An approach to calculate and visualize intraoperative scattered radiation exposure

Transcription

1 Peter L. Reicertz Institut für Medizinische Informatik An approach to calculate and visualize intraoperative scattered radiation exposure Markus Wagner University of Braunschweig Institute of Technology and Hannover Medical School

2 structure purpose scattered radiation intraoperative radiograph generation the CBT system virtx methods GEANT4 simulation setup visualization of the simulation results in virtx results and discussion - 2 -

3 scattered radiation scattered or stray radiation arises every time when radiation penetrates matter a radiograph is generated is emitted in all directions by the irradiated area of the patient intensity and propagation depends on composition of the irradiated material direction of the primary beam intensity of the primary beam scatter radiation source detector absorption body transmission - 3 -

4 intraoperative radiograph generation mobile image intensifier systems (C-arms) are essential tools in treatment of trauma and emergency patients in Germany almost every orthopedic or trauma surgical operation theater (OR) is equipped with a C-arm Siemens Medical Systems - 4 -

5 intraoperative radiograph generation through their mobility C-arms are able to produce X-rays from every direction around the patient for controlling, documentation and monitoring purposes freedom in movement makes radiation shielding arrangements very difficult or sometimes impossible - 5 -

6 scattered radiation + C-arms biggest amount of exposure for ORP and surgeon through scattered radiation: lack of shielding arrangements surgeon and ORP can't leave the OR during radiograph generation knowledge about behavior of scattered radiation and hazard areas essential to minimize exposure source: An Investigation of Operator Exposure in Interventional Radiology - 6 -

7 Courses on radiation protection knowledge about behavior of scattered radiation should be presented to ORP during courses of radiation protection in Germany and other countries ORP have to visit these courses by law currently just theoretically possible with fixed images and pre-calculated videos possible improvement of the teaching procedure by using an interactive simulation and visualization of scattered radiation in a computer based training system - 7 -

8 the CBT-system virtx a computer based training system to train the correct C-arm adjustment developed at the Peter L. Reichertz Institute for Medical Informatics in cooperation with: Georg-August-University, Göttingen University of Applied Sciences and Arts, Hannover - 8 -

9 virtx offers interactive 3D OR scene movable C-arm movable patient movable OR-table visual feedback through a digitally reconstructed radiograph (DRR) simulation of bone movement in special joints - 9 -

10 virtx offers exercise based training task description traffic light indicating the correct adjustment feedback of task execution (time, virtual radiation exposure) tracking the movement of a real C-arm and patient dummy

11 virtx: first simulation of scattered radiation prototypically visualization of scattered radiation through a pulsating three colored sphere radius should indicate radiation intensity no physically correct propagation and intensity of the scattered radiation

12 simulating physically correct scattered radiation: GEANT4 GEANT4 (GEometry ANd Tracking) toolkit ( developed at CERN written in C++ uses Class Library for High Energy Physics (CLHEP) simulates the passage of particles through matter using Monte Carlo methods

13 GEANT4 features (abstract) construct detector geometries with physical characteristics shape materials electromagnetic fields define areas on geometries as sensitive detectors sensitive for impacting photon or particle protocol physical data of detected events define primary generators

14 GEANT4 and virtx integrated the GEANT4 framework into the Visual Studio 2005 project of virtx Monte Carlo simulation very computationally intensive time-consuming simulation setup has to be simple to save computation time

15 simulation setup very simple representation of C-arm and patient iron cylinder and cube water cube world volume (air) sensitive detector spheres (air) primary generator

16 simulation setup water volume: positioned corresponding to patient C-arm correlation in virtx primary generator: user defined number of photons photon energy adjustable through tube voltage in virtx randomly distributed in the area of the central beam

17 simulation setup detector spheres (DS) defined number of interleaving spheres around the center of setup material air avoid interferences each sphere sensitive detector every photon hitting surface of DS is detected with its position and energy

18 visualization in virtx visualization for different table positions (5000 photons, 9 detector spheres) each photon hit on DS surface depicted as a semitransparent color coded voxel

19 tested simulation setups measured on: Intel Core2 Quad Q6700 CPU at 2.66 GHz, 3.5 GB RAM, Nvidia GeForce 8800 GT (DS) and/or (photons) (exact image of scattered radiation) but (calculation time) to use visualization for C-arm training calculations has to be in real time at best

20 results compared to isodose curves measured during operation of a real C-arm: to photons with > 7 DS presents sufficient information to demonstrate propagation of scattered radiation for C-arm training purposes: 9DS and photons were chosen as most adequate (based on calculation times)

21 conclusion and discussion with this calculation and visualization concept integrated in virtx it's possible to demonstrate interactively: behavior of scattered radiation for discrete points in a virtual OR-scene in acceptable calculation time despite of high abstraction level (e.g. patient, small number of photons) images seem to be appropriate for intended education purpose positive questionnaire based evaluation of virtx by surgeons comparison to real isodosis curves

22 conclusion and discussion further goals and improvements: more intuitive visualization (like isodosis curves) consider different densities of the irradiated materials (different types of tissue, bones, etc.) measure photons on every point in the virtual OR and not only on the DS (voxelization of the simulation area) speed-up calculations using GPGPU methods (CUDA) prototype prototype

23 prototype voxelization

24 Thank you for your attention Questions?