- Email: [email protected]
Imaging Dose on a Dual On-board kV X-ray Imaging System in MHI-TM2000
Proceedings of the 50th Annual ASTRO Meeting
3079
Development of a Three Dimensional Anatomical Library
C. Abraham1, D. Low1, L. Liu2, T. Ju2, J. O. Deasy1 1
Department of Radiation Oncology, Washington University, St. Louis, MO, 2Department of Computer Science & Engineering, Washington University, St. Louis, MO Purpose/Objective(s): The early development of 3D conformal therapy parallels the history of computed tomography (CT), the main 3D imaging modality used for treatment planning. As such, segmentation was conducted on transverse planes by manually, semi-automatically, or automatically delineating structures. In spite of the rapid and extensive expansion of imaging technology, specifically with respect to CT, the segmentation process in radiation therapy has failed to evolve. The purpose of this work is to develop a protocol for segmentation on anatomically-defined oblique planes as well as analyze alternative segmentation techniques. Materials/Methods: Clinical treatment contours were retrospectively collected from prostate, lung, and head-and-neck cancer patients. The clinical contours were delineated on CT scans reconstructed at 3mm resolution. For each anatomic site, the clinical cases were chosen at random such that the planner was unaware which studies would be included within the model. After the transverse contours were collected, a sophisticated smoothing algorithm was applied to smooth contour variations. The smoothing algorithm provided a surface that more accurately reflected the topology and geometry of the structure. The surface no longer exactly matched the original contours but did not exhibit transverse-plane to transverse-plane variations. The smoothed structures were then superimposed on the original CT scans to determine if the smoothing process had distorted the shapes relative to the CT image. Once processed and validated the planner was able to rotate, translate, and segment the structure of interest in 3-dimensional space using a software package developed in-house. Results: The use of the anatomical model library has allowed planners to increase their comprehension of three-dimensional anatomy without the distracting digitization features of non-transverse CT image reconstruction. Additionally, this library has served as a set of benchmark data that has allowed our group to begin work on anatomically-based oblique presentation tumor and organ segmentation. Conclusions: With the advent of high resolution CT imaging and adaptive radiotherapy, treatment planners are faced with an increasing segmentation and review burden. As CT image resolution increases it is clear that physicians will need to improve their understanding of tumor and organ segmentation to address this significant increase in contouring. The development of this structure library is the first in a series of studies intended to improve our understanding of anatomical spatial relationships as well as explore non-transverse segmentation techniques. Author Disclosure: C. Abraham, None; D. Low, None; L. Liu, None; T. Ju, None; J.O. Deasy, None.
3080
Feasibility Study of a Multi-aperture Beam Delivery System for Conformal Orthovoltage Micro Irradiators
E. W. Izaguirre, X. Diao, S. Mutic, P. Grigsby, D. A. Low Washington University, Saint Louis, MO Purpose/Objective(s): In vivo Small animal structural (microCT and microMRI) and functional (microSPECT and microPET) imaging fostered the development of radiopharmaceuticals, and fundamental cancer research. Advances of comparable magnitude in the field of radiobiology, radiotherapy planning, and radiation therapy are expected if dedicated small animal micro-conformal radiation instrumentation is developed. We present a computer simulation of a multi-aperture beam delivery system for conformal small animal micro radiation therapy (microRT) to demonstrate the feasibility of achieving sub-millimeter 3-D conformal irradiation. For this purpose each delivered beam cross section is spatially modulated by a computer generated apertures which corresponds to the beam’s eye view of the planning target volume (PTV) back projected along the beam axis. Materials/Methods: The beam delivery system consists of: A) A high power commercially available orthovoltage source with a 0.4x0.4 mm2 focal spot that can be operated at a nominal power of 800W. B) Two variable beam collimator jaws to pre-collimate the radiation beam along each orthogonal beam width. C) An automatic aperture exchange mechanism to conform the beam cross section by using computer generated apertures. We developed a numerical model of the orthovoltage source output using a pencil beam propagation algorithm. We combined this program with a mouse digital phantom to simulate the conformal beam delivered to the irradiated animal. The developed code was used to compute the source spectral output, beam penumbra, soft tissue to bone dose ratio, dose fall off, and total dose delivered to a PTV. Results: A radiation dose rate of 40 Gy/min is possible when the system is filtered to obtain radiotherapy beam with a half value layer of 4.6 mm of Cu. The two orthogonal jaws limit the irradiation beam to rectangular fields from submillimeter size to whole animal in steps of 50mm. The beam penumbra is limited to a maximum of 0.35 mm. High conformality (typ. 95%) can be achieved in irradiation geometries such as total liver irradiation or medium size tumors. Conclusions: We designed and numerically evaluated the performance of an orthovoltage conformal beam delivery system based in multiple computer generated apertures. Computed beam penumbra and conformality shows that the proposed multi-aperture system is suitable for submillimeter conformal small animal orthovoltage irradiation. Author Disclosure: E.W. Izaguirre, None; X. Diao, None; S. Mutic, None; P. Grigsby, None; D.A. Low, None.
