CT Dosimetry Research Articles

A method to estimate transmission profiles of bow-tie filters using rotating tube measurements.

The purpose of this paper was to present a method of determining the dose profile of the beam bow-tie filter (BTF) without the need for fixing the x ray tube in a position or using special instruments or dosimeters other than the ordinary types of ion chambers used for CT dosimetry (e.g., Farmer chamber). The idea behind this method is to try to invert the integral of exposures from axial measurements by decomposing it into fractions per degree of tube rotation. Measurements of the CT tube output were taken with a full tube rotation while the chamber was fixed in air. Starting with isocenter the output measurements were performed at 1-cm interval above the isocenter. Measurements were repeated for three sizes of BTFs; small, medium, and large. Maximum fan angle per chamber position was computed and an effective fan angle was defined to account for the new angular range encountered per chamber position. Variation due to inverse-square law was isolated from each measurement and contribution from the effective fan angle was computed. Resulted profiles from this method were then compared to profiles obtained with direct measurements, when the tube was in a fixed position. Effects of over and under 360° rotation per scan on results accuracy were also investigated. Using the direct measurements as the gold standard, results from this method were accurate to 4% for most of the BTFs angular ranges. The average relative error in the small BTF was 1.5%. In the medium BTF, the average relative error was <3% for up to 16° fan angle. With the large BTF, the mean error was about 4% for up to 22°. The relative error appeared to increase at larger fan angles especially with the large BTF; reaching an average of about 32% for fan angles between 22° and 27.5°. The presented method is relatively easy to perform and provides BTFs profiles with reasonably good accuracy. Associated errors of >10% only appear in high angles of large and medium BTFs.

OA212] A Monte Carlo investigation of dose width product (DWP) as a dose index for CBCT dosimetry

Purpose Dose-length-product (DLP) plays a vital role in assessing the total energy delivered to patients from CT scans. Moreover, DLP along with conversion coefficients are employed in evaluating effective doses from CT scans. The aim of this study is to propose an alternative dose index for cone-beam CT (CBCT) dosimetry analogue to DLP, which shows limitations for scans acquired with wide beams. Methods Monte Carlo simulations based on on-board-imager (OBI) kV system were run to investigate the alternative dose index called dose-width-product (DWP), which has a form similar to that of DLP, where width of the scan beam (W) along the z-axis is multiplied by CTDIw. This was proposed for CBCT scans and requires measurement of CTDI100 for a reference beam (≤40 mm) in the standard CTDI PMMA phantoms and measuring CTDI of the reference beam and a wide beam of interest free-in-air. In order to study suitability of DWP, its efficiency was estimated as a ratio of DWP to DWP∞, and compared to DLP/DLP∞. Head and body phantoms with diameters of 16 and 32 cm, respectively, and a length of 900 mm were simulated to assess DWP∞ and DLP∞, whereas the standard length (150 mm) was used to assess DWP and DLP. The efficiency was estimated using tube potentials of (80, 100, 120, 140) kV and beams of width ranged from 20 – 300 mm. Results The tube potential and width of the scan beam played a minimal role in the efficiency. Values of DLP efficiency were 80.1 ± 0.5% for head and 72.4 ± 2.4% for body under the different conditions studied. DWP efficiency values for head and body phantoms were all within 1.9% of those for DLP, which gives an indication for suitability of using DWP for CBCT scans. Conclusions DWP efficiency values were comparable to those for DLP. The dose index DWP is a modified form or an extension to the DLP concept. It indicates possibility of estimation of the total energy resulted from a given CBCT scan with a level of accuracy matching that of DLP. DWP can also be utilized to derive conversion coefficients used to assess effective dose.

