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• Radiotherapy – disease treatment using ionizing radiation. Goal is maximum dose, minimal exposure and damage to healthy tissue.

  Destruction – direct/indirect. Direct is using ionizing radiation which damages DNA. Indirect is ionizing water molecules. Forms radicals. Causes damage.

  Cure – malignant cell selsctively destroyed as it is more sensitive to radiation. DNA targeted.
• Brachytherapy – disease treatment using radiation internally (implants)

  Implants – high dose rate (few minutes insertion) or low dose rate (few days insertion) – some are permanent.
• Brachytherapy catheters – strategic insertion into breast. During treatment radioactive material injected into catheter.
• Also used for prostate gland – seed therapy.
• Prostate brachytherapy is a low dose rate.
• ALARA – as low as reasonably achievable

  Conforming to principle – Time (minimize), distance (maximise) and shielding (maximize)
• Safety precautions –

  Patient exposure minimal

  Medical exposure justified

  Special categories made for children and pregnant women.

  Evaluate radioactive accidents.
• PET scans produce images using gamma rays that are produced by positron-electron annihilation. Helps to see drug distribution in body to analyse biological processes for diagnosis.
• Position annhilation:

  Beta plus decay/pair production forms positrons. Annihilation from positron and electron interaction leads to gamma ray production. Rays travel in opposite directions from each other.
• PET scans detect the gamma rays. Using the line of coincidence we can pinpoint gamma source.

  Newer systems allow more accurately gamma source detection.
• Detectors – in PET scans, patient surrounded by ring of small scintillator detectors. Detector attached to its own PMT and is synchronized with the opposite detector. Have 45 rings of gamma ray detectors. NaI has low detection efficiency.
• PET reconstruction software analyses coincident events and forms image using this data to understand drug distribution.
•  PET scans use short lived radioactive tracer. This decays by positron emmision. These are incorporated into metabolically active molecules. Once injected, waiting time is an hour. Material is concentrated in area of interest. Patient put under scanner.
• PET scan radionuclides have very short half lives. Require them to be made on site using cyclotron. These are very expensive.

  Radiotracers are made when isotopes are combined with actively used molecules. These are then injected into body.
• PET scanners – provide information on molecular biology and metabolism.

  New PET scanner have CT to give anatomically information.
• In order to determine the post treatment efficacy, PET scans are very effective.
• PET – ionzing radiation. Shielding present. Slow. Expensive. Produced 3D image. Radioactive tracer required.

  MRI – no ionzing radiation. Metal is hazard. Slow. Expensive. Produces 3D image.

  CT – ionizing radiation. Shielding present. Fast. Expensive. Produces 3D image. Metal may cause image disruption.