Frequently Asked Questions

Product Questions:
• Captus 3000 Thyroid Uptake System Questions
• Captus 600 Thyroid Uptake System Questions
• Caprac & Caprac-R Questions
• Dose Calibrator Questions
• Dosimetry Questions
• Surgical Probe Questions
• Absorbed Dose ALERT System Questions

• Captus 3000 Thyroid Uptake System Questions

My new Captus 3000 system has a large accuracy deviation, what is the problem?
All systems are carefully tested using sources before shipment to a customer. Each customer uses a different dedicated check source. Before using your new system, enter the calibration date and activity of your source and re-measure the efficiency. The check source information must be entered in two locations, once for the constancy test and once for the Chi-Square test. Efficiencies must be measured for each detector, well and probe. Follow up by performing the QC tests.

My Captus 3000 deviation exceeds 5% on the uptake probe, what is the problem?
The well accuracy is fine. The check source may not be in the same position as it was during the initial calibration. When measuring a check source in the uptake probe, turn the collimator upwards facing the ceiling and gently place the rod source in the center of the probe. If the source is off center, the lead shielding will attenuate some of the activity.

I cannot find my Captus 3000 manual.
All new systems now have the Owner’s Manual added to the PC. Just click the Captus 3000 Manual icon on your screen.

I made a counting error during a thyroid uptake procedure, is there a way to continue the measurement?
The Captus 3000 includes a 1024 channel fully functional MCA module. Any counting procedure can be performed manually using the MCA. Setup a defined ROI around the region of interest and measure the background and all samples. Manually subtract the background and perform calculations.
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• Captus 600 Thyroid Uptake System Questions

My new Captus 600 system has a large accuracy deviation, what is the problem?
All systems are carefully tested using sources before shipment to a customer. Each customer uses a different dedicated check source. Before using your new system, enter the calibration date and activity of your source and re-measure the conversion factor. Conversion factors must be measured for each detector, well and probe. Follow by performing the QC tests.

I cannot enter a new thyroid uptake patient, why?
The Captus 600 stores measurement data for 15 patients. In order to enter additional new patients, some of the older patients must be deleted.

My Captus 600 system will not autocalibrate, what should I do?
The Captus 600 has a software program which performs an automatic calibration over a wide range of detector responses. When replacing a detector in the field or when an older detector has drifted outside of the automatic calibration range, a manual calibration is necessary. This will require the use of a small screwdriver to adjust the calibration potentiometer and Cs 137 and Co 57 low activity check sources. Contact your Application Specialist for Manual Calibration Procedure and assistance in making the adjustments

I made a counting error during a thyroid uptake procedure, is there a way to continue the measurement?
The Captus 600 includes a 256 channel fully functional MCA module. Any counting procedure can be performed manually using the MCA. The software will automatically define an ROI at the FWTM. Measure the background and all samples. Manually subtract the background and perform calculations.
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• Caprac & Caprac-R Questions

The accuracy test of my Caprac exceeds 5%, what should I do?
First, perform an autocal. The software automatically adjusts the gain to compensate for normal drift of the NaI detectors. Over time, as detectors age, the systems may drift out of the autocalibration range. The user must then make a simple manual adjustment using a small screwdriver to the calibration pot using the Cs 137 check source. A detailed manual calibration procedure is available from your Capintec Application Specialist. Recent engineering changes have extended the automatic calibration range and eliminate the need for manual adjustments. Capracs that have serial numbers greater than 001520 and Caprac Rs with serial number greater than 300205 have the calibration change, also. Older units may be upgraded at the Capintec Service Center.

How do I determine the efficiency of an isotope on my Caprac?
The Caprac uses the term conversion factor, which is the inverse of efficiency, to convert count rates to activity. Capracs have nominal conversion factors for most commonly used isotopes in the software. These default values will provide a +/- 10% to 15% accuracy for a wide variety of wipe test methods, e.g. alcohol wipes, cotton tipped swabs, tissue paper in test tubes, etc. Alternately, a generic conversion factor of the most common isotopes (Tc-99m) or a check source can be used to estimate the activity of all isotopes. To improve accuracy or determine the conversion of an isotope not listed in the database, prepare an aliquot with < 1 uCi activity. In the UTIL menu select CONV FACTOR and follow the prompts. The system will automatically measure, calculate, and store the conversion factor.
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• Dose Calibrator Questions

My dose calibrator has failed the linearity test, what should I do?
The great majority of linearity failures are due to operator errors. Of all the calibrators serviced by Capintec, only a rare few were non linear. For the older analog units, first check the battery voltage (150V), next adjust the zero and then background. For microprocessor calibrators first run the daily test and insure that all tests are within expected limits. Repeat the linearity test using the decay method. Carefully record the actual time (not the expected time) using the same clock or calibrator clock for each measurement. For low activity measurements, insure that no sources or other activity is near the calibrator. If a linearity test fails using a Calicheck system, repeat the test using the decay method. Calicheck correction factors must be measured independently for each dose calibrator and for each set of sleeves.

What does the calibration number mean? The source has a large error using the calibration number in the manual, what is wrong?
All calibration numbers are based upon the NIST (NBS) geometry, which is 5 ml of solution in a flame sealed glass ampoule with 0.6 mm wall thickness. This geometry provides a good estimate for most commonly used radiopharmaceuticals in vials or plastic syringes. For isotopes with significant abundance of low energy photons, pure beta emitters or different geometries such as capsules, wires or seeds, geometry correction factors are required. Request a NIST traceable sample from the source manufacturer and use the sample to determine the correct calibration number. Many times the source manufacturer can also provide a calibration number for Capintec dose calibrators and for their unique source configuration. For some sources, an ADCL lab can also provide a highly accurate calibration number. Due to the large number of available vials and syringes and the lack of standardization of containers in the radiopharmacy industry, Capintec does not supply calibration numbers for different geometries. It should also be noted that the same or similar geometry for the same isotope supplied by two different manufacturers may also require two different calibration numbers.