P020] The influence of phantom diameter on X-ray CT dose evaluation using radiochromic film

Purpose In recent years, one of most important topic for X-ray CT examination is reducing radiation exposure. We have tried to establish the simple and accurate CT dosimetry method using radiochromic (RC) film. In this study, we investigated how the phantom diameter affects the pixel value distribution of RC film. This research is one step of quantifying dose distribution of X-ray CT using RC film. Methods The radiochromic film was exposed by a clinical CT scanner (Aquilion Lightning, Toshiba Medical Systems). Gafchromic XR-QA2 film was irradiated. The film-folding phantom consists of two acrylic semicylinder. In this study, the large phantom (cylinder cross-section diameter is 16 cm) and the small phantom (cylinder cross-section diameter is 10 cm) were used in this research. The scan parameters were as follows: non-helical scan, tube voltage = 120 kV, tube current = 300 mA, slice thickness = 2 cm, scan speed = 1 s per rotation. Image processing and analysis were performed by MATLAB (The Mathworks, Inc.) and Image J (National Institute of Health). The irradiated films were scanned by a commercial scanner (EPSON ES-10000G, Seiko Epson Co.). Results To compare the pixel value distribution using two differently sized phantom, we used the contour line analysis. The differences of distribution were observed between the large phantom and the small phantom. It was found that the distribution using the large phantom changes clearly. Conclusions In conclusion, our method may be useful for analyzing the distribution of pixel value on various conditions.

Estimation of conversion coefficients for absorbed and effective doses for pediatric CT examinations in two different PET/CT scanners

Normally, during medical procedures, special attention must be given to pediatric patients when compared to adults. This is specially relevant during procedures involving ionizing radiation, as CT scans, given that children are considerably more sensitive to radiation induced stochastic effects than adults. In order to investigate the radiation doses on radiosensitive organs of pediatric patients, undergoing head, chest and abdomen CT procedures, numerical dosimetry was employed in this work. The novelty is the use of a new set of pediatric virtual anthropomorphic phantoms, coupled with Monte Carlo simulation, to determine the conversion coefficients for absorbed and effective doses. Two CT equipment were simulated, taking into account the main characteristics of those commercially available. The results were converted to conversion coefficients (mGy/100 mA) for several organs and tissues, and the highest values were obtained for the newborn phantom. This numerical approach employed a new and reliable technique for pediatric CT dosimetry.

Evaluation of coefficients to derive organ and effective doses from cone-beam CT (CBCT) scans: a Monte Carlo study

Regular imaging is used throughout image guided radiation therapy to improve treatment delivery. In order for treatment procedures to be optimized, the doses delivered by imaging exposures should be taken into account. CT dosimetry methods based on the CT dose index (CTDI), measured with a 100 mm long pencil ionization chamber (CTDI100) in standard phantoms, are not designed for cone-beam CT (CBCT) imaging systems used in radiotherapy, therefore a modified version has been proposed for CBCT by the International Electrotechnical Commission (CTDIIEC). Monte Carlo simulations based on a Varian On-Board Imaging system were used to derive conversion coefficients that enable organ doses for ICRP reference phantoms to be determined from the CTDIIEC for different scan protocols and different beam widths (80–320) mm. A dose–width product calculated by multiplying the CTDIIEC by the width of the CBCT beam is proposed as a quantity that can be used for estimating effective dose. The variation in coefficients with CBCT beam width was studied. Coefficients to allow estimation of effective doses were derived, namely 0.0034 mSv (mGy cm)−1 for the head, 0.0252 mSv (mGy cm)−1 for the thorax, 0.0216 mSv (mGy cm)−1 for the abdomen and 0.0150 mSv (mGy cm)−1 for the pelvis, and these may be applicable more generally to other CBCT systems in radiotherapy. If data on effective doses are available, these can be used in making judgements on the contributions to patient dose from imaging, and thereby assist in optimization of the treatment regimes. The coefficients can also be employed in converting dosimetry data recorded in patient records into quantities relating directly to patient doses.

Technical Note: Evaluation of an iterative reconstruction algorithm for optical CT radiation dosimetry.

