Measurement of P-32
Sue Hooper1 & Matthew Talboys2
1
2
Velindre NHS Trust, Cardiff
University Hospital of Wales, Cardiff
Phosphorus-32
Used
to treat polycythaemia vera
Beta
emitter –max energy 1.7Mev
Half
life 14.3 days
The issue
New
supplier for P-32
Received
activity on site higher than
expected (up to 27%)
Is
this genuine -do new calibration
factors need to be derived or are we
receiving something for nothing?!
Factors to consider
Vial size is different to the previous
suppliers –P5 as opposed to a P6/Schott
vial - does this introduce a variation?
Vials initially sent with varying volumes
from one batch to the next –previous
supplier always supplied 1ml–how much of
the variation does this explain?
Example P6 vs Schott vs P5 vial
P6
Schott
P5
Comparison of calculated to
measured activities in Capintec
CRCBeta
‘Expected’
activity
(±10%) MBq
Measured
activity
MBq
%
difference
from calc.
activity
Volume of
solution
(ml)
194
246
27
0.54
Summary of variations
Range
of volumes received:
0.54 →2.73ml : mean 1.34ml
SD = 0.63ml
Range
of % diff. from calc. activity
1.4 → 27% : mean 15.0%
SD = 8.2%
Comparison of calculated to
measured activities in Capintec
CRCBeta
Same despatched volume could not predict a % difference
‘Expected’
activity
(±10%) MBq
Measured
activity
MBq
%
difference
from calc.
activity
Volume of
solution
(ml)
370
375
1.4
1.1
388
447
15.2
1.1
Comparison of calculated to
measured activities in Capintec
CRCBeta
Company have now standardised on 2ml solutions
‘Expected’
activity
(±10%) MBq
Measured
activity
MBq
%
difference
from
calculated
activity
Volume of
solution
(ml)
194.2
231
19%
2
185
211
14
2
388
433
11.6
2
Calibrators used
At Velindre:
Capintec CRC15Beta and
Capintec CRC15R
Ionisation chamber
At University Hospital of Wales:
Capintec CRC15R and Fidelis Secondary
Standard
Checks performed
First Vial checked:
expected 388MBq
measured 482MBq at Vel. (+24%)
measured 477MBq at UHW (CRC15R +23%)
Second Vial checked:
expected 370MBq
measured 446MBq at Vel.
(+20.5%)
measured 439.8MBq in Fidelis (+18.9%)
(10ml Schott vial setting used corr. for volume)
FIDELIS VOLUME
CORRECTIONS
Volume
Schott vial
P6 vial
1ml
None
0.931
2ml
0.972
0.959
3ml
0.987
0.982
4ml
1.000
1.000
From table above, volume changes do not
explain the discrepancies we noted.
NPL measurement (1)
From
supplier:
Ref. activity: 185MBq±10% on 30.7.08
Activity on dispatch date: 273MBq on 22.7.08
Radioactive conc.: 92,500 MBq/cm3!!
Volume: 2ml
Container: P-5 vial
NPL measurement (2)
∴ we would expect:
194.2MBq on 29.7.08 but measured 243MBq
(i.e. 25% too high on factor derived for a P6 vial
on Beta counter) [Conc. 121.5MBq/ml]
Vol. to be dispensed from supplier conc. : 1.91ml
Vol. to be dispensed from our measurements: 1.52 ml
1.6ml of solution dispensed into a 5ml syringe for
NPL to assess
NPL measurement
5/8/08 NPL measurements –
–
–
–
Solution dispensed = 1.4246g
Ionisation chamber measured concentration 84.53MBq/g
liquid scintillation counting 86.2MBq/g
Advised to use the ionisation chamber concentration
∴ total activity in syringe = 120.4MBq
Reference to 29/7/08 measurements at Velindre
– P32 solution was 118.7MBq/g
– ∴ 1.6ml syringe = 189.9MBq
– Activity Measured = 198.3MBq
(in Beta counter at Velindre using a factor derived for a 2ml
syringe))
∴ Velindre measurement is 4.4% too high
(NB. If manufacturer’s value used , 1.91ml dispensed =
226.7MBq)
NPL measurement summary
From Supplier conc. 92.5MBq/ml on 30/7/08
From NPL conc. 113.08MBq/ml on 30/7/08
i.e. 22% higher than expected.
NPL measurement
From NPL data of 118.7MBq/g
Vial activity = 237.4MBq on 29.7.08
In Beta counter
The factor for the vial in the Beta counter
is 2.35% too high.
Can correct for this in the calibrator
CRC15R measurement of the vial on Factor 750 was
236MBq on 29.7.08
= 243MBq on 29.7.08
Conclusions
Take great care if you are using the data
supplied by the company to set your
calibration factors.
Always measure the vial activity before
dispensing an injection to ensure you are
happy with the received activity.
At least standardise a factor for your
patient syringe so that you are confident
with the activity to be administered being
±5% of prescribed activity.