An evaluation of quality assurance guidelines comparing the American College of Radiology and American Association of Physicists in Medicine task group 284 for magnetic resonance simulation.

PURPOSE: The purpose of this study was to evaluate similarities and differences in quality assurance (QA) guidelines for a conventional diagnostic magnetic resonance (MR) system and a MR simulator (MR-SIM) system used for radiotherapy. METHODS: In this study, we compared QA testing guidelines from the American College of Radiology (ACR) MR Quality Control (MR QC) Manual to the QA section of the American Association of Physicists in Medicine (AAPM) Task Group 284 report (TG-284). Differences and similarities were identified in testing scope, frequency, and tolerances. QA testing results from an ACR accredited clinical diagnostic MR system following ACR MR QC instructions were then evaluated using TG-284 tolerances. RESULTS: Five tests from the ACR MR QC Manual were not included in TG-284. Five new tests were identified for MR-SIM systems in TG-284 and pertained exclusively to the external laser positioning system of MR-SIM systems. "Low-contrast object detectability" (LCD), "table motion smoothness and accuracy," "transmitter gain," and "geometric accuracy" tests differed between the two QA guides. Tighter tolerances were required in TG-284 for "table motion smoothness and accuracy" and "low contrast object detectability." "Transmitter gain" tolerance was dependent on initial baseline measurements, and TG-284 required that geometric accuracy be tested over a larger field of view than the ACR testing method. All tests from the ACR MR QC Manual for a conventional MR system passed ACR tolerances. The T2-weighted image acquired with ACR sequences failed the 40-spoke requirement from TG-284, transmitter gain was at the 5% tolerance of TG-284, and geometric accuracy could not be evaluated because of required equipment differences. Table motion passed both TG-284 and ACR required tolerances. CONCLUSION: Our study evaluated QA guidelines for an MR-SIM and demonstrated the additional QA requirements of a clinical diagnostic MR system to be used as an MR-SIM in radiotherapy as recommended by TG-284.

The Improvement of Patient Centering in Computed Tomography Through a Technologist-Focused Education Initiative.

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.

Determining Organ Doses from CT with Direct Measurements in Postmortem Subjects: Part 2--Correlations with Patient-specific Parameters.

PURPOSE: To generate empirical sets of equations that can be used to calculate patient-specific organ doses resulting from a group of computed tomographic (CT) studies by using data from direct dose measurements performed within a human body. MATERIALS AND METHODS: Organ dose measurements were obtained in eight postmortem female subjects. A chest-abdomen-pelvis protocol was used for this study. The relationships among measured organ doses, body mass index, effective diameter (D(eff)), and volume CT dose index (CTDI(vol)) were investigated. Organ dose equations were developed by means of linear regression from organ dose data, with CTDI(vol) and D(eff) as variables, by using Pearson correlation coefficients and P values to determine correlation strength of fit. Measured organ doses were compared with corresponding size-specific dose estimates (SSDEs). RESULTS: The central-section D(eff) presented similar correlations with organ doses to those from D(eff) measured at specific organ locations. The strongest correlations were observed between the central-section D(eff) and CTDI(vol)-normalized organ doses (R(2): 0.478-0.941). The average of measured organ doses for each subject resulted in an average difference of only 5% from SSDE-calculated doses; however, individual organ doses differed from +31% to -61% from the calculated SSDE. CONCLUSION: The organ dose equations developed represent a method for organ dose estimation from direct organ dose measurements that can estimate organ doses more accurately than the calculated SSDE, which provides a less-specific patient dose estimate.

Determining Organ Doses from CT with Direct Measurements in Postmortem Subjects: Part 1--Methodology and Validation.

PURPOSE: To develop a methodology that allows direct measurement of organ doses from computed tomographic (CT) examinations of postmortem subjects. MATERIALS AND METHODS: In this institutional review board approved study, the x-ray linear attenuation coefficients of various tissues were calculated from the mean CT numbers of images that were obtained in eight embalmed adult female cadavers and compared with the corresponding linear attenuation coefficients calculated from CT images obtained in eight living patients that were body mass index (BMI)-matched. Dosimetry was performed in three of the cadavers by accessing organs of interest and affixing partially sealed vinyl tubes inside them. Optically stimulated luminescent dosimeters (OSLDs) were inserted into the tubes and positioned within the organs of interest and on the skin. OSLDs were read with an InLight MicroStar (Landauer, Glenwood, Ill) reader, and readings were corrected for energy and scatter response. Fifteen tubes containing dosimeters were used, and imaging was repeated twice in each cadaver, for a total of five standard clinical protocols. Average dosimetry values were used for analysis. RESULTS: Differences in linear attenuation coefficients between living and embalmed cadaveric tissues were within 3% for the tissues investigated. Measured organ doses for a chest-abdomen-pelvis CT protocol were less than 32 mGy for all organs measured. Organs that were completely irradiated during a given examination received similar doses, whereas organs that were partially irradiated displayed a large variation in measured organ dose. CONCLUSION: The anatomic and radiation attenuation characteristics of cadavers are comparable to those of living human tissue. This methodology allows direct measurement of organ doses from clinical CT examinations.

Use of CT-based intraoperative spinal navigation: management of radiation exposure to operator, staff, and patients.

OBJECTIVE: Radiation exposure represents significant risk to both operating room health care workers and their patients. The commonplace surgical implantation of spinal instrumentation often relies on fluoroscopy for guidance and verification. Advances in computerized tomography (CT)-based intraoperative navigation have improved accuracy of screw placement. The objective of this article is to quantify the radiation exposure from fluoroscopic and CT-based intraoperative navigation and to provide guidance in mitigating the exposure to patient and operating room (OR) staff. METHODS: With radiation measurement devices in place, a female cadaver underwent pedicle screws from T7 to S1. The left side was guided by fluoroscopy, the right side by CT-based navigation. In addition, a CT-based navigation system was placed in an empty OR. Measurements of radiation while scanning phantom were undertaken at various positions around the OR. RESULTS: The use of intraoperative CT-based navigation virtually eliminated radiation exposure to the surgeon. However, the radiation dose to the patient was increased compared with fluoroscopy. In addition, the radiation profile of the CT-based navigation system was not uniform with significantly lower radiation perpendicular to the axis of the patient on the side of the control panel. CONCLUSIONS: Use of intraoperative CT-based navigation systems results in lower radiation dose to the surgeon compared with fluoroscopic-based methods. There is an increase in the radiation to the patient. In addition, it is necessary to consider and eliminate other perioperative sources of radiation, such as a postoperative CT scan, which are made redundant by this technology.