AAPM medical physics practice guideline 6.a.: Performance characteristics of radiation dose index monitoring systems.

The American Association of Physicists in Medicine (AAPM) is a nonprofit professional society whose primary purposes are to advance the science, education and professional practice of medical physics. The AAPM has more than 8,000 members and is the principal organization of medical physicists in the United States. 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. Each medical physics practice guideline represents a policy statement by the AAPM, has undergone a thorough consensus process in which it has been subjected to extensive review, and requires the approval of the Professional Council. The medical physics practice guidelines recognize that the safe and effective use of diagnostic and therapeutic radiology requires specific training, skills, and techniques, as described in each document. Reproduction or modification of the published practice guidelines and technical standards by those entities not providing these services is not authorized. The following terms are used in the AAPM practice guidelines: •Must and Must Not: Used to indicate that adherence to the recommendation is considered necessary to conform to this practice guideline. •Should and Should Not: Used to indicate a prudent practice to which exceptions may occasionally be made in appropriate circumstances.

Estimated skin dose look-up tables and their effect on dose awareness in the fluoroscopy-guided imaging suite.

OBJECTIVE: The displayed air kerma during a fluoroscopy-guided procedure often does not represent the entrance skin dose. The purpose of this work is to develop a system-specific air kerma-to-entrance skin dose look-up table (LUT) for immediate reference and to evaluate its clinical utility. MATERIALS AND METHODS: Physicists are often involved in retrospective dosimetry and risk estimates. Conservative dosimetry conversion factors, represented by the total conversion factor, prospectively estimate the maximum potential skin dose from the displayed air kerma. Air kerma-to-skin dose LUTs with corresponding tissue reactions and approximate time-of-onset can be posted for reference. By developing skin dose LUTs, physicians can actively evaluate during the procedure the potential for deterministic skin reactions. System user surveys evaluated the impact of LUTs on dose awareness. RESULTS: The range of the total conversion factor to the displayed air kerma for the nine systems evaluated was 0.8-1.6 for frontal x-ray tubes. Skin dose LUTs were posted in all imaging suites, and two surveys reported user feedback. Radiology technologists indicated that LUTs improved user dose awareness. Twelve of 14 physician respondents indicated an understanding that entrance skin dose is not equal to the displayed air kerma. CONCLUSION: Our efforts focused on educating fluoroscopy users about differences between displayed air kerma and the entrance skin dose while increasing dose awareness using an accessible and easy-to-understand tool. Skin dose LUTs provide physicians and staff an immediate reference for the maximum estimated entrance skin dose and the associated deterministic skin effects, allowing appropriate patient management.

Radiation-induced complications in endovascular neurosurgery: incidence of skin effects and the feasibility of estimating risk of future tumor formation.

BACKGROUND: The incidence of radiation-induced complications is increasingly part of the informed consent process for patients undergoing neuroendovascular procedures. Data guiding these discussions in the era of modern radiation-minimizing equipment is lacking. OBJECTIVE: To quantify the rates of skin and hair effects at a modern high-volume neurovascular center, and to assess the feasibility of accurately quantifying the risk of future central nervous system (CNS) tumor formation. METHODS: We reviewed a prospectively collected database of endovascular procedures performed at our institution in 2008. The entrance skin dose and brain dose were calculated. Patients receiving skin doses >2 Gy were contacted to inquire about skin and hair changes. We reviewed several recent publications from leading radiation physics bodies to evaluate the feasibility of accurately predicting future cancer risk from neurointerventional procedures. RESULTS: Seven hundred two procedures were included in the study. Of the patients receiving >2 Gy, 39.6% reported subacute skin or hair changes following their procedure, of which 30% were permanent. Increasing skin dose was significantly associated with permanent hair loss. We found substantial methodological difficulties in attempting to model the risk of future CNS tumor formation given the gaps in our current understanding of the brain's susceptibility to low-dose ionizing radiation. CONCLUSION: Radiation exposures exceeding 2 Gy are common in interventional neuroradiology despite modern radiation-minimizing technology. The incidence of side effects approaches 40%, although the majority is self-limiting. Gaps in current models of brain tumor formation after exposure to radiation preclude accurately quantifying the risk of future CNS tumor formation.

Hybrid Modality Fusion of Planar Scintigrams and CT Topograms to Localize Sentinel Lymph Nodes in Breast Lymphoscintigraphy: Technical Description and Phantom Studies.

Lymphoscintigraphy is a nuclear medicine procedure that is used to detect sentinel lymph nodes (SLNs). This project sought to investigate fusion of planar scintigrams with CT topograms as a means of improving the anatomic reference for the SLN localization. Heretofore, the most common lymphoscintigraphy localization method has been backlighting with a (57)Co sheet source. Currently, the most precise method of localization through hybrid SPECT/CT increases the patient absorbed dose by a factor of 34 to 585 (depending on the specific CT technique factors) over the conventional (57)Co backlighting. The new approach described herein also uses a SPECT/CT scanner, which provides mechanically aligned planar scintigram and CT topogram data sets, but only increases the dose by a factor of two over that from (57)Co backlighting. Planar nuclear medicine image fusion with CT topograms has been proven feasible and offers a clinically suitable compromise between improved anatomic details and minimally increased radiation dose.

Optimal (57)Co flood source activity and acquisition time for lymphoscintigraphy localization images.

UNLABELLED: We evaluated different (57)Co flood source activities and acquisition times to obtain an optimal localization image for breast lymphoscintigraphy that would adequately outline the body and allow detection of nodes seen on the emission scan while minimizing unnecessary radiation exposure to the patient. METHODS: An anthropomorphic thorax breast phantom representing an average-size patient was used to simulate nodes on a breast lymphoscintigraphy scan. The activities in the nodes at the time of acquisition ranged from 37 to 185 kBq (1-5 microCi). Four experiments were performed, consisting of 10-min emission and 3-min localization images. Anterior, posterior, and right and left lateral views of the thorax phantom were acquired, using each of 5 different (57)Co flood sources with activities ranging from 37 to 269 MBq (1.0-7.26 mCi). Ten 1-min localization images for each source were acquired and compared for quality. Three-minute localization images for 2 phantom thicknesses of 10 and 20 cm were acquired to determine the contrast-to-noise ratio for each (57)Co source. The total exposure was measured using an ion chamber survey meter. RESULTS: All sources allowed visualization of the lymphatic nodes in acquisitions as short as 3 min. Images using the 126-MBq (3.41-mCi) source demonstrated an adequate body outline along with visualization of all nodes seen on the emission image. The 37-MBq (1.0-mCi) source did not provide sufficient definition of the body outline, whereas the hotter sources decreased node visualization by increasing the background around the nodes at the same time that they increased the patient exposure. Node activity of 37 kBq (1 microCi) became undetectable on the anterior localization images yet was still visible on the lateral image because of greater attenuation of (57)Co photons. The estimated dose rate from the (57)Co sheet sources was 0.641 microSv/MBq/h. CONCLUSION: Acquiring a 3-min localization scan using a 126-MBq (3.41-mCi) source provided the best combination of clear-body outline and visualization of all nodes seen on the emission image. The estimated dose to the patient from the 126-MBq (3.41-mCi) sheet source was very low (8.7 microSv for unilateral and 13.1 microSv for bilateral). Node detectability decreased in localization images acquired using (57)Co sources of higher activity. This effect would be more pronounced in lymphoscintigrams of thin patients compared with those of patients of average thickness.