Category Archives: Nuclear Medicine

Radiation Safety Issues with F-18

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In recent days we’ve been answering specific concerns regarding radiation safety practices associated with PET imaging and F-18.  The International Atomic Energy Agency (IAEA) has a website that addresses specific questions concerning general information about the safe use of F-18.

For all practical purposes, the radiation safety program described in your radioactive materials license application would apply to the use of F-18.

A specific concern is the performance of medical procedures on patients who had received a diagnostic PET procedure earlier in the same day.  This article from the IAEA highlights the fact that general ALARA practices that should already be in use by hospital staff would provide for a safe working environment around patients who have recently undergone a PET procedure.

Radiation Exposure to Sonographers During Cardiac Testing

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An abnormal echocardiogram. Image shows a mid-muscular ventricular septal defect. The trace in the lower left shows the cardiac cycle and the red mark the time in the cardiac cycle that the image was captured. Colors are used to represent the velocity and direction of blood flow.

The magazine, Cardiovascular Business, published an article last September about radiation exposure to sonographers from patients who had previously undergone a cardiac stress test using a radionuclide.  The American Society of Echocardiography (ASE) conducted a survey of 90 sonographers, and 63% percent (or about 56 of the 90 polled) said, “radiation safety is of concern.”

This Health Physics Society article written by Kelly Classic describes the general dose expected for sonographers performing echocardiography shortly after a nuclear medicine stress test.

In keeping with ALARA, it’s best to schedule all echocardiography procedures before nuclear stress tests.  Based on the conservative assumptions and calculations of Ms. Classic, a sonographer has minimal risk from performing his or her duties in proximity to a nuclear stress test patient.  There’s always the option of badging the sonographer to alleviate concerns and demonstrate the effective dose levels involved.

Recommended Testing for the Capintec CRC-Series

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Capintec manufactures the popular CRC line of dose calibrators and well counters. Thanks to Art Hall, Capintec’s Technical and Field Operations Manager, for much of the following basic recommendations for calibrations:

Dose Calibrator Chamber Test:

Daily:

The following tests should be performed on the chamber:

Auto Zero – This will measure the amount of voltage drift that has occurred. If this is out of the expected range, then a message will appear stating that it is out of range.

Background- This will measure the background in the vicinity.  If the background is greater than 27uCi but less than 500 uCi the word ‘HIGH’ will appear on the screen instead of OK.  You can accept this value; however the reason for the high reading should be investigated and resolved.   If the value is greater than 500 uCi then a message will appear stating that the background is too high.

System Test- This test will measure the chamber voltage which is set at the factory.  If the voltage is out of range a message will alert the user that the System Test failed.

Data Check- This test checks to see that the built-in nuclide data is OK.

Constancy- Accuracy as used for daily test will require you to place each of the calibrated sources that you have designated for daily testing to be placed in the chamber per the on screen instructions.  Readout provides the user with the deviation as measured. If this deviation is greater than 20%, the deviation value will be replaced with dashes ‘—–’.  If this occurs, track down the reason for the high deviation.  Most facilities use a Cs-137 rod source as the constancy check source.

Quarterly test:

System Test or Diagnostics:  This is an internal test of the electronic components in the CRC-15.  A report is issued at the completion of this testing which indicates if the system has passed or failed.  This test should be performed quarterly.

Geometry:  This will test the response of the chamber to different volumes and locations within the chamber.  This is critical if you plan on measuring beta emitting nuclides in the chamber since they will be affected by the container as well as the volume.  It is up to your facility to establish what Geometry testing you will conduct, and this should be based on the Radionuclides that you use in your department.

Accuracy:  This is a measure of the chambers ability to accurately reflect the activity of a NIST-traceable source of radiation.  This should be done using several calibrated sources over a wide range of energies.  This should be tailored for your facility so that you are performing an accuracy test on nuclides that are used in the laboratory. This should be done quarterly.  Standard Nuclear Consultants, Inc. uses NIST-traceable Cs-137, Ba-133, and Co-57 radioactive test sources to perform accuracy measurements.