How do I set up a user key on my 15 family dose calibrator?
Under the UTIL menu, select SETUP. Press 4 for other. Enter Password. Select User Keys. Select the desired user key, U1…U5. Then type in the nuclide.

My accuracy test is failed, what is the problem?
First confirm that the calibration date entered into system is correct. Since the system uses a default date as an example, users occasionally forget to change the year.

The accuracy test of my 15W well exceeds 5%, what should I do?
First, perform an autocal. The software automatically adjusts the gain to compensate for normal drift of the NaI detectors. Over time as detectors age, the systems may drift out of the autocalibration range. The user must then make a simple manual adjustment using a small screwdriver to the calibration pot using a check source. A detailed manual calibration procedure is available from your Capintec Application Specialist. Recent engineering changes have extended the automatic calibration range and eliminated the need for manual adjustments. 15Ws with serial numbers greater than 170925 have the new extended calibration change. Older units may also be upgraded at the Capintec Service Center.

How do I determine the efficiency of an isotope on my 15W well?
The 15W well uses the term conversion factor, which is the inverse of efficiency, to convert count rates to activity. 15W wells have nominal conversion factors for most commonly used isotopes in the software. These default values will provide a +/- 10% to 15% accuracy for a wide variety of wipe test methods, e.g. alcohol wipes, cotton tipped swabs, tissue paper in test tubes, etc. Alternately, a generic conversion factor of the most common isotopes (Tc-99m) or a check source can be used to estimate the activity of all isotopes. To improve accuracy or determine the conversion of an isotope not listed in the database, prepare an aliquot with < 1 uCi activity. Then, in the UTIL menu select CONV FACTOR and follow the prompts. The system will automatically measure, calculate and store the new conversion factor.
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• Dosimetry Questions

What is the wall material for Capintec therapy chambers?
The chambers are made from C-552 Air Equivalent Plastic. Material information needed for TG 51 protocol is available from your Capintec Application Specialist.

How do I obtain a BNC connector, does Capintec supply the TNC?
If no connector type is specified, Capintec chambers and electrometers are supplied with a TNC connector. BNC is available but must be specified on the purchase order. Capintec can also provide a TNC to BNC conversion cable if required.

What is the difference between the 292 and 192 electrometers?
The 192 is a direct read analog A/C powered precision electrometer with a wide dynamic range for both therapy and diagnostic applications. The 192 can store conversion factors for up to three chambers. The 292 is a microprocessor based dedicated therapy electrometer which can be A/C or battery operated. The 292 stores chamber calibration and energy correction information, patient and measurement data. The 292 includes a RS 232 feature to transfer data to a PC or printer. Pressure and remote temperature gauges are also optional features.
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• Surgical Probe Questions

What is the calibration procedure for the Gammed VI?
A factory calibration should be performed every 5 years as per manufacturer’s specification. A constancy check source should be measured before each use to insure proper response of the instrument. The software contains many self-diagnostic tests which will flag the user for error conditions such as low battery, high zero offset or background.

Can the Gammed VI be used with FDG?
Yes. However, it requires the addition of a high-energy collimator for use with the CsI detector.
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• Absorbed Dose ALERT System Questions

Currently, isotopes in the Alert software is limited to Co-60, Cs-137, I-131 and Ir-192.  What if the isotope is unknown or known but not on the list?
The conversion data is only available for the isotopes in the list.  As additional data becomes available, software will be updated.  If the isotope is not on the list, the operator will need to use the MCA features to identify individuals with high count rates, and use onsite health physicist (HP) expertise to set count rates limits for follow up.  Alternately, the HP may select an isotope from the list which has a similar response, and apply a correction factor or set the limit differently.  Since the data is directly exportable to Excel, it is very easy to manipulate after collection.

How critical is the exact height and weight in performing exposure calculations?
Exact weight and height are not critical.  The factors in the tables cover a BMI range, not individual values. 

What limits should be set for screening levels?
Initially the recommendation for screening levels by the CDC was 5 x ALI (annual limit of intake), which was considered the CDL (clinical decision level).  However, that number must also be based on screening criteria-e.g. screening 500 people vs. 5,000 may require a different limit.  Also, there is a new guidance document which should be published soon which may change the limits, particularly for certain critical groups, e.g. children, pregnant women.  The HP or public health expert overseeing the process will need to make those decisions.

If the scenario is a dirty bomb, should the assumption always be inhalation versus ingestion?
Inhalation is the most likely route and all of the data in the first release of the Alert software is based on inhalation.  A software upgrade will be sent as soon as the ingestion data is available at no charge.  The route and selection of inhalation/ingestion will require the expertise of the onsite HP overseeing the screening process, because it depends upon many variables, including environmental and human factors.

What assistance is available to help sites prepare an emergency plan?
The CDC guidance documents at the attached link.  http://www.bt.cdc.gov/radiation/index.asp provides a great resource for planning and includes additional references for review.  Additional assistance is available from local public health or emergency planning offices.  Organizational structure and local facilities will vary from state to state; however, all will have some type of emergency response group.  It is important that each facility become familiar with the organizational and communication protocols in place at their locale.

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