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OC-0061 VMAT QUALITY ASSURANCE (QA): SOFTWARE TOOL TO ANALYSE LINEAR ACCELERATOR PARAMETERS ACCURACY
S24
3
ESTRO 31
Politecnico di Milano, Dipartimento di Elettronica e In nformazione, Milano, Italy 4 XGLab SRL, Milano, Italy
PROFFERED PAPERS: PHYSICS 3: QC Q AND AUDITS FOR NEW TECHNIQUES AND TECHNOLO OGY
Purpose/Objective: In order to reduce uncerta ainties on the penetration depth of the beam during proton therap py treatments, a dedicated camera is developed to image prompt gammas g emitted along the proton tracks in pencil beam scanning mod de. This concept uses a knife-edge slit collimator to produce a reverssed 1D image of the proton tracks on a gamma camera. The challenge is to image high energy photons in an important neutron background d with sufficient counting statistics for use in clinical routine. This solu ution is operated in pulse mode with energy discrimination, and withou ut time of flight selection so that it can be placed as close as possib ble to the beam axis. Materials and Methods: An extensive simulation studyy was conducted with Monte Carlo code MCNPX to design and optimize e a camera with both high detection efficiency and sufficient spatia al resolution to measure the range of single spots at all clinical enerrgies with 1 mm accuracy. Spectrometry measurements of prompt gam mmas emitted by a PMMA target during irradiation with 160 MeV proton ns validated the simulations and a first prototype slit camera was prepared. The prototype was based on a 4 cm thick tungsten colllimator and the HiCam gamma camera with a 1 cm thick LYSO crrystal to image photons from 3 to 6 MeV. First tests were successfullyy conducted in a proton therapy facility during irradiation of a PMMA target with 100 and 160 MeV protons. Multiple range shifts were prod duced by moving the target in front of the camera. Results were scale ed for a full size camera (20 cm high, 10 cm large and 1 cm thick crysttal) and a robust range retrieving method based on the comparison of a 3-line-segment fit of the measured profile with reference Monte Carlo simulations was introduced. Results: If we neglect electronic dead times and rejection of detected events, measurements confirm that the current so olution with its collimator at 15 cm from beam axis can achieve a 1-2 mm standard deviation on range estimation in a homogeneous PMMA P target for numbers of protons that correspond to doses in water at a Bragg peak as low as 14 cGy at 100 MeV and 17 cGy at 160 MeV assuming pencil beams with a Gaussian profile of 5 mm sigma at target entrance.
OC-0061 VMAT QUALITY ASSURANCE (QA): SOFTWARE TOOL T TO ANALYSE LINEAR ACCELERATOR PARAMETERS ACCURACY C. Lafond1, C. Odin2, J. Even3, J.P. Manens3 1 Rennes I University, LTSI INSERM U642, RENN NES CEDEX, France 2 Rennes I University, IPR UR1/UMR CNRS 6251 1, RENNES CEDEX, France 3 Centre Eugene Marquis, physics, RENNES CED DEX, France
Figure: Comparison of the accuracy of the range retrieving method in simulations and measurements at 100 MeV beam energgy, as a function of the number of protons in the reference setup (15 cm c between the beam axis and the collimator, and between the collimator and the scintillator) with zero dead time of the electronics and zero rejection of detected events. Conclusions: Measurements were found to be in nice agreement with Monte Carlo predictions, except for the higher background of uncorrelated events in real conditions. Using referen nce simulations, the camera could consistently detect 1 mm range sh hifts at 100 and 160 MeV, laying an important milestone towards the de evelopment of a practical solution for real time range control in proton p therapy. Further measurements will be conducted at 230 MeV and with inhomogeneous targets.