Iterative CT reconstruction algorithms are gaining popularity as GPU-based computation becomes more accessible. These algorithms are desirable in x-ray CT for their ability to achieve similar image quality at a fraction of the dose required for standard filtered backprojection reconstructions. In optical CT dosimetry, the noise reduction capability of such algorithms is similarly desirable because noise has a detrimental effect on the precision of dosimetric analysis, and can create misleading test results. In this study, we evaluate an iterative CT reconstruction algorithm for gel dosimetry, with special attention to the challenging dosimetry of small fields. An existing ordered subsets convex algorithm using total variation minimization regularization (OSC-TV) was implemented. Three datasets, which represent the extreme cases of gel dosimetry, were examined: a large, 15cm diameter uniform phantom, a 1.35cm diameter finger phantom, and a 15cm gel dosimeter irradiated with 3×3, 2×2, 1×1, and 0.6×0.6cm fields. These were scanned on an in-house scanning laser system, and reconstructed with both filtered backprojection and OSC-TV with a range of regularization constants. The contrast to artifact+noise ratio (CANR) and penumbra width measurements (80% to 20% and 95% to 5% distances) were used to compare reconstructions. Our results showed that OSC-TV can achieve 3-5× improvement in contrast to artifact+noise ratio compared to filtered backprojection, while preserving the shape of steep dose gradients. For very small objects (≤0.6×0.6cm fields in a 16×16cm field of view), the mean value in the center of the object can be suppressed if the regularization constant is improperly set, which must be avoided. Overall, the results indicate that OSC-TV is a suitable reconstruction algorithm for gel dosimetry, provided care is taken in setting the regularization parameter when reconstructing objects that are small compared to the scanner field of view.

Effective and organ doses from common CT examinations in one general hospital in Tehran, Iran

Abstract Purpose: It is well known that the main portion of artificial sources of ionizing radiation to human results from X-ray imaging techniques. However, reports carried out in various countries have indicated that most of their cumulative doses from artificial sources are due to CT examinations. Hence assessing doses resulted from CT examinations is highly recommended by national and international radiation protection agencies. The aim of this research has been to estimate the effective and organ doses in an average human according to 103 and 60 ICRP tissue weighting factor for six common protocols of Multi-Detector CT (MDCT) machine in a comprehensive training general hospital in Tehran/Iran. Methods: To calculate the patients' effective dose, the CT-Expo2.2 software was used. Organs/tissues and effective doses were determined for about 20 patients (totally 122 patients) for every one of six typical CT protocols of the head, neck, chest, abdomen-pelvis, pelvis and spine exams. In addition, the CT dosimetry index (CTDI) was measured in the standard 16 and 32 cm phantoms by using a calibrated pencil ionization chamber for the six protocols and by taking the average value of CT scan parameters used in the hospital compared with the CTDI values displayed on the console device of the machine. Results: The values of the effective dose based on the ICRP 103 tissue weighting factor were: 0.6, 2.0, 3.2, 4.2, 2.8, and 3.9 mSv and based on the ICRP 60 tissue weighting factor were: 0.9, 1.4, 3, 7.9, 4.8 and 5.1 mSv for the head, neck, chest, abdomen-pelvis, pelvis, spine CT exams respectively. Relative differences between those values were -22, 21, 23, -6, -31 and 16 percent for the head, neck, chest, abdomen-pelvis, pelvis, spine CT exams, respectively. The average value of CTDIv calculated for each protocol was: 27.32 ± 0.9, 18.08 ± 2.0, 7.36 ± 2.6, 8.84 ± 1.7, 9.13 ± 1.5, 10.42 ± 0.8 mGy for the head, neck, chest, abdomen-pelvis and spine CT exams, respectively. Conclusions: The highest organ doses delivered by various CT exams were received by brain (15.5 mSv), thyroid (19.00 mSv), lungs (9.3 mSv) and bladder (9.9 mSv), bladder (10.4 mSv), stomach (10.9 mSv) in the head, neck, chest, and the abdomen-pelvis, pelvis, and spine respectively. Except the neck and spine CT exams showing a higher effective dose compared to that reported in Netherlands, other exams indicated lower values compared to those reported by any other country.

