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EP-1428 DEVELOPMENT OF A QA TOOL FOR ANALYSIS OF LEAF PERFORMANCE IN INTENSITY MODULATED DELIVERY METHODS
S544
To ensure correct dose delivery, patient specific quality assurance was performed which included the measurement of 2D point doses and 3D QA with IBA compass. The measured doses were compared with Treatment Planning System (TPS) calculated Doses. The patient was treated in Varian Clinac iX with proper immobilization devices like Vac loc and orfit. Care has been laid to minimize random daily setup errors by fusing 2D orthogonal images taken using On-Board Imager (OBI) with the treatment plan generated DRRs. Results: The PTV coverage achieved was D95 (Dose to 95% volume) is 97.5% of prescribed dose. The mean doses of Liver, Heart and Esophagus were 36.2Gy, 21.4Gy and 36.1Gy respectively. The mean dose to that part of liver which is after excluding from PTV is 30Gy. Maximum dose to spinal cord is 50.4Gy with V44 is 1cm3. In Patient specific QA, two dimensional point dose results deviates less than 3%. Gamma analysis performed with the evaluation criteria of 3mm DTA and 3% Dose Difference using three dimensional IBA compass achieved a confidence level of around 96% to the PTV. The daily setup error variations in the Longitudinal, Lateral and Vertical axes were 1.1±1.9, 1.1±1.2 and -0.5± 1.1mm. The figure shows the dose fall of isodose coverage of from 95% to 70%.
ESTRO 31
EP-1428 DEVELOPMENT OF A QA TOOL FOR ANALYSIS OF LEAF PERFORMANCE IN INTENSITY MODULATED DELIVERY METHODS C. Horsfield1, J.E. Marsden1, A.W. Beavis1 1 Hull and East Yorkshire Hospitals NHS Trust, Radiation Physics, Hull, United Kingdom Purpose/Objective: Varian’s MLC system produces log which records the planned and the actual leaf position as well as beam state, gantry angle, collimator angle and other geometrical information every 50ms. An A graphical user interface was written (in Matlab) to enable the interpretation and analysis of statistics on leaf performance. This was able to calculate the error on leaf position based on the difference between that planned and that delivered. It was the aim of this work to characterise the performance of the code as a first step towards using dynalogs as a frequent QA tool for IMRT delivery and for potential use with Rapidarc QA. A secondary objective was to see how the error on leaf position compared to the error seen in the radiation field using an EPID as an independent method. Materials and Methods: A dynamic MLC file was produced in the Varian tool ‘shaper’, designed to produce movements of the leaves at 2.5cm/s (the recommended maximum speed). The file was delivered using decrementing monitor units to increase the speed and hence associated error on leaf position. The exposure was logged using the dynalog system and captured using an EPID on integrated image. Dynalog results were processed using the Matlab software returning statistics on leaf position error and beam hold time. The EPID images were compared using gamma analysis to the reference field (2.5cm/s leaf speed). These were compared at the 1%,1mm level (in Omnipro IMRT) for comparison to the error on the leaves. Results:
Conclusions: The case of Malignant Mesothelioma was successfully treated with Rapid Arc technique and this technique is feasible where other modality technique fails. EP-1427 ANALYSIS OF DYNAMIC MLC LOG-FILES AS A TOOL FOR QUALITY ASSURANCE IN INTENSITY-MODULATED RADIOTHERAPY H. Hentschel1, O. Hentschel1, B. Pakisch1, M. Stock2 1 Landesklinikum Wiener Neustadt, Radioonkologie, Wiener Neustadt, Austria 2 Medical University of Vienna Vienna Austria, Department of Radiation Oncology & Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria Purpose/Objective: Modern radiation therapy techniques like sliding window Intensity Modulated Radio--therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) employ dynamic MLCs. These techniques are working with very conformal dose distributions to the planning target volume by efficiently sparing normal tissue or organs at risk, so it is of peculiar importance to check the accuracy of the delivered dose distribution which is mainly shaped by the MLC. The aim of this work is to provide a software application which allows for the analysis of so called Dynalogs (Varian) which are textfiles that contain the actual position of all leaves. Materials and Methods: Using our homemade program, we analyzed the Dynalog files of 37 patients (2556 fields). The differences between planned and actual leaf positions were retrieved to calculate the rootmean-square error and error histograms. The outcome of our verification was similar to the data of other groups (Ling et al and Teke). Results: For RapidArc treatments, 90-95% of errors were below 1mm. IMRT techniques resulted in better error histograms, showing that 98% to almost 100% of errors were smaller than 1mm. Conclusions: Summarizing the results, we can say that our software performs as intended in analyzing the precision of leaf motions. The evaluation of the created data proved that our MLC is capable of delivering highly conformal, intensity modulated treatments.
Figure 1: Graph to show (left) Leaf error versus gamma analysis. (right) Maximum and average error against leaf speed and beam hold time. The results showed a steady increase in the maximum and average error on leaf position from that planned as the required leaf speed was increased. As expected, a ‘beam hold off’ was implemented when the leaves breached the leaf position tolerance of 0.5cm assigned to the MLC file. The introduction of the beam hold for the same field that breached the position tolerance serves as some validation that the code is returning correct information and also shows the correct functioning of this feature on the MLC control system. As the leaf speed was increased further the total length of beam hold off increased. The average leaf error remained below 0.1cm for speeds up to 5.7 cm/s (theoretically required speed-not achieved as maximum speed was 3.5cm/s). As the error on leaf position became large, the pass rate from gamma analysis dropped. As shown in the left image in figure 1, the gamma analysis results showed >95% agreement to the reference field at the 1% 1mm level for errors below 0.1cm. Conclusions: The information returned from the log file interface shows good potential for use as a QA tool for Intensity Modulated delivered such as Rapidarc.
