what is nuclear medicine and pet?

Todd Charge Senior Nuclear Medicine Technologist

Hunter Health Imaging Service

What is Nuclear Medicine?

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What is Nuclear Medicine

• Branch of medicine that uses unsealed radioactive substances in diagnosis and therapy

• These substances consist of pharmaceuticals labelled with radioisotopes - “radiopharmaceuticals”

• In diagnosis, radioactive substances are administered to patients and the radiation emitted is measured and location recorded

• In therapy, radioisotopes are administered to treat disease

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Administration of Radioactivity • The routes of administration for radiopharmaceuticals

include:

• Intravenous injection: The radiopharmaceutical is injected into a vein

• Subcutaneous injection: The radiopharmaceutical is injected under the skin.

• Inhalation: Some radiopharmaceuticals and radioisotopes are inhaled by the patient

• Ingestion: Radiopharmaceuticals can be ingested

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Diagnostic Nuclear Medicine

• In diagnostic nuclear medicine, a radiopharmaceutical is chosen that is known to follow a particular desired metabolic pathway

• After comparing the observed biodistribution with that expected for a healthy person, a diagnosis is made

• Exploits the way that the body handles substances differently when there is disease or pathology present

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Therapeutic Nuclear Medicine

• Nuclear Medicine therapy agents are usually based on beta-emitting radioisotopes although not always

• Beta particles have a much shorter range in tissue than do gamma rays so the radiation dose associated with therapeutic radiopharmaceuticals is limited to the treatment site

• Exploits the way that the body handles substances differently when there is disease or pathology present

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Production of Radioactivity

• Radioisotopes for use in nuclear medicine are derived from fission processes in reactors or cyclotrons

• The most commonly used liquid radioisotopes are: technetium-99m

iodine-123 and 131

thallium-201

gallium-67

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Production of Radiopharmaceuticals

• In larger departments production is done in-house in what is know as a “hot lab”

• For smaller departments specialist outside companies can provide individual patient doses delivered to your department

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Imaging

• The radiation emitted from the radionuclide inside the body is detected using a gamma camera

• Gamma-cameras consist of a large sodium-iodide scintillation crystal, coupled with an array of associated electronics

• Resolution of approx. 4 to 6 mm and can capture several hundred thousand gamma-ray 'events' per second

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Imaging

• The gamma-camera will detect the X and Y position of each gamma-ray event, and these coordinates will be used to build an image

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Imaging

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Imaging

• Fundamentally different from radiology, magnetic resonance imaging and ultrasound

• These modalities are capable of producing excellent images of internal structural anatomy

• Nuclear medicine images display details of organ function in terms of the uptake and clearance of radiopharmaceuticals

• Research is directed towards the development of new radiopharmaceuticals that follow unexplored metabolic pathways

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Imaging

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Imaging

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Imaging

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Radiation Safety

• Fundamental difference in the source of radiation exposure

• In Radiology the source of radiation exposure is the imaging equipment eg x-ray tube, CT

• In Nuclear Medicine the source of exposure is the radiopharmaceutical and after administration, the patient

• A gamma-camera does not produce any radiation

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Radiation Safety - Patients

• A patient undergoing a nuclear medicine procedure will receive a radiation dose

• Doses are adjusted by weight for children

• Some studies are performed on pregnant women

• Doses calculated to give just enough for imaging

• Estimated that every person in Australia will have at least one Nuclear Medicine procedure in their lifetime

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Radiation Safety - Patients Study Activity Effective Dose Bone scan 800MBq HDP 4.6mSv Lung scan 200MBq MAA 2.2mSv

Renal scan 200MBq MAG3 1.4mSv Myocardial perfusion scan

300 / 1000MBq of MIBI 10.6mSv

Gallium scan 200MBq of Ga 20.0mSv

CXR 0.04mSv Abdo XRay 1.2mSv Lumbar Spine 2.1mSv CT chest 7.8mSv Barium enema 8.7mSv

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Radiation Safety - Patients

• Natural background radiation in the Sydney area

• 1.4 – 2.5 mSv/y

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Radiation Safety - Staff

• Three principles Time Distance Shielding

• Staff still work whilst pregnant, right up to time of choosing. Recommend pelvic shielding

• No infertility to staff

• All staff monitored monthly

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PET

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What is PET

• Positron Emission Tomography (PET) is rapidly becoming a major diagnostic imaging modality

• Used predominantly in determining

presence and severity of cancers

neurological conditions

cardiovascular disease

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What is PET

• PET camera measures the biodistribution of positron emitting radionuclides after injection into the patient

• Positron emitting radionuclides are used for their unique simultaneous emission of back to back gamma rays

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What is PET

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What is PET

• Is currently the most effective way to check for cancer recurrences

• Studies demonstrate that PET offers significant advantages over other forms of imaging such as CT or MRI scans in diagnosing disease

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PET

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PET Radiopharmaceuticals

• Most widely used is F-18 (Fluorine)

• F-18 is labelled to a glucose analog (DeoxyGlucose)

• Forming FDG

• Follows glucose pathway from plasma into cells

• Unlike glucose, FDG is not metabolised and is trapped in cells allowing imaging

• Half-Life 109mins

• Produced in cyclotron

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Biodistribution

• Every cell in the body uses glucose

• After IV injection patients rest for 40-50mins to allow organ uptake of FDG and clearance from blood plasma into cells

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Biodistribution

• Any metabolically active muscles will show increased uptake

• Many malignant tumours accumulate FDG due to glycolysis and cell proliferation rate

• Benign tumours usually uptake less FDG so can be potentially distinguished from malignant tumours

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Use • Cancers for which PET is considered particularly

effective include Lung Head and Neck Colorectal Oesophageal Lymphoma Melanoma Breast Thyroid Cervical Pancreatic Brain

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Use

• PET is effective in identifying

whether cancer is present or not

if it has spread

if it is responding to treatment

if a person is cancer free after treatment

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Use

• Early Detection:

Because PET images biochemical activity, it can accurately characterise a tumour as benign or malignant, thereby avoiding surgical biopsy when the PET scan is negative. Conversely, because a PET scan images the entire body, confirmation of other metastasis can alter treatment plans in certain cases from surgical intervention to chemotherapy.

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Use

• Staging of Cancer: PET is extremely sensitive in determining the full

extent of disease, especially in lymphoma, malignant melanoma, breast, lung, colon and cervical cancers. Confirmation of metastatic disease allows the physician and patient to more accurately decide how to proceed with the patient's management

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Use

• Assessing the Effectiveness of Chemotherapy:

The level of tumour metabolism is compared on PET scans taken before and after a chemotherapy cycle. A successful response seen on a PET scan frequently precedes alterations in anatomy and would therefore be an earlier indicator of tumour response than that seen with other diagnostic modalities

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Use

• Checking for recurrences: PET is currently considered to be the most accurate diagnostic procedure to differentiate tumour recurrences from radiation necrosis or post-surgical changes. Such an approach allows for the development of a more rational treatment plan for the patient.