Can the Day 0 CT-scan predict the post-implant scanning? Results from 136 prostate cancer patients

PurposePost-implant CT-scanning is an essential part of permanent prostate brachytherapy. However, the evaluation of post-implant CT dosimetry is not straightforward due to the edema that can modify the dose to the prostate and to the organs at risk. The aim of this study is to evaluate the impact of the timing of the post-implant CT-scan on the dosimetric results and to verify if the Day 0 scan findings can predict Day 50 scanning. Methods136 consecutive patients who received monotherapy with I-125 implants were selected for this study. Two sets of 8 dosimetric quality parameters corresponding to 2 different CT-scans (Day 0 and Day 50) were calculated and compared. The dosimetric parameters included are the percentage volume of the post-implant prostate receiving 80%, 100% and 150% of the prescribed dose, the doses covering 80% and 90% of the prostate volume and the Dose Homogeneity Index. The values of the dose covering 1cm3 of the rectum and urethra were assessed. ResultsAll the dosimetric parameters of the Day 50 were higher than those of the Day 0 scan. Linear functions were obtained that calculate D90 and V100 values at Day 50 based on the Day 0 findings. Rectal and urethral parameters tended to be underestimated on Day 0 CT-scan relative to Day 50 based dosimetry. ConclusionsPredicting the Day 50 dosimetry from the Day 0 scan could be a possible alternative to a Day 50 scan only in specific situations, but with a degree of uncertainty in the predicted values.

The effect of iodine uptake on radiation dose absorbed by patient tissues in contrast enhanced CT imaging: Implications for CT dosimetry.

To investigate the effect of iodine uptake on tissue/organ absorbed doses from CT exposure and its implications in CT dosimetry. The contrast-induced CT number increase of several radiosensitive tissues was retrospectively determined in 120 CT examinations involving both non-enhanced and contrast-enhanced CT imaging. CT images of a phantom containing aqueous solutions of varying iodine concentration were obtained. Plots of the CT number increase against iodine concentration were produced. The clinically occurring iodine tissue uptake was quantified by attributing recorded CT number increase to a certain concentration of aqueous iodine solution. Clinically occurring iodine uptake was represented in mathematical anthropomorphic phantoms. Standard 120kV CT exposures were simulated using Monte Carlo methods and resulting organ doses were derived for non-enhanced and iodine contrast-enhanced CT imaging. The mean iodine uptake range during contrast-enhanced CT imaging was found to be 0.02-0.46% w/w for the investigated tissues, while the maximum value recorded was 0.82% w/w. For the same CT exposure, iodinated tissues were found to receive higher radiation dose than non-iodinated tissues, with dose increase exceeding 100% for tissues with high iodine uptake. Administration of iodinated contrast medium considerably increases radiation dose to tissues from CT exposure. • Radiation absorption ability of organs/tissues is considerably affected by iodine uptake • Iodinated organ/tissues may absorb up to 100 % higher radiation dose • Compared to non-enhanced, contrast-enhanced CT may deliver higher dose to patient tissues • CT dosimetry of contrast-enhanced CT imaging should encounter tissue iodine uptake.

A novel method for CT dosimetry with a suspended phantom setup

PurposeThis work presents a method for estimating CT dosimetric indices with a prototype designed for suspending the phantom/ion chamber system fixed at the CT isocenter. The purpose of this study was to validate the proposed methodology, which can be used to provide a direct assessment of dosimetric indices in helical scans. MethodsThe method is based on a reference setup in which the measuring system for CT dosimetry is in a stationary configuration, i.e. not bound to the CT table, and on a mathematical formalism developed for the proposed reference system. The reliability of the method was demonstrated through a set of experimental measurements. Firstly, dosimetric indices were measured with the new method and compared with the indices obtained with the procedure currently used for CT dosimetry (measuring system bound to the CT table). Secondly, dosimetric indices measured with the new method were compared with those displayed on the CT console. ResultsThere is good agreement between the dosimetric indices obtained with the standard setup and those obtained with the suspended phantom setup, within the expected range of errors. The difference between dosimetric indices estimated with the proposed method and those displayed on the CT console is below 2%. ConclusionsThe method enables CT dosimetry to be performed with the dose detector in a stationary longitudinal position thanks to the newly introduced suspended phantom setup. Using this approach, CT dose can be assessed for high pitch helical scans, acquisitions without complete tube rotation and for cases where dynamic collimation is used.

