- Email: [email protected]
CT in PBS Proton Therapy
E304
International Journal of Radiation Oncology Biology Physics
Results: High soft tissue contrast with MRI reduces GTV delineation uncertainty as compared to CT and PET for cervical cancer. However, the GTVs defined by different imaging modalities are different. The average GTV volumes for T1, T2, ADC, and T1F+ were (in cm3) 62.8 62.1, 58.4 61.2, 50.9 59.8, 66.4 64.9, respectively. The differences between T2 and other MRI sequences are significant (P<0.05). The average ORs for GTVT1, GTVT1F+, and GTVADC related to GTVT2 were 86.3%, 81.6% and 61.6% while the corresponding average RVRs were 113.8%, 112.3% and 77.2%, respectively. There is no significant difference between GTVT1 and GTVT1F+ and these two are considered equivalent. GTVT1 is generally larger than GTVT2, which is mainly due to the lower soft tissue contrast at the tumor boundary in T1 compared to T2. In contrast, GTVADC is generally smaller than GTVT2 and encompasses suspicious regions that are sometimes not revealed by T2 because of different imaging mechanisms. The uncovered volume accounts for up to 16% of the GTVT2. In this sense, the MRI-based GTV (GTVMRI, generated from the union of the GTVT2 and GTVADC) may be more appropriate than individual GTVT2 and GTVADC. There was a significant difference between GTVMRI, GTV2.5, GTV40%, and GTVCT in volumes. On average, GTVMRI is 18.4% smaller than GTVCT for the cases studied. Conclusion: MRI provides improved visualization of disease than CT or PET for cervical cancer. Among the image modalities studied, the combination of T2 and ADC provided a reasonable GTV definition without including excessive surrounding normal tissues. The GTVMRI generated based on the union of T2 and ADC is substantially smaller than conventional CT defined GTVCT. Further studies are required to confirm that the use of GTVMRI for EBRT of cervical cancer is appropriate. Author Disclosure: Y. Song: None. X. Chen: None. B.A. Erickson: None. A. Li: None.
IMPT plans gave lowest dose to ABM, however, IMPT plans produced clinically-unacceptable hot spots when evaluated on verification scans. All SFUD proton plans were robust when evaluated on verification scans. Conclusion: Using [18F]FLT-PET/CT scans to identify ABM in patients prior to undergoing radiation therapy can provide significant dosimetric advantage for sparing ABM versus current methods of optimizing on PB. This strategy used in conjunction with an AO+PA SFUD beam arrangement can provide a robust plan that spares ABM. The feasibility of using IMPT could improve by incorporating robust optimization into planning. Further clinical studies are needed to determine if ABM-sparing proton radiation therapy results in improved hematologic toxicity with concurrent chemotherapy.
2744 Sparing Active Bone Marrow for Gynecologic Cancer Patients Using FLT-PET/CT in PBS Proton Therapy J. Scholey,1 M.L. Kirk,2 S.M. McGuire,3 B.K. Teo,2 and L.L. Lin4; 1The University of Pennsylvania, Philadelphia, PA, 2Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 3University of Iowa, Iowa City, IA, 4University of Pennsylvania, Department of Radiation Oncology, Philadelphia, PA Purpose/Objective(s): The objective of this study is to evaluate methods to reduce active bone marrow (ABM) dose for patients receiving pelvic radiation therapy using [18F]FLT-PET/CT imaging to identify ABM regions used for planning in pencil beam scanning (PBS) proton therapy. Materials/Methods: Seven patients with gynecologic cancer were enrolled in an IRB-approved prospective study and underwent [18F]FLT-PET/CT scans in their treatment position prior to undergoing radiation therapy. ABM regions (defined as bone marrow with standard-uptake value>3) were identified on the [18F]FLT-PET/CT scan and contoured on the registered planning CT scan. Single field uniform dose (SFUD) and intensity modulated (IMPT) proton PBS plans were generated using a beam arrangement of two anterior-oblique beams plus a posterior beam (AO+PA) using objectives chosen to minimize low dose to ABM. To assess the impact of using [18F] FLT-PET/CT, plans were generated using