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Science at Work: Radiation Physics Division Highlights

Dr. Michael Mitch Named Fellow of the American Association of Physicist in Medicine (AAPM)

Dr. Michael Mitch, Leader of the Dosimetry Group of the Radiation Physics Division, ahs been elected as a Fellow of the American Association of Physicists in Medicine (AAPM). A member of the AAPM since 2000, Mitch currently represents NIST on several committees, including the Therapy Physics Committee, Brachytherapy Subcommittee, Working Group on Brachytherapy, and the Calibration Laboratory Accreditation Subcommittee. He has participated as NIST representative on assessment teams for the AAPM Accredited Dosimetry Calibration Laboratories, and has co-authored several task group reports. Dr. Mitch has served on the Editorial Board of the AAPM journal Medical Physics, and is currently a Senior Associated Editor. He has made numerous presentations at AAPM meetings, and served as a faculty member for the 2009 AAPM Summer School.

For more information please contact Dr. Mitch by email at:

Measuring Radiation Dose in Computed Tomography (CT)

The Dosimetry Group of the Radiation Physics Division has an on-going collaboration with the FDA, NIH, and the Walter Reed National Military Medical Center to characterize clinical dosimeters for the purpose of monitoring the radiation dose delivered to patients during computed tomography (CT) exams. One of the motivations for the work was to establish what variation is observed across different CT facilities of the dose delivered to a patient undergoing a given procedure (for example a head scan). Furthermore, is there a way of relating machine parameters that are readily available on the console of every CT machine with an actual dose value? And if so, what dowe metric should be used to characterize the dose delivered to a patient - organ doses, peak skin doses, and/or dose at a given point in the human body? In our quest to answer these and other questions, this work has focused primarily on the CT procedure, a head CT exam, but methods used are equally valid for scans of the chest or abdomen. A proper assessment of patient radiation exposure risk should consider both the deep tissue and surface dose. To this end, measurements were performed by placing dosimeters inside and on the surface of physical phantoms which were an then imaged using typical scanning protocols. the physical phantoms included an acrylic cylinder from NIST and an anthropomorphic phantom from the FDA, and the dosimeters included optically stimulated luminescent dosimeters (OSLs) and radiochromic film.

The results of the measurements from the head scan (made with OSLs) provided an estimate of the dose to the primary critical organs - the eye lenses, skin and brain. The doses ranged from 36 mGy to 47 mGy for the set of CT scanner parameters used during these experiments (tube current, voltage, scan type, number of slices), which corresponded to those used routinely in the clinical for patient procedures. In contrast, the measurements made with radiochromic films explored dose values delivered to the surface of the head phantom with routine and non-routine scanner parameters. Doses measured on the surface of the head phantom correspond to the peak skin dose (PSD). These film measurements showed that the PSD values for the head phantom ranged between 27 mGy and 136 mGy among all the CT scanners studied here. In addition, an ionization chamber was placed inside the acrylic cylinder phantom to measure the volume CT dose index (CTDIvol), a machine parameter (displayed on the console of all CT scanners) which serves as a measure of the radiation output of the CT scanner. The measurements were performed during CT machines from 4 different manufacturers and, in each case, the measured CTDIvol values were compared to the nominal planned values displayed by the CT scanner prior to initiating the scan. The CTDIvol for different values of the x-ray tube current setting were correlate to PSD measurements performed simultaneously using radiochromic film. Such a relationship is useful because it allows one to directly relate a machine parameter readily available and displayed on the CT console to a more accurate measue of patient dose. The ratio was determined for the measured PSD values to the CTDIvol displayed on the CT for all four machines studied. the values obtained were: 0.84 ± 0.04, 0.75 ± 0.04, and 0.87 ± 0.04, which compared quite well with recent Monte Carlo calculations performed by other groups, thus providing validation of these calculations.