Operational and Dosimetric Aspects of Pediatric PET/CT.

No consistent guidelines exist for the acquisition of a CT scan as part of pediatric PET/CT. Given that children may be more vulnerable to the effects of ionizing radiation, it is necessary to develop methods that provide diagnostic-quality imaging when needed, in the shortest time and with the lowest patient radiation exposure. This article describes the basics of CT dosimetry and PET/CT acquisition in children. We describe the variability in pediatric PET/CT techniques, based on a survey of 19 PET/CT pediatric institutions in North America. The results of the survey demonstrated that, although most institutions used automatic tube current modulation, there remained a large variation of practice, on the order of a factor of 2-3, across sites, pointing to the need for guidelines. We introduce the approach developed at our institution for using a multiseries PET/CT acquisition technique that combines diagnostic-quality CT in the essential portion of the field of view and a low-dose technique to image the remainder of the body. This approach leads to a reduction in radiation dose to the patient while combining the PET and the diagnostic CT into a single acquisition. The standardization of pediatric PET/CT provides an opportunity for a reduction in the radiation dose to these patients while maintaining an appropriate level of diagnostic image quality.

Body Size-Specific Organ and Effective Doses of Chest CT Screening Examinations of the National Lung Screening Trial.

We calculated body size-specific organ and effective doses for 23,734 participants in the National Lung Screening Trial (NLST) using a CT dose calculator. We collected participant-specific technical parameters of 23,734 participants who underwent CT in the clinical trial. For each participant, we calculated two sets of organ doses using two methods. First, we computed body size-specific organ and effective doses using the National Cancer Institute CT (NCICT) dosimetry program, which is based on dose coefficients derived from a library of body size-dependent adult male and female computational phantoms. We then recalculated organ and effective doses using dose coefficients from reference size phantoms for all examinations to investigate potential errors caused by the lack of body size consideration in the dose calculations. The underweight participants (body mass index [BMI; weight in kilograms divided by the square of height in meters] < 18.5) received 1.3-fold greater lung dose (median, 4.93 mGy) than the obese participants (BMI > 30) (3.90 mGy). Thyroid doses were approximately 1.3- to 1.6-fold greater than the lung doses (6.3-6.5 mGy). The reference phantom-based dose calculation underestimates the body size-specific lung dose by up to 50% for the underweight participants and overestimates that value by up to 200% for the overweight participants. The median effective dose ranges from 2.01 mSv in obese participants to 2.80 mSv in underweight participants. Body size-specific organ and effective doses were computed for 23,734 NLST participants who underwent low-dose CT screening. The use of reference size phantoms can lead to significant errors in organ dose estimates when body size is not considered in the dose assessment.

Mathematical modelling of scanner-specific bowtie filters for Monte Carlo CT dosimetry

