bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐41: Study On the CT Radiation Attenuation Characteristics of Human Body for Phantom Design Using Monte Carlo Simulations
Authors: Liu h , Gao Y , Zhuo W , Wu J , Xu X
Published: July 2013

Purpose: The CTDI values measured with standard PMMA phantoms were now being challenged due to the clinical application of new technologies such as automatic tube current modulation(TCM), the aim of this study is to simulate the CT radiation attenuation characteristics of human body along Z‐axis which were the basic data of developing new phantoms used to evaluate TCM. Methods: The CT model used in this study has been modeled including the source energy spectrum, the bow‐tie filter as well and the beam shape. The voxel phantoms RPI Adult Male designed to match the ICRP anatomical references for average individuals were also selected in this study. MCNPX 2.5.0 was used to simulate the 120 kVp CT X‐ray attenuation of voxel phantom along the z‐axis. Averaged photon flux was tallied before and after it passed though the phantom separately, simulations were also carried out using different thickness of PMMA plates instead of the voxel phantom. Results: The CT X‐ray attenuation of PMMA and its thickness presents a significant negative exponential relationship with the r2=0.9975. The CT X‐ray attenuation data of every 2cm along Z‐axis direction of voxel phantom were obtained, combined with characteristics of CT X‐ray attenuation of PMMA, the PMMA equivalent thickness of the voxel phantom torso along the Z‐axis direction in terms of CT X‐ray attenuation were calculated. The PMMA equivalent thickness ranges from 5.5cm to 30.1cm. The liver and spleen plane, which contents substantive organs such as the liver and spleen, and bone structure as ribs and the lumbar, was the maximum attenuation plane. Conclusion: The trend of the overall attenuation characteristics of the human body in terms of CT X‐ray was in accord with the anatomical structure, these results could be used to develop new dose phantoms which were used to evaluate automatic tube current modulation with further study. This project was partially funded by National Institutes of Health (National Library of Medicine R01LM009362 and National Institute of Biomedical Imaging and Bioengineering R42EB010404)
SU‐E‐I‐45: Dose Received by One‐Year‐Old Children During CT Scanning in Japan
Authors: Suzuki S , Shirakawa S , Takei Y , Matsunaga Y , Kawaguchi A , Akahane K , Shimada Y
Published: July 2013

Purpose: CT scanning involves a higher radiation dose compared with X‐ray scanning, and children are believed to be more sensitive to radiation compared with adults. However, the reality of pediatric CT scanning in Japan is unclear. We therefore performed dose evaluation by using a pediatric phantom representing a one‐year‐old child in order to assess the actual dose received. Methods: Dose measurement was performed under the protocols used in each institution. Solid‐state detectors were used to measure doses. These solid‐state detectors were placed at 150 points on the surface of and inside the phantom. The data obtained were used to calculate the average absorbed dose for each organ, which were multiplied by tissue weighting factors to derive the effective doses. This study covered cranial and abdominal plain CT scans. When positioning scanning was performed, this was included in dose measurements, which were evaluated for the entire scan series. Measurements were performed at 13 institutions using devices made by five manufacturers. Results: The minimum dose received directly by the head during cranial CT scanning was 8 mGy, the maximum dose was 40 mGy, and the mean dose was 22 mGy. The minimum effective dose was 0.4 mSv, the maximum effective dose was 2 mSv, and the mean effective dose was 1 mSv. The minimum dose received directly by the stomach during abdominal CT scanning was 3 mGy, the maximum dose was 22 mGy, and the mean dose was 8 mGy. The minimum effective dose was 0.4 mSv, the maximum effective dose was 2 mSv, and the mean effective dose was 1 mSv. Conclusion: The mean doses received from direct radiation during cranial and abdominal CTs were 22 mGy for the former and 8 mGy for the latter, an approximately threefold difference. There was almost no difference in effective dose, which was 1 mSv in both cases.
SU‐E‐I‐46: Monte Carlo‐Calculated Patient Organ Doses From a Diagnostic X‐Ray CT
Authors: Ono T , Araki F
Published: July 2013

