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EP-1466: Implementation of a linac head-mounted matrix detector to clinical use for dynamic technique
S783 ESTRO 36 _______________________________________________________________________________________________
Material and Methods 50 different treatments according to VMAT plans were selected from our database; 20 prostate, 20 gynecology and 10 brain. The QA results were divided based on the mean gamma index and the 3%/3mm and 1%/1mm criteria. Results from OmiPro were compared with Compass and TPS. Additionally, recalculation plan from TPS (Monte Carlo) in Compass system based on the different algorithm (Collapse Cone Convolution) were performed. MLC tests (3ABUT, 7SegA, FOURL plan) were implemented before each set of measurements for evaluation of interleaf leakage, tongue and groove effect. Results Mann-Whitney test showed good agreement between Compass 3D-reconstructed dose and OmniPro results (mean gamma 0.23 ±0.03 for 3%/3mm and 0.53±0.06 for 1%/1mm criteria). Scatter plot of results from TPS vs. Compass against TPS vs. OmniPro showed small differences in the region of gamma between 0.2 and 0.4. Comparison TPS vs. Compass mean dose in PTV and OAR did not reveal significant differences for prostate 50.04 Gy±0.4, 50.35Gy±0.33, bladder 32.04 Gy±0.41, 32.45 Gy±0.23; gynecology 45.07 Gy±0.34, 45.02 Gy±0.25, bladder 35.04 Gy±0.74, 35.75 Gy±0.49; brain 60.07 Gy±0.53, 60.02 Gy±0.71, brain stem dmax 40.04 Gy±0.83, 39.08 Gy±0.33 respectively. Conclusion Agreement between results obtained from Compass and OmniPro was reached. 3D dose reconstructions in CT patient allowed to evaluate the dosimetric errors and their clinical relevance. Compass reconstruction offers good opportunities to examine dynamic plans and check characteristics of MLC.
Conclusion The manufacturer's defined criteria for beam matching are not strict enough and should be evaluated before to interchange patients between two matched linacs. We described a method of evaluation and a procedure of beam matching for VMAT . EP-1466 Implementation of a linac head-mounted matrix detector to clinical use for dynamic technique L. Szczurek1 1 International Oncology Centre Affidea Poznan, Medical Physics, Poznan, Poland Purpose or Objective Quality assurance of VMAT plans based on the results in 2D phantom plane is not sufficient. Clinical interpretation of 2D measurements is difficult. The main purpose of this study is transition from 2D QA to 3D dose reconstruction in a patient CT scan which could be achieved using dose reconstruction method from 2D detector array in the Compass system. The first step in the clinical introduction of this system, instead of currently used 2D QA in OmniPro system, is to test reliability of dose reconstructions. In this work we investigated the validation of the method with OmniPro results as a reference. We check whether the Compass QA measurements of VMAT plans fulfill the QA requirements.
EP-1467 IPEM Code of Practice for proton and ion beam dosimetry: update on work in progress S. Green1, R. Amos2, F. Van den Heuvel3, A. Kacperek4, R.I. MacKay5, H. Palmans6, D. D'Souza2, R. Thomas6 1 Hall-Edwards Radiotherapy Research Group- Queen Elizabeth Hospital, Medical Physics, Birmingham, United Kingdom 2 University College London Hospitals, Radiotherapy Physics, London, United Kingdom 3 Churchill Hospital, Radiotherapy Physics, Oxford, United Kingdom 4 Clatterbridge Cancer centre, Physics Department, Wirral, United Kingdom 5 The Christie NHS Foundation Trust, Medical Physics, Manchester, United Kingdom 6 National Physical Laboratory, Radiation Dosimetry Group, London, United Kingdom Purpose or Objective Current standard methods for reference dosimetry of proton and ion beams typically involve the use of an ionization chamber calibrated in a cobalt-60 beam, with a beam quality correction factor applied to account for the difference between the chamber response in the proton and the calibration beams. This approach gives rise to uncertainties (at 68% confidence level) on the reference dosimetry of 2.4% for proton beams and 3.4% for carbon ion beams when using a plane-parallel ionization chamber. This poster provides an update on the development of a new Code of Practice for reference dosimetry of proton and ion beams, applicable to both scanned and scattered beam configurations. It is aimed to deliver an uncertainty on reference dosimetry for protons of approximately 2% and will utilise a primary standard graphite calorimeter that is robust and portable enough to be used in the enduser facility. Material and Methods This project involves a core team (authors on this submission) plus a group of experts in the field to provide
