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The AAPM has long advocated a consistent level of medical physics practice, and has published many recommendations and position statements toward that goal, such as Science Council Task Group reports related to calibration and quality assurance, Education Council and Professional Council Task Group reports related to education, training, and peer review, and Board‐approved Position Statements related to the Scope of Practice, physicist qualifications, and other aspects of medical physics practice. Despite these concerted and enduring efforts, the profession does not have clear and concise statements of the acceptable practice guidelines for routine clinical medical physics. As accreditation of clinical practices becomes more common, Medical Physics Practice Guidelines (MPPGs) will be crucial to ensuring a consistent benchmark for accreditation programs. To this end, the AAPM has recently endorsed the development of MPPGs, which may be generated in collaboration with other professional societies. The MPPGs are intended to be freely available to the general public. Accrediting organizations, regulatory agencies and legislators will be encouraged to reference these MPPGs when defining their respective requirements. MPPGs are intended to provide the medical community with a clear description of the minimum level of medical physics support that the AAPM would consider to prudent in all clinical practice settings. Support includes but is not limited to staffing, equipment, machine access, and training. These MPPGs are not designed to replace extensive Task Group reports or review articles, but rather to describe the recommended minimum level of medical physics support for specific clinical services. This session will describe the purpose, scope, and procedure for development of MPPGs and introduce the first two recently published MPPGs: (1) IGRT Commissioning and QA, and (2) CT Protocol Management and Review. Learning Objectives: 1. Understand the purpose and scope of MPPG from the AAPM 2. Understand the benefits and process of the development of MPPG by the AAPM 3. Introduce the first two AAPM MPPGs

The AAPM CT Working Group on Nomenclature and Protocols (CT WGNP) was established in 2010; this working group is comprised of AAPM members with considerable CT experience, as well as representatives from each of the major CT manufacturers, ASRT, ACR, DICOM, FDA and Image Gently. The CT WGNP has two charges: 1. To develop consensus protocols for frequently performed CT examinations, summarizing the basic requirements of the exam and giving several model‐specific examples of scan and reconstruction parameters. 2. To develop by consensus a set of standardized terms for use on CT scanners, including all parameters that control the scan acquisition or reconstruction that are programmed by the user, are displayed on the final image or included in a DICOM‐specified tag, or describe a fundamental CT setting that is not always user selectable (such as a beam‐shaping filter). This working group has developed a set of tools for members and the general public that is available on the AAPM website. These tools include a Lexicon to allow users to translate important CT acquisition and reconstruction terms between different manufacturers' systems, thereby improving understanding of scan parameter meanings and decreasing the potential for parameter errors. A set of routine adult CT protocols have been provided that include Brain CT Perfusion, Routine Head, Routine Chest and Routine Abdomen/Pelvis exams. These provide a set of reasonable reference protocols for frequently performed CT examinations, summarizing the basic requirements of the exam and giving several model‐specific examples of scan and reconstruction parameters. These resources directly address the original charges of the working group and continue to be the main focus of effort. Pediatric versions of these protocols are now under development. In addition, the working group has been asked by MITA to develop additional resources specific to CT. The working group provides an excellent venue for discussion of issues that affect each of the primary stakeholders in the CT community.Recommendations were developed regarding default values for use in the CT Dose Check feature that has been incorporated into newer CT systems. Additionally, a set of educational slides specific to radiation dose issues in CT have been made created and made available. Versions of the slides that include manufacturer‐specific information, particularly with respect to radiation dose reduction features available on CT scanners, are under development. These resources will be reviewed during this lecture and directions regarding how to find and utilize this information will be given. Dr. Cody receives ‘in‐kind’ support of research from GE Healthcare.

Purpose: The purpose of this study was to extend the validation of Monte Carlo (MC) simulation based dose estimates by comparing simulated values with in‐vivo measurements from clinical patient scans. Methods: The Institutional Review Board approved the acquisition of in‐vivo rectal dose measurements in a pilot study of 9 patients undergoing CT Colonography on an MDCT (LightSpeed VCT, GE Healthcare). Per patient, two scans, prone and supine, were acquired both using a fixed mAs technique. In‐vivo dose measurements were obtained using TLD capsules that were affixed to the inner lumen of rectal catheters. Dose from the TLDs were determined taking into account their energy response. Simulations were performed using voxelized models of the patients and the TLDs based on CT image data. A previously developed MC based model was used to simulate the scanner and each patient scan. Dose to the TLD was estimated for each patient scan. The measured and simulated in‐vivo TLD dose values were compared for all 9 patients and the Root Mean Square (RMS) error was calculated as well as the correlation. Additionally the simulated results were compared with calculated Size Specific Dose Estimates (SSDEs) for each patient. Results: The RMS error between TLD measurements and MC simulations was 12.2% with a maximum of 20.3% and minimum of ‐ 19.7%. Comparison of simulations and SSDE resulted in an RMS of 17.0% with a minimum of ‐ 22.9% and maximum of 22.8%. Conclusion: The results of this study demonstrated that MC simulations using voxelized patient and equivalent source model Result in reasonably accurate doses compared to actual measured doses. Several possible improvements to the performance of the MC model were identified (including reconstructing images at the biggest field of view for full coverage of the anatomy, etc.) Dr. Michael McNitt‐Gray; Institutional research agreement, Siemens AG; Recipient research support Siemens AG; Consultant, Flaherty Sensabaugh Bonasso PLLC; Consultant, Fulbright and Jaworski, LLC; Maryam Khatonabadi and Kyle McMillan ripient research support Siemens AG