The purpose of bowtie filters in CT scanners is to homogenize the x-ray intensity measured by the detectors in order to improve the image quality and at the same time to reduce the dose to the patient because of the preferential filtering near the periphery of the fan beam. For CT dosimetry, especially for Monte Carlo calculations of organ and tissue absorbed doses to patients, it is important to take the effect of bowtie filters into account. However, material composition and dimensions of these filters are proprietary. Consequently, a method for bowtie filter simulation independent of access to proprietary data and/or to a specific scanner would be of interest to many researchers involved in CT dosimetry. This study presents such a method based on the weighted computer tomography dose index, CTDIw, defined in two cylindrical PMMA phantoms of 16 cm and 32 cm diameter. With an EGSnrc-based Monte Carlo (MC) code, ratios CTDIw/CTDI100,a were calculated for a specific CT scanner using PMMA bowtie filter models based on sigmoid Boltzmann functions combined with a scanner filter factor (SFF) which is modified during calculations until the calculated MC CTDIw/CTDI100,a matches ratios CTDIw/CTDI100,a, determined by measurements or found in publications for that specific scanner. Once the scanner-specific value for an SFF has been found, the bowtie filter algorithm can be used in any MC code to perform CT dosimetry for that specific scanner. The bowtie filter model proposed here was validated for CTDIw/CTDI100,a considering 11 different CT scanners and for CTDI100,c, CTDI100,p and their ratio considering 4 different CT scanners. Additionally, comparisons were made for lateral dose profiles free in air and using computational anthropomorphic phantoms. CTDIw/CTDI100,a determined with this new method agreed on average within 0.89% (max. 3.4%) and 1.64% (max. 4.5%) with corresponding data published by CTDosimetry (www.impactscan.org) for the CTDI HEAD and BODY phantoms, respectively. Comparison with results calculated using proprietary data for the PHILIPS Brilliance 64 scanner showed agreement on average within 2.5% (max. 5.8%) and with data measured for that scanner within 2.1% (max. 3.7%). Ratios of CTDI100,c/CTDI100, p for this study and corresponding data published by CTDosimetry (www.impactscan.org) agree on average within about 11% (max. 28.6%). Lateral dose profiles calculated with the proposed bowtie filter and with proprietary data agreed within 2% (max. 5.9%), and both calculated data agreed within 5.4% (max. 11.2%) with measured results. Application of the proposed bowtie filter and of the exactly modelled filter to human phantom Monte Carlo calculations show agreement on the average within less than 5% (max. 7.9%) for organ and tissue absorbed doses.

大規模災害時における携帯型口内法X線撮影装置の安全使用について

Objective: The needs of intraoral radiography are increasing for home care and especially for victim identification after the Great East Japan Earthquake. In this study, we evaluated the characteristics of output X-rays and measured air kermas of stray radiation from three battery-powered portable intraoral X-ray units.Materials and Methods: The air kermas of stray radiation, generated from an IEC CT dosimetry head phantom and the X-ray units, which included DEXICO ADX4000, DEXICO ADX4000W, and DEXICO DX3000 （10DR Japan）, were measured using Pitman 37D and the 350cc ionization chamber attached （Pitman）.Results: If an operator works in a sectioned area with a central angle of 180±60 degrees and a radius of 0.5m, the mean stray radiation was 0.353μGy for the ADX4000, 0.297μGy for the ADX4000W, and 0.288μGy for the DX3000 per 1mGy at the cone tip of each unit.Discussion: In the event of a large-scale disaster, an operator would be taking many radiographs for victim identification each day. Therefore, this can be done by setting up a control area that ensures a sufficient distance from the radiation source, wearing a lead apron and using a protection board.

CTDI versus New AAPM Metrics to assess Doses in CT: a case study

In modern CT, CTDI 100 measurements would underestimate accumulated dose at the gantry center. AAPM TG 111 report proposed improved metrics for CT dosimetry, mainly for helical and wide beam width scanning. In this study, a methodology to assess CT dose, inspired on TG 111, was applied. Dosimeters were firstly calibrated in lab in beams like those utilized clinically. Using a reference 0.6cc Farmer chamber, two CT “pencil” chambers were calibrated in P KL by substitution method. Results showed differences ≤ 2% in the calibration coefficients, for three collimation apertures. A small 0.6cc chamber was calibrated in air kerma with this setup, without any collimator. After this, in a private Brazilian hospital, the small chamber was applied in dosimetry tests of a CT scanner, according to TG 111, determining Dose profiles and Equilibrium dose free-in-air (D eq,air ) for some protocols and pitch values. Results showed that D eq,air increased when reducing pitch and Equilibrium dose-pitch product free-in-air (p.D eq,air ) remain constant. In measurements with a 450mm CT phantom, differences between Planar Average Equilibrium Dose (D eq,p ) and CTDI vol ranged between 30-37%. This occurs because CTDI vol cannot include dose profile tail contribution, caused by scattering in phantom, especially for wide beam widths.