Material and Methods 50 different treatments according to VMAT plans were selected from our database; 20 prostate, 20 gynecology and 10 brain. The QA results were divided based on the mean gamma index and the 3%/3mm and 1%/1mm criteria. Results from OmiPro were compared with Compass and TPS. Additionally, recalculation plan from TPS (Monte Carlo) in Compass system based on the different algorithm (Collapse Cone Convolution) were performed. MLC tests (3ABUT, 7SegA, FOURL plan) were implemented before each set of measurements for evaluation of interleaf leakage, tongue and groove effect. Results Mann-Whitney test showed good agreement between Compass 3D-reconstructed dose and OmniPro results (mean gamma 0.23 ±0.03 for 3%/3mm and 0.53±0.06 for 1%/1mm criteria). Scatter plot of results from TPS vs. Compass against TPS vs. OmniPro showed small differences in the region of gamma between 0.2 and 0.4. Comparison TPS vs. Compass mean dose in PTV and OAR did not reveal significant differences for prostate 50.04 Gy±0.4, 50.35Gy±0.33, bladder 32.04 Gy±0.41, 32.45 Gy±0.23; gynecology 45.07 Gy±0.34, 45.02 Gy±0.25, bladder 35.04 Gy±0.74, 35.75 Gy±0.49; brain 60.07 Gy±0.53, 60.02 Gy±0.71, brain stem dmax 40.04 Gy±0.83, 39.08 Gy±0.33 respectively. Conclusion Agreement between results obtained from Compass and OmniPro was reached. 3D dose reconstructions in CT patient allowed to evaluate the dosimetric errors and their clinical relevance. Compass reconstruction offers good opportunities to examine dynamic plans and check characteristics of MLC.
Conclusion The manufacturer's defined criteria for beam matching are not strict enough and should be evaluated before to interchange patients between two matched linacs. We described a method of evaluation and a procedure of beam matching for VMAT . EP-1466 Implementation of a linac head-mounted matrix detector to clinical use for dynamic technique L. Szczurek1 1 International Oncology Centre Affidea Poznan, Medical Physics, Poznan, Poland Purpose or Objective Quality assurance of VMAT plans based on the results in 2D phantom plane is not sufficient. Clinical interpretation of 2D measurements is difficult. The main purpose of this study is transition from 2D QA to 3D dose reconstruction in a patient CT scan which could be achieved using dose reconstruction method from 2D detector array in the Compass system. The first step in the clinical introduction of this system, instead of currently used 2D QA in OmniPro system, is to test reliability of dose reconstructions. In this work we investigated the validation of the method with OmniPro results as a reference. We check whether the Compass QA measurements of VMAT plans fulfill the QA requirements.
EP-1467 IPEM Code of Practice for proton and ion beam dosimetry: update on work in progress S. Green1, R. Amos2, F. Van den Heuvel3, A. Kacperek4, R.I. MacKay5, H. Palmans6, D. D'Souza2, R. Thomas6 1 Hall-Edwards Radiotherapy Research Group- Queen Elizabeth Hospital, Medical Physics, Birmingham, United Kingdom 2 University College London Hospitals, Radiotherapy Physics, London, United Kingdom 3 Churchill Hospital, Radiotherapy Physics, Oxford, United Kingdom 4 Clatterbridge Cancer centre, Physics Department, Wirral, United Kingdom 5 The Christie NHS Foundation Trust, Medical Physics, Manchester, United Kingdom 6 National Physical Laboratory, Radiation Dosimetry Group, London, United Kingdom Purpose or Objective Current standard methods for reference dosimetry of proton and ion beams typically involve the use of an ionization chamber calibrated in a cobalt-60 beam, with a beam quality correction factor applied to account for the difference between the chamber response in the proton and the calibration beams. This approach gives rise to uncertainties (at 68% confidence level) on the reference dosimetry of 2.4% for proton beams and 3.4% for carbon ion beams when using a plane-parallel ionization chamber. This poster provides an update on the development of a new Code of Practice for reference dosimetry of proton and ion beams, applicable to both scanned and scattered beam configurations. It is aimed to deliver an uncertainty on reference dosimetry for protons of approximately 2% and will utilise a primary standard graphite calorimeter that is robust and portable enough to be used in the enduser facility. Material and Methods This project involves a core team (authors on this submission) plus a group of experts in the field to provide