Purpose:The development of computer-aided diagnostic ͑CAD͒ methods for lung nodule detection, classification, and quantitative assessment can be facilitated through a well-characterized repository of computed tomography ͑CT͒ scans. The Lung Image Database Consortium ͑LIDC͒ and Image Database Resource Initiative ͑IDRI͒ completed such a database, establishing a publicly available reference for the medical imaging research community. Initiated by the National Cancer Institute ͑NCI͒, further advanced by the Foundation for the National Institutes of Health ͑FNIH͒, and accompanied by the Food and Drug Administration ͑FDA͒ through active participation, this public-private partnership demonstrates the success of a consortium founded on a consensus-based process. Methods: Seven academic centers and eight medical imaging companies collaborated to identify, address, and resolve challenging organizational, technical, and clinical issues to provide a solid foundation for a robust database. The LIDC/IDRI Database contains 1018 cases, each of which includes images from a clinical thoracic CT scan and an associated XML file that records the results of a two-phase image annotation process performed by four experienced thoracic radiologists. In the initial blinded-read phase, each radiologist independently reviewed each CT scan and marked lesions belonging to one of three categories ͑"noduleՆ 3 mm," "noduleϽ 3 mm," and "non-noduleՆ 3 mm"͒. In the subsequent unblinded-read phase, each radiologist independently reviewed their own marks along with the anonymized marks of the three other radiologists to render a final opinion. The goal of this process was to identify as completely as possible all lung nodules in each CT scan without requiring forced consensus. Results:The Database contains 7371 lesions marked "nodule" by at least one radiologist. 2669 of these lesions were marked "noduleՆ 3 mm" by at least one radiologist, of which 928 ͑34.7%͒ received such marks from all four radiologists. These 2669 lesions include nodule outlines and subjective nodule characteristic ratings. Conclusions:The LIDC/IDRI Database is expected to provide an essential medical imaging research resource to spur CAD development, validation, and dissemination in clinical practice.

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Purpose:A recent work has demonstrated the feasibility of estimating the dose to individual organs from multidetector CT exams using patient-specific, scanner-independent CTDI vol -to-organ-dose conversion coefficients. However, the previous study only investigated organ dose to a single patient model from a full-body helical CT scan. The purpose of this work was to extend the validity of this dose estimation technique to patients of any size undergoing a common clinical exam. This was done by determining the influence of patient size on organ dose conversion coefficients generated for typical abdominal CT exams. Methods: Monte Carlo simulations of abdominal exams were performed using models of 64-slice MDCT scanners from each of the four major manufacturers to obtain dose to radiosensitive organs for eight patient models of varying size, age, and gender. The scanner-specific organ doses were normalized by corresponding CTDI vol values and averaged across scanners to obtain scannerindependent CTDI vol -to-organ-dose conversion coefficients for each patient model. In order to obtain a metric for patient size, the outer perimeter of each patient was measured at the central slice of the abdominal scan region. Then, the relationship between CTDI vol -to-organ-dose conversion coefficients and patient perimeter was investigated for organs that were directly irradiated by the abdominal scan. These included organs that were either completely ͑"fully irradiated"͒ or partly ͑"partially irradiated"͒ contained within the abdominal exam region. Finally, dose to organs that were not at all contained within the scan region ͑"nonirradiated"͒ were compared to the doses delivered to fully irradiated organs. Results: CTDI vol -to-organ-dose conversion coefficients for fully irradiated abdominal organs had a strong exponential correlation with patient perimeter. Conversely, partially irradiated organs did not have a strong dependence on patient perimeter. In almost all cases, the doses delivered to nonirradiated organs were less than 5%, on average across patient models, of the mean dose of the fully irradiated organs. Conclusions: This work demonstrates the feasibility of calculating patient-specific, scannerindependent CTDI vol -to-organ-dose conversion coefficients for fully irradiated organs in patients undergoing typical abdominal CT exams. A method to calculate patient-specific, scanner-specific, and exam-specific organ dose estimates that requires only knowledge of the CTDI vol for the scan protocol and the patient's perimeter is thus possible. This method will have to be extended in future 820 820 Med. Phys. 38 "2…,