objectives on pelvic bone (PB) instead of ABM. Dosimetric parameters were compared to our institution’s clinically acceptable posterior-oblique (PO) SFUD proton and volumetric arc therapy photon plans using the Wilcoxon signed rank test. P values<0.05 were considered statistically significant. To evaluate interfraction plan robustness, patients received weekly verification CT scans to assess the impacts of anatomical changes such as bladder filling and bowel gas. Robustness with respect to isocenter shifts and error in conversion from Hounsfield Unit to relative proton stopping power was evaluated on verification scans using 3% range uncertainty and 2mm setup error. Results: PTV coverage amongst all plans was similar (P>0.05). AO+PA SFUD plans had a significant reduction in volume of ABM receiving 10Gy and 20Gy versus photon plans and PO proton plans. AO+PA SFUD plans optimized on ABM showed a significant reduction in ABM V10Gy of 2.9% (1.35.1) and V20Gy of 7.1% (1.6-11.4) versus plans optimized on PB. AO+PA
Abstract 2744; Table 1. AO+PA IMPT AO+PA SFUD ABM V10Gy (%) ABM V20Gy (%) Small bowel V15Gy (cc) PTV V95% (%)
PO SFUD
Photon
41.7 14.3 65.8 12.7 73.4 12.6 86.7 7.6 29.7 10.7 45.2 17.4 60.9 13.9 73.8 8.8 336.2 140.7 287.5 114.4 202.8 92.9 426.1 168.0 98.6 0.5
98.6 0.7
98.9 0.7
98.6 0.6
Author Disclosure: J. Scholey: None. M.L. Kirk: None. S.M. McGuire: None. B.K. Teo: None. L.L. Lin: None.
2745 Multi-Institutional Comparative Study of MRI Technique in Cervical Cancer Image-Based Brachytherapy (IGBT): 3D MRI With High Sampling Efficiency Versus Conventional 2D Multiplanar MRI M. Watanabe Nemoto,1 Y. Ikeda,2 N. Ii,3 T. Toita,4 G. Togasaki,2 A. Kanazawa,2 M. Kurokawa,2 R. Harada,2 H. Kobayashi,2 K. Matsumoto,2 Y. Masuda,2 and T. Uno1; 1Diagnostic Radiology and Radiation Oncology, Graduate School of Medicine, Chiba University, Chiba, Japan, 2Chiba University Hospital, Chiba, Japan, 3Mie University Hospital, Mie, Japan, 4Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, Okinawa, Japan Purpose/Objective(s): In order to elucidate the role of 3D MRI in image guided brachytherapy (IGBT) for cervical cancer, a multicenter study to compare the contrast ratio (CR) and contrast-to-noise ratio (CNR) against the gold-standard 2D approach was conducted. In addition, delineation variability assessment to clarify how different sequences affect the contouring was also performed. Materials/Methods: A composite phantom consisting of six syringes filled with different T2/T1 relaxation, which comprise the range of relaxation values for representative uterus normal tissues (cervix, myometrium and endometrium) and tumor of three different types of relaxation at 1.5 Tesla, was developed. MRI was performed on a Signa 1.5 T system (General Electric Medical Systems, Milwaukee, WI), an Ingenia 1.5 T system (Pinnacle-Treatment planning system, Best, The Netherlands) and a magnetic resonance diagnostic device 1.5 T system. The imaging protocol consisted of two sequences; a 2D T2 weighted FSE sequence (slice thickness 3 mm) in the axial plane, and an isotropic 3D T2 volumetric sequence (isotropic voxel size of 1.4 mm, acquisition time <6 minutes) acquired in the sagittal plane, which were recommended by manufacturers and considered to be widely available in current clinical practice. From the 3D data-set, axial images were resampled with 1.4 mm slice thickness. The signal intensity in order to calculate the CR and CNR referenced to the cervix syringe was measured. Four radiation oncologists contoured high risk CTV (HR CTV) and GTV of the FIGO IIB case on the post-insertion MR images. MR images included two sets; (A) 3 mm slice thickness 2D T2w axial images, (B) 1.4 mm slice thickness axial images resampled from isotropic 3D T2 volumetric sequence. The values compared between 2D and 3D included volume, DICE coefficient, D90 and V100 to HR CTV. Results: The median CR of 3D and 2D sequence was 0.20 (range, 0.058 0.36) and 0.20 (range, 0.062 - 0.35), respectively. CR of 3D sequence was not inferior to that of 2D sequence. The median CNR of 3D and 2D sequence was 51.6 (range, 11.5 - 126.3) and 26.4 (range, 8.3 - 52.7),
