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Treatment verification systems in radiation therapy


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Treatment verification systems in radiation therapy

  2. 2. All radiotherapy involves risk because even a small error in treatment planning , delivery or dosimetry can lead to negative consequences. This is because human body is a complex organism and tumors are often located close proximity to the normal tissue and critical organs. So ensuring that the right radiation dose has been given to the right place.
  3. 3. set-up difficulties soft tissue deformation tumor growth/shrinkage irregular respiration spontaneous motion
  5. 5.  EPID = Electronic portal imaging device  Daily imaging for treatment localization and verification may become feasible  Acquisition, analysis, storage and distribution of portal images can be performed with relative ease  Mount on the linear accelerator
  6. 6.  Electronic portal imaging devices-EPID can used for daily imaging for treatment localization and verification.  The portal image can be analyzed with computer software and before the treatment, no significant additional dose is required for patient.  The image can be saved in DICOM file format and it can be reviewed at any time.
  7. 7.  The first EPID system was video based.  The beam transmitted through the patient excite a metal fluorescent screen.  A front-silvered mirror , placed diagonally, reflects the fluorescent light by 90 degree into the video camera.  The analog output of the video camera is converted into a digital array with a ADC known as “ frame grabber ”.  The special resolution depends on phosphor thickness.
  8. 8.  Another kind of EPID has a matrix ionization chamber system that consist of 256*256 liquid ionization chamber(scanning liquid ionization chamber-SLIC).
  9. 9. Fluoroscopy based system (Video based) Matrix ionization chamber based system Amorphous silicon based system
  10. 10. Detector : Amorphous silicon flat panel imager Active imaging area : 40 x 30 cm2 Resolution : 1024 x 768 pixels Spatial resolution : 0.391 mm Max frame acquisition rate : 9.574 frames/second Energy range : 4 - 25 MV Dose rate range : 50 - 600 MU/min SPECIFICATIONS:
  11. 11.  Within this unit a scintillator converts the radiation into visible light  The light is detected by an array of photodiodes implanted on an amorphous silicon panel  The photodiodes integrate the light into charge captures  Resolution and contrast greater than other system
  12. 12. EPID
  13. 13.  CBCT is an imaging modality that provide high imaging quality .  It has ability to provide submillimeter resolution in terms of images.
  14. 14.  Its called 3D cone beam imaging . It is fast , simple and completely painless.  3D cone beam imaging system is basically a digital x ray scanner mounted on a rotating arm . Like a digital camera. Its called “CONE BEAM”.  Because the scanner projects x rays in a carefully controlled ,cone shaped beam.
  15. 15.  In CBCT planar projection images are obtained from multiple directions as the source with the opposing detector panel rotates around the patient through 180 degree or more .  These multidirectional images provide sufficient information to reconstruct patient anatomy in three dimensions , including cross- sectional , sagittal and coronal planes.
  16. 16.  Conventional CT scanner has circular ring of detectors , rotating opposite to X-ray tube . However , it is possible to perform CT scans with detectors embedded in a flat panel instead of circular ring . CT scanning that uses this type of geometry is known as CBCT.
  17. 17. CBCT system can be implemented either by using  kilovoltage x ray source or  The megavoltage therapeutic source
  18. 18.  KILOVOLTAGE x rays for a KVCBCT system are generated by a conventional x ray tube that is mounted on a retractable arm at 90 degree to the therapy beam direction .  A flat panel of x ray detectors is mounted opposite to the x ray tube.
  19. 19. Its an ability to produce volumetric CT images with good contrast and submillimeter spatial resolution. Acquire images in therapy room coordinates Use 2-D radiographic and fluoroscopic modes to verify portal accuracy , management of patient motion and making positional and dosimetric adjustments before and during treatment.
  20. 20.  Megavoltage cone beam (MVCBCT) uses the megavoltage x ray beam of the linear accelerator and its EPID opposite to the source .  EPIDs with a- Si flat panel detectors are sensitive enough to allow rapid acquisition of multiple , low dose images as the gantry is rotated through 180 degrees or more . From these multidirectional 2D images , volumetric CT images are constructed.
  21. 21. MVCBCT system has a good image quality for the bony anatomy . MVCBCT is a great tool for on-line or pretreatment CT, avoidance of critical structures such as spinal cord, and identification of implanted metal markers if used for patient setup.
  22. 22.  Less susceptibility to artifacts due to high objects such as metallic markers in the target , metallic hip implants , and dental fillings.  No need for extrapolating attenuation coefficients from KV to megavoltage photon energies for dosimetric corrections.
  23. 23.  Portal dosimetry using EPID for IMRT plans can be performed in less time compared to other existing tools.  High density data points and direct to digital data capture makes it easier to evaluate complex IMRT fields.  CBCT has high ability to provide submillimeter resolution in terms of images.  In radiation therapy treatment verification is an important process . And at that time make sure that right amount of radiation will given to the right place.