3081
Imaging Dose on a Dual On-board kV X-ray Imaging System in MHI-TM2000
K. Takayama1, K. Nagano2, S. Kaneko3, H. Nakayama3, N. Kawada3, K. Takahashi3, Y. Narita1, T. Mizowaki1, M. Kokubo2, M. Hiraoka1 1 Kyoto University, Kyoto, Japan, 2Institute of Biomedical Research and Innovation, Kobe, Japan, 3Mitsubishi heavy industries, LTD., Hiroshima, Japan
Purpose/Objective(s): We have developed a new image-guided radiotherapy (IGRT) system named MHI-TM2000, which has a dual on-board kV X-ray imaging system on a ring-shaped gantry. The aim of this study was to investigate imaging dose on
S655
I. J. Radiation Oncology d Biology d Physics
S656
Volume 72, Number 1, Supplement, 2008
the imaging system when used to take a planar radiography or cone beam computed tomography (CBCT) images for imageguided setup. Materials/Methods: The kV imaging system in the MHI-TM2000 consists of 2 sets of kV X-ray tube combined with a flat panel detector (FPD). The distance between the X-ray source and the isocenter is 100 cm and the distance between the source and the FPD is 188cm. The FPD has an aperture of 40 cm 30 cm, the spatial resolution is 1024768 pixels and the density resolution is 14 bits. The imaging system provides two orthogonal planar radiographies simultaneously, because each kV beam axis aligns orthogonally. It also provides CBCT images reconstructed from 391 projections taken during 195 degrees gantry rotation. In the beginning of this study, half value thickness was measured and effective energy was calculated in order to evaluate the Xray quality in each tube. Then imaging dose of planar radiography was measured using a spherical chamber (model A4, Exradin) at the isocenter position. For evaluation of imaging dose of CBCT, acrylic cylindrical CTDI phantoms (diameter of 16 cm and 32 cm, PTW) and a CT chamber (Type 30009, PTW) were used to measure central and peripheral doses, and then weighted CT dose index (CTDIw) was calculated. The measured values were compensated for temperature, air pressure, chamber correction and materials. Results: The dose of a planar radiography in the condition for head region (tube voltage: 80 kV, tube current: 200 mA, pulse time: 10 ms) was 0.12 mGy, that for thoracic region (100 kV, 200 mA, 10 ms) was 0.22 mGy, and that for pelvic lateral projection (120 kV, 320 mA, 25 ms) was 1.24 mGy. The center dose, the maximum peripheral dose and the CTDIw of one CBCT scan in the condition for head region (phantom diameter: 16 cm, 120 kV, 100 mA, 5 ms) were 11.2 mGy, 21.7 mGy, 13.0 mGy, respectively. Those for thoracic region (32 cm, 100 kV, 100 mA, 10 ms) were 3.6 mGy, 14.8 mGy, 6.8 mGy, respectively. Those for pelvic region (32 cm, 120 kV, 200 mA, 10 ms) were 11.0 mGy, 41.7 mGy, 19.4 mGy, respectively. When a short pulse time of 5 ms was used, small amount of dose difference between two X-ray tubes was observed because of small difference in the tube character. Conclusions: The imaging dose on the imaging system in the MHI-TM2000 was at the same level as the dose reported for other IGRT machines. In the clinical application of the IGRT system, we will make clinical protocols regarding the exposure condition, examination frequency, etc., under the balance of advantages in the image guidance and disadvantages in the imaging dose. Author Disclosure: K. Takayama, Mitsubishi Heavy Industries, LTD., A. Employment; K. Nagano, None; S. Kaneko, Mitsubishi Heavy Industries, LTD., A. Employment; H. Nakayama, Mitsubishi Heavy Industries, LTD., A. Employment; N. Kawada, Mitsubishi Heavy Industries, LTD., A. Employment; K. Takahashi, Mitsubishi Heavy Industries, LTD., A. Employment; Y. Narita, None; T. Mizowaki, None; M. Kokubo, None; M. Hiraoka, None.