Purpose: To calculate patient organ doses from a diagnostic X‐ray CT, using Monte Carlo (MC) simulations. Methods: A MDCT (Aquilion 16, TOSHIBA Medical Systems) was modeled with the GMctdospp (IMPS, Germany) software based on the EGSnrc MC code. The X‐ray spectrum and configuration of a bowtie filter (Teflon) were determined from a half value layer (HVL) of aluminum (Al) and dose profile (off‐center ratio, OCR) measured in air under the body irradiation (120 kV). The MC‐calculated dose was calibrated with the absorbed dose‐to‐acrylic obtained from the chamber measurement at a central axis in a CT water phantom with 30 cm diameter and 50 cm length. The dose distribution in patient was calculated using the CT images on beam setting for pelvis. The internal organ doses in pelvis were calculated from DVH. Results: The calculated Al HVL was in agreement with 0.3% to the value of 5.2 mm measured. The calculated profile in air matched to that measured within 5% in a range of 15 cm from the central axis. The calibrated CT absorbed dose‐to‐acrylic was in agreement within 5% with the chamber measurement at peripheral four points. The calculated mean doses for prostate, rectum, and bladder were 2.38 cGy, 2.40 cGy, and 2.84 cGy, respectively, under irradiation condition of 120 kV, 200 mA, and slice thickness of 2 mm. For bones of femur and pelvis, mean doses were 5.61 cGy and 6.36 cGy, respectively. The doses for bone increased by up to 2–3 times compared to those for soft tissue. The CT dose also became much higher near body surface. Prostate and rectum were exposed uniformly. Meanwhile, bones of femur and pelvis were non‐uniformity depending on their density. Conclusion: Monte Carlo calculations are useful for evaluation of patient organ doses from a diagnostic X‐ray CT.
SU‐E‐I‐52: Improvement in CT Contrast‐To‐Noise Ratio in Low Contrast Spherical Simulated Liver Lesions Using Iterative Reconstruction
Authors: Dong F , Herts B , Baker M , Goenka A , Primak A
Published: July 2013

Purpose: Contrast‐to‐Noise ratio (CNR) is one measure to assess image quality and lesion detectability for CT exams. The purpose of this study is to calculate the change in CNR between standard filtered back‐projection (FBP) and sinogram‐affirmed iterative reconstruction (SAFIRE) by using an anthropomorphic phantom with spherical simulated liver lesions. Methods: An anthropomorphic phantom with embedded spherical liver lesions was custom‐designed to assess low contrast lesion detection at different CT doses and reconstruction techniques. This phantom consists of 36 spherical lesions with 3 different sizes (5mm, 10mm, and 15mm). Each size has three different contrast levels. All spherical lesions were embedded non‐uniformly to minimize the memory bias for a concurrent human observer study. Phantom was scanned with a MDCT (Siemens Definition Flash) at 4 dose levels and images were reconstructed with both FBP and SAFIRE using strength setting 3. CNR was computed as the ratio of the difference of the mean CT number at the center of the lesion and the liver background to the standard deviation of the CT numbers from the liver background. CNR was evaluated for the each lesion size at the center slice that intersected the middle of the lesion to minimize the error from the partial volume effect. Results: Averaged across all lesion sizes and the contrast levels (vs. the liver background), the CNR improvement from FBP to SAFIRE (strength 3) was 34% ±10% (mean ± standard deviation) at 50mAs,(p<0.0001), 33%±11% at 100mAs (p<0.0002), 36% ± 9% at 150mAs (p<0.0001) and 36% ± 7% at 200mAs (p<0.0003). Noise reduction from SAFIRE contributed almost entirely to the CNR improvement. Conclusion: Iterative reconstruction (SAFIRE) improved CNR of spherical low‐contrast liver lesions, but almost entirely due to noise reduction, with little improvement in lesion contrast. The overall CNR improvement was uniform for each dose level tested. Dr. Herts and Dr. Baker are funded by Siemens Healthcare for research in the field of abdominal CT imaging.
SU‐E‐I‐54: Using Quantitative Measurement of Image Quality to Standardize Clinical Performance Across a Diverse Population of CT Scanners
Authors: Och J , Kresge W , Snyder D , Lock J , Moshiri S
Published: July 2013

Purpose: To develop an Image Quality metric, in order to establish consistent Image Quality among a population of CT scanners, of different make/model and locations in a health system. Methods: Through discussion with radiologists, it was decided to use image noise as a metric. Image noise was defined as the standard deviation of an ROI placed in the image. Radiologists selected target values for the desired level of image noise. For head examinations, the ROI was placed in the solid tissue at the level of the fornix. For abdomen images, the ROI was placed at mid‐liver. For the actual metric, the average of two ROI's was used. For each scanner in t he system, two data sets (brain and abdomen) of 100 images each were evaluated. Population statistics were acquired and the range of variation was measured. Data analysis was done on the entire population of images, as well as subsets, specifically location and scanner make/model.Based on the results of the analysis, protocols were revised, where necessary, to address excessive variation, and to correlate with the desired image noise target, 4.0 for the brain and 11.5 for the abdomen. Results: Use of the application resulted in a decrease in the range of image noise for brain images from 3.6 ‐ 5.5 to 4.1 ‐ 4.9. The range for abdomen images decreased from 7.0 ‐ 17.4 to 9.6 ‐ 14.1. Average noise values for abdomen images decreased from 12.3 to 11.8. Average Image Noise for the brain decreased from 4.6 to 4.3.The initial difference in average image noise between the two main scanner populations was 2.9 for abdomen scans. After the project the interscanner abdomen image noise difference decreased to 1.3. Conclusion: Image noise is a viable metric for comparing scanner performance and standardizing protocols.
SU‐E‐I‐55: An Automated Technique to Determine Patient Size for Obtaining Size Specific Dose Estimates From System Reported CT Dose Index
Authors: Dave J , Zohrabian V , Gingold E
Published: July 2013