Purpose: The results of a long-term, comprehensive CT quality control (QC) program were analyzed to investigate differences in failure rates based on QC test, scanner utilization pattern, and number of channels, as well as explore issues regarding testing frequency. Methods: CT QC data were collected over a 4-yr period for 26 CT scanners representing two different vendors and using three different QC programs culminating in over 100 scanner-years of QC data. QC tests analyzed included water tests [mean CT number, standard deviation, and uniformity], linearity tests [air, water, and acrylic], and artifact analysis [water phantom and large phantom]. The data were organized based on scanner use, number of channels, scanner modality, and QC test. Logistic regression model analysis with generalized estimating equation method was used to estimate failure rates for each group. Results: A significant difference between failure rates with respect to QC test was found (p-value = 0.02). Large phantom artifacts, standard deviation of water, and water phantom artifacts had the three highest failure rates. No significant difference was found between failure rates organized by scanner use, scanner modality, or number of channels. Conclusions: Standard deviation of water is the most important quantitative value to collect as part of a daily QC program. Uniformity and linearity tests have relatively low failure rates and, therefore, may not require daily verification. While its failure rates were moderate, daily artifact analysis is suggested due to its potentially high impact on clinical image quality. Weekly or monthly large phantom artifact analysis is encouraged for those sites possessing an appropriate phantom.

Models which are based on non-invasive bone measurements may in the future be able to successfully identify individual subjects at an increased risk for hip fracture; thus, we designed a study to determine the usefulness of dual-energy X-ray absorptiometry (DXA) and quantitative computed tomography (QCT) in predicting the local material properties of human proximal femoral cancellous bone. There has been some disagreement in the scientific literature regarding appropriate predictive models for local material properties of cancellous bone. We sought to confirm that density-mechanical property relationships were consistent from subject to subject, and that three-dimensional QCT measurements were stronger predictors of mechanical properties than two-dimensional DXA results. Linear and power fit relationships between these densitometric measures and material properties were also examined to determine which were more appropriate. Bone cubes from specific regions of highly oriented trabeculae were analyzed separately to determine if cube orientation had an effect on mechanical properties independent of bone density. Ten pairs of ex vivo femurs (five male, five female; age 30-93, mean age 62) were prepared such that specific anatomic planes were visible radiographically. Both QCT and DXA measurements were made on all 20 femurs. Cancellous bone cubes were obtained proceeding along two distinct directions from the proximal end of each femur pair. Unexpectedly, the density-modulus relationships among these ten donors were found to be significantly different at p0.01 (83 percent of the tests were different at p0.0001). Density-strength regressions were also significantly different at p0.01, but this effect was not as consistent nor as statistically significant. In general, the QCT method did not produce predictions of local cancellous bone material properties superior to the DXA method. The linear and power fit models appeared to produce consistent results, with neither being obviously more advantageous. These density measurements explained at best 30-40 percent of the variance in modulus and 50-60 percent of the variance in ultimate stress. The orientation of cancellous cubes in the principal compressive trabeculae region was a significant contributor to mechanical properties (p= 0.0001) independent of bone density. This finding was not as dramatic in the femoral neck cancellous bone region.

Purpose: Calcific and hemorrhagic foci of susceptibility are frequently encountered in routine brain MR studies and are difficult to distinguish. Single‐energy CT can be used to identify lesions with attenuation over 100 HU as calcific however those lesions with lower attenuation cannot be reliably identified1. While calcific lesions are unlikely to cause harm, hemorrhagic lesions carry a risk of subsequent intracranial bleeding. A methodology was developed using dual‐energy Gemstone Spectral Imaging‐CT (GSI‐CT) to take advantage of the unique attenuation properties of calcium and iron to distinguish between these two etiologies. Methods: Ferric oxide and hydroxyapatite were used to model hemorrhage and calcification respectively. A uniform distribution of these compounds was suspended in 1 % agarose gels to model elemental concentrations of iron and calcium over a range of 0.005M to 0.25M. The gels were imaged in an anthropomorphic head phantom with a single‐energy routine brain protocol. These scans were utilized to create HU matched gels of calcium and iron from 0 to 100HU which were verified using the single‐energy routine brain protocol. The HU matched gels were imaged with a dual‐energy protocol which had similar dose and imaging parameters to the single‐energy protocol. Material decomposition was used to create water and calcium density images from the dual‐energy data. Water/calcium scatterplots were created from measurements on the material density images. For each HU matched pair, the separation between the mean values along each axis was measured and plotted against the HU. The uncertainty in the separation was calculated as the quadrature sum of the standard deviations along both the water and calcium axes. Results: Matched HU pairs yielded separation greater than the uncertainty for 40HU and above along both the calcium and water axes of the material decomposition scatterplot. Conclusions: HU matched iron and calciumgels of 40HU and above could be distinguished using dual‐energy GSI‐CT.

Serial evaluation of pagetic lesions is handicapped by the inability of conventional methods to reproduce precisely the positioning of the area of interest. A computed tomography method that provides visual and quantitative comparisons between data sets acquired at different times has been developed. The utility of this method is illustrated with an example of serial examinations that demonstrate the effect of treatment on small lytic lesions in the lumbar spine. A further demonstration is made of the ability of this method to identify and quantify lytic changes within the cochlear capsule.