International Journal of Radiation Oncology Biology Physics
Results: High soft tissue contrast with MRI reduces GTV delineation uncertainty as compared to CT and PET for cervical cancer. However, the GTVs defined by different imaging modalities are different. The average GTV volumes for T1, T2, ADC, and T1F+ were (in cm3) 62.8 62.1, 58.4 61.2, 50.9 59.8, 66.4 64.9, respectively. The differences between T2 and other MRI sequences are significant (P<0.05). The average ORs for GTVT1, GTVT1F+, and GTVADC related to GTVT2 were 86.3%, 81.6% and 61.6% while the corresponding average RVRs were 113.8%, 112.3% and 77.2%, respectively. There is no significant difference between GTVT1 and GTVT1F+ and these two are considered equivalent. GTVT1 is generally larger than GTVT2, which is mainly due to the lower soft tissue contrast at the tumor boundary in T1 compared to T2. In contrast, GTVADC is generally smaller than GTVT2 and encompasses suspicious regions that are sometimes not revealed by T2 because of different imaging mechanisms. The uncovered volume accounts for up to 16% of the GTVT2. In this sense, the MRI-based GTV (GTVMRI, generated from the union of the GTVT2 and GTVADC) may be more appropriate than individual GTVT2 and GTVADC. There was a significant difference between GTVMRI, GTV2.5, GTV40%, and GTVCT in volumes. On average, GTVMRI is 18.4% smaller than GTVCT for the cases studied. Conclusion: MRI provides improved visualization of disease than CT or PET for cervical cancer. Among the image modalities studied, the combination of T2 and ADC provided a reasonable GTV definition without including excessive surrounding normal tissues. The GTVMRI generated based on the union of T2 and ADC is substantially smaller than conventional CT defined GTVCT. Further studies are required to confirm that the use of GTVMRI for EBRT of cervical cancer is appropriate. Author Disclosure: Y. Song: None. X. Chen: None. B.A. Erickson: None. A. Li: None.
IMPT plans gave lowest dose to ABM, however, IMPT plans produced clinically-unacceptable hot spots when evaluated on verification scans. All SFUD proton plans were robust when evaluated on verification scans. Conclusion: Using [18F]FLT-PET/CT scans to identify ABM in patients prior to undergoing radiation therapy can provide significant dosimetric advantage for sparing ABM versus current methods of optimizing on PB. This strategy used in conjunction with an AO+PA SFUD beam arrangement can provide a robust plan that spares ABM. The feasibility of using IMPT could improve by incorporating robust optimization into planning. Further clinical studies are needed to determine if ABM-sparing proton radiation therapy results in improved hematologic toxicity with concurrent chemotherapy.
2744 Sparing Active Bone Marrow for Gynecologic Cancer Patients Using FLT-PET/CT in PBS Proton Therapy J. Scholey,1 M.L. Kirk,2 S.M. McGuire,3 B.K. Teo,2 and L.L. Lin4; 1The University of Pennsylvania, Philadelphia, PA, 2Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, 3University of Iowa, Iowa City, IA, 4University of Pennsylvania, Department of Radiation Oncology, Philadelphia, PA Purpose/Objective(s): The objective of this study is to evaluate methods to reduce active bone marrow (ABM) dose for patients receiving pelvic radiation therapy using [18F]FLT-PET/CT imaging to identify ABM regions used for planning in pencil beam scanning (PBS) proton therapy. Materials/Methods: Seven patients with gynecologic cancer were enrolled in an IRB-approved prospective study and underwent [18F]FLT-PET/CT scans in their treatment position prior to undergoing radiation therapy. ABM regions (defined as bone marrow with standard-uptake value>3) were identified on the [18F]FLT-PET/CT scan and contoured on the registered planning CT scan. Single field uniform dose (SFUD) and intensity modulated (IMPT) proton PBS plans were generated using a beam arrangement of two anterior-oblique beams plus a posterior beam (AO+PA) using objectives chosen to minimize low dose to ABM. To assess the impact of using [18F] FLT-PET/CT, plans were generated using objectives on pelvic bone (PB) instead of