- Email: [email protected]
[I091] Clinical deployment of the mridian linac
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Abstracts / Physica Medica 52 (2018) 1–98
Purpose. To develop a method to evaluate the cumulative dose when using Multi Lumen Cylinder (MLC) applicator in vaginal cuff brachytherapy. Methods. A retrospective analysis of 25 patients treated in 2017 with the MLC applicator 3 cm diameter, were considered for this study. All patients received 5 fractions with 5 Gy each delivered twice a week and prescribed to the applicator’s surface for2/3 of the vaginal length. The CT scans of these patients, taken for treatment plan were separately imported into the treatment planning system and paired with the initial CT scan after completing the contouring. Two sets of CT images were fused at a time together with respective to the applicator, using mutual registration. Dosimetric evaluations were performed. The maximum doses received by the rectum wall, bladder wall, bowels and PTV on were analyzed and traced over the five fractions to determine the total dose distribution over the entire prescribed treatment. Results. No contour of any of the OAR was exactly similar when the CT images were fused each other. Depending on the depth of the insertion the PTV varied minimal. Each plan was performed independently and cumulated 2 at a time until all 5 fractions were added to the initial fraction. There is a difference between the doses received by the OARs between treatments and between the points of maximum dose. The maximum dose varied between 15% and 25% in rectum wall and bladder neck. The minimum dose varied between 3% and 6% in rectum wall and bladder neck. The average dose varied between 10% and 22% in rectum and bladder. The cumulative treatment does do not indicate a total maximum dose exceeding the tolerances for the rectum and bladder. Conclusion. The variations in volumes of the PTVs and isodoses are minor, indicating that the desired area receives the entire prescribed treatment. Rectum wall will not exceed 85% of the prescribed cumulative dose and the bladder neck will not exceed 75% of the prescribed dose. https://doi.org/10.1016/j.ejmp.2018.06.162
and RT, one important test was for example the coincidence of both isocenters. Furthermore, phantoms for RT-QA with adequate MR imaging contrast were developed and evaluated. Regarding the clinical integration, we follow a step-by-step concept. In the first step, patients with not too complicated, i.e. 3D conformal treatment plans are treated, in order to enable the whole team to get acquainted with the workflow and all novel concepts and processes coming along with daily MR imaging. For the second step, inclusion of IMRT treatments as well as gating are planned, which both should involve additional QA tests. Thirdly, the goal is to implement on-table adaption of treatments, which will also need additional verification. Conclusions. Commissioning tests and workflow considerations were presented for the clinical deployment of an MR-Linac. https://doi.org/10.1016/j.ejmp.2018.06.163
[I092] Initial experience with the elekta unity system Daniela Thorwarth a,* a
University of Tübingen, Department of Radiation Oncology, Section for Biomedical Physics, Tübingen, Germany ⇑ Corresponding author. In this presentation, a brief overview on the potential and also the challenges of online adaptive MR-guided radiotherapy (MRgRT) will be given. Moreover, the technical characteristics of the hybrid MRLinac system Unity (Elekta AB, Stockholm, Sweden) will be discussed including implications for clinical workflows, dosimetry and treatment planning. General aspects related to MRgRT as well as specific issues with respect to the Elekta Unity system consisting of a 1.5 T MRI and a 7MV linear accelerator will be presented. Futhermore, first experiences, dosimetric characterisations and phantom/ patient data will be discussed. https://doi.org/10.1016/j.ejmp.2018.06.164
[I091] Clinical deployment of the mridian linac Sebastian Klüter a,* a