For more information please contact Dr. Ronaldo Minniti by email at:

International Metrology Outreach to Saudi Arabia

Lisa Karam, from the Radiation Physics Division, was invited to the international workshop "Frontiers of Nuclear Data Evaluation and Related Applications" held at the King Abdulaziz University in Jeddah, Kingdom of Saudi Arabia (2-3 March 2015). This meeting presented a unique opportunity to learn of the current status of nuclear radiation physics efforts in Saudi Arabia and give a variety of colleagues and students the opportunity to gain fundamental knowledge on the international organization of metrological efforts. In particular, as one of only two female speakers, this presented a particularly noteworthy opportunity for the women of this university to visualize a role for them in measurements.

For more information please contact Dr. Karam by email at:

Consultative Committees on Ionizing Radiation - An International Strategy for Ionizing Radiation Measurements

The three Sections of the Consultative Committee on Ionizing Radiation (on neutron measurements, radioactivity measurement, and radiation dosimetry) each have (or will) meet in March 2015 for their biennial meetings at the International Office of Weights and Measures (BIPM) in Paris, France. These meetings (on of which is chaired by NIST) allow NIST and the American Metrology Organization (SIM) to have strong influence on the direction of ionizing radiation metrology efforts in the international community, as well as providing necessary information to facilitate our own strategic planning and efforts in international comparisons, calibration services, and the research to advance the next generation of ionizing radiation measurements to support manufacturing, health care, environmental stewardship, energy, and security and defense.

For more information please contact Dr. Lisa Karam, by email at:

Refurbishment of Van de Graaff Accelerator

The Van de Graaff accelerator maintained the Dosimetry Group of the Radiation Physics Division, has provided high-energy electronbeams for high-dose research for 50 years. Recent upgrades, including the installation of a new type of charging belt and charge extraction screens for the high voltage terminal, have resulted in increased output, energy stability, and greater operation efficiency. These improvements will allow the facility to continue to support dosimetry research as well as allow NIST to address the needs of collaborators from industry and universities to determine the effects of high radiation fields on electronics, such as those employed in satellites, and perform physical property studies of materials.

For more information please contract Dr. Fred Bateman, by email at:

Computing for Improved Radiation Therapy

Physicists in the Dosimetry Group of the Radiation Physics Division have developed and maintain standards for the accurate measurement of dose from small, encapsulated radioactive sources used in brachytherapy for the treatment of cancer. Recently, a new standard has been realized for electronic brachytherapy sources, which employ a miniature x-ray tube operated at 50 kV. The Division's newest NRC postdoc is using state-of-the-art Monte Carlo methods to calculate radiation interaction parameters and to determine correction factors for primary standard instruments. Future extension of these methods to "virtual patient" simulations will enable the identification and characterization of potential dosimetric errors due to simplifying assumptions used by clinical treatment planning systems.

For more information please contact Dr. Matthew Mille, by email at:

Physical Model for α/β-γ Anticoincidence Counting

Emerging challenges in nuclear forensics require absolute radionuclide measurements with extremely-low uncertainties. In response, researchers in the Radioactivity Group have developed a physical Monte Carlo extrapolation model for the α/β-γ anticoincidence-counting methods that have so-far relied on generic polynominal efficiency extrapolations. This new method has already uncovered hidden uncertainties, which were ignored in previous work, and then combined with the new NIST digital coincidence system, has the potential to improve the accuracy fo anticoincidence counting to the levels necessary to meet these new challenges. The progress will be presented in a paper that has been submitted to an upcoming meeting of the International committee for Radionuclide Metrology in Vienna, Austria.

For more information please contact Dr. Ryan Fitzgerald, by email at:

NIST Contributes to Report on Airline Incident

In December 2014, the National Transportation Safety Board (NTSB) released its Aircraft Incident Report on the Japan Airlines Boeing 787 fire that occurred in Boston, MA, in January 2013, concluding that it was probably caused by an internal short circuit within a sell of the lithium-ion-battery. To reach the conclusion, the agency relied in part on neutron imaging of the incident battery cell components conducted at NIST, which convincingly ruled out one alternative explanation. The NIST neutron imaging data showed that there was on lithium deposit on the battery header that could result in an external short, which supported the internal battery short as a source of the fire.

For more information, please contact Dr. Michael Huber at:

Created December 12, 2014, Updated May 19, 2017