Purpose: Size‐Specific Dose Estimate (SSDE) uses patient size to produce an estimate of the radiation dose to the patient resulting from a CT scan. The purpose of this work was to develop an automated technique to determine patient size based on localizer radiograph and the center slice of the scanned volume for SSDE calculations. Methods: This retrospective study was approved by the Institutional Review Board. Abdominal CT studies of 38 patients (age range:12−86 years) were evaluated. An automated software algorithm was developed in Matlab (The Mathworks Inc.). Using information from the dose report images, series that resulted in radiation dose to the patient and the central slice of each series were identified. The lateral dimensions for the patient size were obtained from the localizer radiograph and the central transaxial slice by calculating the FWHM of the Gaussian function fit using a linear least squares estimation to the central row profile in each image. Similarly the anterior posterior (AP) patient dimensions were calculated from the central column profile of the central transaxial slice. These dimensions were compared with manual measurements performed by a radiology resident blinded to the algorithm results. Results: A significant difference was observed between manual size measurements (range:27.1–49.9cm) and automated measurements (range:24.2–45.5cm) techniques (p<0.001, mean difference: 6.0cm, 95% CI: 4.7 to 7.3cm) for lateral measurements from the localizer radiograph. For measurements from the center transaxial slice images, the mean difference between the manual (range:16.6– 42.4cm) and automated techniques (range:16.4–42.5cm) was 1cm (95% CI: 0.4 to 1.7cm; p<0.001) for the lateral dimension and was 0cm (95% CI: −0.4 to 0.4cm; p>0.821) for the AP dimension. Conclusion: This automated algorithm may be used to obtain patient dimensions from CT images for calculation of the size specific dose estimate, and may eliminate the need to perform these measurements manually.
SU‐E‐I‐58: Understanding Uncertainties in Quantitative Image Features Extracted From Contrast‐Enhanced CT Images
Authors: Court L , Yang J , Hunter L , Ng C
Published: July 2013

Purpose: Quantitative image features have been shown to be predictive of treatment outcomes for some patients groups. We examine two sources of uncertainty in these features for contrast‐enhanced CT images of lung cancer patients: (1) The time between contrast injection and CT scan (which depends on local practice) (2) the reproducibility of features between scans. Methods: Eight patients received two contrast‐CT scans, 2–4 days apart. Each session included 6 repeat scans of the same anatomy taken every 20seconds, starting 50seconds after contrast injection. The timing of the scans encompasses the range expected during routine acquisition of contrast‐CT images. For each patient, the lung tumor was manually delineated on the first scan, and propagated to each subsequent scan using deformable image registration. Image features based on tumor geometry, intensity histogram, absolute gradient image (IGR), co‐occurrence matrix (COM) and run‐length matrix (RLM) were then extracted from the tumor for each image set. Pearsons correlation coefficient was used to examine correlation between the features and time from contrast injection (each imaging session considered separately), with values over 0.60 considered to have a time‐trend. The concordance correlation coefficient (CCC) was calculated to examine the reproducibility of each feature between sessions, with values greater than 0.90 considered reproducible. Results: Variations in the image features attributed to cardiac pulsing was larger than any monotonic trends with time, and none of the image features were found to be correlated with time from injection. All geometric features and most histogram‐based features (except maximum and minimum values) were found to be reproducible between scans. The majority of IGR‐, COM‐and RLM‐based features were reproducible, and CCC was greater than 0.80 for all features. Conclusion: The quantitative image features tested here were mostly reproducible, and have little dependence on the exact time between the contrast injection and the CT scan.
SU‐E‐I‐59: Patient‐Based Average Glandular Dose Estimations in Taiwan
Authors: Hwang YS , Tsai HY , Chen HY , Wei HW , Lin JH , Liu HL
Published: July 2013

