Sue Hooper Principal Physicist Nuclear Medicine Velindre ... · PDF filePrincipal Physicist...
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31/1/07 NPL Calibrator Workshop
Radium-223 Calibration
Sue Hooper
Principal PhysicistNuclear Medicine
Velindre NHS Trust
31/1/07 NPL Calibrator Workshop
What is Ra-223?Ra-223 (Alpharadin) –is an alpha emitting radionuclide-supplied by Algeta ASA in Norway
227 Ac ⇒227Th ⇒
223Ra
31/1/07 NPL Calibrator Workshop
Why use Ra-223?It is being used in a phase II, multicentre study for the palliation of painful bone metastases in hormone refractory prostate cancer patients
cf Sr-89 (Metastron) and Sm-153 (Quadramet) - both β emitters
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Range in tissue
Tissue range for 223 Ra < 100 µm (α)
Cf
Tissue range for 89Sr < 8mm (β)
Quality F actor: α particles = 20γ rays & β particles =1
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Activities of Ra-223 involved
Patients are entered into one of four randomisation arms:
5, 25, 50 or 100 kBq/kg
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Physical Properties of Ra-223
T½ = 11.43 daysα energy (average) = 5.78 MeV (accounts for 93.5% of
emitted energy); <4% as β particles; <2% as γradiation
β energy/decay: 1MeV (ave)γ energy/decay: 0.4 MeVγ energy: 269 keV (13.6%)
154 keV (6.04%)324 keV (3.9%)
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Decay Scheme of Ra-223223Ra11.43 d
219Rn3.96 s
α, 5.78 ΜeV
211Bi2.17 m
211Pb36.1 m
215Po1.78 ms
207Tl4.77 m
207Pbstable
211Po516 ms
α, 6.88 MeV
α, 7.53 MeV
α, 7.59 MeV
β-, 0.45 MeV
β- (0.273 %), 0.01 MeV
β-, 0.49 MeV
α (99.727 %), 6.68 MeV
Combined energyfor the complete decay of Ra-223 & daughters
= 28MeV
Some γ (0.9 MeVtotal) is also emitted
Courtesy of Algeta
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Container for Ra-223• 20 ml glass vial• Conc 500 or 1000 kBq/ml• Maximum activity in vial =23 MBq• Dose rate from unshielded vial
outer wall: 100µSv/h/MBq10cm from vial : 6µSv/h/MBq100 cm from vial: 0.06 µSv/h/MBq
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Calibration Procedure (SOP)
The company send out a SOP “Dial setting of Radioisotope Dose Calibrators for measurement of the radioisotope Radium-223 at clinical centres prior to clinical trials with Alpharadin.”
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Calibration Procedure (SOP)1. Purpose - to find the dial
setting for the Dose Calibrator!
2. Responsibility and Authority -tells you to follow SOP and return the results
3. Definitions –None
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Calibration Procedure (SOP)4. Procedure : Scheme 1 is used
to decay correct the activity in the Ra-223 solutionScheme 2 is used to document the affirmative measurements for the dial setting
(more detail to follow)
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Calibration Procedure (SOP)• Perform standard QA & bkgd
checks for calibrator• Read stated activity of Ra-223 on
label of vial. Use supplied Volume Correction chart to correct the stated activity for decay to the measuring time. Corr act = Ac
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Vol corr chartDays from ref date Vol. x factor (Vmf)
-5 0.74-4 0.78-3 0.83-2 0.88-1 0.940 11 1.062 1.133 1.204 1.27
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Calibration Procedure (SOP)• Place the Ra-223 in the calibrator making
sure it is centred in the measuring chamber• Adjust the calibrator until it displays the
decay corr activity Ac• Note the calibrator factor/setting for
further measurements of unknown activity• Perform 3 measurements with the Ra-223
standard source. Allow calibrator to return to bkgd between the measurements. All three measurements should be ± 5% of Ac
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Calibration Procedure (SOP)5. References –None6. Revision –First7. Appendices –Scheme 1 and
Scheme 2
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Calibrator at Velindre• Capintec CRC15 Beta- consists of a chamber (for γemitters) and a beta counter (for pure β emitters)
- measurements of Ra-223 performed in the ionisation chamber
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In practice!• Receive vial of Ra-223
Activity (MBq) on date @ 1200 CET(no hours on decay chart – so can only do approximate activity if measurements not made at this time)
Our factor appeared to be between Cal #240 and Cal #250 (1 dec place)
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In practice!• Measurement repeated the following
day at 12:00 (should have been 11:00!)Activity in vial calculated to 2 decplaces using Vol Corr Chart.
SPC button pressed to display 2 decplaces on calibrator -factor then appeared to CAL #251 using the vial jig supplied with the calibrator.
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ResultsScheme 1-Decay correction of Ra-223 standard soln
Stated Act(A)
Calib date(std soln)
Date of Calib of dose calib
Decay corract in std solnAc= A x cffrom volcorr table
Ra-223 calibno/factor
6MBq 21.7.05@12:00
13.7.05 @12:00
9.67MBq CAL #251
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ResultsScheme 2 Affirmative measurements
Decay corrected Activity
Ac
(MBq)
Activity Affirmative
measurement 1
(MBq)
Activity Affirmative
measurement 2
(MBq)
Activity Affirmative
measurement 3
(MBq)
9.67 9.62 9.60 9.76
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In practice!• Results faxed off to company – no
information ever received back if we were right or wrong despite me asking.
• As for syringe measurements…….Every centre involved in the trial is using the same factor as derived for the vial. Our syringe jig drops activity down into calibrated part of the chamber. Purely go on volume dispensed. Vial activity means Ra-223 solution in equilibrium, not necessarily the case for the syringe.
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New Calibration SOP• Purpose and Responsibility not changed much
• Definitions – now defines a dose calibrator, sample calib date (prior to calib date the activity is higher than stated, after the activity is less), isotope calibration factor or number
• Procedure –corr the std activity for decay according to the formula
Ac = A0 . e
where
A0 is stated activity of the viald = no of days (this number is below zero in the case where the dose calibrator dial setting is performed before the sample calibration date)
Recording the measurements appears to be the same
( - ln2 * d )11.43
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New Calibration SOP• References None
• Revision – Second -changes from the first edition:The procedure for decay correction of the stated activity is converted from a correction based on a decay table to a direct decay correction by means of a standard decay formula for radioactive substance.
Minor linguistic updates are performed.A user friendlier version of Scheme 1 and 2 is presented.