University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany ⇑ Corresponding author. Purpose. The introduction of MR-guided radiotherapy (MRgRT) into clinical practice opens a lot of new possibilities and at the same time presents novel challenges. Funded by the German Research Foundation, a Viewray MRIdian Linac was installed in our department in 2017 with the first patient treatments in April 2018. Methods. The Viewray MRIdian Linac combines a 0.345T magnetic resonance imaging system with a 6 MV FFF linac. Fields are shaped by a double-stack, double-focus MLC, enabling the delivery of static conformal beams as well as step-and-shoot IMRT. 3D-MRI scans performed prior to treatment are used for patient positioning as well as adaption of treatment plans. Additionally, single slices of cine MRI can be continuously acquired during treatment and used for gating. Results. The commissioning tests can be divided into RT-tests, MRtests and tests for the combination of both. RT-related tests in general followed existing recommendations for commissioning and quality assurance (QA), but needed to be adapted due to the presence of the magnetic field. For the MR-related tests of the MRIdian system, the customer is presented with a set of MR-phantoms and test recommendations by the vendor. Those verifications comprised tests of field homogeneity, spatial integrity, uniformity and signalto-noise ratio. Other MR-related tests as the ACR-test may be adapted from diagnostic MRI. Regarding the combination of MR
[I093] Mr-guided radiotherapy at the LMU in Munich: Preliminary studies Florian Kamp a,*, Sebastian Neppl a, Moritz Rabe a, Lukas Nierer a, Christopher Kurz a, Michael Reiner a, Claus Belka a a
University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany ⇑ Corresponding author. Purpose. The clinical introduction of an MR-guided radiotherapy unit offers great potential to improve future patient treatment but is at the same time associated with several challenges from the perspective of medical physics. Before the final implementation of an MR-Linac in our clinical environment several preliminary studies are performed to prepare the introduction of the new system into the routine patient care as well as covering medical physics related research aspects. Methods. One focus of the projects is a comparison of the adaptive workflow based on daily MR and daily cone beam CT imaging. In order to mimic the MR-guided radiotherapy workflow an MRcompatible flat table top is equipped with immobilization devices for offline MR imaging in treatment position. A flexible, modular phantom is developed based on lego bricks, enabling fast distortion phantom prototyping and consequently distortion measurements. The effect of magnetic fields on dose measurements with thermoluminescent dosimeters is evaluated. Image registration methods are applied to time-resolved 4D MR and 4D CT images of patients as well
Abstracts / Physica Medica 52 (2018) 1–98
Purpose. To develop a method to evaluate the cumulative dose when using Multi Lumen Cylinder (MLC) applicator in vaginal cuff brachytherapy. Methods. A retrospective analysis of 25 patients treated in 2017 with the MLC applicator 3 cm diameter, were considered for this study. All patients received 5 fractions with 5 Gy each delivered twice a week and prescribed to the applicator’s surface for2/3 of the vaginal length. The CT scans of these patients, taken for treatment plan were separately imported into the treatment planning system and paired with the initial CT scan after completing the contouring. Two sets of CT images were fused at a time together with respective to the applicator, using mutual registration. Dosimetric evaluations were performed. The maximum doses received by the rectum wall, bladder wall, bowels and PTV on were analyzed and traced over the five fractions to determine the total dose distribution over the entire prescribed treatment. Results. No contour of any of the OAR was exactly similar when the CT images were fused each other. Depending on the depth of the insertion the PTV varied minimal. Each plan was performed independently and cumulated 2 at a time until all 5 fractions were added to the initial fraction. There is a difference between the doses received by the OARs between treatments and between the points of maximum dose. The maximum dose varied between 15% and 25% in rectum wall and bladder neck. The minimum dose varied between 3% and 6% in rectum wall and bladder neck. The average dose varied between 10% and 22% in rectum and bladder. The cumulative treatment does do not indicate a total maximum dose exceeding the tolerances for the rectum and bladder. Conclusion. The variations in volumes of the PTVs and isodoses are minor, indicating that the desired area receives the entire prescribed treatment. Rectum wall will not exceed 85% of the prescribed cumulative dose and the bladder neck will not exceed 75% of the prescribed dose. https://doi.org/10.1016/j.ejmp.2018.06.162
