pet only.txt

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  1. What is Positron emission tomography (PET)?
    • • PET creates “functional” images of blood flow or metabolic processes
    • • Tumours have higher than normal metabolic rates, therefore increased uptake of FDG
    • • FDG – 2-fluoro-2-deoxy-D-glucose usually tagged with 18F
    • • Measures important body functions such as blood flow, oxygren use and sugar (glucose) metabolism to help evaluate how well organs and tissues are functioning
    • • Helps to accurately diagnose the extent of the disease
  2. How is PET used in Nasopharynx Ca patients?
    • • Very useful in NPC for detecting local and regional disease as well as distant mets, can be considered for initial evaluation and staging especially in N3 patients
    • • Must be fused with a CT study set if used for planning purposes
    • • Use of PET combined with CT & MRI information in the planning process can lead to a change in disease staging in NPC patients and often this may change the treatment volume
    • • Evaluation of response early during treatment using PET will give the possibility to adapt radiotherapy to the PET findings.
    • • Note – FDG-PET/CT is not absolutely specific to tumours and false positive findings can occur in inflammatory states.
    • Pet may have a role in the treatment planning of:
    • - Brain - H&N - Lung -Oesophagus -Pelvis
  3. Advantages of PET-CT in 3D tmt planning
    • 1) Anatomical and functional information
    • • Improved visualisation of tumour volumes
    • • Improved tumour volume delineation
    • • Conformal radiation therapy & intensity – modulated radiation therapy require precise target volumes.
    • • PET-CT inter-observer variability is minimised
    • • Provides standardised tmt
    • Significant alteration in target volume has been found by incorporating PET information into treatment planning:
    • Volume found to decrease:
    • > Benign tissue exclusion
    • > Reduces dose to dose limiting structures
    • > Opportunity for dose escalation
    • Volume found to increase:
    • > Improved tumour volume definition
    • > Improved tumour coverage
    • > Improved tumour control
    • 2) Treatment Intent:
    • PET can identify:
    • • Metastatic sites in lymph nodes
    • • Distant metastases
    • • Sites of occult tumour
    • • Therefore, potentially change treatment intent from radical? palliative
    • • Biological aspect of the disease, which is not detected by CT, plays an important role in 3D treatment planning.
    • • 30% unexpected distant metastasis detected by FDG-PET
    • • 5% unknown 2nd malignancies diagnosed
    • 3) Evaluation of treatment outcome
    • • PET-CT may also play a role in the role in the response of the tumour to different treatment modalities, both during and after treatment.
    • • Especially evaluation of response early during treatment will give the possibility to adapt radiotherapy to the PET findings.
  4. Limitations of PET in 3D tmt planning
    • > FDG-PET/CT is not absolutely specific for tumour, and false positive findings can occur in inflammatory states.
    • > False negative findings
    • > Cost
    • > Exact tumour borders are not well defined
    • > Scanning protocols and SUV levels are not standardised
    • > SUV influenced by may factors; reconstruction algorithm, kind of PET scanner used, resolution, noise and biological factors.
    • > Subclinical disease not adequately detected
    • > Relative low spatial resolution of 6-7mm
    • > Organ & tumour movements influence PET findings
    • > In the thoracic region respiratory motion causes image artefacts.
    • > Artefacts also seen in bowel & bladder
    • > CT data acquired more rapidly, therefore, may lead to fusion problems
    • ? CT represents “snapshot” breathing position
    • ? PET scan data acquired in a mean respiratory position
  5. Does PET improve the outcome for RT patients? Potentially by:
    • - Dose escalation
    • - Improved tumour volume delineation
    • - Improved tumour coverage
    • - The use of IMRT
    • - Knowledge on biological characteristics of the tumour
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pet only.txt
2014-05-27 13:27:45

PET information in detail
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