VIII.0 VIII.0 Medical Exposures in Medical Exposures in

Nuclear Medicine.Nuclear Medicine.

1. Overview1. Overview

Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources

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WHAT IS NUCLEAR MEDICINE?WHAT IS NUCLEAR MEDICINE?

Clinical problem

Radiopharmaceutical Instrumentation

Diagnosis and therapy withunsealed sources

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• Most radiopharmaceuticals used in nuclear Most radiopharmaceuticals used in nuclear medicine procedures can be detected externally medicine procedures can be detected externally using special detectors. e.g. gamma cameras, PET using special detectors. e.g. gamma cameras, PET scanners.scanners.

What is nuclear medicine (cont)?

• Cameras work in conjunction with computers to form images that provide data and information about the organ or area of body being imaged.

• The radiation dose received from a diagnostic nuclear medicine procedure is comparable to that received from some diagnostic x-ray examinations.

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•There are nearly 100 different nuclear medicine There are nearly 100 different nuclear medicine imaging procedures in use today, including:-. imaging procedures in use today, including:-.

• diagnosis and treatment of hyperthyroidism;

• cardiac stress tests to analyze heart function;

• bone scans for metastatic growths;

• lung scans for blood clots;

• kidney, liver and gall bladder procedures to diagnose abnormal function or blockages.

What is nuclear medicine (cont)?

Some examples will be presented below

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For diagnostic procedures, the objective is For diagnostic procedures, the objective is to:-to:-

Objectives of Nuclear Medicine

• obtain clinical data regarding the distribution of radiopharmaceuticals that reflect a combination of blood flow, capillary permeability and tissue extraction, and

• record images of the activity distribution to determine organ function (e.g., determine cerebral blood flow, ventricular function, thyroid uptake).

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Diagnostic Nuclear MedicineDiagnostic Nuclear Medicine

Preparation of Preparation of radiopharmaceutical radiopharmaceutical AdministrationAdministration ExaminationExamination Evaluation and Evaluation and reporting reporting

Request of examinationRequest of examination Prescribed activityPrescribed activity

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•The prescribed activity of a The prescribed activity of a radiopharmaceutical is that activity radiopharmaceutical is that activity documented in a written directive or in the documented in a written directive or in the diagnostic clinical procedures manual, in diagnostic clinical procedures manual, in accordance with the direction of the accordance with the direction of the authorized user.authorized user.

Prescribed activity

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• administer a prescribed absorbed dose to administer a prescribed absorbed dose to the target tissue to obtain the desired the target tissue to obtain the desired effect (e.g. reduce tumor size).effect (e.g. reduce tumor size).

•For therapeutic procedures, the objective is to:-For therapeutic procedures, the objective is to:-

Objectives of Nuclear Medicine

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Nuclear Medicine TherapyNuclear Medicine Therapy

Prepare radiopharmaceuticalPrepare radiopharmaceutical and activity and activity

Determine biokinetic data Determine biokinetic data

Administer the treatmentAdminister the treatment Patient follow upPatient follow up

Request of examinationRequest of examination Prescribed absorbed dosePrescribed absorbed dose

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•The prescribed dose is that absorbed dose The prescribed dose is that absorbed dose that is aimed to give the desired therapeutic that is aimed to give the desired therapeutic effect on the irradiated organ or tissue. The effect on the irradiated organ or tissue. The absorbed dose should, for each individual absorbed dose should, for each individual patient, be prescribed by the medical patient, be prescribed by the medical practioner. practioner.

•The corresponding activity to be The corresponding activity to be administered should be calculated for each administered should be calculated for each patient and be based on known or estimated patient and be based on known or estimated biokinetic data.biokinetic data.

Prescribed dose

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Instrumentation in nuclear medicine

• Activity meter• Sample counters• Single- and multi-probe systems• Gammacamera• Positron camera (PET)

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• The instrument measures The instrument measures the quantity of radioactive the quantity of radioactive material in the prepared material in the prepared radiopharmaceutical prior radiopharmaceutical prior to administration to the to administration to the patient.patient.

Activity meterActivity meter (dose calibrator)dose calibrator)

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• a cylindrically shaped, gas filled a cylindrically shaped, gas filled sealed chamber with a well;sealed chamber with a well;

• The instrument comprisesThe instrument comprises::

• high voltage supply applied to electrodes;

• specific energy settings for different radionuclides;

• an activity readout (e.g. in MBq, GBq, etc).

Activity meterActivity meter (dose calibrator)dose calibrator)

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• mainly to count blood mainly to count blood and urine samples.and urine samples.

• to count wipe test to count wipe test samples to identify if samples to identify if radioactive radioactive contamination exists in contamination exists in the area surveyed.the area surveyed.

Sample countersSample counters

•Scintillation Well Counters are used:-Scintillation Well Counters are used:-

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•Scintillation detector mainly used for counting Scintillation detector mainly used for counting during thyroid uptake studies.during thyroid uptake studies.

