In-room Radiotherapy Imaging Equipment Flashcards
What is MV x-ray portal imaging?
- Source: Treatment beam.
- Detector: Electronic Portal Imaging Device.
- Image acquisition: Single or pair of 2D planar images or continuous imaging during treatment.
What is MV x-ray portal imaging?
- Source: Treatment beam.
- Detector: Electronic Portal Imaging Device.
- Image acquisition: Single or pair of 2D planar images or continuous imaging during treatment.
- These images are compared against planning CT data to ensure correct patient positioning.
How does the electronic portal imaging device (EPID) detector work?
- Cu conversion layer attenuates MV beam producing secondary electrons. This increases detection efficiency due t the high energy of the incident photons. Note that this process will affect spatial resolution, as will scintillation layer thickness.
- A subsequent scintillation layer will convert these secondary electrons to photons.
- An array of photodiodes then converts these photons to to charge for an image to be formed.
What are some advantages and disadvantages of MV portal imaging?
Advantages:
- Simple geometry with use of treatment beam.
- Continuous imaging can give reassurance target remains within treatment beam.
Disadvantages:
- Contrast is low due to the high energy of the beams.
- Scatter can affect image quality.
What is MV cone beam CT?
- CBCT acquisition using the same equipment as for MV portal imaging.
- This allows for direct comparison with planning CT
- Still low contrast just to beam energy.
- The cone beam means increased scatter.
- The cone beam means some areas of the patient that are irradiated will not correspond to full image reconstruction.
What is helical tomotherapy MVCT?
- Modified tomotherapy treatment beam for imaging.
- Detector is the same as for CT.
- A helical acquisition is acquired and this can be compared to CT planning reference data.
What are some advantages and disadvantages of helical tomotherapy MVCT?
Avantages:
- 3D imaging.
- Lower MV, therefore, better contrast than MV CBCT.
- Fan beam, therefore, less scattered induced noise than MV CBCT.
Disadvantages:
- Detector not designed for MV.
- Higher dose and reduced contrast when compared to kV imaging.
How does linac kV imaging work?
- Imaging beam is a modified treatment beam or a separate kV tube.
- Detector: Flat panel CsI based detector.
- A range of image acquisition techniques: Single or orthogonal, fluoroscopic, CBCT.
What are some advantages/disadvantages or linac kV imaging?
Advantages:
- 3D information.
- Good contrast.
Disadvantages:
- Take longer to acquire.
- Two different isocentres for imaging and treatment.
What is kVCT imaging? What are the advantages/disadvantages?
- Conventional CT scanner attached to treatment unit.
Advantages:
- Diagnostic quality image.
- Direct comparison with planning CT.
- Soft tissue matching possible.
Disadvantages:
- Couch moves between imaging and treatment.
- Imaging and treatment isocentres different.
- Time and space considerations.
What is external kV imaging?
- kV tubes recessed in floor either side of gantry.
- Flat panels suspended from ceiling opposite.
- Image acquisition: Orthogonal image pair at unconventional angles.
What are the advantages/disadvantages of external kV imaging?
Advantages:
- Fixed geometry independent of linac.
- Quick acquisition.
- Can monitor during treatment.
- Imaging at different couch angles possible.
Disadvantages:
- External system can present problems,
- Unconventional views.
What non-ionising techniques can be used for in-room imaging?
- Surface scanning via projection of speckle pattern onto patient.
- Ultrasound with infrared markers and mechanical tracking arm.
- MRI (early stages of development and implementation).