Purpose/Objective: In VMAT technique, many dynamic parameters must be synchronized together to provide accurate treatments. To investigate the mechanical and dosimettric accuracy of linear accelerator during VMAT delivery, we have developed a home-made software to visualize and compare ma achine output delivery parameters to the expected DICOM input values. We have established tolerance levels of the linear accelerator para ameters. Materials and Methods: Twenty prostatte cases planned with Pinnacle/Philips (version 9.0) were analysed d. The linear accelerator was a Synergy/ Elekta (RTD: version 7.0) with MLCi2. The dosimetric QA was performed with an ionization chamb ber matrix inserted in an octogonal phantom and for coronal and sagitttal plans (Octavius PTW). During VMAT delivery, the linear accelerato or parameters have been recorded in real time and saved in a text t file. The software, developed in MATLAB, used this output file e and the DICOM-RT plan data to provide visualizations tools and stattistical information about variations and deviations for field shapes, gantry g speed, dose rate, deviations of monitor units (MU), jaws an nd leaves positions as a function of gantry angle. Parameters errors during d treatment delivery deduced from the software were correlated against the QA results measured at the same time. Results: The mean absolute error on MU U was -0.4 with a very asymmetric distribution. The mean error fo or the active leaves was 0.07 mm with a symmetric distribution; Boxxplots of the SD values of active leaves are reported for each patient in n the graphic. Over the 20 runs, the estimated mean leaf dispersion is i 1.82mm (SE=0.04mm), with a standard deviation of 0.66mm. For the jaws that are orthogonal to the leaves motion, the mean position error was -0.14 mm. We confirmed that the jaws motion wa as well correlated to the leaves motion. On average, we noticed thatt the gantry stopped and went back 11 times for the full arc.The dosim metric QA results showed 97.8 % (SD=1.59 %) of points were in agreem ment to 3 % or 3 mm with gamma index test and the mean gamma valu ue was 0.39 (SD=0.04) on average. These values were always in agree ement with our tolerance level of 95% and 0.5 respectively.
Conclusions: The software we developed offers o the opportunity to directly visualize and check the mechanical and dosimetric accuracy of linear accelerator in VMAT technique. Over O the twenty prostate plans,the recorded dynamic deviations havve a confidence interval IC95=0.66-3.26mm, but provided acceptablle dosimetric QA. These results points out the need for an overalll study of the dynamic fluctuations of the linear accelerator parameters in correlation to dosimetric delivery accuracy. This work is an illustration of the potentialities of our software.
3
ESTRO 31
Politecnico di Milano, Dipartimento di Elettronica e In nformazione, Milano, Italy 4 XGLab SRL, Milano, Italy
PROFFERED PAPERS: PHYSICS 3: QC Q AND AUDITS FOR NEW TECHNIQUES AND TECHNOLO OGY
Purpose/Objective: In order to reduce uncerta ainties on the penetration depth of the beam during proton therap py treatments, a dedicated camera is developed to image prompt gammas g emitted along the proton tracks in pencil beam scanning mod de. This concept uses a knife-edge slit collimator to produce a reverssed 1D image of the proton tracks on a gamma camera. The challenge is to image high energy photons in an important neutron background d with sufficient counting statistics for use in clinical routine. This solu ution is operated in pulse mode with energy discrimination, and withou ut time of flight selection so that it can be placed as close as possib ble to the beam axis. Materials and Methods: An extensive simulation studyy was conducted with Monte Carlo code MCNPX to design and optimize e a camera with both high detection efficiency and sufficient spatia al resolution to measure the range of single spots at all clinical enerrgies with 1 mm accuracy. Spectrometry measurements of prompt gam mmas emitted by a PMMA target during irradiation with 160 MeV proton ns validated the simulations and a first prototype slit camera was prepared. The prototype was based on a 4 cm thick tungsten colllimator and the HiCam gamma camera with a 1 cm thick LYSO crrystal to image photons from 3 to 6 MeV. First tests were successfullyy conducted in a proton therapy facility during irradiation of a PMMA target with 100 and 160 MeV protons. Multiple range shifts were prod duced by moving the target in front of the camera. Results were scale ed for a full size camera (20 cm high, 10 cm large and 1 cm thick crysttal) and a robust range retrieving method based on the comparison of a 3-line-segment fit of the measured profile with reference Monte Carlo simulations was introduced. Results: If we neglect electronic dead times and rejection of detected events, measurements confirm that the current so olution with its collimator at 15 cm from beam axis can achieve a 1-2 mm standard deviation on range estimation in a homogeneous PMMA P target for numbers of protons that correspond to doses in water at a Bragg peak as low as 14 cGy at 100 MeV and 17 cGy at 160 MeV assuming pencil beams with a Gaussian profile of 5 mm sigma at target entrance.