Purpose: Reduced kVp scanning is being recommended for pediatric patients as well as when contrast studies are being performed. The purpose of this work is to quantitatively compare the organ doses resulting from scans at different kVP and determine the ratio of mAs at each kVp that results in equivalent organ dose. Methods: Using Monte Carlo simulations, two fixed tube current chest exams with 120kVp and 80kVp were simulated for 18 voxelized adult female patient models. Each patient had lung and glandular breast tissues contoured, so that doses to these tissues could be estimated. The resulting organ doses for two kVps were compared for a given mAs, which allowed a comparison to identify the ratio of mAs values needed to achieve the same organ dose for 120kVp and 80kVp. For a further comparison, these values were compared to CTDIw values obtained at both kVps in both 16cm and 32cm CTDI phantoms. Results: For lung dose, the ratio of dose from 120kVp to 80kVp was 3.96 (standard deviation of 0.17) for a given mAs across all 18 patient models; similarly, the glandular breast dose ratio was 4.15 (standard deviation of 0.12). For the CTDIw phantom values, the ratio of dose values from 120kVp to 80kVp were 3.37 and 3.78 for 16 cm and 32 cm phantoms, respectively. Conclusions: Monte Carlo simulation results indicate that lowering tube voltage from 120 to 80 results in almost 4 fold radiation dose reduction for a given mAs. Stated another way, the mAs at 80kVp could be increased by up to a factor of four compared to mAs used at 120kVp and still receive a similar organ dose in chest scans. This is an even higher ratio than predicted by CTDI phantom results. Future studies include pediatric models with contoured lungs and breast.

Three-dimensional tomographic data sets are routinely produced in CT and MRI studies. Particularly good quality sagittal and coronal views can be obtained when the z-slice thickness is similar to the x and y pixel size within the original transverse views. When image data has been acquired on the same subject at two separate occasions, it may be useful or necessary to rotate and translate the data from the second study so that it is spacially aligned with the first study. We have developed interactive graphic software to interpolate image files in three orthogonal planes which can be arbitrarily oriented and to align the data from two studies using subtraction views as an indicator of alignment and differential value. The design elements for this software are described in this paper. Two thin slice x-ray CT studies from the same subject are used to illustrate the software.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The measurement of regional bone mineral density (rBMD) is a new method of evaluation of the human temporal bone in vitro or in vivo. Modified computed tomography (CT) enables us to collect a three-dimensional array of precise, reproducible bone density values, as well as high-quality CT images. Measurements are calibrated using phantoms of known composition and density. Conventional CT provides density information that is relative, qualitative, and lacks precise reproducibility over time. The rBMD technique provides precise numeric density measurements. Additional image processing capabilities are described. In vivo data from six normal temporal bones and from two patients with Paget's disease involving the temporal bone are presented to demonstrate the technique.

On a macroscopic scale, the structural characteristics of whole bone are likely dependent on the distribution of typically applied loads to the bone surface, the full bone shape, the thickness of the cortex at the various surface positions, and the distribution of cancellous bone material. X-ray computed tomography is presently the best available method for assessing the macroarchitecture of bone in-vivo. Fine detail, three-dimensional CT methods are available to measure regional bone mineral density (rBMD) in contiguously spaced small volumes and have been applied to the assessment of macroarchitecture in vertebrae. The more detailed rBMD methods produce radiation exposures to the subject similar to lumbar radiography and substantially higher than traditional QCT. The cancellous bone within lumbar vertebral bodies has been found in cross-sectional studies to have increased density in the inferior, posterior and lateral regions. Notably, regions with higher density at age 40 have a larger decline with age. The vertebral body cortex declines with age at a slower rate than observed for cancellous bone; however, the decline with age of cortical bone appears to vary substantially amongst subjects. The amount of cortical bone in the anterior portion of the body is less than in the lateral portion, which may explain previous discrepancies in assessing the fraction of vertebral body bone in the cortex.

Purpose: To share our experience implementing new strategies (as technology became available) to reduce Computed Tomography(CT) radiation dose to pediatric patients at a high‐volume cancer center housing 13 General Electric (GE) multidetector row CT (MDCT) scanners representing various models.Method and Materials: In October of 2008, tube current modulation (TCM) was implemented and protocols were created based on the display field of view parameter. Approximately 10 months later, the noise index for all protocols was increased by 2. Three months after increasing the noise index, the minimum and maximum tube current (mA) values were both dropped by 20% across all protocols. A chart review was used to identify eight pediatric patients (from 1 – 15 years old) that received chest CT scans before and after implementation of each of the three dose‐reduction strategies; within each patient, all technical parameters other than effective mAs were constant between scans. Results: The average effective mAs (across all eight patients) dropped from 103 mAs (49 – 171 mAs) prior to October 2008 to 75 mAs (42 – 109 mAs) after implementing all of three strategies. TCM alone reduced dose by an average of 19 %, increasing the noise index combined with TCM by 20% on average, and dropping the minimum and maximum mA values combined with the other two strategies by an average of 23%. All of the exams included in this study were of diagnostic quality with respect to the imaging task. Conclusion: To date, the combination of these efforts has led to an average reduction in dose of 23%. Additional approaches (adaptive statistical iterative reconstruction and organ shielding) are currently being evaluated and are expected to provide even greater dose‐savings to our pediatric patients.