3082
Frameless Hypofractionated Stereotactic Radiotherapy using Cone Beam CT Image Guidance for Intracranial Metastases
S. Lappi1, F. Fiorica2,3, S. Fabbri1, S. Ursino2, C. Flammia1, E. De Guglielmo1, L. Perazzini1, B. Boarini2, F. Cartei2 1
Health Physics Department, Ferrara, Italy, 2Radiotherapy Department, Ferrara, Italy, 3University of Catania, Catania, Italy
Purpose/Objective(s): Hypofractionated stereotactic radiotherapy (HSRT) for lesions in the brain typically uses relocatable systems to obtain target localization and immobilization. This study was designed to determine the set-up displacements during frameless HSRT using a heat-flexible mask and a set-up correction CBCT guided. Materials/Methods: Data from 12 patients undergoing 40 stereotactic radiation therapy procedures in 2007, were analyzed. In all patients, a heat-flexible mask with 3-points was employed. Prior to treatment a CBCT scan (On-Board Imager, Varian Medical Systems) was acquired and matched to the planning CT aligning bone anatomy: the displacements obtained were corrected online. A second CBCT was used to confirm the re-positioning shifts. We analyzed isocenter translations in all three axes, the absolute magnitude of isocenter dislocation. The rotations were assessed using an independent image registration software (Syntegra, Philips). Results: The average applied shifts for the three axes were 0.8 ± 1.2 mm, 0.3 ± 0.8 mm and 0.2 ± 0.3 mm respectively for the lateral (X), caudocranial (Y) and antero-posterior (Z) directions. The absolute magnitude of the isocenter dislocation was 1.6 ± 0.7 mm. The average rotational deviation around Z axis was 0.05 ± 0.64 ; no detectable rotational deviations around the X and Y axes were observed. Conclusions: A heat-flexible mask provides an immobilization accuracy of the patient similar to relocatable systems. Furthermore, the use of CBCT allows determining and correcting the set-up errors to obtain the same positioning of the planning CT. Author Disclosure: S. Lappi, None; F. Fiorica, None; S. Fabbri, None; S. Ursino, None; C. Flammia, None; E. De Guglielmo, None; L. Perazzini, None; B. Boarini, None; F. Cartei, None.
3083
Physical Aspects of Volumetric Modulated Arc Therapy (VMAT) using Elekta Synergy and ERGO++ Treatment Planning System
A. Haga1, K. Nakagawa1, K. Shiraishi1, K. Ohtomo1, Y. Okano1, T. Oritate1, K. Yoda2, R. G. Pellegrini3 1
University of Tokyo Hospital, Tokyo, Japan, 2Elekta KK, Kobe, Japan, 3Elekta 3Dline Research & Development, Milano, Italy
Purpose/Objective(s): Volumetric Modulated Arc Therapy (VMAT) has been implemented on Elekta Synergy using ERGO++ treatment planning system (TPS), and various physics tests have been performed including verification of isocenter dose and dose distribution. Materials/Methods: To modulate beam intensity during dynamic conformal arc delivery, dose rate and gantry speed are varied based on optimized MUs for all divided arcs. ERGO++ TPS can optimize MUs according to the prescription given for the inverse planning. Each collimator angle for each control angle is separately optimized to maximize conformity. Dose was delivered to a water phantom in a cylindrical acrylic enclosure. Then, the isocenter dose was measured by a pin-point chamber and it compared with the calculated one. In order to verify the dose distribution, also, an EDR2 films were placed inside a multi-layer acrylic phantom and they were compared with calculated one. For DMLC verification in VMAT test, the isocenter dose with various speed in MLC open
3079
Development of a Three Dimensional Anatomical Library
C. Abraham1, D. Low1, L. Liu2, T. Ju2, J. O. Deasy1 1
Department of Radiation Oncology, Washington University, St. Louis, MO, 2Department of Computer Science & Engineering, Washington University, St. Louis, MO Purpose/Objective(s): The early development of 3D conformal therapy parallels the history of computed tomography (CT), the main 3D imaging modality used for treatment planning. As such, segmentation was conducted on transverse planes by manually, semi-automatically, or automatically delineating structures. In spite of the rapid and extensive expansion of imaging technology, specifically with respect to CT, the segmentation process in radiation therapy has failed to evolve. The purpose of this work is to develop a protocol for segmentation on anatomically-defined oblique planes as well as analyze alternative segmentation techniques. Materials/Methods: Clinical treatment contours were retrospectively collected from prostate, lung, and head-and-neck cancer patients. The clinical contours were delineated on CT scans reconstructed at 3mm resolution. For each