Installation und Kommissionierung des Viewray MRIdian Linac Hamburg, 28. Mai 2018 Sebastian Klüter

Transcription

1 Installation und Kommissionierung des Viewray MRIdian Linac Hamburg, 28. Mai 2018 Sebastian Klüter

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3 MR-guided RT in Heidelberg Funded by the German Research Foundation (DFG) Heidelberg consortium received one of two grants (project # ) for a comprehensive research program on MRgRT Timeline Mar. 2017: mid Aug. 2017: Dec. 2017: April 2018: start of vault remodeling start of Installation start of Commissioning first patient treatment

4 The MRIdian Linac Split superconducting magnet with 0.35T field strength Radiation gantry in 28cm gap between the two magnet halves, split gradient coils

5 The MRIdian Linac Buckets shield the Linac from the B 0 -Field as well as the MR from the Linac Linac: 6MV FFF, 600 MU/min, 90cm SAD Magnetron Circulator Puls Transformer Linac Gun Driver

6 RayZR MLC double stack, double focus MLC, 138 tungsten-alloy leaves max. Fieldsize 27.4 x 24.1 cm², min. Fieldsize 2 x 4.15 mm² each Leaf is 5.5cm high 8.3 mm Two different MLC configurations for a 4.15mm beam

7 The MR in MRIdian 0.35T magnetic field strength Split Gradients: slew 200mT/m/ms, 18mT/m peak pulse sequence: truefisp (bssfp) T2/T1-weighted contrast, highlighting fat and fluids cine-mr with 4 frames/s

8 MR Imaging: coils Gradient coils: Body coil:

9 MR Imaging: coils Surface coils: Torso Head and Neck Attenuation of treatment beam approx. 0.5%, Simulation coils for CT sim

10 Installation The Viewray MRIdian can be installed in a standard vault In Heidelberg: old Siemens MEVATRON machine in a two-storey vault

11 Installation The Viewray MRIdian can be installed in a standard vault In Heidelberg: old Siemens MEVATRON machine in a two-storey vault

12 Installation The Viewray MRIdian can be installed in a standard vault In Heidelberg: old Siemens MEVATRON machine in a two-storey vault

13 Installation: before: after:

14 Quench vent

15 Fringe fields 5 gauss line (usually the controlled zone ) is close to the machine 1 gauss line is (in our case) at bunker door comparison: the earth s magnetic field is around 0.5 gauss

16 RF shielding copper cage encompassing the whole room RF filters and waveguides for every cable or duct RF cage is customizable: additional RF filters and waveguides combined RT/RF door: 15.5 tons of lead and heavy concrete air gasket seals RF cage with compressed air

17 MR-Commissioning: B 0 -Homogeneity Measured with a 45cm FOV field camera: 16 ppm for our system within 24cm DSV: DSV = Diameter Spherical Volume, defines usable imaging volume at isocenter spherical phantom, filled with water + nickel sulfate hexahydrate spectral peak analysis: frequency spread measured for different gantry angles

18 MR-Commissioning: SNR and Uniformity SNR analysis as defined in NEMA MS : Noise-Image without excitation SNR = 0.66 ROI signal mean ROI Noise SD Uniformity Uniformity % =100 1 (ROI Signal max ROI Signal min ) (ROI Signal max +ROI Signal min ) SNR of single coil elements: 2x6 per Coil-pair

19 Spatial Integrity Viewray 2D Spatial Integrity Phantom, placed TRA/COR and SAG plus lateral shifts of ±7cm and ±12.5cm Specification: < 1mm over 20cm DSV < 2mm over 35cm DSV Analysis: software tool percentage of points passing

20 ACR phantom test: software for automated analysis

21 Commissioning: RT part Equipment needs to be MR-safe (not ferromagnetic / no artifacts) MR compatible ionization chambers detector arrays: Sun Nuclear: IC-Profiler MR, ArcCheck MR PTW: Octavius 1500 MR, StarCheck maxi MR Scandidos: prototype Delta4 MR manual water tanks: no motorized 3D-tanks commercially available automated rotation devices do not work Effects on dose response due to magnetic field??

22 B-field effects on measuring equipment Ionization chambers diodes ionization chamber arrays film OSLD TLD Alanine Water calorimeters Thijs Perik, Master-Thesis U of Heidelberg, 2017

23 Reference Dosimetry Absolute dose calibration Use real water and prevent air gaps Adequately sized ionization chamber, for example 0.125ccm, (k Q,B ±0.003) Always parallel to B 0 Reference condition for the MRIdian: 90cm SAD, 1.6cm depth Field size 10 x 9.96 cm² Measurement per calibration protocol (AAPM TG-51, IAEA TRS 398, DIN )

24 B-field effects on measuring equipment without B-field Example: Air cavity similar to an array of airfilled Ionization Chambers with B-field

25 Tests covered in FTP and ATP MR & RT Isocenter, Laser alignment Gantry rotation Isocentricity Output consistency with Gantry Angle Dose/MU linearity Uniformity of radiation field with Gantry Rotation MLC transmission (spec: av. < 0.375%, max. < 1%) Linac head leakage (spec: < 0.2% at 1m distance) MLC accuracy (spec: < 1mm) Couch attenuation Monte Carlo Beam Model validation IMRT delivery verification Gating tests...

26 Profile comparison Elekta Synergy 6MV FFF (blue) vs Viewray MRIdian Linac (red)

27 New Phantoms needed Viewray QA Phantom Filled with water for MR signal Can be used for several tests, holds film as well as different ionization chambers check for imaging isocenter, output consistency, couch (re)positioning, coil tests, MRI spot checks

28 Vielen Dank an: DFG Alle beteiligten Heidelberger Teams!