Probe systemProbe system

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Gamma cameraGamma cameraGamma cameraGamma camera

Used to measure the spatial and temporal distribution of a radiopharmaceutical

Siemens

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Gamma cameraGamma camera((principle of operation)principle of operation)

PM-tubes

Position XPosition Y

Detector

Collimator

Scintillation

PHAEnergy Z

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Gamma cameraGamma camera(static aquisition)(static aquisition)

Collect a certain numberof events to build up the image

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Gamma cameraGamma camera(dynamic acquisition)(dynamic acquisition)

Collect events at a certain frame rate

•Define region of interest

•Generate time- activity curve

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Gamma cameraGamma camera(tomographic acquisition) (tomographic acquisition) (SPECT)(SPECT)

•Collect events at different angles•Reconstruct data•Present the result as transversal, coronal, sagittal or oblique slices

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• Processes studied include Processes studied include blood flow, oxygen, blood flow, oxygen, glucose and fatty acid glucose and fatty acid metabolism, amino acid metabolism, amino acid transport, pH and transport, pH and neuroreceptor densities.neuroreceptor densities.

Positron Emission Tomography (PET) is used to study physiologic and biochemical processes within the body

PET - ScanningPET - Scanning

• An on-site cyclotron is required to produce the very short half life PET radiopharmaceuticals.

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PET-scannerPET-scannerprincipleprinciplePET-scannerPET-scannerprincipleprinciple

Detector Detector

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PET-SCANNERPET-SCANNERPET-SCANNERPET-SCANNER

M Dahlbom, UCLA

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RadionuclidesRadionuclides

Radionuclide Halflife Particle energyRadionuclide Halflife Particle energy (mean)(mean)

C-11C-11 20.4 min20.4 min 0.39 MeV0.39 MeVN-13N-13 10 min10 min 0.50 MeV0.50 MeVO-15O-15 2.2 min2.2 min 0.72 MeV0.72 MeVF-18F-18 110 min110 min 0.25 MeV0.25 MeVCu-62Cu-62 9.2 min9.2 min 1.3 MeV1.3 MeVGa-68Ga-68 68.3 min68.3 min 0.83 MeV0.83 MeVRb-82Rb-82 1.25 min1.25 min 1.5 MeV1.5 MeV

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PET in oncologyPET in oncologyPET in oncologyPET in oncology

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BONE SCANBONE SCAN

Normal Pathologic

• Bone uptake of Tc99m MDP reflects bone metabolism and blood flow, and allows functional analysis of bone turnover

• Intravenous injection of 400-600 MBq

Tc99m MDP . Whole body scanning 3h after injection

• The ability to image bone metabolism alterations enables detection of lesions such as

Bone metastasisBenign or malignant bone tumorsBone trauma

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LUNG SCAN

An embolization of the pulmonary capillary bed yields an image reflecting the lung blood perfusion (Tc99m MAA).Ventilation studies (Tc99m -aerosols) reflect the regional and segmental ventilation.Diagnosis of pulmonary emboli.Intravenous injection (perfusion) of 100 MBq Tc99m MAA. Inhalation of 100MBq Tc99m aerosol (ventilation). Immediate scanning.

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Kidney functionKidney function

Dynamic renal scintigraphy reflects renal blood perfusion, uptake and excretion. The acquisition yields a series of images. By calculating count rate in a defined ROI, a renogram is created, providing quantitative data. Different radiopharmaceuticals, such as Tc99m-MAG3, Tc99m-DTPA and I123-Hippuran, are used for renal clearance and function assessment. Administered activity 100-200 MBq.

ROI:s (region of interest) Renogram

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Myocardial perfusionMyocardial perfusion Accumulation of Tl201, Tc99m MIBI or Tetrofosmin in the myocard depends on blood flow

and cellular metabolism, hence, reflects regional perfusion and viability of the cardiac muscle.

The evaluation of a patient suspected or known for C.A.D. is based on image interpretation or quantitative analysis from reconstructed tomographic slices, which also yields regional perfusion information.

The examination is performed under maximum stress condition and after rest. Injected activity 1000 MBq Tc99m or 100 MBq Tl201. Tomographic study.

Stress Rest

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ECG-gated myocardial ECG-gated myocardial perfusionperfusion

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Nuclear imaging detects functional properties of the human tissue. Anatomical information is found with conventional X-rays, CT or MR

Nuclear medicine imagesNuclear medicine images

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CURRENT METHODS-THERAPY

Radiopharmaceutical For treatment of Route of Maximum administration activity

I-131 iodide Thyrotoxicosis Oral 1 GBqI-131 iodide Carcinoma of thyroid Oral 20 GBqI-131 MIBG Malignancy IV 10 GBqP-32 phosphate Polycythaemia vera IV or oral 200 MBqSr-89 chloride Bone metastases IV 150 MBqY-90 colloid Arthritic conditions Intra-articular 250 MBq

malignant effusions Intra-cavitary 5 GBqEr-169 colloid Arthritic conditions Intra-articular 50 MBqRe-186 colloid Arthritic conditions Intra-articular 150 MBqSm-153 EDTMP Bone metastases IV 5 GBq

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I-131 therapy

The absorbed dose to be delivered should be determinedfrom uptake measurements, effective half-life of the radio-pharmaceutical and the size of the thyroid.

The radiopharmaceutical is administered p.o.

Hyperthyroidism

Cured after Hypothyroidism3-4 months 1 year after <7 years after >7 years 85% 98% 14.8% 27.9%

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RadiosynovectomyRadiosynovectomy

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PAIN PALLIATIONPAIN PALLIATION

Intravenous injection ofa radiopharmaceutical whichincludes e.g. Sr-89 or Sm-153

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No! Nuclear medicine is an efficient diagnostic and therapeutic tool and is justified from a medical point of view.Do we need radiation protection then?

No! Nuclear medicine is an efficient diagnostic and therapeutic tool and is justified from a medical point of view.Do we need radiation protection then?

Nuclear medicine - unclear medicine?