OC-0061 VMAT QUALITY ASSURANCE (QA): SOFTWARE TOOL T TO ANALYSE LINEAR ACCELERATOR PARAMETERS ACCURACY C. Lafond1, C. Odin2, J. Even3, J.P. Manens3 1 Rennes I University, LTSI INSERM U642, RENN NES CEDEX, France 2 Rennes I University, IPR UR1/UMR CNRS 6251 1, RENNES CEDEX, France 3 Centre Eugene Marquis, physics, RENNES CED DEX, France
Figure: Comparison of the accuracy of the range retrieving method in simulations and measurements at 100 MeV beam energgy, as a function of the number of protons in the reference setup (15 cm c between the beam axis and the collimator, and between the collimator and the scintillator) with zero dead time of the electronics and zero rejection of detected events. Conclusions: Measurements were found to be in nice agreement with Monte Carlo predictions, except for the higher background of uncorrelated events in real conditions. Using referen nce simulations, the camera could consistently detect 1 mm range sh hifts at 100 and 160 MeV, laying an important milestone towards the de evelopment of a practical solution for real time range control in proton p therapy. Further measurements will be conducted at 230 MeV and with inhomogeneous targets.
Purpose/Objective: In VMAT technique, many dynamic parameters must be synchronized together to provide accurate treatments. To investigate the mechanical and dosimettric accuracy of linear accelerator during VMAT delivery, we have developed a home-made software to visualize and compare ma achine output delivery parameters to the expected DICOM input values. We have established tolerance levels of the linear accelerator para ameters. Materials and Methods: Twenty prostatte cases planned with Pinnacle/Philips (version 9.0) were analysed d. The linear accelerator was a Synergy/ Elekta (RTD: version 7.0) with MLCi2. The dosimetric QA was performed with an ionization chamb ber matrix inserted in an octogonal phantom and for coronal and sagitttal plans (Octavius PTW). During VMAT delivery, the linear accelerato or parameters have been recorded in real time and saved in a text t file. The software, developed in MATLAB, used this output file e and the DICOM-RT plan data to provide visualizations tools and stattistical information about variations and deviations for field shapes, gantry g speed, dose rate, deviations of monitor units (MU), jaws an nd leaves positions as a function of gantry angle. Parameters errors during d treatment delivery deduced from the software were correlated against the QA results measured at the same time. Results: The mean absolute error on MU U was -0.4 with a very asymmetric distribution. The mean error fo or the active leaves was 0.07 mm with a symmetric distribution; Boxxplots of the SD values of active leaves are reported for each patient in n the graphic. Over the 20 runs, the estimated mean leaf dispersion is i 1.82mm (SE=0.04mm), with a standard deviation of 0.66mm. For the jaws that are orthogonal to the leaves motion, the mean position error was -0.14 mm. We confirmed that the jaws motion wa as well correlated to the leaves motion. On average, we noticed thatt the gantry stopped and went back 11 times for the full arc.The dosim metric QA results showed 97.8 % (SD=1.59 %) of points were in agreem ment to 3 % or 3 mm with gamma index test and the mean gamma valu ue was 0.39 (SD=0.04) on average. These values were always in agree ement with our tolerance level of 95% and 0.5 respectively.
Conclusions: The software we developed offers o the opportunity to directly visualize and check the mechanical and dosimetric accuracy of linear accelerator in VMAT technique. Over O the twenty prostate plans,the recorded dynamic deviations havve a confidence interval IC95=0.66-3.26mm, but provided acceptablle dosimetric QA. These results points out the need for an overalll study of the dynamic fluctuations of the linear accelerator parameters in correlation to dosimetric delivery accuracy. This work is an illustration of the potentialities of our software.