Purpose: To explore alternative techniques for the measurement of CTskin dose and compare with the CTDI method. Method and Materials: Using a Farmer chamber point doses were measured under various scan conditions on the surface of anthropomorphic phantoms as well as at the top‐hole position of CTDI phantoms on two CTscanners of different manufacturers. Also at the top‐hole position of CTDI head and body phantoms CTDI100 values were measured using a 100mm pencil ion chamber. These CTDI100 (top) values were then normalized by the pitch factors. The ratio of CTDI100 (top)/pitch over the point dose was obtained under each scan condition and evaluated for quantitatively determining if the CTDI method underestimates or overestimates skin dose. Size of the Farmer chamber (length 18.8mm) prompted the use of nanoDOT dosimeters (4mm diameter Landauer) for additional point dose measurements under the same conditions as the Farmer chamber. The nano DOTs were calibrated using the same kVp as the CT scans;calibration was conducted separately for each ∼20–65%. Results: For cine scans CTDI100 (top)/pitch overestimated skin dose by‐20–65%. For helical scans CTDI100 (top)/pitch overestimated skin dose by ∼20–50%. The variations mainly depend on the size and shape of the phantom and on the type of scanner. The nanoDOT system produced results in general agreement (within 15%) of those obtained using a Farmer chamber. Conclusion: Alternative techniques using Farmer chamber and nanoDOTs for determination of CTskin dose were evaluated and compared to CTDI results. Farmer chamber produces readily available dose reading vs the nanoDOTs which must be processed using a separate readout system. On the other hand nanoDOTs can be attached to a patient's skin for monitoring skin dose during a clinical exam and do not cause artifacts in images. Both techniques show promise for clinically practical skin dose CTdosimetry.

Purpose: To determine whether a dose penalty exists when scanning patients in axial scan mode on General Electric (GE)Computed Tomography(CT)scanners. A 10‐millisecond‐long rise of the x‐ray tube output occurs immediately before image acquisition and is suspected to contribute additional dose near the start angle of the x‐ray tube. This dose penalty may exist for axial scanning because the rise time occurs for every 360° rotation of the x‐ray tube, whereas rise time only occurs once in helical scan mode. Method and Materials: 10‐, 15‐, and 32‐cm CTDI phantoms were scanned on a GE VCT scanner for a single axial rotation in service mode. Exposure was measured at a constant peripheral location (12:00) and recorded for various x‐ray tube start angles. These methods were repeated on the 32‐cm phantom, changing its vertical position in 2‐cm increments from 6‐cm below to 12‐cm above iso‐center. Results: Exposure, measured at the 12:00 peripheral chamber position, was 5.5%, 1.8%, and 1.0% higher in the 32‐, 15‐, and 10‐cm phantom, respectively, when a start angle of 0° was used versus a start angle of 270° (this start angle was used for comparison to avoid attenuation from the patient table). The exposure penalty ranged from 2.9% to 12.7% when the 32‐cm phantom was 6‐cm below and 12‐cm above iso‐center, respectively. Conclusion: In light of the dose penalty observed in this study, axial acquisitions should feature a start angle of 180° to avoid imparting this penalty on superficial radiosensitive organs (i.e. breast, testes, and thyroid), which are near the anterior side of patients. Also, dose is not consistent around the periphery of a phantom scanned in axial mode and contiguous helical scanning (pitch = 1.0) provides a dose advantage over axial scanning (all other technique factors being equal).

Purpose: Traditionally, half‐value layer (HVL) of an x‐ray beam has been calculated through either linear (Eq. 2) or semi‐logarithmic (Eq. 3) interpolation under the assumption that attenuation varies linearly or monochromatically over a small range of attenuator thicknesses. Our aim is to evaluate the accuracy of HVL calculation using Lambert W interpolation (Eq. 4–6) and compare it to the traditional methods. Method and Materials: X‐ray exposure was measured over a wide range of attenuator thicknesses on a CT scanner (range: 0.49 mm Al – 33.03 mm Al), a mammography system (range: 0.1 mm Al – 1.08 mm Al), and a general radiography system (range: 0.5 mm Al – 10 mm Al; range: 0.1 mm Cu – 0.45 mm Cu). Exposure was measured using a RadCal exposure meter connected to a 10‐cm pencil ionization chamber for the CT scanner, a mammography chamber for the mammography system, and a 6 cc chamber for the general radiography system. Exposure values were measured at two different techniques for each system. Results: The percent transmission of the measured data was calculated and plotted versus measured attenuator thickness. The three interpolation methods used two measured data points that bracketed the HVL to construct percent transmission versus material thickness curves. Using data measured on a CT scanner for120 kVp, Lambert W interpolation yielded less than 5% error in the calculated HVL for approximately 89% of all possible interpolation and extrapolation point combinations. Using the same data, semi‐logarithmic and linear interpolation yielded less than 5% error in the calculated HVL for approximately 38% and 5.6% of all possible interpolation and extrapolation point combinations, respectively. Conclusion: Lambert W interpolation is more accurate and less sensitive to the choice of interpolation points compared to traditional methods.