Purpose: The objective of the study was to investigate the average glandular dose (AGD) distributions based on the patients with average‐sized breasts in Taiwan. Methods: Patient data were collected from 199 mammography units of 167 facilities (76% of the units in Taiwan) during 2012 in Taiwan. For each unit, exposure parameters including target/filter, kVp and tube loadings of 15 patients with average‐compressed breast size of 4.2±0.5 cm in craniocaudal (CC) views were recorded by the technologists. Half value layer (HVL) and radiation exposure per mAs were measured at specific beam quality during the annual on‐site inspection. Entrance skin exposure for each patient was thus estimated based on the radiation output data, patient exposure techniques and compressed breast thickness. Both the conversion factors calculated by Dance and Wu were used for further AGD calculations for comparisons. Average of the AGDs of the 15 patients may served as the represented mean AGD for each mammographic unit, and dose distributions could also be obtained for further evaluations. Results: Based on the conversion factors calculated by Dance, AGDs ranged from 95.8 to 505.7 mrad, and the mean, median and 3rd quartile of the estimated AGD of the 199 mammographic units was 191.9 mrad, 172.2 mrad, and 228.0 mrad, respectively. By calculating AGDs using Wu's conversion factors, AGDs ranged from 73.3 to 390.4 mrad, and the mean, median and 3rd quartile of the estimated AGD of the 199 mammographic units was 156.1 mrad, 143.5 mrad, and 186.2 mrad, respectively. Estimated AGDs using Wu's correction factors got the lower AGD values compared to the AGDs estimated by Dance method. Conclusion: AGD distributions based on nationwide represented patient data may serve as a baseline dose database for future diagnostic reference level (DRL) establishment in mammography in Taiwan. This work was supported by grants from Atomic Energy Council of Taiwan(AEC10101003L).
SU‐E‐I‐61: Modification of An Anthropomorphic Phantom to Accommodate OSL Dosimeters
Authors: Ogden K , Roskopf M
Published: July 2013

Purpose: To modify an anthropomorphic (Rando) phantom designed for use with TLD dosimeter chips to accept OSL dosimeters. Methods: An adult male anthropomorphic phantom (Alderson Rando) has arrays of 5mm holes in each phantom slice that are designed to accept TLD dosimeter chips. Current OSL dosimeters are available in a small, 1 cm × 1 cm form factor that is convenient for external use clinically, but will not fit into the 5mm holes in Rando. The first (top) ten slices of an adult male Rando phantom (head and neck) were modified by machining 2mm slots 1.2 cm wide x 1.7 cm deep centered over the existing holes to allow placement of OSL dosimeters. Placing the slots coincident with the existing holes minimizes the amount of material removed from the phantom. Results: Each modified hole in the phantom required the removal of approximately 0.25 cmA3 of phantom material. The use of OSL dosimeters has greatly simplified the measurement process and reduced the total time required to load, unload, and read the dosimeters. For the head and neck, a total time of approximately 4 hours is required for loading, scanning, unloading, and reading OSL chips. With TLD dosimeters, the time for the equivalent data collection was 10‐12 hours. Conclusion: Total time for dosimetry measurements using TLD chips in Rando is significant due to the care required in handling TLDs, as well as the time required for the anneal and read processes. Modification of the Rando phantom has greatly increased the efficiency of making in‐phantom dose measurements. The total material removed from the phantom to accommodate the OSL dosimeters is less than 1% of the total material and so should have a negligible impact on overall phantom attenuation.
SU‐E‐I‐63: In Vivo Proton MR Spectroscopy Quantification of Cerebral Neurochemical Changes in Acute Binge Ethanol Exposed Rats
Authors: Lee Do‐Wan , Kim Jae‐Hwa , Kim Sang‐Young , Kim Dai‐Jin , Jung Jin‐Young , Song Kyu‐Ho , Choe Bo‐Young
Published: July 2013