anatomic site, the clinical cases were chosen at random such that the planner was unaware which studies would be included within the model. After the transverse contours were collected, a sophisticated smoothing algorithm was applied to smooth contour variations. The smoothing algorithm provided a surface that more accurately reflected the topology and geometry of the structure. The surface no longer exactly matched the original contours but did not exhibit transverse-plane to transverse-plane variations. The smoothed structures were then superimposed on the original CT scans to determine if the smoothing process had distorted the shapes relative to the CT image. Once processed and validated the planner was able to rotate, translate, and segment the structure of interest in 3-dimensional space using a software package developed in-house. Results: The use of the anatomical model library has allowed planners to increase their comprehension of three-dimensional anatomy without the distracting digitization features of non-transverse CT image reconstruction. Additionally, this library has served as a set of benchmark data that has allowed our group to begin work on anatomically-based oblique presentation tumor and organ segmentation. Conclusions: With the advent of high resolution CT imaging and adaptive radiotherapy, treatment planners are faced with an increasing segmentation and review burden. As CT image resolution increases it is clear that physicians will need to improve their understanding of tumor and organ segmentation to address this significant increase in contouring. The development of this structure library is the first in a series of studies intended to improve our understanding of anatomical spatial relationships as well as explore non-transverse segmentation techniques. Author Disclosure: C. Abraham, None; D. Low, None; L. Liu, None; T. Ju, None; J.O. Deasy, None.
3080
Feasibility Study of a Multi-aperture Beam Delivery System for Conformal Orthovoltage Micro Irradiators
E. W. Izaguirre, X. Diao, S. Mutic, P. Grigsby, D. A. Low Washington University, Saint Louis, MO Purpose/Objective(s): In vivo Small animal structural (microCT and microMRI) and functional (microSPECT and microPET) imaging fostered the development of radiopharmaceuticals, and fundamental cancer research. Advances of comparable magnitude in the field of radiobiology, radiotherapy planning, and radiation therapy are expected if dedicated small animal micro-conformal radiation instrumentation is developed. We present a computer simulation of a multi-aperture beam delivery system for conformal small animal micro radiation therapy (microRT) to demonstrate the feasibility of achieving sub-millimeter 3-D conformal irradiation. For this purpose each delivered beam cross section is spatially modulated by a computer generated apertures which corresponds to the beam’s eye view of the planning target volume (PTV) back projected along the beam axis. Materials/Methods: The beam delivery system consists of: A) A high power commercially available orthovoltage source with a 0.4x0.4 mm2 focal spot that can be operated at a nominal power of 800W. B) Two variable beam collimator jaws to pre-collimate the radiation beam along each orthogonal beam width. C) An automatic aperture exchange mechanism to conform the beam cross section by using computer generated apertures. We developed a numerical model of the orthovoltage source output using a pencil beam propagation algorithm. We combined this program with a mouse digital phantom to simulate the conformal beam delivered to the irradiated animal. The developed code was used to compute the source spectral output, beam penumbra, soft tissue to bone dose ratio, dose fall off, and total dose delivered to a PTV. Results: A radiation dose rate of 40 Gy/min is possible when the system is filtered to obtain radiotherapy beam with a half value layer of 4.6 mm of Cu. The two orthogonal jaws limit the irradiation beam to rectangular fields from submillimeter size to whole animal in steps of 50mm. The beam penumbra is limited to a maximum of 0.35 mm. High conformality (typ. 95%) can be achieved in irradiation geometries such as total liver irradiation or medium size tumors. Conclusions: We designed and numerically evaluated the performance of an orthovoltage conformal beam delivery system based in multiple computer generated apertures. Computed beam penumbra and conformality shows that the proposed multi-aperture system is suitable for submillimeter conformal small animal orthovoltage irradiation. Author Disclosure: E.W. Izaguirre, None; X. Diao, None; S. Mutic, None; P. Grigsby, None; D.A. Low, None.
