Repeated intakes of I-131.v


This case study  was also part of the intercomparison exercise organized in 2004 by IDEAS in cooperation with IAEA. 


The case happened in a chemical laboratory in a medical institution. The person was handling radiopharmaceuticals of I-131.v for therapeutic purposes (physical state of I-131: vapour) . This type of work with highly radioactive material had just started in the laboratory. The person who did the work carried out the same procedure, handling the same amount of radioactive material, on 3 consecutive days of the week, namely Tuesday, Wednesday and Thursday. During the work no uncommon event was observed. On the following Monday the person was routinely monitored via thyroid measurement. This measurement revealed a thyroid activity of 21 kBq I-131. Because of this high activity two more measurements have been performed on the following two days (special monitoring). The person (female) was 28 years old. Her body weight was 60 kg. The case is available in the standard database of IDEA System and can be selected via the Person ID IAEA-IDEAS-4. After having selected the case you will see the person data. The data of birth was set to 01.01.1976 and the begin of monitoring was set hypothetically to 01.08.2004.








After having switched to the window "Measuring data" you will see all measuring data of the case. On the right hand side you see a table with a listing of all data. On the left hand side you see the detailed information for the measuring value which is marked with the black triangle in the list on the right hand side. You can move the triangle to any measured value by clicking in the respective line of the table. The values for the lower limit of detection (LLD) have been allocated automatically by the IDEA software because there is no other information available in the case description. The uncertainty has been calculated according to the IDEAS General Guidelines.



















For evaluating the measured values you have to switch to the "Evaluation" window.

For the evaluation all data should be used. So you click on "Mark all" to identify all available data and then on "Select data" in order to select the marked data to be used for evaluation.


The system checks automatically the earlest time of intake (in this case the begin of monitoring is selected by the system; this information, however, is not relevant for the evaluation because the time of intake is known).



















After confirmation of this message the system checks automatically if there are records of previous intakes of I-131 for this person in the database.


























In the next step you may choose the evaluation procedure. In this case some of the intake parameters (time pattern and pathway of intake) are known and so you should choose the standard evaluation procedure with selected parameters (Standard (Level 2; selected parameters). After having chosen this procedure a frame opens where you can select the evaluation parameters. According to the case description there is evidence for a continuous intake over 3 days rather than a single intake. So you should select "Continuous intake" for a "Duration of 3 days".

In the next step you have to select the "Time of intake". In the case of continuous intake the "Time of intake" corresponds to the begin of the continuous intake. In this case the begin of the continuous intake is assumed to be the begin of handling, i.e. Tuesday, 03.08.2004.
















After having completed the selection of the evaluation parameters you can start the evaluation. The system checks automatically the significance of the data according to the IDEAS General Guidelines and comes to the conclusion "There is a new intake".
























After confirmation of that message a window opens with the results of this evaluation. The left part of the window gives an overview over the evaluation procedure, the evaluation parameters and the most important results in terms of intake and dose (intake 130 KBq I-131.v and committed effective dose 2.59 mSv). In the right part of the window you see a table with more detailed information about the committed effective dose and all organ doses (column D(QD)) as well as the doses in terms of dose limit fractions (column DR(QD)). In this case the organ with the maximum dose limit fraction (critical organ) is the thyroid (organ dose 5.06 mSv, corresponding to 16.9 % of the limit.  The effective dose is in between 1 and 6 mSv. Thus, the case is allocated to "Level 2" according to the IDEAS General Guidelines.


The potential error (emprical scattering factor SF from the IDEAS Guidelines) of the evaluation is 1.24, this indicating an acceptable fit. 










The plot confirms the good quality of the fit.


Thus, according to the IDEAS General Guidelines, the evaluation procedure can be finished at this point because (i) the fit is acceptable and (ii) the committed effective dose is less than 6 mSv.


P.S. This is an artificial case where the "real" value of the intake is known: The "real" intake is 130 kBq I-131.v,  this being identical with the result obtained with IDEA. 










Prof. Dr.-Ing. Hans Richard Doerfel

IDEA System GmbH, Am Burgweg 4, D-76227 Karlsruhe, Germany.