Purpose: To investigate why organ doses for helical computed tomography(CT) scans were found to be up to 25% less than similar axial scans. The organ dose measurements were performed previously using thermoluminescent point dosimeters (TLD) in a pediatric phantom. Method and Materials: Tension rods were placed across the bore of the CT scanners, flanking the scan region, in order to support measurement devices without relying on the patient table which moves during helical scans. Under this configuration, the table was kept out of the scan region for all measurements. Beam profile measurements were made for 20mm and 40mm beam configurations using computed radiography(CR) plates and software to compute the FWHM of the profile. Exposure measurements were made with a 10cm pencil ion chamber in a 16cm head phantom, similar to standard CTDImeasurements. These measurements were made for multiple 64‐channel CT scanners in both axial and helical modes. For the exposure measurements, multiple scan parameters were varied including kVp, focal spot size, field of view, rotation time, exposure time, and pitch. Differences between axial and helical measurement results were compared. Results: Differences in FWHM values for the beam width measurements between axial and helical scan modes were found to be less than 1%. The normalized exposure values between axial and helical scans were found to be less than 1% in general. The only exceptions were caused by differing focal spot sizes and rotation times of less than 1 second, for which the difference was up to 2.5%, but still well within the manufacturer's tolerance. Conclusion: There were no substantial differences between axial and helical scans for the radiation profiles and exposure parameters we examined. Therefore, we conclude that the explanation for the axial/helical point dose differences must lie elsewhere. One possibility might be patient table mechanic.

CT technology has improved dramatically over the past decade and its clinical utilization has increased significantly as well. While CT can yield exquisite descriptions of anatomy that were not previously possible (at least not with noninvasive techniques), its increased utilization has led concerns over radiationdose;CT has now been identified as the single largest contributor to medical radiationdose to the population and accounts for approximately 50% of medical exposure. Methods to reduce radiationdose have been the focus of all stakeholders (medical physicists, technologists, radiologists, manufacturers and regulators). Reducing dose while maintaining acceptable image quality can be complex and this is made even more complex when considering patients of different sizes. This talk will first describe methods currently used, and some being developed, to estimate radiationdose in patients. This will include a discussion of measurement techniques as well as Monte Carlo simulation‐based techniques. Specific attention will be paid to the differences in dose to patients of different sizes ranging from pediatric patients to obese adult patients. Tradeoffs in image quality and radiationdose will also be described in this context as well. Radiationdose reduction techniques, including a review of various tube current modulation schemes currently being employed will also be described. The effect of these dose reduction methods on both radiationdose and image quality will be discussed, again with attention to how they can be deployed with patients of different size. Learning Objectives: 1. Understand how radiationdose for CT studies is currently estimated 2. Understand the trade‐offs of dose and image quality, especially for large (obese) patients and in pediatric patients 3. Review of the manufacturers' dose modulation methods and how these affect dose in different patients

In clinical practice, decisions must be made about whether and how to convert to newer technologies. To address this issue, two separate studies were conducted. We evaluated the relationships between results of lumbar spine measurements using two dual photon absorptiometry (DPA1 and DPA2) instruments and one dual energy X-ray (DXA) instrument with the same subjects (49 volunteers), and also in 65 patients who were measured on the DPA1 and DXA machines. Second, we measured the lumbar spine and the proximal femur in three groups of 12 female volunteers three times on one instrument within 1 week. We purposely simulated a busy clinic setting with different technologists, older radioactive sources, and a heterogeneous patient group. The comparison study indicated a significant difference between the mean bone density values reported by the machines, but the results were highly correlated (R 2 = 0.89–0.96). The short-term precision errors (coefficients of variation) differed among the instruments, ranging from 1.3% (DXA of the spine) to 5.1% (DPA1 of the spine), and in the femoral neck, 2.3% and 2.4% (DXA and DPA1, respectively) versus 3.5% by DPA2. This study emphasizes the differences between instruments, the potential for greater error in busy clinic environments, and the apparent superiority of dual energy X-ray absorptiometry under these less than ideal conditions.

Purpose: To develop a filmless technique for the measurement of CT beam width for QA. Method and Materials:Images of pre‐patient collimated CT beams were acquired using Fuji computed radiography(CR) cassettes and direct‐exposure film (DF). CR cassettes were exposed using 80kV, 10mAs to avoid signal saturation. The DF was exposed at 80kV, 30mAs to achieve a proper optical density. The DF image was digitized then linearized. To achieve a proper signal range for CR, various plate‐reading protocols were evaluated. An IDL program was developed to automatically handle both the digitized film and a variety of CRimage sizes. “Unprocessed” logarithmic CR data were linearized, which is critical to validate the FWHM. The program executes in an interactive fashion, whereby the user selects the beam to analyze. The program determines the background signal for subtraction then samples multiple cross‐beam profiles to form an averaged profile. The profile is smoothed and the FWHM is determined. Results: Under proper conditions of image acquisition, results show both DF and CR are appropriate techniques for beam width measurements. The CR technique demonstrated a high level of reproducibility with a coefficient of variation below 0.5%. Also, the CR results were within 0.3mm of specifications. Using various sizes of CR cassettes had a minimal effect on the results. However, if the properly exposed image is saturated due to an inappropriate CR plate reading protocol, the inaccuracy is substantial (>1mm). The technique worked well for annual tests of six GEscanners. Over a wide range of beam width configurations, all measurements were within 0.9mm of specifications. Conclusion: A technique for determination of CT beam width in a filmless environment was developed and tested. The results obtained using CR yield accurate measurements of CT beam profile width. The technique is effective, practical, and has proven to be robust.