Linearity:  This is a measure of the dose calibrator’s ability to measure a known radioactive source over several scales in the system.  This is most often performed with Technetium using a sleeve method.  Decay method can be used for nuclides that are not suitable for the sleeve method or you can use the proportional method for longer lived nuclides. The range for the linearity test should cover the range of activity that you use in your laboratory. This should be done quarterly.

Well Test:

Daily:

Background:  This test should be performed daily and more frequently if the room background changes.  Once the background has completed counting, it must be saved by selecting Enter or Well.   Background limitation is established by placing a value in the background limitation level established when the instrument was initialized.  Enter or Well must be depressed to save the background count.

Test:  This test is performed daily.  This test is performed with the source used for Auto Calibration and if there is a deviation greater than a factor of 2 an error message will be displayed.  The Energy Deviation should fall within 3% and if it is greater than 5%, an error message will be displayed.

WEEKLY

Auto Calibration:  This test sets the high voltage so there is a correct relationship between high voltage, energy and channel.  This test should be performed if the Well counter test fails.  Auto Cal attempts to bring the energy calibration within 2.0%.   If this fails, manual calibration must be preformed.  Recently, we have encountered several dose calibrators that required a manual calibration as a result of technologists not performing a weekly auto calibration.  Please consult your Capintec operators manual, or contact SNCI if you need specific instructions for performing a weekly auto calibration.

Quarterly:

System Test or Diagnostics:  This is an internal test of the electronic components in the CRC-15.  A report is issued at the completion of this testing which indicates if the system has passed or failed.  This test should be performed quarterly.

As needed:

CF:  Conversion Factors for known radionuclide sources should be established by the user for the laboratory and used as needed in the laboratory to estimate the energy and activity of unknown sources.

Medical Facilities Offering DaTscan

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We first mentioned the new DaTscan nuclear medicine scan in an article last month.  Sean Price, Manager of Non Invasive & Nuclear Cardiology at Central DuPage Hospital (CDH) in Winfield, Illinois, mentioned that in addition to the video produced by WGN Chicago, the Chicago Tribune ran an article in November explaining the benefits of the scan for determining the presence of Parkinson’s disease.  CDH has offered the procedure since June, the same month that GE made DaTscan available to U.S. hospitals. From June to November 2011, 25 patients have been tested for Parkinson’s disease using DaTscan at CDH.

Chicagoland patients have several medical centers to choose from that offer this recently-approved nuclear medicine imaging procedure, including CDH and St. Alexius Medical Center in the western suburbs.

Prenatal Radiation Exposure Limits

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The Nuclear Regulatory Commission (NRC) publishes guides that provide advice to licensees on how best to satisfy regulatory requirements.  Regulatory Guide (RG) 8.13 discusses the limits on prenatal radiation exposure.

For Illinois, dose to the fetus/embryo is governed by 32 Ill. Adm. Code 340.280.  Section 340.280 states, “[Licensees] shall ensure that the dose equivalent to an embryo/fetus during the entire pregnancy, due to occupational exposure of a declared pregnant woman, does not exceed 5 mSv (0.5 rem).  In addition, if a woman does not notify the administration of the estimated date of conception, Section 340.280 (d) states that, “…the licensee or registrant shall ensure that the dose equivalent to an embryo/fetus, as specified in subsection (b) of this Section, due to occupational exposure of the declared pregnant woman does not exceed 0.5 mSv (0.05 rem) per month, during the remainder of the pregnancy.”

It’s interesting to note that if a woman does not declare her pregnancy in writing, the standard occupational dose limits are applied to her, and not the more restrictive dose limits assigned to a woman with a declared pregnancy. So, if you’re pregnant and you don’t declare, a male member of the public has a lower limit placed on him than that of the effective limit placed on your unborn child – by a factor of 50. (5000 mrem for pregnant undeclared worker versus 100 mrem for a male member of the public).  Dr. Michael Stabin, Ph.D. of Vanderbilt wrote an excellent article about radiation as a carcinogen, and the regulatory contradictions surrounding dose equivalent limits for radiation workers and members of the public.  Be sure to take the test at the bottom of his article.