To ensure correct dose delivery, patient specific quality assurance was performed which included the measurement of 2D point doses and 3D QA with IBA compass. The measured doses were compared with Treatment Planning System (TPS) calculated Doses. The patient was treated in Varian Clinac iX with proper immobilization devices like Vac loc and orfit. Care has been laid to minimize random daily setup errors by fusing 2D orthogonal images taken using On-Board Imager (OBI) with the treatment plan generated DRRs. Results: The PTV coverage achieved was D95 (Dose to 95% volume) is 97.5% of prescribed dose. The mean doses of Liver, Heart and Esophagus were 36.2Gy, 21.4Gy and 36.1Gy respectively. The mean dose to that part of liver which is after excluding from PTV is 30Gy. Maximum dose to spinal cord is 50.4Gy with V44 is 1cm3. In Patient specific QA, two dimensional point dose results deviates less than 3%. Gamma analysis performed with the evaluation criteria of 3mm DTA and 3% Dose Difference using three dimensional IBA compass achieved a confidence level of around 96% to the PTV. The daily setup error variations in the Longitudinal, Lateral and Vertical axes were 1.1±1.9, 1.1±1.2 and -0.5± 1.1mm. The figure shows the dose fall of isodose coverage of from 95% to 70%.
ESTRO 31
EP-1428 DEVELOPMENT OF A QA TOOL FOR ANALYSIS OF LEAF PERFORMANCE IN INTENSITY MODULATED DELIVERY METHODS C. Horsfield1, J.E. Marsden1, A.W. Beavis1 1 Hull and East Yorkshire Hospitals NHS Trust, Radiation Physics, Hull, United Kingdom Purpose/Objective: Varian’s MLC system produces log which records the planned and the actual leaf position as well as beam state, gantry angle, collimator angle and other geometrical information every 50ms. An A graphical user interface was written (in Matlab) to enable the interpretation and analysis of statistics on leaf performance. This was able to calculate the error on leaf position based on the difference between that planned and that delivered. It was the aim of this work to characterise the performance of the code as a first step towards using dynalogs as a frequent QA tool for IMRT delivery and for potential use with Rapidarc QA. A secondary objective was to see how the error on leaf position compared to the error seen in the radiation field using an EPID as an independent method. Materials and Methods: A dynamic MLC file was produced in the Varian tool ‘shaper’, designed to produce movements of the leaves at 2.5cm/s (the recommended maximum speed). The file was delivered using decrementing monitor units to increase the speed and hence associated error on leaf position. The exposure was logged using the dynalog system and captured using an EPID on integrated image. Dynalog results were processed using the Matlab software returning statistics on leaf position error and beam hold time. The EPID images were compared using gamma analysis to the reference field (2.5cm/s leaf speed). These were compared at the 1%,1mm level (in Omnipro IMRT) for comparison to the error on the leaves. Results:
Conclusions: The case of Malignant Mesothelioma was successfully treated with Rapid Arc technique and this technique is feasible where other modality technique fails. EP-1427 ANALYSIS OF DYNAMIC MLC LOG-FILES AS A TOOL FOR QUALITY ASSURANCE IN INTENSITY-MODULATED RADIOTHERAPY H. Hentschel1, O. Hentschel1, B. Pakisch1, M. Stock2 1 Landesklinikum Wiener Neustadt, Radioonkologie, Wiener Neustadt, Austria 2 Medical University of Vienna Vienna Austria, Department of Radiation Oncology & Christian Doppler Laboratory for Medical Radiation Research for Radiation Oncology, Vienna, Austria Purpose/Objective: Modern radiation therapy techniques like sliding window Intensity Modulated Radio--therapy (IMRT) and Volumetric Modulated Arc Therapy (VMAT) employ dynamic MLCs. These techniques are working with very conformal dose distributions to the planning target volume by efficiently sparing normal tissue or organs at risk, so it is of peculiar importance to check the accuracy of the delivered dose distribution which is mainly shaped by the MLC. The aim of this work is to provide a software application which allows for the analysis of so called Dynalogs (Varian) which are textfiles that contain the actual position of all leaves. Materials and Methods: Using our homemade program, we analyzed the Dynalog files of 37 patients (2556 fields). The differences between planned and actual leaf positions were retrieved to calculate the rootmean-square error and error histograms. The outcome of our verification was similar to the data of other groups (Ling et al and Teke). Results: For RapidArc treatments, 90-95% of errors were below 1mm. IMRT techniques resulted in better error histograms, showing that 98% to almost 100% of errors were smaller than 1mm. Conclusions: Summarizing the results, we can say that our software performs as intended in analyzing the precision of leaf motions. The evaluation of the created data proved that our MLC is capable of delivering highly conformal, intensity modulated treatments.
Figure 1: Graph to show (left) Leaf error versus gamma analysis. (right) Maximum and average error against leaf speed and beam hold time. The results showed a steady increase in the maximum and average error on leaf position from that planned as the required leaf speed was increased. As expected, a ‘beam hold off’ was implemented when the leaves breached the leaf position tolerance of 0.5cm assigned to the MLC file. The introduction of the beam hold for the same field that breached the position tolerance serves as some validation that the code is returning correct information and also shows the correct functioning of this feature on the MLC control system. As the leaf speed was increased further the total length of beam hold off increased. The average leaf error remained below 0.1cm for speeds up to 5.7 cm/s (theoretically required speed-not achieved as maximum speed was 3.5cm/s). As the error on leaf position became large, the pass rate from gamma analysis dropped. As shown in the left image in figure 1, the gamma analysis results showed >95% agreement to the reference field at the 1% 1mm level for errors below 0.1cm. Conclusions: The information returned from the log file interface shows good potential for use as a QA tool for Intensity Modulated delivered such as Rapidarc.