Search

The aim of this study was to report a single‐institution experience and commissioning data for Elekta VersaHD linear accelerators (LINACs) for photon beams in the Eclipse treatment planning system (TPS). Two VersaHD LINACs equipped with 160‐leaf collimators were commissioned. For each energy, the percent‐depth‐dose (PDD) curves, beam profiles, output factors, leaf transmission factors and dosimetric leaf gaps (DLGs) were acquired in accordance with the AAPM task group reports No. 45 and No. 106 and the vendor‐supplied documents. The measured data were imported into Eclipse TPS to build a VersaHD beam model. The model was validated by creating treatment plans spanning over the full‐spectrum of treatment sites and techniques used in our clinic. The quality assurance measurements were performed using MatriXX, ionization chamber, and radiochromic film. The DLG values were iteratively adjusted to optimize the agreement between planned and measured doses. Mobius, an independent LINAC logfile‐based quality assurance tool, was also commissioned both for routine intensity‐modulated radiation therapy (IMRT) QA and as a secondary check for the Eclipse VersaHD model. The Eclipse‐generated VersaHD model was in excellent agreement with the measured PDD curves and beam profiles. The measured leaf transmission factors were less than 0.5% for all energies. The model validation study yielded absolute point dose agreement between ionization chamber measurements and Eclipse within ±4% for all cases. The comparison between Mobius and Eclipse, and between Mobius and ionization chamber measurements lead to absolute point dose agreement within ±5%. The corresponding 3D dose distributions evaluated with 3%global/2mm gamma criteria resulted in larger than 90% passing rates for all plans. The Eclipse TPS can model VersaHD LINACs with clinically acceptable accuracy. The model validation study and comparisons with Mobius demonstrated that the modeling of VersaHD in Eclipse necessitates further improvement to provide dosimetric accuracy on par with Varian LINACs. [ABSTRACT FROM AUTHOR]

The purpose of this study is to perform dosimetric validation of Monaco treatment planning system version 5.1. The Elekta Versa HD linear accelerator with high dose rate flattening filter-free photon modes and electron energies was used in this study. The dosimetric output of the new Agility head combined with the FFF photon modes warranted this investigation into the dosimetric accuracy prior to clinical usage. A model of the Versa HD linac was created in Monaco TPS by Elekta using commissioned beam data including percent depth dose curves, beam profiles, and output factors. A variety of 3D conformal fields were created in Monaco TPS on a combined Plastic water/Styrofoam phantom and validated against measurements with a calibrated ion chamber. Some of the parameters varied including source to surface distance, field size, wedges, gantry angle, and depth for all photon and electron energies. In addition, a series of step and shoot IMRT, VMAT test plans, and patient plans on various anatomical sites were verified against measurements on a Delta4 diode array. The agreement in point dose measurements was within 2% for all photon and electron energies in the homogeneous phantom and within 3% for photon energies in the heterogeneous phantom. The mean ± SD gamma passing rates of IMRT test fields yielded 93.8 ± 4.7% based on 2% dose difference and 2 mm distance-to-agreement criteria. Eight previously treated IMRT patient plans were replanned in Monaco TPS and five measurements on each yielded an average gamma passing rate of 95% with 6.7% confidence limit based on 3%, 3 mm gamma criteria. This investigation on dosimetric validation ensures accuracy of modeling Versa HD linac in Monaco TPS thereby improving patient safety. [ABSTRACT FROM AUTHOR]

