• Most investigations deliver an ED of 1 mSv or less → no greater than the variation, from place to place and individual to individual, in the annual dose of natural radiation. • Some, such as bone or static brain imaging, deliver doses in the region of 5 mSv. • Few examinations, such as tumor or abscess imaging with 67Ga, deliver higher
doses → undertaken only when other imaging modalities are inappropriate (Table 5.2). Table 5.2 Typical activities and doses
Site Agent Activity (MBq) Effective dose (mSv) Bone Lung ventilation Lung perfusion Kidney Tumor 99mTc phosphonate 99mT DTPA aerosol 81mKr gas 99mT HA Macroaggregates 99mT DTPA gluconate 99mT MAG3 67GaGa3+ 600 80 6000 100 80 100 150 5 0.6 0.1 1 1 1 18
In order to minimize patient dose, patients should drink a good deal of water and empty the bladder frequently to reduce the dose to the gonads and pelvic bone marrow.
The activity of each administration of radiopharmaceutical is kept within the limits set by the Administration of Radioactive Substances Advisory Committee (ARSAC) of the UK Department of Health (Section 6.6), and checked & recorded before administration. The phial is placed in the "well' of a large re-entrant ionization chamber, know as:
The radionuclide or dose calibrator
8 The ionization current produced by the gamma rays is: 9 Proportional to the activity of the sample.
9 Depends on the gamma energy and half-life of the radionuclide.
8 The radionuclide is entered on the control panel and the activity in MBq is displayed on a digital read-out.
The accuracy of the radionuclide calibrator must be checked regularly using a reasonably long-lived source, such as 57Co.
The calibrator can also be used with a lead sleeve to check for the higher-energy gamma rays from molybdenum impurity.
5.7 PRECAUTIONS TAKEN IN THE HANDLING OF RADIONUCLIDES When handling radionuclides, in addition to the hazard from external radiation there is also a potential hazard from internal radiation due to accidental ingestion or inhalation of the radionuclide or its entry through wounds.
Generally, the risk from contamination is greater than that from external radiation. It is therefore important to avoid contamination of the environment, the workplace, and persons, and to control any spread of radioactive materials.
Segregation
• A nuclear medicine facility must have separate areas for: (a) Preparation and storage of radioactive materials. (b) Injection of patients.
(c) Patients to wait. (d) Imaging.
(e) Temporary storage of radioactive waste.
• Patients containing radioactivity are a source of external radiation → should be spaced apart in the waiting area.
• Departmental layout should make use of the "inverse square law" to reduce the effect of background radiation from other patients and sources, particularly in the imaging areas. Personal protection
• Use should be made of distance, shielding, and time.
• Staff should only enter areas where there is radioactivity when it is strictly necessary; all procedures must be carried out expeditiously and efficiently.
• Departmental local rules must be followed. • Some general guidance follows.
1. Radionuclides are contained in shielded generators or in bottles in lead pots.
2. Where feasible, bottles and syringes are handled with long-handled forceps (tongs).
3. Manipulations, such as the labeling of pharmaceuticals and the loading of syringes, are carried out with the arms behind a lead barrier which protects the body and face, and over a tray, lined with absorbent paper, to catch any drips.
4. Syringes are protected by heavy metal or lead glass sleeves (which can reduce radiation doses by 75%) → & transported in special containers or on a kidney dish.
5. Before injection, syringes are vented into swabs or closed containers and not into the atmosphere.
6. Lead-rubber aprons are ineffective against the high-energy gamma rays of 99mTc.
7. To avoid accidental ingestion → waterproof (double-latex) surgical gloves are worn when handing radionuclides.
Cuts and abrasions must be covered first.
8. There must be no eating, drinking, or facial contact.
9. Hands and work surfaces are routinely monitored for radioactive contamination. 10. The air in Radiopharmacies may also be sampled and monitored.
11. Staff will be monitored for external radiation doses to the body and possibly the hands. They may also be monitored for internal contamination.
12. Swabs are taken from the workstation to monitor for radioactive and bacterial contamination. 13. Hands should be washed regularly at special wash basins. Where necessary, and particularly after spills, decontamination may be carried out. This normally involves the use of water, mild detergents, and swabs, which are then sealed in plastic bags and disposed of as radioactive waste in marked bins.
14. Any use of a nail brush should be gentle; if contamination is obstinate, special detergent solutions may be necessary.
Patient protection
• Every radionuclide should be checked for activity before administration, using a radionuclide ('well') calibrator.
• The patient's identity must he checked against the investigation to be made and the activity to be administered, and this must be recorded.
• Particular care should be taken to avoid contamination during oral administrations. • Special circumstances apply for pregnant patients and those with babies they are breast-
feeding.
Dealing with a radioactive spill
In the case of a radioactive spill, vomiting, incontinence, etc.: 1. Clear the area of non-essential persons.
2. Wearing gloves, aprons, and overshoes.
3. Mop the floor with absorbent pads and seal the swabs in designated plastic bags. If necessary, continue with wet swabs.
4. Continue until monitoring shows the activity to be at a satisfactorily low level.
5. If necessary, cordon off the area or cover it with impervious sheeting until sufficient decay has occurred.
6. Contaminated materials are treated as waste. Disposal of radioactive waste:
These follow the two principles of:
Containment and decay; and
Dilution by dispersal to the environment.
• Special rules and authorizations cover the accumulation, storage, and disposal of radioactive waste.
• Every hospital is subject to strict limitations on the amount which can be disposed of by each of the following routes.
Gaseous waste can be vented to the atmosphere:
In lung ventilation studies, 133Xe and 99mTc aerosols should be exhausted to the exterior of the building; this is not necessary with the very short-lived 81mKr.
Aqueous liquid waste → well diluted with water → disposed of via designated sinks or sluices with drains running direct to the foul drain.
Solid waste (swabs, syringes, bottles, etc.) → placed in designated sacks for disposal by incineration or, if suitably diluted with ordinary waste, to waste disposal sites.
Old generators are kept in a secure shielded store until they are returned to the manufacturer.
Contaminated clothing and bedding is appropriately bagged and stored in a secure protected area until sufficiently decayed for release to the laundry.
• Records must be kept, for inspection, of all deliveries, stocks, administration, stored waste, and disposals of waste.