Purpose: The cerebral metabolite changes in vivo were quantitatively assessed in binge ethanol ‐ intoxicated rats by using a 4.7‐T proton magnetic resonance spectroscopy (1H‐MRS). Methods: Thirteen 8‐week‐old, male Sprague‐Dawley rats were used and divided into 2 groups (control group: n=6; binge ‐ ethanol group: n=7). 7 binge ethanol group rats received an initial dose of 5 g/kg (30% w/v solution) via oral gavage method, followed by a maximum dose of 2 g/kg (25% w/v solution) every 8‐h (at 1400, 2200, and 0600) for 4 days. The 6 control group rats simultaneously received equal volumes (about 3.55ml) of normal saline (at 1500, 2300, and 0700). Oral gavage ethanol was administered based on body weight. After 4‐days of oral gavage, in vivo scanning was performed on all animals by using a 4.7‐T Bruker BIOSPEC. The volume of interest (VOI, 6×2×3 mm3; volume: 36 μL; Thirteen water suppressed 1H‐MRS spectra were acquired using PRESS sequences (TR/TE = 4000/20 ms; number of acquisitions = 384; number of data points = 2048). Results: Figure 1 shows the representative fitted spectra from hippocampus of binge ethanol and control group rats. Our results showed that total choline (tCho; phosphocholine+glycerophosphocholine [GPC+PCh]) concentrations were significantly lower (p=0.038) in the binge ethanol group than that in the control group (Fig.2). Moreover, tCho/total N‐acetylaspartate (tNAA: NAA+N‐acetylaspartylglutamate [NAAG]) ratios were significantly lower (p=0.043) in the binge‐ethanol group than that in the control group (Fig.3). However, Glutamine/Glutamate ratios showed no significant differences between the 2 groups. Conclusion: According to our findings and from results in previous studies, significantly low tCho concentrations and tCho/tNAA ratios may indicate the cell membrane turnover abnormalities of phosphatidylcholine and changed adaptive mechanism in the hippocampus of binge ethanol intoxicated rats. Thus, we provide quantitative in vivo evidence that binge‐ethanol exposure causes cerebral neurochemical profile changes in rats, in the hippocampal region.
SU‐E‐I‐80: Development of a Compton Camera for Online Range Monitoring of Laser‐Accelerated Proton Beams
Authors: Thirolf P , Aldawood S , Lang C , Parodi K
Published: July 2013

Purpose: Development of a versatile detector system primarily designed for online range monitoring of proton beams generated via the novel technique of particle acceleration from high‐power, short‐pulse lasers to be used in bio‐medical applications. Methods: While so far mostly offline diagnostics tools are used in this context, we aim at developing a technique based on the position‐sensitive detection of prompt gamma rays emitted from nuclear reactions between the proton beam and the biological sample. For this purpose, we develop a Compton camera capable to track not only the Compton scattered primary photon, but also the secondary Compton electron. Results: Extensive simulation studies resulted in an optimized design of the Compton camera based on a LaBr3(Ce) scintillation crystal (50×50×30 mm3 block crystal, read out by a multi‐anode PMT) acting as absorber, preceded by a stack of 6 double‐sided silicon strip detectors as scatterers (500 μm thick, 128 strips/side, pitch 390 μm). From the design simulations an angular resolution of <= 2° (at 2–6 MeV) and a source image reconstruction efficiency of 10−3 −10−3 (at 1–5 MeV) can be expected. The LaBr3 crystal has been characterized with laboratory sources, resulting in a time resolution of 540 ps and a position‐dependent energy resolution (best in the central region). Using a collimated source the point‐spread function was determined from the pixelated light distribution, yield a (preliminary and by software optimization improving) spatial resolution of < 3mm. Conclusion: The Compton camera based approach for prompt‐γ detection from nuclear interactions of therapeutic ion beams offers very promising perspectives for online range monitoring. An arrangement of several camera modules could even be used in a γ‐PET mode to additionally detect delayed annihilation radiation from positron emitters in the irradiation interrupts (with improved performance in the presence of an additional third (prompt) γ (as e.g. in 10C, 14O). Funding support via German Science Foundation: DFG Cluster of Excellence MAP (Munich Centre for Advanced Photonics)
SU‐E‐I‐86: Evaluation of Segmentation Based Attenuation Correction Methods for PET/MR in the Thorax
Authors: Ai H , Pan T
Published: July 2013

Purpose: To compare and estimate the accuracy of different segmentation‐based approaches for attenuation correction of the thoracic PET data in PET/MR. Methods: PET/CT data were retrospectively collected from 26 patients who underwent whole‐body PET/CT scan. CT images of each patient were segmented into five categories, including air, lung, fat, soft tissue and bone, with a fast 3D fuzzy c‐means clustering algorithm. The mean CT numbers of different segments for each patient were measured. For the 20 patients who have legions found in the thorax, 4 sets of CTAC images were created according to the segmentation results, simulating the attenuation maps with four different approaches: 5‐class segmentation assigned with individually measured CT number (SFLAB) and with mean CT number of the 26 patients (SFLAB mean), 4‐class with mean CT number (SFLA mean) and 3‐class with mean CT number (SLA mean). Attenuation corrected PET images were generated with these CTAC images and compared to the original attenuation corrected PET images using the maximum SUV of 35 legions identified in the thorax, both inside and outside of the lung. Results: The mean/standard deviation of the measured CT number in the 26 patients are −703/58 (lung), −105/6 (fat), 37/8 (soft tissue) and 483/63 (bone), with air CT number = −1000. The maximum SUV differences in the 35 thoracic legions are −0.7%±3.2% (SFLAB), − 1.0%±5.0% (SFLAB mean), −4.0%±5.7% (SFLA mean) and 5.7%±6.3% (SLA mean), with p‐values being 0.2069, 0.2303, 1.752e10‐4 and 5.737e10‐6, respectively. Conclusion: 5‐class segmentation methods achieved the highest quantification accuracy of PET activity in the thorax. 4‐class method tends to under‐estimate while 3‐class method tends to over‐estimate the maximum SUV. Despite the simplicity of the approaches, segmentation‐based methods can achieve reasonably high accuracy in the quantification of thoracic PET data.
SU‐E‐I‐94: Correction to Improve X‐Ray Focal Spot Measurements by Image Detector Blur Deconvolution
Authors: Rana R , Jain A , Bednarek D , Rudin S
Published: July 2013