and RT, one important test was for example the coincidence of both isocenters. Furthermore, phantoms for RT-QA with adequate MR imaging contrast were developed and evaluated. Regarding the clinical integration, we follow a step-by-step concept. In the first step, patients with not too complicated, i.e. 3D conformal treatment plans are treated, in order to enable the whole team to get acquainted with the workflow and all novel concepts and processes coming along with daily MR imaging. For the second step, inclusion of IMRT treatments as well as gating are planned, which both should involve additional QA tests. Thirdly, the goal is to implement on-table adaption of treatments, which will also need additional verification. Conclusions. Commissioning tests and workflow considerations were presented for the clinical deployment of an MR-Linac. https://doi.org/10.1016/j.ejmp.2018.06.163
[I092] Initial experience with the elekta unity system Daniela Thorwarth a,* a
University of Tübingen, Department of Radiation Oncology, Section for Biomedical Physics, Tübingen, Germany ⇑ Corresponding author. In this presentation, a brief overview on the potential and also the challenges of online adaptive MR-guided radiotherapy (MRgRT) will be given. Moreover, the technical characteristics of the hybrid MRLinac system Unity (Elekta AB, Stockholm, Sweden) will be discussed including implications for clinical workflows, dosimetry and treatment planning. General aspects related to MRgRT as well as specific issues with respect to the Elekta Unity system consisting of a 1.5 T MRI and a 7MV linear accelerator will be presented. Futhermore, first experiences, dosimetric characterisations and phantom/ patient data will be discussed. https://doi.org/10.1016/j.ejmp.2018.06.164
[I091] Clinical deployment of the mridian linac Sebastian Klüter a,* a
University Hospital Heidelberg, Department of Radiation Oncology, Heidelberg, Germany ⇑ Corresponding author. Purpose. The introduction of MR-guided radiotherapy (MRgRT) into clinical practice opens a lot of new possibilities and at the same time presents novel challenges. Funded by the German Research Foundation, a Viewray MRIdian Linac was installed in our department in 2017 with the first patient treatments in April 2018. Methods. The Viewray MRIdian Linac combines a 0.345T magnetic resonance imaging system with a 6 MV FFF linac. Fields are shaped by a double-stack, double-focus MLC, enabling the delivery of static conformal beams as well as step-and-shoot IMRT. 3D-MRI scans performed prior to treatment are used for patient positioning as well as adaption of treatment plans. Additionally, single slices of cine MRI can be continuously acquired during treatment and used for gating. Results. The commissioning tests can be divided into RT-tests, MRtests and tests for the combination of both. RT-related tests in general followed existing recommendations for commissioning and quality assurance (QA), but needed to be adapted due to the presence of the magnetic field. For the MR-related tests of the MRIdian system, the customer is presented with a set of MR-phantoms and test recommendations by the vendor. Those verifications comprised tests of field homogeneity, spatial integrity, uniformity and signalto-noise ratio. Other MR-related tests as the ACR-test may be adapted from diagnostic MRI. Regarding the combination of MR
[I093] Mr-guided radiotherapy at the LMU in Munich: Preliminary studies Florian Kamp a,*, Sebastian Neppl a, Moritz Rabe a, Lukas Nierer a, Christopher Kurz a, Michael Reiner a, Claus Belka a a
University Hospital, LMU Munich, Department of Radiation Oncology, Munich, Germany ⇑ Corresponding author. Purpose. The clinical introduction of an MR-guided radiotherapy unit offers great potential to improve future patient treatment but is at the same time associated with several challenges from the perspective of medical physics. Before the final implementation of an MR-Linac in our clinical environment several preliminary studies are performed to prepare the introduction of the new system into the routine patient care as well as covering medical physics related research aspects. Methods. One focus of the projects is a comparison of the adaptive workflow based on daily MR and daily cone beam CT imaging. In order to mimic the MR-guided radiotherapy workflow an MRcompatible flat table top is equipped with immobilization devices for offline MR imaging in treatment position. A flexible, modular phantom is developed based on lego bricks, enabling fast distortion phantom prototyping and consequently distortion measurements. The effect of magnetic fields on dose measurements with thermoluminescent dosimeters is evaluated. Image registration methods are applied to time-resolved 4D MR and 4D CT images of patients as well