 16% and (4) no findings 12%. The proportion of emphysema grade 2-4 was significantly higher in patients who had no radiological findings 6 weeks after treatment (p = 0.021). On the contrary, patchy GGO was more frequent in patients with grade 0-1 emphysema (p = 0.058). Patchy consolidation and GGO pattern resulted to be significantly more frequent in patients who were not administered steroids (p = 0.0351). No relationship was found with the smoking habits, PTV dimension and radiation dose. Conclusions: The majority of patients (54.4%) didn’t have any evidence of radiation injury 6 weeks after SBRT. Diffuse or patchy GGO were the most frequent patterns of radiation pneumonitis early after radiation (29.4%), while diffuse or patchy consolidation patterns tended to develop 2-6 months after SBRT (60%). Modified conventional pattern was the most represented in the late periods (4454%). Baseline emphysema grade 2 or higher is significantly associated with the absence of radiological findings 6 weeks after SBRT. Author Disclosure: M. Trovo, None; A. Linda, None; I. El Naqa, None; J.D. Bradley, None.
2633
Interior Landmarks Improve Deformable Image Registration Spatial Accuracy in the Lung 1
R. Castillo , T. McPhail2, R. Guerra2, J. Warren2, A. Garg1, T. Guerrero1 1
UT MD Anderson Cancer Center, Houston, TX, 2Rice University, Houston, TX
Purpose/Objective(s): To compare the spatial accuracy and work flow limitations of surface- versus volume-landmark based deformable image registration (DIR) algorithms applied to lung CT data. Materials/Methods: A tool for computer-assisted manual registration of naturally occurring landmark points was developed. Landmark point pairs were selected from the extreme inhale and exhale phases of five 4D CT images. The points were characterized by a thoracic CT image expert reader with a subset repeated for intra-observer variance estimation. Two additional readers also repeated the subset for inter-observer variance estimation. The number of point correspondences per case varied from 1,166 to 1,561. Surface-based deformations were performed in Pinnacle 8.1u using the EBS Gauss basis function. Left and right lung, heart, and spinal cord contours were generated from provided organ models in order to deform the inhale and exhale volumes. Volumebased deformations were performed using in-house software. The number of lung surface or volume points was chosen to be consistent between the two algorithms for each case (range: 256-368). Point correspondences within the lung volume were generated automatically based on local correlation of edge-enhanced image features. A moving least squares algorithm was then employed to generate a global deformation field. Using the expert determined displacement field as the standard, we compared the spatial accuracy of surface-based landmark DIR (sDIR) with volume-based landmark DIR (vDIR) within the lungs. Results: Average displacement (SD) of landmark points ranged from 4.01 (2.91)-9.42 (4.81) mm and showed marked regional heterogeneity in each case. Average magnitude error (SD) ranged from 2.29 (1.27)-6.71 (2.92) mm for sDIR and 0.94 (1.16)2.55 (1.92) mm for vDIR. Over the set of 6762 landmark pairs, the average magnitude errors (SE) for sDIR and vDIR were 4.35 (0.03) mm and 1.93 (0.02) mm, respectively. For each of the five cases, average vDIR error was lower (p \ 0.0005) than that of sDIR, both in three-dimensional magnitude, as well as in individual RL, AP, and SI directions. Conclusions: The volume-landmark DIR algorithms performed with significantly greater spatial accuracy than the surface-landmark DIR for registration of lung CT image volumes. The heterogeneous distribution of motion within the lung is more accurately captured using interior control points to correctly drive the global deformation, as evidenced by visual inspection of the resulting deformation fields and the smaller errors. Author Disclosure: R. Castillo, None; T. McPhail, None; R. Guerra, None; J. Warren, None; A. Garg, None; T. Guerrero, None.
2634
High-dose Bronchial Irradiation is a Statistically Significant Risk Factor for Radiation Pneumonitis within Logistic-multivariate Modeling
E. X. Huang1, J. D. Bradley1, M. Trovo2, Y. Mu1, I. El Naqa1, A. Apte1, D. Khullar1, J. O. Deasy1 1
Washington University School of Medicine, St. Louis, MO, 2University of Milan, Milan, Italy
Purpose/Objective(s): We hypothesize that there may be a differential effect on the risk of radiation pneumonitis (RP) from irradiating bronchial vs. non-bronchial regions within normal lung. We studied this potential effect within a multivariate framework, for patients treated with radiation therapy for lung cancer.
