June 2024
DOSIMETRY
Technetium (99mTc) is produced by means of a (99Mo/99mTc) generator and decays with the emission of gamma radiation with a mean energy of 140keV and a half-life of 6.02 hours to technetium (99Tc) which, in view of its long half-life of 2.13 x 105 years can be regarded as quasi stable
The estimated absorbed radiation doses to an average adult patient (70kg) from intravenous injections of tetrofosmin (99mTc) are listed below. The values are calculated assuming urinary bladder emptying at 3.5 hour intervals.
Frequent bladder emptying should be encouraged after dosing to minimize radiation exposure.
The table below shows the dosimetry according to ICRP Publication 128 (International Commission of Radiological Protection, Radiation Dose to Patients from Radiopharmaceuticals: A Compendium of Current Information Related to Frequently Used Substances, Ann ICRP 2015).
| | Absorbed dose per unit of activity administered (mGy/MBq) |
| Organ | Exercise | Rest |
| Adrenals | 4.40E-03 | 4.20E-03 |
| Bone surfaces Brain Breast | 6.3E-03 2.7E-03 2.20E-03 | 5.8E-03 2.3E-03 1.80E-03 |
| Gallbladder wall Gastrointestinal tract Stomach wall Small intestine wall Colon wall (Upper large intestine wall (Lower large intestine wall Kidneys Liver Lungs Muscles Oesophagus Ovaries Pancreas Red marrow Skin Spleen Testes Thymus Thyroid Urinary bladder wall Uterus Remaining organs | 2.7E-02 4.6E-03 1.1E-02 1.8E-02 2.0E-02 1.5E-02 1.0E-02 3.3E-03 3.2E-03 3.5E-03 3.3E-03 7.7E-03 5.0E-03 3.9E-03 2.2E-03 4.1E-03 3.4E-03 3.3E-03 4.7E-03 1.4E-02 7.0E-03 3.8E-03 | 3.6E-02 4.5E-03 1.5E-02 2.4E-02 2.7E-02) 2.0E-02) 1.3E-02 4.0E-03 2.8E-03 3.3E-03 2.8E-03 8.8E-03 4.9E-03 3.8E-03 2.0E-03 3.9E-03 3.1E-03 2.8E-03 5.5E-03 1.7E-02 7.8E-03 3.8E-03 |
| Effective Dose (mSv/MBq) | 6.9 E-03 | 8.0 E-03 |
99mTc-tetrofosmin is administered as two intravenous injections either rest first and stress second or stress first and rest second. The recommended activity range for the first dose is 250-400 MBq; the recommended activity range for the second dose given at least 1 hour later, is 600-800 MBq.
Myocardial Imaging
The effective dose resulting from administration of 800 MBq for an adult weighing 70 kg at rest is about 6.4 mSv. After exercise, the same administered activity results in a dose of 5.5 mSv.
For an administered activity of 800 mBq, the absorbed radiation dose for the resting subject in the heart is 3.8 mGy and after exercise is 4.2 mGy. The absorbed radiation dose in the urinary bladder wall(3.5 hour voiding) is 13.6 mGy at rest or 11.2 mGy after exercise.
Breast imaging
The effective dose resulting from the administration of 750 MBq for an adult weighing 70 kg at rest is about 6.0 mSv.
For an administered activity of 750 MBq, the absorbed radiation dose to the breast is 1.7 mGy. The absorbed radiation dose in the urinary bladder wall (3.5 hours voiding) is 12.8 mGy.
INSTRUCTIONS FOR PREPARATION OF RADIOPHARMACEUTICALS
Withdrawals should be performed under aseptic conditions. The vials must not be opened before disinfecting the stopper, the solution should be withdrawn via the stopper using a single dose syringe fitted with suitable protective shielding and a disposable sterile needle or using an authorised automated application system.
If the integrity of this vial is compromised, the product should not be used.
Method of preparation:
The following steps as detailed are critical and should be followed to ensure adequate preparation of the product.
Use aseptic technique throughout.
(1) Place the vial in a suitable shielding container and sanitize the rubber septum with the swab provided.
(2) Insert a sterile needle (the venting needle, see Note a) through the rubber septum. Using a shielded, 10 ml sterile syringe, inject the required activity of Sodium Pertechnetate (99mTc) Injection Ph.Eur. (appropriately diluted with 0.9% Sodium Chloride Injection BP) into the shielded vial (see Notes b to d). Before removing the syringe from the vial, withdraw 5 ml of gas from above the solution (see Note e). Remove the venting needle. Shake the vial to ensure complete dissolution of the powder.
(3) Incubate at room temperature for 15 minutes.
(4) During this time assay the total activity, complete the user label provided and attach it to the vial.
(5) Store the reconstituted injection below 25°C and do not freeze. Use within 12 hours of preparation. Dispose of any unused material and its container via an authorised route.
Notes:
(a) A needle of size 19G to 26G may be used.
(b) The Sodium Pertechnetate (99mTc) Injection Ph.Eur. used for reconstitution should contain less than 5ppm aluminium.