Purpose: To deconvolve the inherent blur of a standard flat panel detector (FPD) when measuring x‐ray focal spots and to evaluate the method for three focal spots and different magnifications. Methods: A 30 micron pinhole was used to get the images of three focal spots (small, medium and large) of an x‐ray tube using a FPD for different magnifications (3.16,2.66 and 2.16) implemented by varying the source to image distance. The tube parameters were kept low (50kVp) to avoid spurious effects like blooming, pinhole penetration, etc. The detector blur, characterized by its MTF was divided into the Fourier Transform of the focal spot images and Result inverse transformed to obtain a deconvolved focal spot spread function from which the full width at tenth maximum (FWTM) focal spot measurements were obtained and compared with those of the uncorrected original profiles. Results: We measured the corrected focal spot size for small, medium and large focal spot using FWTM to be 0.41mm, 0.57mm, and 1.54mm respectively. The corrected focal spot sizes demonstrated reduced values of up to 25%, 18% and .7% compared to the uncorrected for the small, medium, and large focal spots respectively. Also, we observed that the difference between the focal spot size before and after deconvolution increases with the decrease in magnification (smaller SIDs) supporting the fact that the effect of detector blur can be reduced significantly by using a higher magnification. Conclusion: For improved accuracy in x‐ray focal spot measurements, deconvolving the detector resolution characteristics can be used to get rid of the excessive blur which can also be minimized by using the maximum magnification possible. NIH Grant 2R01EB002873
SU‐E‐I‐97: Direct Calculation of Patient Absorbed Dose From X‐Ray Beam Variables and Anatomy
Authors: Soares F , Borba A , Moreira T
Published: July 2013

Purpose: Develop a direct equation to estimate patient absorbed dose under x‐ray exams using electrical, geometrical and filtration parameters combined with anatomy data. The equation can further be used in radiology departments to record patient dose data and help to decide the best parameters set for each patient exam. Methods: To determine the absorbed dose received by patients, Entrance Skin Dose (ESD) is used with the irradiated area and patient mean thickness for specific anatomy. ESD is calculated from a developed equation, where entrance surface air‐KERMA (ESAK) and backscatter factor are taking into account, with air‐to‐skin coefficient conversion. Air‐KERMA rate has its equation derived from IPEN/UK simulation data. The input variables in ESD equation are: voltage and its ripple, total bean filtration, anode angle, current, time, distance, patient area under irradiation and patient thickness. We developed specific Lambert‐Beer attenuation equations derived from mass energy‐absorption coefficients data (NIST/USA), for each anatomy: chest, upper arm, hand and thigh. The anatomy mean thickness was estimate by summing skin, muscle, fat and bone thickness at central ray location, in antero‐posterior incidence, for standard male. Results: The final equations, one for each anatomy, although complex in its whole format, simplifies the direct determination of absorbed dose from the variables involved. There is no need to look up tables, interpolation, or restrictions due to small ranges of variables. After one time input data, total absorbed dose (mGy) is calculated instantaneously. The final Result mean error, compare to available data, was equal to 5%. Conclusion: The complex equations developed has its use simplified by one time input data, with no look up tables or data interpolation. Besides dose calculation for a given exam and patient, the operator can chose the best variables that will deposit less radiation into patient by means of a previous analysis of each variables combination. This research is support by CNPq, the Federal research supporting agency of Brazil.
SU‐E‐J‐02: GPU‐Accelerated Polyenergetic DRR Generation Based On Data Parallelism and Task Parallelism with a Dispatcher Using OpenCL: Effect of the Numbers of Tasks and Energies
Authors: Zhou L , Chao K , Chang J
Published: July 2013