Purpose: It is the expectation of CT simulations to get the best CTimages with free breathing scans. CTimaging protocol settings needed to achieve optimal image quality have been identified for every scanner in a Radiation Oncology Department having various makes and models of CT simulators. Method and Materials: A Catphan® phantom was used to evaluate the image quality of 5 different makes/models. Various pitch, detector configuration, and gantry speed parameters were studied, while maintaining constant kVp, effective mAs, head display field of view (DFOV), reconstruction filter, and image thickness settings. Three aspects of image quality were evaluated: 1) helical artifact presence, 2) high contrast resolution, and 3) low contrast resolution. Results: For all CTs, more artifacts appear when the channel width is equal to the image thickness. Less helical artifacts are present if the channel width is half or less of the image thickness. At these settings, however, artifacts are still present in varying degrees depending on pitch. For a 16‐channel CT of one manufacturer, the artifact‐free pitch setting is 1.4 or less, but for their 16‐channel large bore CT, it is 0.9 or less. For another manufacturer's 16‐channel CT, the channel width has to be 1/4 of the image thickness with a pitch of 0.6 to obtain artifact‐free images. The optimal settings for all scanners are different. Only slight differences in high and low contrast resolution are observed, even at varying gantry rotation speeds; these differences seem insignificant at body DFOV (clinical setting). Conclusions: In order to obtain optimal CTimage settings, a study should be conducted for each CT model, for there is a vast difference in optimal settings among them. Faster rotation gantry speed should be used as possible, for reduced motion artifact is expected for patient free‐breathing scans.

Purpose: To determine radiation dose to specific organs in a pediatric phantom from a CT scan, and to determine if there is a significant difference between: axial (step and shoot) and helical acquisitions, when using very similar photon flux values (effective mAs). Method and Materials: An anthropomorphic pediatric phantom (5 year old equivalent) was used to investigate organ dose at the surface and internal to the phantom. The phantom contains four different tissue equivalent materials: soft tissue, bone, brain, and lung, and was imaged on a 64‐channel CTscanner with a head protocol [axial and two helical scans (pitch = 0.516 and 0.984)], and a chest protocol [axial and three helical scans (pitch = 0.516, 0.984, and 1.375)]. Effective mAs was kept constant (within 3%) for head and chest protocols. Dose measurements were acquired using thermoluminescent dosimeter(TLD)powder in capsules placed in the phantom sections in plug holes. The organs of interest for this study were: brain, both eyes, thyroid, sternum, both breasts, and both lungs.Results: All axial organ dose measurements were significantly higher (p 0.05) in organ dose values between the pitch values 0.516 and 0.984 for both head and chest scans. The chest organ dose measurements obtained using a pitch of 1.375 were significantly higher (p

CT technology continues to develop at a rapid pace, offering imaging options and features that can dramatically improve image quality. Multichannel systems are now commonplace and the number of channels continues to increase, allowing greater coverage per rotation, shorter scan times, and thinner images. Isotropic volumetric data acquisition permits retrospective reconstructions of many different image thicknesses and reformats can be created through multiple planes. These and many other advances have escalated and expanded the utility of CTimaging as a core diagnostic tool. However, coupled with the improved CT technology is the increased complexity of operating the scanners and the elevated potential of increasing the radiation dose. CT operators must choose from multiple options, many of which are interdependent, for the control of the multitude of available features. The impact of each of these options on image quality and radiation dose can range from subtle to substantial, and may not necessarily be obvious to the operator. This lecture will focus on the clinical implications of CT scan parameters and provide guidance on achieving an optimal compromise between image quality and radiation dose when constructing CT scan protocols. Educational Objectives: 1. Understand the influence of primary CT scan parameters on image quality and radiation dose. 2. Learn how to use imaging task‐specific priorities with consideration for radiation dose when determining scanner settings.

Purpose: To compare methods of quantifying lung damage based on noninvasive flat‐panel CTimages with the standard method based on histologic section analysis.Method and Materials:Lung damage was induced in mice with bleomycin and damage progression followed with fpCT on days 10, 14, and 21 and with postmortem histological examination on day 21. Ten mice, five control and five treated, were scanned under breath hold with flat‐panel CT (fpCT). Prior to scanning, a tail vein catheter was inserted for administration of IV contrast. The percent lung damage calculated from fpCT (PLDfpCT) imagedata sets was compared to that obtained from sequential histological sections (PLDH). Results: IV contrast was helpful in separating vessels from regions of lung damage. PLDfpCT calculations were on average 2 times greater than PLDH calculations. Linear trendlines were fit between PLDH and PLDfpCT to all data (n=10) and then to only the treated mice (n=5); the resultant R2 values were 0.87 and 0.89, respectively. The fpCT scans allowed for observation of the progression of damage over time versus the single snapshot sampled with histology. Less damage was observed at day 14 than at either day 10 or day 21, which could be due to a transition from an acute inflammatory reaction to inflammation with formation of collagen. Conclusion: The quantification of lung damage based on fpCT images was strongly correlated to the conventional histological section analysis. Although the overall change in damage is consistent between histology and fpCT the magnitude of measured damage differs which may be explained by an inflammatory response throughout the lung which is not detected with histology. A potential strength of these longitudinal studies is the ability to follow individual animals over time to investigate biological affects such as a transition from acute to chronic damage patterns.

This presentation will focus on examples and causes of artifacts produced by modern multi‐slice CTscanners. Many of these artifacts were recognized because of a stringent quality control program implemented in our institution. The design of this quality control program will be described, along with its relative costs and benefits. Extending such a program among scanners produced by different vendors will be discussed. Learning Objectives: 1. To recognize basic artifacts in patient and phantom images generated by modern multi‐slice CTscanners. 2. To understand some basic requirements of a quality control program for multi‐slice CTscanners.