(c) The volume of diluted Sodium Pertechnetate (99mTc) Injection Ph.Eur. added to the vial must be in the range 4-8 ml.
(d) The radioactive concentration of the diluted Sodium Pertechnetate (99mTc) Injection Ph.Eur. must not exceed 1.5 GBq/ml when it is added to the vial.
(e) For preparation volumes of more than 6 ml, the remaining vial headspace is less than the 5 ml added air volume. In these cases, the withdrawal of a 5 ml volume of gas ensures that all of the vial headspace is replaced by air.
(f) The pH of the prepared injection is in the range 7.5-9.0.
Quality Control:
Radiochemical Purity (RCP) by ascending chromatography on TLC-SA (method 1).
Equipment and eluent
(1) Glass Microfiber Chromatography Paper impregnated with Silicic Acid (GMCP-SA) TLC strip (2cm x 20cm) – Do not heat activate
(2) Ascending chromatography tank and cover
(3) 65:35% v/v acetone: dichloromethane mixture (prepared fresh daily)
(4) 1ml syringe with 22-25G needle
(5) Suitable counting equipment
Method
(1) Pour the 65:35% v/v acetone:dichloromethane mixture into the chromatography tank to a depth of 1cm and cover the tank to allow the solvent vapour to equilibrate.
(2) Mark a Glass Microfiber Chromatography Paper impregnated with Silicic Acid (GMCP-SA) TLC strip with a pencil line at 3cm from the bottom and, using an ink marker pen, at 15cm from the pencil line. The pencil line indicates the origin where the sample is to be applied and movement of colour from the ink line will indicate the position of the solvent front when upward elution should be stopped.
(3) Cutting positions at 3.75cm and 12cm above the origin (Rf's 0.25 and 0.8 respectively) should also be marked in pencil.
(4) Using a 1ml syringe and needle, apply a 10μl sample of the prepared injection at the origin of the strip. Do not allow the applied sample to come into contact with the pencil mark. Do not allow the spot to dry. Place the strip in the chromatography tank immediately and replace the cover. Ensure that the strip is not adhering to the walls of the tank.
Note: A 10μl sample will produce a spot with a diameter of approximately 10mm. Different sample volumes have been shown to give unreliable radiochemical purity values.
(5) When the solvent reaches the ink line, remove the strip from the tank and allow it to dry.
(6) Cut the strip into 3 pieces at the marked cutting positions and measure the activity on each using suitable counting equipment. Try to ensure similar counting geometry for each piece and minimize equipment dead time losses.
(7) Calculate the radiochemical purity from:-

Note: Free (99mTc) pertechnetate runs to the top piece of the strip. Tetrofosmin (99mTc) runs to the centre piece of the strip. Reduced hydrolysed-99mTc and any hydrophilic complex impurities remain at the origin in the bottom piece of the strip.
Do not use material if the radiochemical purity is less than 90%
Simplified Chromatographic Procedure for Rapid Quality Control (method 2):
Equipment and eluent
(1) Solid Phase Extraction (SPE) C18 cartridge (360 mg Sorbent, 55 – 105 µm particle size), e.g. Waters Sep-Pak® or equivalent)
(2) 3 x 10ml vials and caps, Labelled “A”, “B” and C
(3) Lead pots
(4) 0.9% Sodium chloride
(5) Ethanol
(6) Dose calibrator
Method
Note: all loading steps (sample and solvents) must be performed using a slow flow rate (i.e. drop by drop application of the mobile phase). If the flow is too high, components may not interact sufficiently with the stationary phase which will give an inaccurate result for radiochemical purity.
1. Place the cartridge in the correct orientation (short end facing upwards) in a clamp stand and place behind a suitable lead shield
2. Place the vial labelled 'A' under the cartridge as a collection vial.
3. Condition the stationary phase by flushing with 2ml 0.9% Sodium Chloride collecting in vial 'A'.
4. Carefully load 25 - 50µL of the preparation onto the cartridge.
5. Elute the cartridge with 2ml 0.9% Sodium chloride, collecting the eluate in vial 'A'.
6. Cap vial 'A' and place in a shielded container. Cap and retain for measurement.
7. Place vial 'B' under the cartridge as a collection vial.
8. Elute the cartridge with 5ml ethanol, collecting the eluate in vial 'B'.
9. Cap vial 'B' and place in a shielded container. Cap and retain for measurement.
10. Remove the SPE cartridge using tweezers and place into vial 'C' and place in a shielded container. Cap and retain for measurement.
11. Measure the activity of each of the vials labelled A to C using a dose calibrator. Under the test conditions employed:
• Free 99mTc O4- (pertechnetate) is eluted from the cartridge with 2ml 0.9% Sodium Chloride (Vial A)
• 99mTc - tetrofosmin is retained on the stationary phase and is eluted with 5ml ethanol (Vial B)
• Reduced hydrolysed 99mTc (RHT) and hydrophilic impurities remain on the cartridge (Vial C)
12. Calculate the % 99mTc-tetrofosmin as follows:

13. Do not use material if the radiochemical purity is less than 90%.