- Email: [email protected]
215 speaker QA FOR VOLUMETRIC-MODULATED ARC THERAPY AT THE NKI-AVL
T UESDAY, M AY 10, 2011
test used for IMRT is a control of the leaf position and the distance between two facing leaves. The MLC leaf pairs sweep synchronously across a field with a constant distance of 1 mm between the leaves. Ten times, the leaves stopped irradiating a small strip to a higher dose. Both visual and analytical methods have been used for the evaluation of the PF test. In the DRGS and DRMLC tests, different combinations of dose rate, gantry speed and MLC leaf speed were used to deliver identical doses to separate parts of the EPID. The tests were evaluated by looking for deviations in the constancy of the measured dose for the preset combinations of dose rate, gantry speed and MLC leaf speed. Results: The three studies find that errors of 0.3 to 0.5 mm in MLC leaf position are detected by the PF test. For the DRGS test maximum deviations of 1 to 2 % was observed in the three studies, revealing a high reliability of the test. For the DRMLC test, the maximum errors found in the three tests differed considerably between the three studies. Fredh et al.[4] observed maximum errors of 5 % and rejected the test for QC of VMAT. These findings were not confirmed in the other studies where maximum errors of 1 to 2 % were found. Conclusion: The PF, the DRGS and the DRMLC tests offer a convenient, fast and accurate machine QC program for linear accelerators used for VMAT. The MLC positional tolerance and the deviations of the DRGS and DRMLC speed tests are within the recommendations of 0.5 mm and 3 % of the ESTRO guidelines[1]. These tolerances seem to be compatible to the performance of the accelerators in most cases.[2,4,5] The use of the EPID for QC is very fast and efficient compared to film measurements. However, communication problems between the EPID and the accelerator may be an issue. Patient specific QC may be performed instead of the proposed machine QC program. But this is very time consuming and it is desirable to skip the patient specific QC after an implementation period. M. Alber, S. Broggi, C. de Wagter, I. Eichwurzel, P. Engstrm, C. Fiorino, D. Georg, G. Hartmann, T. Kns, A. Leal, H. Marijnissen, B. Mijnheer, M. Paiusco, F. Shez-Doblado, R. Schmidt, M. Tomsej, H. Welleweerd, "ESTRO booklet no. 9: Guidelines for verification of IMRT," ESTRO (2008). C. C. Ling, P. Zhang, Y.Archambault, J. Bocanek, G. Tang and T. LoSasso, "Commissioning and quality assurance of rapidarc radiotherapy delivery system," Int. J. Radiat. Oncol. Biol. Phys. 72(2) 575-581 (2008). C.-S. Chui, S. Spirou and T. LoSasso, "Testing of dynamic multileaf collimation," Med. Phys. 23(5), 635-641 (1996). A. Fredh, S. Korreman, P. Munck af Rosenschld, "Automated analysis of images acquired with electronic portal imaging device during delivery of quality assurance plans for inversely optimized arc therapy," Radiother. and Oncol. 94, 195-198 (2010). M. K. Jrgensen, L. Hoffmann, J. B.B. Petersen, L. H. Pregaard, R. Hansen, and L. P. Muren,"Tolerance levels of EPID-based quality control for volumetric modulated arc therapy" submitted for publication. 214 speaker SPECIFIC QA ISSUES FOR TOMOTHERAPY: INTRODUCTION OF NEW QA TOOLS V. Althof1 , D. Kramer1 , R. Westendorp1 , T. Nuver1 , A. Minken1 , M. Ikink1 , G. Hilgers1 1 R ADIOTHERAPEUTIC I NSTITUTE RISO, Deventer, Netherlands
Purpose: To review filmless QA tools for rotational radiotherapy using the Tomotherapy system. Materials and Methods: Helical Tomotherapy differs from conventional linear accelerators in a number of ways, i.e. helical delivery, binary MLC and couch movement during radiation delivery. Tomotherapy provides QA tools which are integrated in the planning- and delivery system. An example is the Delivery QA (DQA) which allows to recalculate the patient plan on a phantom and to compare ionization chamber and film measurements with dose calculations. New QA procedures, with user configured MLC delivery patterns (sinograms) and procedure parameters, were developed. These procedures use the build in MVCT detector to measure open lateral beam profiles and phantom- and patient transmission profiles. Transmission measurements of a steplike phantom, allows for measurement of beam energy consistency, couch speed, laser position, slit width and synchronization of gantry with couch movement and gantry with leaf dynamics. Because of the high detector sample frequency (max. 300 Hz), the system is suitable to detect highly dynamic processes like the movement of the leaves (transit time 20 ms) and to measure with high temporal accuracy the abutment of an interrupted treatment and the completion of the treatment. Simultaneously with the sampling of the lateral beam profile during beam on, 85 system signals are sampled. Profiles and system signals are available for trend analysis. Most of these developments are incorporated in the Tomotherapy TQA™product. We developed a number of additional tools, like a monitor of system signals during delivery of a QA procedure and a sinogram analyzer that analyses the treatment planning solution by showing the distribution of beamlets passing through a voxel selected in the patient CT study. A hardware tool is developed which allows to diagnose problems in the pulse forming circuit by measurement of health signals during rotational procedures with a standard non-rotating oscilloscope.