The first day of the Molecular Imaging Symposium (MI‐1) will focus on the technology aspects of molecular, functional, and small animal imaging. Modalities which will be discussed include micro‐CT, micro‐PET, and high resolution MRI for small animal imaging. The presentation on micro‐CT technology will include an introduction to the basic requirements of the scanner hardware, examples of the images and biological applications in which micro‐CT is useful, and the radiation dose to the small animal undergoing micro‐CT will also be discussed. Micro‐CT techniques require longer acquisition times than human scanners, and thus maintaining the animal in a viable but motionless state is of clear importance. Therefore, issues surrounding animal support including anesthesia and respiratory gating will also be presented. Micro‐PET systems are widely used in small animal imaging for genome research, and represent probably the mainstay of truly molecular imaging modalities at this point in time. The presentation on micro‐PET will include a description of micro‐PET scanner hardware, a discussion of PET‐radiotracers, and an overview of current small animal PET systems. The limitation of current micro‐PET system design will be discussed, and ideas for overcoming some of these limitations will be presented. High resolution MRI systems have the benefit of delivering exquisite contrast with excellent spatial resolution, with no ionizing radiation. The presentation on micro‐MRI techniques for phenotype imaging will describe the integration of physics, biology, chemistry, engineering, and computer science which is necessary to achieve state‐of‐the‐art small animal MRIimaging. The use of hyperpolarized gases for lung imaging and MR histology will be discussed as well. The availability of small animal imaging systems across a number of modalities has proved essential for a large number of research applications. The primary goal of MI‐1 is to help familiarize medical physicists with the technical design and capabilities of these high resolution small animal imaging systems, and to highlight research applications of their use. Different modalities are used to address different research questions, and this symposium will emphasize the strengths and weaknesses of each modality in regards to various research applications. Differences between animal imaging and human scanners will also be discussed.

Introduction Lung adenocarcinomas (ADCs) with k-ras mutation are reported to be resistant to tyrosine kinase inhibitors of the epidermal growth factor receptor. Alternative therapies are needed for these specific ADCs. The serine/threonine kinase AKT and its downstream mediator mammalian target of rapamycin (mTOR) are activated in human lung ADC and clinical trials are underway to test whether mTOR inhibition is useful in treating lung cancer. The goal of this study is to treat the K-ras LAI mice, which undergo somatic activation of the K-ras oncogene and recapitulate morphologic changes of alveolar epithelial cells that precede human lung ADC with an mTOR inhibitor (CCI-779). Methods K-ras LA1 mice were treated for 1 month with CCI-779 at high dose (20 mg/kg/day), low dose (0.1 mg/kg/day) and vehicle. Micro-CT scan was performed before and after completion of treatment. Tumor numbers and volume were evaluated at micro-CT scan and autopsy exam. Expression of downstream mediators of mTOR was studied by immunohistochemistry and western blot on lung tissue. Mechanistic studies were performed on LKR-13, a lung ADC cell line derived from K-ras LA1 mice. The results were extrapolated to human ADC based on samples from a cohort of 400 patients. Results The levels of phosphorylated AKTSer473 (p-AKT) and S6Ser236/235 (p-S6), a downstream mediator of mTOR, increased with malignant progression (normal alveolar epithelial cells to ADC) in K-ras LAI mice and patients with lung ADC. Macrophages were prominently associated with atypical alveolar hyper-plasia (AAH), an early neoplastic change, and expressed high levels of p-S6. mTOR inhibition in K-ras LAI mice inhibited the progression of AAH to adenoma, decreased the size of adenomas, and induced apoptosis of intra-epithelial macrophages. LKR-13 was resistant to treatment with CCI-779 in vitro . However, as syngeneic tumors in wild type littermates LKR-13 cells recruited intra-epithelial macrophages and regressed in response to treatment with CCI-779. Conclusions These findings provide evidence that the expansion of lung ADC precursors induced by oncogenic k-ras requires mTOR-dependent signaling and suggest that host factors derived from macrophages may contribute to ADC progression [1].

Purpose: To develop a technique capable of generating a high resolution 3D ventilation image in a rat model from a series of CTimages. This technique will be invaluable in developing strategies for radiation treatmentoptimization and characterization of pulmonary disease states. Method and Materials: A series of three 150gram Fischer 344 rats were euthanized and intubated. The lungs were equilibrated to ambient pressure, then serially inflated and imaged at approximately 1ml increments. A GE flat panel CT scanner capable of 0.15mm resolution was utilized for image acquisition. A deformable image registration algorithm, utilizing 3D optical flow, was applied to each pair of CTimages to map, on a voxel by voxel basis, corresponding tissue elements. The difference in average CT number of a nine voxel region surrounding each pair of mapped voxels was then utilized to compute the change in fraction air per voxel (i.e. regional ventilation). This local ventilation measurement was then superimposed onto each voxel of the CTimage to generate a 3D ventilation image. The sum of each voxel's ventilation (i.e. total lung ventilation) was then compared to the change in manually segmented lung volumes between each of a series of twenty‐two pair of CTimages.Results: Visualization of the 3D ventilation images revealed regional heterogeneity of ventilation throughout the lung fields. The images required smoothing by averaging over a 0.75mm cube surrounding each voxel to minimize artifacts. The calculated total lung ventilation compared favorably with the change in manually segmented lung volumes, with a slope of unity, as expected, and a correlation coefficient of R=0.99. Conclusion: We have demonstrated a unique method of quantifying regional lung ventilation with sub‐millimeter accuracy in a rat model. This model has been developed in order to study lung function and radiation injury.