Studies involving Monte Carlo simulations are common in both diagnostic and therapy medical physics research, as well as other fields of basic and applied science. As with all experimental studies, the conditions and parameters used for Monte Carlo simulations impact their scope, validity, limitations, and generalizability. Unfortunately, many published peer-reviewed articles involving Monte Carlo simulations do not provide the level of detail needed for the reader to be able to properly assess the quality of the simulations. The American Association of Physicists in Medicine Task Group #268 developed guidelines to improve reporting of Monte Carlo studies in medical physics research. By following these guidelines, manuscripts submitted for peer-review will include a level of relevant detail that will increase the transparency, the ability to reproduce results, and the overall scientific value of these studies. The guidelines include a checklist of the items that should be included in the Methods, Results, and Discussion sections of manuscripts submitted for peer-review. These guidelines do not attempt to replace the journal reviewer, but rather to be a tool during the writing and review process. Given the varied nature of Monte Carlo studies, it is up to the authors and the reviewers to use this checklist appropriately, being conscious of how the different items apply to each particular scenario. It is envisioned that this list will be useful both for authors and for reviewers, to help ensure the adequate description of Monte Carlo studies in the medical physics literature.

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A preliminary report on medical radiation exposures to the US population based on publicly available sources of data estimated that the collective dose received from medical uses of radiation has increased by Ͼ700% between 1980 and 2006. 1 Computed tomography (CT) has had an annual growth rate of Ͼ10% per year and accounted for Ϸ50% of the collective dose in 2006. Approximately 65% of the collective CT dose is from studies of chest, abdomen, and pelvis. In 2006, cardiac CT accounted for 1.5% of the collective CT dose; however, utilization of cardiac CT is expected to rise, with the potential to further increase exposure to the population. 1 Nuclear medicine studies in the United States have increased by 5% annually to 20 million in 2006 and accounted for Ϸ25% of the 2006 collective medical radiation dose. Among nuclear medicine studies, cardiac imaging represented 57% of the number of studies and Ϸ85% of the radiation dose. 1 A number of publications on imaging with CT, fluoroscopy, or radioisotopes have emphasized the risks that may be associated with exposure to ionizing radiation. [2][3][4] To make informed decisions concerning the use of medical radiation in imaging procedures, the following are important components: (1) A working knowledge of the principles and uncertainties of the estimation of patient dose and biological risk; (2) a comparison of the risks of radiation exposure with the risks of activities in daily life; and (3) recognition of the potential risk of failing to make important diagnoses or treatment decisions if imaging is not performed because of safety concerns.There is no federal regulation of patient radiation dose, with the exception of mammography. Most federal and state regulations are aimed at equipment performance or the handling of nuclear materials. Therefore, appropriate utilization of the equipment or nuclear material in cardiac imaging, to maintain the dose as low as reasonably achievable, is the responsibility of the imaging physician and facility. The purpose of this Science Advisory is to provide a conceptual framework and make general recommendations for the safe use of cardiac imaging that relies on ionizing radiation. Parameters of Dosimetry CT and FluoroscopyThe parameters by which ionizing radiation is quantified differ among imaging modalities. 4 The amount of radiation produced by an imaging device can be described using exposure, expressed in International System of Units (SI) units of coulombs per kilogram (C/kg), or air kerma, expressed in SI units of milligrays (mGy). This document will use the term exposure, which refers to the amount of ionization produced in air by photon irradiation. Exposure can be measured for CT and fluoroscopy with ionization chambers within test objects (phantoms) or at body surfaces with minimal difficulty. Measurable or easily derived parameters, such as entrance skin exposure in radiography and fluoroscopy and the weighted CT dose index (CTDI w ) in CT, are useful to establish diagnostic reference levels for radioThe American Heart Ass...

This work has revealed that there is considerable variation among modern MDCT scanners in both CTDIvol and organ dose values. Because these variations are similar, CTDIvol can be used as a normalization factor with excellent results. This demonstrates the feasibility of establishing scanner-independent organ dose estimates by using CTDIvol to account for the differences between scanners.