An image-based skeletal dosimetry model for internal electron sources was created for the ICRP-defined reference adult female. Many previous skeletal dosimetry models, which are still employed in commonly used internal dosimetry software, do not properly account for electron escape from trabecular spongiosa, electron cross-fire from cortical bone, and the impact of marrow cellularity on active marrow self-irradiation. Furthermore, these existing models do not employ the current ICRP definition of a 50 µm bone endosteum (or shallow marrow). Each of these limitations was addressed in the present study. Electron transport was completed to determine specific absorbed fractions to both active and shallow marrow of the skeletal regions of the University of Florida reference adult female. The skeletal macrostructure and microstructure were modeled separately. The bone macrostructure was based on the whole-body hybrid computational phantom of the UF series of reference models, while the bone microstructure was derived from microCT images of skeletal region samples taken from a 45 years-old female cadaver. The active and shallow marrow are typically adopted as surrogate tissue regions for the hematopoietic stem cells and osteoprogenitor cells, respectively. Source tissues included active marrow, inactive marrow, trabecular bone volume, trabecular bone surfaces, cortical bone volume, and cortical bone surfaces. Marrow cellularity was varied from 10 to 100 percent for active marrow self-irradiation. All other sources were run at the defined ICRP Publication 70 cellularity for each bone site. A total of 33 discrete electron energies, ranging from 1 keV to 10 MeV, were either simulated or analytically modeled. The method of combining skeletal macrostructure and microstructure absorbed fractions assessed using MCNPX electron transport was found to yield results similar to those determined with the PIRT model applied to the UF adult male skeletal dosimetry model. Calculated skeletal averaged absorbed fractions for each source-target combination were found to follow similar trends of more recent dosimetry models (image-based models) but did not follow results from skeletal models based upon assumptions of an infinite expanse of trabecular spongiosa.

The AAPM will periodically define new practice guidelines for medical physics practice to help advance the science of medical physics and to improve the quality of service to patients throughout the United States. Existing medical physics practice guidelines will be reviewed for the purpose of revision or renewal, as appropriate, on their fifth anniversary or sooner.

Proper patient centering is fundamental to the operation of CT. Misalignment of the patient is known to have a negative impact on image quality and dose. The purpose of this study was to improve patient centering in CT and examine the efficacy of several educational methods that could be implemented at any clinical site. The IRB determined the study was not human subjects research, and oversight was waived. Three interventions were examined. The first intervention involved a discussion on patient centering at a staff meeting. As the second intervention, an educational presentation was developed and delivered to CT technologists addressing the physics behind the importance of patient centering in CT. As the third intervention, individual technologist centering performance reviews were conducted by the modality supervisor. Clinical scan data was collected for each study period via a cloud-based software to examine the efficacy of each intervention in terms of lateral and vertical offset. The mean vertical offset of the baseline data was −1.97 cm. After the staff meeting, the mean vertical offset decreased to −1.60 cm ( p < 0.001). Following the educational presentation, the mean vertical offset decreased to −1.14 cm ( p < 0.001). After the technologist performance reviews, the mean vertical offset decreased to −0.86 cm ( p < 0.001). This research examined a quality improvement initiative to improve patient centering at our institution which focused on communication and education. Through this initiative, the mean vertical positioning error decreased, the percentage of exams within 0–1 cm of isocenter increased, and the percentage of exams misaligned by greater than 3 cm decreased. This work has shown that patient centering can be improved with education.