Purpose: To improve the performance of parallel processing of multi‐energetic digitally reconstructed radiograph (DRR) generation using a task‐overlap strategy on heterogeneous platforms. Methods: A segmented 512 ×512 ×223 head‐neck phantom was used to generate 512 ×512 polyenergetic DRR based on Mohan4 and Mohan6 spectrums containing 16 and 24 energy bins, respectively. The DRR formation for each energy bin comprises three steps: (1) phantom conversion, (2) line integral and (3) exponential and weighting of projection. The parallel computing ecosystem consisted of one 8‐core CPU and one general purpose graphics processing unit (GPGPU). We used Open Computing Language (OpenCL) to decompose the low‐degree parallel and serial workloads into multiple tasks on CPU using task parallelism, and partition the high‐degree parallel workloads on GPGPU using data parallelism. Two sequential task partitions for the first DRR formation were tested: (A) Step1 as Task1 on CPU, Step2 as Task2 on GPU and Step3 as Task3 on CPU; and (B) Step1 as Task1 on CPU and Step2 and Step3 as Task2 on GPU. The subsequent DRR generation does not need Step 1 so Step1 as Task1 was excluded in each partition. A task‐overlap method driven by a dispatcher was also implemented using regular single‐threaded host program to further improve the performance. Results: For the first DRR formation and Partition A, the task‐overlap strategy was 5.8 and 6.5 times faster than sequential method for 16‐energy‐bin Mohan4 and 24‐energy‐bin Mohan6 spectrums, respectively. For Partition B, the speedup of the task‐overlap strategy was 5.2 and 5.5 times for Mohan4 and Mohan6 spectrums, respectively. For the following DRR formation, the speedups were 1.16 and 1.165 times in two‐task scenario for Mohan4 and Mohan6 spectrums. Conclusion: The task‐overlap strategy significantly improves the performance for parallel processing of multi‐energetic DRR generation. The parallelism is increased when more energies and tasks are driven by the dispatcher.
SU‐E‐J‐11: ExacTrac Setup Uncertainties in Intracranial and HN Patients: Comparison with CT‐On‐Rail
Authors: Wang X , Zhao Z , Wang H , Yang J
Published: July 2013

Purpose: To evaluate the accuracy of ExacTrac system based setup in intracranial and HN patients, and provide quantitative data to reduce PTV margin. Methods: The accuracy of ExacTrac system based patient setup depends on both the excellence of its image registration and the reliability of the congruence of its image isocenter with the linac radiation isocenter. The accuracy of ExacTrac system's image registration was studied by marking the ExacTrac determined isocenter (< 1mm residual translation, and < 2 degree residual rotation) with 2 mm in diameter BBs using the room laser and comparing it with CT determined isocenter. CT‐on‐rail was used to acquire the 3D‐data using the same scan parameters as the planning CT. An in‐house software registered the daily CT with the planning CT on the fly and calculated the difference between the CT determined isocenter and BB marked isocenter. The small residual rotations were manually examined with the in‐house software using boney landmark. A total of 68 fractions spread over 12 patients were used in this study. Short Orfit masks were used as the patient immobilization device. Both daily and weekly QA were performed to ensure the agreement between the laser and Exactrac image isocenter was within 1 mm. Results: The distance between ExacTrac and CT‐on‐rail determined isocenter were 1.66±0.9 mm with 95% less than 3 mm. For the small residual rotation angle detected by the ExacTrac, CT data also showed good agreement. ExacTrac snap data between beams of an IMRT delivery demonstrated the intra‐fraction motion can be controlled within 2 mm Conclusions: CT data confirmed that ExacTrac can accurately setup both intracranical and HN patients. PTV margin for patients with the Orfit masks can be reduced to 3 mm based on the image isocenter QA, image registration accuracy and motion tracking ability of ExacTrac system.
SU‐E‐J‐15: Weekly Bladder V65 and V40 Changes in Correlation to the CBCT Bladder Filling
Authors: Grimm L , Ma C , Scharf L , Sobczak M
Published: July 2013