Energy response characteristics of radiochromic film at CT radiation quality

Introduction Radiochromic films (RF) have been developed for measurement of the absorbed dose of low-energy photons and to measure CT dose profiles. RF are self-developing and radiation sensitive, and the amount of darkening is proportional to the absorbed dose. RF are easy to handle due to their insensitivity to interior room light. Purpose In this study, energy response of GAFCHROMIC XR-QA2 film (XR-QA2) was evaluated to obtain an accurate measurement of CT dose. Materials and methods The measured dose and energy range of the XR-QA2 was designed to be 2–500 mGy and 20–200 kVp. XR-QA2 is a reflective-type film, and a flatbed scanner was used for the measurement of image density. To obtain the calibration curves, XR-QA2 were irradiated at 0–120 mGy (air-kerma) using 10–150 kVp (10 kVp intervals) photon beam with industrial X-ray System(Titan;GE). For image density acquisition, XR-QA2 were scanned before and after irradiate using a flatbed scanner (Epson GS-11000) in RGB (48 bit) mode, 150 dpi. Results The calibration curves varied according to the tube voltage. The energy response was best at 50 kVp and decreased according to increase tube voltage within the range of 50–150 kVp. Additionally, energy response was decreased rapidly below 40 kVp. Conclusion The dose differences were around 10% at 80–140 kVp. This indicated that single calibration curve is not adequate for CT dosimetry performed at different energies. To obtain an accurate measurement of CT dose, calibration curve has to make based on used energy. Disclosure We have no disclosure and financial support.

Survey of CT practice in sudan: Updates on radiation exposure and setting national diagnostic reference levels

Introduction The increase in the use of mutislice CT in Sudan has resulted in an increased examinations frequency and population radiation burden. Dose surveys are important for medical exposure control. Purpose The aims of this survey were to updates on radiation exposure, and use the results in setting national diagnostic reference levels. Materials and methods Scan parameters were collected from 840 CT examinations in patients carried out in eight CT scanners comprising one (128 Slice), five (64 Slice) and two (16 Slice) mulitislice CT scanners in Khartoum State, Sudan. CTDIvol and DLP and effective dose were calculated by using CT-Expo 2.5 CT dosimetry software were compared with published data. Results Doses are presented Brian, PNS, and Chest, pulmonary, Abdomen-Pelvis, Pelvis, KUB and CTU CT examinations. Mean CTDIvol ranged: from 63.8 to 16.4 mGy in Brain and KUB; respectively; Mean DLP ranged from 1744 to 670 mGy.cm in CTU and Pelvic CT; respectively; While mean effective dose ranged from 21.71 to 1.96 mSv in CTU and BNS; respectively. The results presented wide variations in technique and radiation dose for similar examinations indicating significant room for dose optimisation. Conclusion 75 percentile of hospital mean doses obtained in this study were used to propose a national DRLs. Study highlighted the radiation protection challenge and dose consequences of Mutislice CT in a developing country. Disclosure Authors do not have any relationship that may bias their presentation. The increase in the use of mutislice CT in Sudan has resulted in an increased examinations frequency and population radiation burden. Dose surveys are important for medical exposure control. The aims of this survey were to updates on radiation exposure, and use the results in setting national diagnostic reference levels. Scan parameters were collected from 840 CT examinations in patients carried out in eight CT scanners comprising one (128 Slice), five (64 Slice) and two (16 Slice) mulitislice CT scanners in Khartoum State, Sudan. CTDIvol and DLP and effective dose were calculated by using CT-Expo 2.5 CT dosimetry software were compared with published data. Doses are presented Brian, PNS, and Chest, pulmonary, Abdomen-Pelvis, Pelvis, KUB and CTU CT examinations. Mean CTDIvol ranged: from 63.8 to 16.4 mGy in Brain and KUB; respectively; Mean DLP ranged from 1744 to 670 mGy.cm in CTU and Pelvic CT; respectively; While mean effective dose ranged from 21.71 to 1.96 mSv in CTU and BNS; respectively. The results presented wide variations in technique and radiation dose for similar examinations indicating significant room for dose optimisation. 75 percentile of hospital mean doses obtained in this study were used to propose a national DRLs. Study highlighted the radiation protection challenge and dose consequences of Mutislice CT in a developing country.