S452
2632
Volume 72, Number 1, Supplement, 2008
Early and Late Lung Injury Following Stereotactic Radiation Therapy
1
M. Trovo , A. Linda2, I. El Naqa3, J. D. Bradley3 1
University of Milan, Milan, Italy, 2Department of Radiology, University of Udine, Udine, Italy, 3Washington University in St. Louis, St. Louis, MO Purpose/Objective(s): To describe the early and late radiographic pattern of lung injury after hypofractionated stereotactic body radiation therapy (SBRT) for primary and metastatic lung cancer, and to correlate the radiological findings to patient and treatment characteristics. Materials/Methods: The follow-up CT scans of 68 patients with 70 lung tumors were reviewed. All patients were enrolled with an IRB-approved consent form. The typical fractionation was 54 Gy in 3 fractions using 9-12 beams. The follow-up was divided into 4 study periods: (1) 6 weeks; (2) 2-6 months; (3) 7-12 months and (4) 13-18 months after the completion of SBRT. Early (within 6 months) and late radiological injuries were evaluated according to Ikezoe and Koening, respectively. Baseline images were used for comparison and for pulmonary emphysema assessment according to Satoh grades: grade 0, no low-attenuation areas (LLAs); Grade 1, sparse, scattered small LLAs up to 5 mm in diameter; Grade 2, adjacent LLAs up to 10 mm in diameter; Grade 3, LLAs .10 mm that were adjacent to or indistinguishable from each other; and Grade 4, absence of normal lung parenchyma. Results: In the first 6 weeks the radiological findings were: (1) Linear consolidation 1.5%, (2) Diffuse consolidation 1.5%, (3) Patchy consolidation and ground-glass opacity (GGO) 13.2%, (4) Diffuse GGO 13.2%, (5) Patchy GGO 16.2%, and (6) no findings 54.4%. From 2-6 months the findings were: (1) Diffuse consolidation 27%, (2) Patchy consolidation and GGO 33%, (3) Diffuse GGO 21%, (4) Patchy GGO 6%, and (5) no findings 21%. The late injuries between 7-12 months were: (1) Modified conventional pattern (consolidation, volume loss, bronchiectasis) 54%, (2) Mass-like 20%, (3) Scar-like 14% and (4) no findings 20%. In the fourth period (13-18 months): (1) Modified conventional pattern 44%, (2) Mass-like 28%, (3) Scar-like 16% and (4) no findings 12%. The proportion of emphysema grade 2-4 was significantly higher in patients who had no radiological findings 6 weeks after treatment (p = 0.021). On the contrary, patchy GGO was more frequent in patients with grade 0-1 emphysema (p = 0.058). Patchy consolidation and GGO pattern resulted to be significantly more frequent in patients who were not administered steroids (p = 0.0351). No relationship was found with the smoking habits, PTV dimension and radiation dose. Conclusions: The majority of patients (54.4%) didn’t have any evidence of radiation injury 6 weeks after SBRT. Diffuse or patchy GGO were the most frequent patterns of radiation pneumonitis early after radiation (29.4%), while diffuse or patchy consolidation patterns tended to develop 2-6 months after SBRT (60%). Modified conventional pattern was the most represented in the late periods (4454%). Baseline emphysema grade 2 or higher is significantly associated with the absence of radiological findings 6 weeks after SBRT. Author Disclosure: M. Trovo, None; A. Linda, None; I. El Naqa, None; J.D. Bradley, None.
2633
Interior Landmarks Improve Deformable Image Registration Spatial Accuracy in the Lung 1
R. Castillo , T. McPhail2, R. Guerra2, J. Warren2, A. Garg1, T. Guerrero1 1
UT MD Anderson Cancer Center, Houston, TX, 2Rice University, Houston, TX
Purpose/Objective(s): To compare the spatial accuracy and work flow limitations of surface- versus volume-landmark based deformable image registration (DIR) algorithms applied to lung CT data. Materials/Methods: A tool for computer-assisted manual registration of naturally occurring landmark points was developed. Landmark point pairs were selected from the extreme inhale and exhale phases of five 4D CT images. The points were characterized by a thoracic CT image expert reader with a subset repeated for intra-observer variance estimation. Two additional readers also repeated the subset for inter-observer variance estimation. The number of point correspondences per case varied from 1,166 to 1,561. Surface-based deformations were performed in Pinnacle 8.1u using the EBS Gauss basis function. Left and right lung, heart, and spinal cord contours were generated from provided organ models in order to deform the inhale and exhale volumes. Volumebased deformations were performed using in-house software. The number of lung surface or volume points was chosen to be consistent between the two algorithms for each case (range: 256-368). Point correspondences within the lung volume were generated automatically based on local correlation of edge-enhanced image features. A moving least squares algorithm was then employed to generate a global deformation field. Using the expert determined displacement field as the standard, we compared the spatial accuracy of surface-based landmark DIR (sDIR) with volume-based landmark DIR (vDIR) within the lungs. Results: Average displacement (SD) of landmark points ranged from 4.01 (2.91)-9.42 (4.81) mm and showed marked regional heterogeneity in each case. Average magnitude error (SD) ranged from 2.29 (1.27)-6.71 (2.92) mm for sDIR and 0.94 (1.16)2.55 (1.92) mm for vDIR. Over the set of 6762 landmark pairs, the average magnitude errors (SE) for sDIR and vDIR were 4.35 (0.03) mm and 1.93 (0.02) mm, respectively. For each of the five cases, average vDIR error was lower (p \ 0.0005) than that of sDIR, both in three-dimensional magnitude, as well as in individual RL, AP, and SI directions. Conclusions: The volume-landmark DIR algorithms performed with significantly greater spatial accuracy than the surface-landmark DIR for registration of lung CT image volumes. The heterogeneous distribution of motion within the lung is more accurately captured using interior control points to correctly drive the global deformation, as evidenced by visual inspection of the resulting deformation fields and the smaller errors. Author Disclosure: R. Castillo, None; T. McPhail, None; R. Guerra, None; J. Warren, None; A. Garg, None; T. Guerrero, None.
2634
High-dose Bronchial Irradiation is a Statistically Significant Risk Factor for Radiation Pneumonitis within Logistic-multivariate Modeling
E. X. Huang1, J. D. Bradley1, M. Trovo2, Y. Mu1, I. El Naqa1, A. Apte1, D. Khullar1, J. O. Deasy1 1
Washington University School of Medicine, St. Louis, MO, 2University of Milan, Milan, Italy
Purpose/Objective(s): We hypothesize that there may be a differential effect on the risk of radiation pneumonitis (RP) from irradiating bronchial vs. non-bronchial regions within normal lung. We studied this potential effect within a multivariate framework, for patients treated with radiation therapy for lung cancer.