Introduction The objective of this study is to compare the dosimetric and geometric performances of the CyberKnife (Accuray) and VersaHD (Elekta) with the ExacTrac system (BrainLab) in stereotactic radiotherapy for brain metastases. Material and method This study was conducted on 5 patients for a prescribed dose of 27 Gy in 3 fractions with a margin of 1 mm between CTV and PTV for the Cyberknife and 2 mm for the VersaHD in accordance with our clinical practices. The dosimetric study was also conducted with a 2 mm margin for the Cyberknife to assess the dosimetric impact of the margins. Plans have been computed for the CyberKnife M6 v10.6 with non-isocentric multi-beams generated by inverse optimization on Multiplan v5.3 (Accuray). For the VersaHD equipped with ExacTrac v6.1 and used with the Frameless system (BrainLab), 4 non-coplanar arcs (VMAT) has been generated by inverse optimization on Pinnacle v9.10 (Philips). The dosimetric evaluation focused on the coverage of PTV and volume of brain outside PTV receiving 23.1 Gy corresponding to the main criteria of medical approval. The volume of isodoses 6 Gy, 2.7 Gy and 1 Gy and the ratio of the volume of isodose 13.5 Gy and 27 Gy have been reported to characterize the spread of low doses and the dose gradient around the PTV. Quality controls have been performed with radiochromic films (EBT3/Ashland) and with an ionization chamber (Pinpoint 31014/PTW) in an anthropomorphic phantom (STEEV/CIRS). The dose measured by film has been compared to the calculated dose according to the method of the gamma index with 3% (local)/2 mm criteria (analytical threshold: 30% of the maximum dose). The geometric difference between the measured and calculated dose distribution has been also reported. Results Table 1 shows that validation criteria were reached for both modalities. For an equivalent PTV coverage, dose gradients obtained with the Cyberknife were greater than those obtained with the VersaHD and lower volumes of healthy tissue received doses lower than 6 Gy. The mean differences between the dose measured by ionization chamber and the calculated dose were 2.3% and − 0.5% with Cyberknife and VersaHD respectively. The mean value of the gamma index was 0.41 for the Cyberknife and 0.35 for the VersaHD. The mean geometric differences between the measured and calculated dose distributions were 0.86 mm and 0.50 mm Cyberknife to VersaHD. Conclusion Both treatment modalities, Cyberknife and VersaHD with ExacTrac, allow compliance to dosimetric criteria in the stereotactic treatment of brain metastases. The Cyberknife provides higher dose gradients than the VersaHD and limit irradiation of healthy tissues at low doses. The agreement between calculated dose and measured dose was acceptable for both modalities with mean gamma values lower than 0.5. An investigation will be performed to evaluate low margins (1 mm) with the VersaHD/ ExacTrac due to the very low geometric deviations. [ABSTRACT FROM AUTHOR]

The purpose of this study is to perform dosimetric validation of Monaco treatment planning system version 5.1. The Elekta VersaHD linear accelerator with high dose rate flattening filter-free photon modes and electron energies was used in this study. The dosimetric output of the new Agility head combined with the FFF photon modes warranted this investigation into the dosimetric accuracy prior to clinical usage. A model of the VersaHD linac was created in Monaco TPS by Elekta using commissioned beam data including percent depth dose curves, beam profiles, and output factors. A variety of 3D conformal fields were created in Monaco TPS on a combined Plastic water/Styrofoam phantom and validated against measurements with a calibrated ion chamber. Some of the parameters varied including source to surface distance, field size, wedges, gantry angle, and depth for all photon and electron energies. In addition, a series of step and shoot IMRT, VMAT test plans, and patient plans on various anatomical sites were verified against measurements on a Delta 4 diode array. The agreement in point dose measurements was within 2% for all photon and electron energies in the homogeneous phantom and within 3% for photon energies in the heterogeneous phantom. The mean ± SD gamma passing rates of IMRT test fields yielded 93.8 ± 4.7% based on 2% dose difference and 2 mm distance-to-agreement criteria. Eight previously treated IMRT patient plans were replanned in Monaco TPS and five measurements on each yielded an average gamma passing rate of 95% with 6.7% confidence limit based on 3%, 3 mm gamma criteria. This investigation on dosimetric validation ensures accuracy of modeling VersaHD linac in Monaco TPS thereby improving patient safety., (© 2017 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)