Purpose: Acquiring Micro‐CT images of murine lungsin vivo requires respiratory gating to achieve optimal tissuecontrast at full inspiration. The use of a custom small‐animal ventilator and a specific acquisition technique has resulted in a dramatic improvement in image quality. Method and Materials: A commercially available small animal ventilator was customized for use with our commercially available micro‐CT scanner. The modified ventilator can hold the pressure in rodent lungs at a constant level (essentially perform a series of short breath‐holds at full inspiration), and can be programmed to trigger the scanner acquisition phase. The ventilator is set to cyclicly achieve a pre‐set pressure level of the anesthetic gas mixture (inspiration), trigger the x‐ray on phase of the scanner, acquire a single frame during the stable pressure phase, close the x‐ray shutter, and finally release the pressure of the anesthetic gas mixture (expiration) while the scanner rotates to the next view position, at which point the cycle repeats. Images can be reconstructed with either 90 or 45 micron isotropic voxels. Example images of several mice with lungtumors will be presented. Radiation dose is estimated to be about 0.26 Gy per scan session using this methodology. Results: This implementation has produced images with improved visibility of the tissue components, including airways and pulmonary blood vessels. The margins of individual lung lobes can be identified, which is very helpful when determining the location of a pathologic structure (lesion) for research purposes or subsequent necropsy. The improved image quality is also very helpful in the detection of small (0.3–0.5 mm diameter) lung lesions. Conclusion:Lungcancer research can benefit from extensive use of mouse models to investigate potential new treatment approaches. The use of improved non‐invasive imaging has positively impacted our lungcancer research program.

Purpose: Compare two x‐ray computed tomographic approaches to non‐invasively assess lung damage in mice: a commercially available micro‐CT and a prototype flat panel CT (fpCT) system. Method and Materials: The micro‐CT system requires respiratory gating, has a fixed tungstenanode x‐ray tube, and a CCDcamera. A technique of 81 mA•sec at 80 kVp (0.16Gy) was utilized. The fpCT system accommodates a breath hold method, has a conventional CT x‐ray tube, and two CsI flat‐panel detectors. A technique of 800 mA•sec at 70 kVp (0.032Gy) with 200 μL of IV contrast was used. In this pilot investigation a subset of ten C57Bl/6 mice were analyzed; these mice received either 3 U/kg of Bleomycin to induce lung damage or saline for the control group by intratracheal administration. Both groups were serially scanned with both devices at baseline, 10, 14, and 21 days. Lung volumes at each time point were calculated using Analyze 5.0 for both the micro‐CT and fpCT imagedata sets.Results:Analysis of micro‐CT images resulted in smaller lung volumes than fpCT, most likely due to the gating procedure. Although the micro‐CT images exhibited more detail, the fpCT images had less noise and more tissue contrast within the lung regions, enabling easier detection of lung damage. The net decrease in measured lung volume due to damage accumulation over 21 days was 40 % from micro‐CT and 37 % from fpCT with respect to the average baseline lung volumes. Control mice lung volumes were stable to within 20% for both CT systems. Conclusion: The use of IV contrast with the fpCT system more than compensated for the reduced spatial resolution in this study. These mice survived multiple CT sessions even though lung damage was quickly accumulating in some cases. Additional data will be presented representing the complete study (n=19 mice).

The Americal College of Radiology introduced an accreditation program for Computed Tomography(CT) in 2002. The CT accreditation application requires the participation of a qualified medical physicist (with specific credentials) in order to submit appropriate phantom images and radiationdose measurements for CT scanners. Examples of acceptable CT accreditation phantom images will be presented, along with examples of the more commonly made mistakes. A brief review of the dosimetry procedures to follow, and pitfalls to avoid, will also be covered. Special attention will be directed toward the accreditation process for multi‐slice CT scanners.

The bone mineral density of 22 random, fresh proximal human femora was estimated by roentgenography using the Singh index (SI) and measured using a regional bone mineral density computed tomographic protocol. Uniaxial compression was used to produce an impacted subcapital fracture. The femoral heads then were isolated and mounted on a sliding screw plate compression device and loaded to failure in a push-out or hip-screw penetration mode. Wide intraobserver variation, poor reproducibility, and poor prediction of the experimental fracture properties of the proximal femur were noted for SI values. Regional bone mineral density provided a reliable estimate of both the gross fracture loads and hip-screw penetration loads. In addition, there was a high correlation between trabecular density and the experimental fracture properties of the proximal femur. Therefore, The validity of the SI as an indicator of the mechanical properties of the proximal femur should be reconsidered.

A method for measuring the regional bone mineral density (rBMD) in human lumbar vertebral bodies using a series of contiguous computed tomography images, each 1 mm thick, is fully described. The technique has a sample volume of 0.004 cm3, a sample spacing of 0.8 X 0.8 X 1.0 mm, and results in a bone marrow radiation dose of 1.59 to 2.75 rads (0.016-0.028 Gy). The use of physical density (mg/cm3) is introduced and the measurement noise (0.7-1.3%), accuracy (2.7%), and serial precision (0.2%) have been evaluated in vitro using appropriate phantoms. The corresponding percentage errors for accuracy and precision relative to K2HPO4 concentration were 6.9% and 2.0%, respectively. A multiple region density measurement is described and evaluated.