Dose Calibrator Quality Control in Nuclear Medicine
السلام
عليكم الناهرده هاتكمل عن اذاى تخبر ال
Dose calibrator فى المعمل وتتاكد من كفائته وده هايتم عن طريق
الاختبارات التاليه :-
1.
Accuracy at installation :-
2.
Constancy daily test
3.
Linearity
4.
Geometry at installation
Accuracy
at installation
1-
انا
عايز اتاكدان الdose calibrator قرائته سليمه فبالتالى محتاج مصدر معلوم
القوه الاشعاعيه مثل ((57Co,
133Ba and 137Cs ويكون له long half live وابتدى احسب القوه الاشعاعيه
للمصدر فى تاريخ القياس بمعلومية نشاطه الاشعاعى فى تاريخ سابق يبقى انا كده عندى
الoriginal activity( A0) ومحتاج احسب النشاط الاشعاعى عند زمن القياس A(t) وممكن
تستخدم المعادلات التاليه :-
A(t)=A(0)/2*n
n = (no of days left from the activity measurment day) /T1/2
2-
يمكنك
استخدام اتنين isotope معلومين القوه
الاشعاعيه وتتم مقارنه القوه الاشعاعيه المقاسه من خلال الdose calibrator بالقوه الاشعاعيه المحسوبه
theoritical من ال stated activity of source sheet
3-
لايد
ان لا يحدث deviation اكبر
من ±5% بين القيمه المقاسه والقيمه الحقيقيه للactivity
4-
ويتم
هذا الاختبار عند استلام الdose calibrator او عند ملاحظه تغيير فى القراءات ولو ذاد انحراف
القيم عن ± 5% لابد
من ابلاغ الشركه للاصلاح .
5-
هيتم
تكرار القرائه خمس مرات لكل مصدر وتحسب المتوسط
6-
ولازم
كمان تقيس الbackground خدبالك وتطرحه من القيمه
المقاسه للactivity فى
كل مره
7-
فى
شويه data analysis مهمين عشان تحسب الprecision وال
accuracy
1. To assess precision, calculate for each source
the percentage differences between the individual measured activities, Ai
,and
their mean, A, that is:
100 (Ai – A)/
A) )
2. To assess accuracy, calculate for each
source the
percentage difference between the mean
measured activity, A, and the certified activity of the source corrected for
radioactive decay to the day of measurement, C, that is:
100(A-C)/C %
Constancy
daily test
1-
وده
ذى الaccuracy بالظبط بس بيحصل يوميا وبنستخدم (226Ra, 137Cs, or 57Co)
2-
,وهنا تسيه الreading deviation لاتذيد
عن 10%
3-
لابد
ان تستخدم مصدر واحد على الاقل فى هذا الاختبار
4-
ومدى
الطاقات للمصدر من100
to 500 Kev-
Linearity
·
الاختبار
ده معناه انك تختبر الdose
calibrator مع اضمحلال decay الماده المشعه بمعنى اوضح هل لو انا قمت بقياس جرعه
اشعاعيه عند زمن T ,ومع
مررو الوقت الجرعه هاتقل قوتها لان بيحصلها decay لو انا قمت بقياس الجرعه
عمليا واقدر احسبها نظريا وابتدى اقارن عندdifferent times القوه الاشعاعيه اللى قام بقياسها الdose calibrator واللى
حسبتها نظريا لو كان الdeviation
less than 10% اذا ده accepted بالنسبه
ليه.
·
الrange of dose اللى
هاقوم باختباره من اعلى جرعه ممكن احقنها للمريض الى ان اصل الى 30 micro Ci
·
بستخدم
الshort live sources (99mTC,
Procedure
1. Transfer the radionuclide solution to the sample vial by
means of the remote pipetting device. Cap the vial firmly.
2. Select the operational conditions
appropriate to the
radionuclide concerned.
3. Note the background reading to be subtracted from
subsequently measured activities. Alternatively, if an adjustable zero
control is provided, adjust this for zero reading.
4. Insert the sample vial into the source holder by means of
the remote handling device and introduce the source holder into the
instrument.
5. Allow sufficient time for the reading to stabilize.
6. Measure and record the activity, subtracting the background
reading if necessary. Record the exact time of day corresponding to
the
measurement.
7. Remove the source holder from the instrument and extract
the sample vial by means of the remote handling device.
8. Repeat steps 2-7 regularly over a. period
several times
greater than the physical half-life of the radionuclide, sufficient
for the source to decay to an activity equal to or less than the lowest activity
for which the instrument is to be used.
Data
analysis
1. Record the results on a graph showing measured activity
against lapsed time on 3- or 4-cycle
log-linear paper
2. With the aid of a transparent ruler,
fit the best straight line possible to the data points in the lower activity region.
3.Extrapolate this line upward to obtain an activity value
corresponding to
the time of the initial reading measurement.
4. Check the negative slope of the line
to ensure that it is
consistent with the known physical half-life of the radionuclide. This
may conveniently be done by dividing the time for the measured activity to
fall to 1/10 of its initial value, determined in step 2, by 3.32 and
comparing the result with the physical half-life.
5. Examine the graph for systematic departures of the data
points from the fitted straight line; such discrepancies indicate non-linearity
of the activity response of the instrument.
Geometry at installation
Variations in sample volumes or geometric
configurations of the container
can affect the accuracy of measurements in a dose calibrator because of the
attenuation of radiations, particularly the weak gamma radiations such as
those of 125I and 201Tl. Thus, the same activity in different volumes [1 mCi(37
MBq) in 1 ml or 1 mCi (37 MBq) in 30 ml], in different containers (3-ccsyringe
or 10-cc syringe or 10-ml vial) or in containers of different material(glass or
plastic) may give different readings in the dose calibrators. Correction factors
must be established for changes in volume or container configuration while
measuring the activity of the radionuclide in question and mustbe applied to
similar measurements, if the difference exceeds 10%.
So, we have two methods:-
·
·
مره هانغير الvolume وتثبيت ال geometry of container
·
ومره هانغير ال container geometry مع تثبيت الvolume
·
والحالتين لنفس قيمه الactivity وشوف مقدار الdeviation فى القؤاءات المفروض اقل من 10%
·
ولوقسمت قيمه متوسط الactivities على الtrue activity تقدر تحسبvolume correction factor
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