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Transmission measurements of the patient allows for reconstruction of the treatment sinogram and hence subsequent 3D in vivo dose reconstruction using the patient MVCT or kVCT. This has the potential to replace DQA measurements. Results: Examples of the QA tools and test results of prereleased Tomotherapy software for in vivo dose reconstruction will be given. Trending data of QA items was obtained for a 4 year period on both of our Hi-Art II machines and will be shown as well. Conclusion: The Tomotherapy system offers the user tools to design his own QA treatment procedures and to collect system data which can be used in trend analysis. The MVCT detector is crucial for fast QA procedures and dose reconstruction. 215 speaker QA FOR VOLUMETRIC-MODULATED ARC THERAPY AT THE NKI-AVL A. Mans1 , I. Olaciregui1 , R. Rozendaal1 , R. Tielenburg1 , R. Vijlbrief1 , J. J. Sonke1 , B. Mijnheer1 , M. van Herk1 , J. Stroom1 1 T HE N ETHERLANDS C ANCER I NSTITUTE - A NTONI VAN L EEUWENHOEK H OSPITAL, Radiation Oncology , Amsterdam, Netherlands
Purpose: Since early 2008, all treatments with curative intent are verified by means of portal dosimetry in the Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital (NKI-AVL). If possible, verification is performed in vivo, otherwise pre-treatment. In august 2009, VMAT was clinically introduced in our department, and the portal dosimetry method was adapted to allow verification of VMAT treatments. Currently, VMAT is used routinely for prostate and stereotactic lung and brain treatments. Here we report on the first year of clinical experience with EPID-based VMAT verification, and compare results to IMRT. Methods and Materials: For IMRT, the portal dose is back-projected per beam to a plane parallel to the EPID, intersecting the isocentre, and compared to a corresponding slice from the planned dose distribution of that beam. The transmission (necessary for the back-projection) is determined from the ratio of portal and open images. Three modifications were needed to adapt the back-projection method to VMAT. 1) Continuous acquisition of EPID data in "movie-mode". 2) Calculation of the transmission from CT data. 3) Back-projection in 3D. With these modifications, an EPID movie acquired during VMAT delivery can be converted into a 3D dose distribution in the planning CT scan. Comparison of EPID-reconstructed and planned dose distributions for VMAT (IMRT) is done by a 3D (2D) γ -evaluation method (3%/3mm); γ -evaluation statistics is performed within the 50% isodose surface (20% isodose line) of the planned dose distribution. In 3D, the 50% isodose was chosen to exclude the buildup region. VMAT plans are created using the ’SmartArc’ module of Pinnacle 9.0 (Philips Medical Systems), and delivered using Elekta SL20i accelerators with standard MLC. Brain (1x18 Gy) treatments are verified pre-treatment on a slab phantom, lung SBRT and prostate treatments are verified in vivo. Results: The average values of the dose difference at the isocentre, the mean γ and the percentage of points with γ <1 are presented in Table 1 for both VMAT and IMRT for the three treatment sites. There is a small but systematic underestimation of the isocentre dose by the portal dosimetry method. VMAT and IMRT show similar values for the isocentre dose difference, although the standard deviation is somewhat larger for VMAT verification. This is probably caused by an increased susceptibility to anatomical changes when calculated transmission is used. The γ statistics are remarkable similar, especially considering the γ evaluation dimensionality: 2D for IMRT and 3D for VMAT. Conclusion: Our portal dosimetry method was successfully implemented for routine dosimetric verification of VMAT, both pre-treatment and in vivo. The main VMAT verification results (isocentre dose difference and γ statistics) are similar to IMRT. Consequently, VMAT treatments are included in our (in vivo) portal dosimetry programme for every single treatment with curative intent.