3081
Imaging Dose on a Dual On-board kV X-ray Imaging System in MHI-TM2000
K. Takayama1, K. Nagano2, S. Kaneko3, H. Nakayama3, N. Kawada3, K. Takahashi3, Y. Narita1, T. Mizowaki1, M. Kokubo2, M. Hiraoka1 1 Kyoto University, Kyoto, Japan, 2Institute of Biomedical Research and Innovation, Kobe, Japan, 3Mitsubishi heavy industries, LTD., Hiroshima, Japan
Purpose/Objective(s): We have developed a new image-guided radiotherapy (IGRT) system named MHI-TM2000, which has a dual on-board kV X-ray imaging system on a ring-shaped gantry. The aim of this study was to investigate imaging dose on
S655
I. J. Radiation Oncology d Biology d Physics
S656
Volume 72, Number 1, Supplement, 2008
the imaging system when used to take a planar radiography or cone beam computed tomography (CBCT) images for imageguided setup. Materials/Methods: The kV imaging system in the MHI-TM2000 consists of 2 sets of kV X-ray tube combined with a flat panel detector (FPD). The distance between the X-ray source and the isocenter is 100 cm and the distance between the source and the FPD is 188cm. The FPD has an aperture of 40 cm 30 cm, the spatial resolution is 1024768 pixels and the density resolution is 14 bits. The imaging system provides two orthogonal planar radiographies simultaneously, because each kV beam axis aligns orthogonally. It also provides CBCT images reconstructed from 391 projections taken during 195 degrees gantry rotation. In the beginning of this study, half value thickness was measured and effective energy was calculated in order to evaluate the Xray quality in each tube. Then imaging dose of planar radiography was measured using a spherical chamber (model A4, Exradin) at the isocenter position. For evaluation of imaging dose of CBCT, acrylic cylindrical CTDI phantoms (diameter of 16 cm and 32 cm, PTW) and a CT chamber (Type 30009, PTW) were used to measure central and peripheral doses, and then weighted CT dose index (CTDIw) was calculated. The measured values were compensated for temperature, air pressure, chamber correction and materials. Results: The dose of a planar radiography in the condition for head region (tube voltage: 80 kV, tube current: 200 mA, pulse time: 10 ms) was 0.12 mGy, that for thoracic region (100 kV, 200 mA, 10 ms) was 0.22 mGy, and that for pelvic lateral projection (120 kV, 320 mA, 25 ms) was 1.24 mGy. The center dose, the maximum peripheral dose and the CTDIw of one CBCT scan in the condition for head region (phantom diameter: 16 cm, 120 kV, 100 mA, 5 ms) were 11.2 mGy, 21.7 mGy, 13.0 mGy, respectively. Those for thoracic region (32 cm, 100 kV, 100 mA, 10 ms) were 3.6 mGy, 14.8 mGy, 6.8 mGy, respectively. Those for pelvic region (32 cm, 120 kV, 200 mA, 10 ms) were 11.0 mGy, 41.7 mGy, 19.4 mGy, respectively. When a short pulse time of 5 ms was used, small amount of dose difference between two X-ray tubes was observed because of small difference in the tube character. Conclusions: The imaging dose on the imaging system in the MHI-TM2000 was at the same level as the dose reported for other IGRT machines. In the clinical application of the IGRT system, we will make clinical protocols regarding the exposure condition, examination frequency, etc., under the balance of advantages in the image guidance and disadvantages in the imaging dose. Author Disclosure: K. Takayama, Mitsubishi Heavy Industries, LTD., A. Employment; K. Nagano, None; S. Kaneko, Mitsubishi Heavy Industries, LTD., A. Employment; H. Nakayama, Mitsubishi Heavy Industries, LTD., A. Employment; N. Kawada, Mitsubishi Heavy Industries, LTD., A. Employment; K. Takahashi, Mitsubishi Heavy Industries, LTD., A. Employment; Y. Narita, None; T. Mizowaki, None; M. Kokubo, None; M. Hiraoka, None.