ABM. Dosimetric parameters were compared to our institution’s clinically acceptable posterior-oblique (PO) SFUD proton and volumetric arc therapy photon plans using the Wilcoxon signed rank test. P values<0.05 were considered statistically significant. To evaluate interfraction plan robustness, patients received weekly verification CT scans to assess the impacts of anatomical changes such as bladder filling and bowel gas. Robustness with respect to isocenter shifts and error in conversion from Hounsfield Unit to relative proton stopping power was evaluated on verification scans using 3% range uncertainty and 2mm setup error. Results: PTV coverage amongst all plans was similar (P>0.05). AO+PA SFUD plans had a significant reduction in volume of ABM receiving 10Gy and 20Gy versus photon plans and PO proton plans. AO+PA SFUD plans optimized on ABM showed a significant reduction in ABM V10Gy of 2.9% (1.35.1) and V20Gy of 7.1% (1.6-11.4) versus plans optimized on PB. AO+PA
Abstract 2744; Table 1. AO+PA IMPT AO+PA SFUD ABM V10Gy (%) ABM V20Gy (%) Small bowel V15Gy (cc) PTV V95% (%)
PO SFUD
Photon
41.7 14.3 65.8 12.7 73.4 12.6 86.7 7.6 29.7 10.7 45.2 17.4 60.9 13.9 73.8 8.8 336.2 140.7 287.5 114.4 202.8 92.9 426.1 168.0 98.6 0.5
98.6 0.7
98.9 0.7
98.6 0.6
Author Disclosure: J. Scholey: None. M.L. Kirk: None. S.M. McGuire: None. B.K. Teo: None. L.L. Lin: None.
2745 Multi-Institutional Comparative Study of MRI Technique in Cervical Cancer Image-Based Brachytherapy (IGBT): 3D MRI With High Sampling Efficiency Versus Conventional 2D Multiplanar MRI M. Watanabe Nemoto,1 Y. Ikeda,2 N. Ii,3 T. Toita,4 G. Togasaki,2 A. Kanazawa,2 M. Kurokawa,2 R. Harada,2 H. Kobayashi,2 K. Matsumoto,2 Y. Masuda,2 and T. Uno1; 1Diagnostic Radiology and Radiation Oncology, Graduate School of Medicine, Chiba University, Chiba, Japan, 2Chiba University Hospital, Chiba, Japan, 3Mie University Hospital, Mie, Japan, 4Department of Radiology, Graduate School of Medical Science, University of the Ryukyus, Okinawa, Japan Purpose/Objective(s): In order to elucidate the role of 3D MRI in image guided brachytherapy (IGBT) for cervical cancer, a multicenter study to compare the contrast ratio (CR) and contrast-to-noise ratio (CNR) against the gold-standard 2D approach was conducted. In addition, delineation variability assessment to clarify how different sequences affect the contouring was also performed. Materials/Methods: A composite phantom consisting of six syringes filled with different T2/T1 relaxation, which comprise the range of relaxation values for representative uterus normal tissues (cervix, myometrium and endometrium) and tumor of three different types of relaxation at 1.5 Tesla, was developed. MRI was performed on a Signa 1.5 T system (General Electric Medical Systems, Milwaukee, WI), an Ingenia 1.5 T system (Pinnacle-Treatment planning system, Best, The Netherlands) and a magnetic resonance diagnostic device 1.5 T system. The imaging protocol consisted of two sequences; a 2D T2 weighted FSE sequence (slice thickness 3 mm) in the axial plane, and an isotropic 3D T2 volumetric sequence (isotropic voxel size of 1.4 mm, acquisition time <6 minutes) acquired in the sagittal plane, which were recommended by manufacturers and considered to be widely available in current clinical practice. From the 3D data-set, axial images were resampled with 1.4 mm slice thickness. The signal intensity in order to calculate the CR and CNR referenced to the cervix syringe was measured. Four radiation oncologists contoured high risk CTV (HR CTV) and GTV of the FIGO IIB case on the post-insertion MR images. MR images included two sets; (A) 3 mm slice thickness 2D T2w axial images, (B) 1.4 mm slice thickness axial images resampled from isotropic 3D T2 volumetric sequence. The values compared between 2D and 3D included volume, DICE coefficient, D90 and V100 to HR CTV. Results: The median CR of 3D and 2D sequence was 0.20 (range, 0.058 0.36) and 0.20 (range, 0.062 - 0.35), respectively. CR of 3D sequence was not inferior to that of 2D sequence. The median CNR of 3D and 2D sequence was 51.6 (range, 11.5 - 126.3) and 26.4 (range, 8.3 - 52.7),