test used for IMRT is a control of the leaf position and the distance between two facing leaves. The MLC leaf pairs sweep synchronously across a field with a constant distance of 1 mm between the leaves. Ten times, the leaves stopped irradiating a small strip to a higher dose. Both visual and analytical methods have been used for the evaluation of the PF test. In the DRGS and DRMLC tests, different combinations of dose rate, gantry speed and MLC leaf speed were used to deliver identical doses to separate parts of the EPID. The tests were evaluated by looking for deviations in the constancy of the measured dose for the preset combinations of dose rate, gantry speed and MLC leaf speed. Results: The three studies find that errors of 0.3 to 0.5 mm in MLC leaf position are detected by the PF test. For the DRGS test maximum deviations of 1 to 2 % was observed in the three studies, revealing a high reliability of the test. For the DRMLC test, the maximum errors found in the three tests differed considerably between the three studies. Fredh et al.[4] observed maximum errors of 5 % and rejected the test for QC of VMAT. These findings were not confirmed in the other studies where maximum errors of 1 to 2 % were found. Conclusion: The PF, the DRGS and the DRMLC tests offer a convenient, fast and accurate machine QC program for linear accelerators used for VMAT. The MLC positional tolerance and the deviations of the DRGS and DRMLC speed tests are within the recommendations of 0.5 mm and 3 % of the ESTRO guidelines[1]. These tolerances seem to be compatible to the performance of the accelerators in most cases.[2,4,5] The use of the EPID for QC is very fast and efficient compared to film measurements. However, communication problems between the EPID and the accelerator may be an issue. Patient specific QC may be performed instead of the proposed machine QC program. But this is very time consuming and it is desirable to skip the patient specific QC after an implementation period. M. Alber, S. Broggi, C. de Wagter, I. Eichwurzel, P. Engstrm, C. Fiorino, D. Georg, G. Hartmann, T. Kns, A. Leal, H. Marijnissen, B. Mijnheer, M. Paiusco, F. Shez-Doblado, R. Schmidt, M. Tomsej, H. Welleweerd, "ESTRO booklet no. 9: Guidelines for verification of IMRT," ESTRO (2008). C. C. Ling, P. Zhang, Y.Archambault, J. Bocanek, G. Tang and T. LoSasso, "Commissioning and quality assurance of rapidarc radiotherapy delivery system," Int. J. Radiat. Oncol. Biol. Phys. 72(2) 575-581 (2008). C.-S. Chui, S. Spirou and T. LoSasso, "Testing of dynamic multileaf collimation," Med. Phys. 23(5), 635-641 (1996). A. Fredh, S. Korreman, P. Munck af Rosenschld, "Automated analysis of images acquired with electronic portal imaging device during delivery of quality assurance plans for inversely optimized arc therapy," Radiother. and Oncol. 94, 195-198 (2010). M. K. Jrgensen, L. Hoffmann, J. B.B. Petersen, L. H. Pregaard, R. Hansen, and L. P. Muren,"Tolerance levels of EPID-based quality control for volumetric modulated arc therapy" submitted for publication. 214 speaker SPECIFIC QA ISSUES FOR TOMOTHERAPY: INTRODUCTION OF NEW QA TOOLS V. Althof1 , D. Kramer1 , R. Westendorp1 , T. Nuver1 , A. Minken1 , M. Ikink1 , G. Hilgers1 1 R ADIOTHERAPEUTIC I NSTITUTE RISO, Deventer, Netherlands
Purpose: To review filmless QA tools for rotational radiotherapy using the Tomotherapy system. Materials and Methods: Helical Tomotherapy differs from conventional linear accelerators in a number of ways, i.e. helical delivery, binary MLC and couch movement during radiation delivery. Tomotherapy provides QA tools which are integrated in the planning- and delivery system. An example is the Delivery QA (DQA) which allows to recalculate the patient plan on a phantom and to compare ionization chamber and film measurements with dose calculations. New QA procedures, with user configured MLC delivery patterns (sinograms) and procedure parameters, were developed. These procedures use the build in MVCT detector to measure open lateral beam profiles and phantom- and patient transmission profiles. Transmission measurements of a steplike phantom, allows for measurement of beam energy consistency, couch speed, laser position, slit width and synchronization of gantry with couch movement and gantry with leaf dynamics. Because of the high detector sample frequency (max. 300 Hz), the system is suitable to detect highly dynamic processes like the movement of the leaves (transit time 20 ms) and to measure with high temporal accuracy the abutment of an interrupted treatment and the completion of the treatment. Simultaneously with the sampling of the lateral beam profile during beam on, 85 system signals are sampled. Profiles and system signals are available for trend analysis. Most of these developments are incorporated in the Tomotherapy TQA™product. We developed a number of additional tools, like a monitor of system signals during delivery of a QA procedure and a sinogram analyzer that analyses the treatment planning solution by showing the distribution of beamlets passing through a voxel selected in the patient CT study. A hardware tool is developed which allows to diagnose problems in the pulse forming circuit by measurement of health signals during rotational procedures with a standard non-rotating oscilloscope.