3082
Frameless Hypofractionated Stereotactic Radiotherapy using Cone Beam CT Image Guidance for Intracranial Metastases
S. Lappi1, F. Fiorica2,3, S. Fabbri1, S. Ursino2, C. Flammia1, E. De Guglielmo1, L. Perazzini1, B. Boarini2, F. Cartei2 1
Health Physics Department, Ferrara, Italy, 2Radiotherapy Department, Ferrara, Italy, 3University of Catania, Catania, Italy
Purpose/Objective(s): Hypofractionated stereotactic radiotherapy (HSRT) for lesions in the brain typically uses relocatable systems to obtain target localization and immobilization. This study was designed to determine the set-up displacements during frameless HSRT using a heat-flexible mask and a set-up correction CBCT guided. Materials/Methods: Data from 12 patients undergoing 40 stereotactic radiation therapy procedures in 2007, were analyzed. In all patients, a heat-flexible mask with 3-points was employed. Prior to treatment a CBCT scan (On-Board Imager, Varian Medical Systems) was acquired and matched to the planning CT aligning bone anatomy: the displacements obtained were corrected online. A second CBCT was used to confirm the re-positioning shifts. We analyzed isocenter translations in all three axes, the absolute magnitude of isocenter dislocation. The rotations were assessed using an independent image registration software (Syntegra, Philips). Results: The average applied shifts for the three axes were 0.8 ± 1.2 mm, 0.3 ± 0.8 mm and 0.2 ± 0.3 mm respectively for the lateral (X), caudocranial (Y) and antero-posterior (Z) directions. The absolute magnitude of the isocenter dislocation was 1.6 ± 0.7 mm. The average rotational deviation around Z axis was 0.05 ± 0.64 ; no detectable rotational deviations around the X and Y axes were observed. Conclusions: A heat-flexible mask provides an immobilization accuracy of the patient similar to relocatable systems. Furthermore, the use of CBCT allows determining and correcting the set-up errors to obtain the same positioning of the planning CT. Author Disclosure: S. Lappi, None; F. Fiorica, None; S. Fabbri, None; S. Ursino, None; C. Flammia, None; E. De Guglielmo, None; L. Perazzini, None; B. Boarini, None; F. Cartei, None.
3083
Physical Aspects of Volumetric Modulated Arc Therapy (VMAT) using Elekta Synergy and ERGO++ Treatment Planning System
A. Haga1, K. Nakagawa1, K. Shiraishi1, K. Ohtomo1, Y. Okano1, T. Oritate1, K. Yoda2, R. G. Pellegrini3 1
University of Tokyo Hospital, Tokyo, Japan, 2Elekta KK, Kobe, Japan, 3Elekta 3Dline Research & Development, Milano, Italy
Purpose/Objective(s): Volumetric Modulated Arc Therapy (VMAT) has been implemented on Elekta Synergy using ERGO++ treatment planning system (TPS), and various physics tests have been performed including verification of isocenter dose and dose distribution. Materials/Methods: To modulate beam intensity during dynamic conformal arc delivery, dose rate and gantry speed are varied based on optimized MUs for all divided arcs. ERGO++ TPS can optimize MUs according to the prescription given for the inverse planning. Each collimator angle for each control angle is separately optimized to maximize conformity. Dose was delivered to a water phantom in a cylindrical acrylic enclosure. Then, the isocenter dose was measured by a pin-point chamber and it compared with the calculated one. In order to verify the dose distribution, also, an EDR2 films were placed inside a multi-layer acrylic phantom and they were compared with calculated one. For DMLC verification in VMAT test, the isocenter dose with various speed in MLC open