A model of CT dose profiles in Banach space; with applications to CT dosimetry

In this paper the scatter component of computed tomography dose profiles is modeled using the solution to a nonlinear ordinary differential equation. This scatter function is summed with a modeled primary function of approximate trapezoidal shape. The primary dose profile is modeled to include the analytic continuation of the Heaviside step function. A mathematical theory is developed in a Banach space. The modeled function is used to accurately fit data from a 256-slice GE Revolution scanner. A 60 cm long body phantom is assembled and used for data collection with both a pencil chamber and a Farmer-type chamber.

MO‐AB‐206‐01: PET Physics

This education session will cover the physics and operation principles of gamma cameras and PET scanners.The first talk will focus on PET imaging. An overview of the principles of PET imaging will be provided, including positron decay physics, and the transition from 2D to 3D imaging. More recent advances in hardware and software will be discussed, such as time‐of‐flight imaging, and improvements in reconstruction algorithms that provide for options such as depth‐of‐interaction corrections. Quantitative applications of PET will be discussed, as well as the requirements for doing accurate quantitation. Relevant performance tests will also be described. Learning Objectives: Be able to describe basic physics principles of PET and operation of PET scanners. Learn about recent advances in PET scanner hardware technology. Be able to describe advances in reconstruction techniques and improvements Be able to list relevant performance tests.The second talk will focus on gamma cameras. The Nuclear Medicine subcommittee has charged a task group (TG177) to develop a report on the current state of physics testing of gamma cameras, SPECT, and SPECT/CT systems. The report makes recommendations for performance tests to be done for routine quality assurance, annual physics testing, and acceptance tests, and identifies those needed satisfy the ACR accreditation program and The Joint Commission imaging standards. The report is also intended to be used as a manual with detailed instructions on how to perform tests under widely varying conditions.Learning Objectives:At the end of the presentation members of the audience will: Be familiar with the tests recommended for routine quality assurance, annual physics testing, and acceptance tests of gamma cameras for planar imaging. Be familiar with the tests recommended for routine quality assurance, annual physics testing, and acceptance tests of SPECT systems. Be familiar with the tests of a SPECT/CT system that include the CT images for SPECT reconstructions. Become knowledgeable of items to be included in annual acceptance testing reports including CT dosimetry and PACS monitor measurements.T. Turkington, GE Healthcare

MO‐AB‐206‐00: Nuclear Medicine Physics and Testing

This education session will cover the physics and operation principles of gamma cameras and PET scanners.The first talk will focus on PET imaging. An overview of the principles of PET imaging will be provided, including positron decay physics, and the transition from 2D to 3D imaging. More recent advances in hardware and software will be discussed, such as time‐of‐flight imaging, and improvements in reconstruction algorithms that provide for options such as depth‐of‐interaction corrections. Quantitative applications of PET will be discussed, as well as the requirements for doing accurate quantitation. Relevant performance tests will also be described. Learning Objectives: Be able to describe basic physics principles of PET and operation of PET scanners. Learn about recent advances in PET scanner hardware technology. Be able to describe advances in reconstruction techniques and improvements Be able to list relevant performance tests.The second talk will focus on gamma cameras. The Nuclear Medicine subcommittee has charged a task group (TG177) to develop a report on the current state of physics testing of gamma cameras, SPECT, and SPECT/CT systems. The report makes recommendations for performance tests to be done for routine quality assurance, annual physics testing, and acceptance tests, and identifies those needed satisfy the ACR accreditation program and The Joint Commission imaging standards. The report is also intended to be used as a manual with detailed instructions on how to perform tests under widely varying conditions.Learning Objectives:At the end of the presentation members of the audience will: Be familiar with the tests recommended for routine quality assurance, annual physics testing, and acceptance tests of gamma cameras for planar imaging. Be familiar with the tests recommended for routine quality assurance, annual physics testing, and acceptance tests of SPECT systems. Be familiar with the tests of a SPECT/CT system that include the CT images for SPECT reconstructions. Become knowledgeable of items to be included in annual acceptance testing reports including CT dosimetry and PACS monitor measurements.T. Turkington, GE Healthcare