S YMPOSIUM
S 83
Transmission measurements of the patient allows for reconstruction of the treatment sinogram and hence subsequent 3D in vivo dose reconstruction using the patient MVCT or kVCT. This has the potential to replace DQA measurements. Results: Examples of the QA tools and test results of prereleased Tomotherapy software for in vivo dose reconstruction will be given. Trending data of QA items was obtained for a 4 year period on both of our Hi-Art II machines and will be shown as well. Conclusion: The Tomotherapy system offers the user tools to design his own QA treatment procedures and to collect system data which can be used in trend analysis. The MVCT detector is crucial for fast QA procedures and dose reconstruction. 215 speaker QA FOR VOLUMETRIC-MODULATED ARC THERAPY AT THE NKI-AVL A. Mans1 , I. Olaciregui1 , R. Rozendaal1 , R. Tielenburg1 , R. Vijlbrief1 , J. J. Sonke1 , B. Mijnheer1 , M. van Herk1 , J. Stroom1 1 T HE N ETHERLANDS C ANCER I NSTITUTE - A NTONI VAN L EEUWENHOEK H OSPITAL, Radiation Oncology , Amsterdam, Netherlands
Purpose: Since early 2008, all treatments with curative intent are verified by means of portal dosimetry in the Netherlands Cancer Institute-Antoni van Leeuwenhoek Hospital (NKI-AVL). If possible, verification is performed in vivo, otherwise pre-treatment. In august 2009, VMAT was clinically introduced in our department, and the portal dosimetry method was adapted to allow verification of VMAT treatments. Currently, VMAT is used routinely for prostate and stereotactic lung and brain treatments. Here we report on the first year of clinical experience with EPID-based VMAT verification, and compare results to IMRT. Methods and Materials: For IMRT, the portal dose is back-projected per beam to a plane parallel to the EPID, intersecting the isocentre, and compared to a corresponding slice from the planned dose distribution of that beam. The transmission (necessary for the back-projection) is determined from the ratio of portal and open images. Three modifications were needed to adapt the back-projection method to VMAT. 1) Continuous acquisition of EPID data in "movie-mode". 2) Calculation of the transmission from CT data. 3) Back-projection in 3D. With these modifications, an EPID movie acquired during VMAT delivery can be converted into a 3D dose distribution in the planning CT scan. Comparison of EPID-reconstructed and planned dose distributions for VMAT (IMRT) is done by a 3D (2D) γ -evaluation method (3%/3mm); γ -evaluation statistics is performed within the 50% isodose surface (20% isodose line) of the planned dose distribution. In 3D, the 50% isodose was chosen to exclude the buildup region. VMAT plans are created using the ’SmartArc’ module of Pinnacle 9.0 (Philips Medical Systems), and delivered using Elekta SL20i accelerators with standard MLC. Brain (1x18 Gy) treatments are verified pre-treatment on a slab phantom, lung SBRT and prostate treatments are verified in vivo. Results: The average values of the dose difference at the isocentre, the mean γ and the percentage of points with γ <1 are presented in Table 1 for both VMAT and IMRT for the three treatment sites. There is a small but systematic underestimation of the isocentre dose by the portal dosimetry method. VMAT and IMRT show similar values for the isocentre dose difference, although the standard deviation is somewhat larger for VMAT verification. This is probably caused by an increased susceptibility to anatomical changes when calculated transmission is used. The γ statistics are remarkable similar, especially considering the γ evaluation dimensionality: 2D for IMRT and 3D for VMAT. Conclusion: Our portal dosimetry method was successfully implemented for routine dosimetric verification of VMAT, both pre-treatment and in vivo. The main VMAT verification results (isocentre dose difference and γ statistics) are similar to IMRT. Consequently, VMAT treatments are included in our (in vivo) portal dosimetry programme for every single treatment with curative intent.