Purpose: Full bladder at time of simulation and daily treatment is requested of prostate/prostate‐bed patients; however, not all patients comply. This study is to analyze the V65 and V40 changes in correlation with CBCT bladder filling. Methods: Daily 2D KV/KV IGRT using implanted radio‐opaque markers and weekly 3D CBCT IGRT direct visualization of target volume were routinely performed. Physicians compared the pre‐treatment CBCT bladder filling to the planned CT bladder filling to identify the poor bladder fillers. Weekly CBCT bladder volumes were contoured of poor bladder fillers, and VMAT/IMRT plans recalculated to obtain the actual bladder dose, using the commercially available DVH Evaluator to obtain the V65 and V40 values promptly and accurately. Results: From Jan 2012‐Nov 2012, a total of 181 prostate/prostate‐bed patients were analyzed. 47 patients were classified as poor‐average bladder fillers. A total of 358 CBCT bladders were contoured to obtain bladder volumes/doses. The 358 CBCT images were grouped into 10 bins to differentiate bladder volumes from baseline. The median change in V65 and V40 bins were both monotonically increasing for this dataset. Despite this evident trend, no statistically significant correlation in IPSS scores was found in relation to the change in V65 or V40. Conclusions: The V65 <= 25% and V40 <= 50% are among the tightest bladder constraints in common clinical use. Since the image registration aligns the prostate and the daily bladder volumes vary, the resulting tightly conformal plans are robust to daily bladder filling variations. No statistically significant correlation to IPSS score changes were identified thus far in relation to the bladder filling changes. Additional follow‐up is required to ensure that there are no long‐term adverse effects based on poor bladder filling during care. Intellectual property rights for the DVH Evaluator software tool, which was used for this analysis
SU‐E‐J‐17: Assessment for Setup Uncertainty of Frameless Localization System of Stereotactic Radiosurgery Using Cone Beam Computed Tomography
Authors: Baek J , Oh Y , Park S , Choi E , Jeon K , Kim O , Kim J
Published: July 2013

Purpose: The purpose of this study was to assess setup uncertainties and quantify the magnitudes of setup corrections of frameless localization system using cone beam computed tomography (CBCT). Methods: This study involved 28 patients who were treated single fraction stereotactic radiosurgery (SRS) by Varian Clinac IX equipped with a micro‐multileaf‐collimator (m3). All patients were simulated and setup with BrainLab immobilization mask and localization system, also they underwent a kV‐CBCT imaging before treatment. Setup corrections between acquired CBCT and planning CT were performed by automatic adjustment couch system, and collected into registration software as Offline Review (Varian Medical System, Palo Alto, CA) and the data were analyzed in 4 directions: lateral (x) longitudinal (y), vertical (z), rotational (yaw). Results: The mean setup corrections were 0.07 mm, ‐ 0.43 mm, 0.50 mm, and −0.11° in x, y, z and yaw directions, respectively. The mean radial correction was 1.85 mm. The standard deviations of setup corrections were 0.77 mm, 1.73 mm, 0.69 mm, and 0.40° in x, y, z and yaw directions, respectively. The maximum shifts were 2 mm, ‐ 5 mm, 2 mm, and 1° in x, y, z and yaw directions, respectively. The mean setup corrections represent systematic errors of localization system and the standard deviations indicated random setup errors of BrainLab specific thermoplastic mask. The systematic error of localization system was small of less than 0.5 mm or −0.1°, whereas patient random errors still inherent and the largest magnitude of setup error was −5 mm in y direction. There were rotational setup errors and the highest magnitude was 1°. Conclusion: Therefore, CBCT image guidance should be performed before SRS treatment to verify setup errors more accurately.
SU‐E‐J‐32: The Dosimetric Impact of Both a Rigid and a Flexible Radiofrequency Coil in a Hybrid 1.5T MRI and 6 MV Linac System for Online MR‐Guided Radiotherapy
Authors: Hoogcarspel S , Crijns S , Vulpen M , Lagendijk J , Raaymakers B
Published: July 2013

Purpose: To investigate the dosimetric impact of both a rigid and a flexible radiofrequency coil in a hybrid 1.5T MRI and 6 MV linac system for online MR‐guided radiotherapy. Methods: We evaluated the dosimetric impact of a flexible Synergy MR coil (Philips, Best) on both a simple and a complex irradiation strategy for treating spinal bone metastases by Monte‐Carlo simulations. This tumor site, in combination with this MR coil may be chosen for the first in‐man treatments with the UMC Utrecht MRL‐system. Second, we investigated the dosimetric impact of a rigid pelvis coil as used in the interventional Philips MRI HIFU system. This coil consists of a hard plastic shell with the actual coil elements and electronics inside it. We took a separate look at the influence of the shell and the coil components on the dose distribution. Results: For the flexible coil, the dose to the target volume was underestimated up to 2.2% as a Result of beam attenuation in the MR coil in case a single posterior‐anterior field was applied (Figure 1). This underestimation however, decreased to 1% when a stereotactic treatment strategy was employed (Figure 2). For the rigid HIFU coil, the shell without electronic components introduced a homogenous 4% dose decrease when an anterior‐posterior rectangular field was utilized. The dose to the skin however, was increased dramatically as a Result of additional electrons generated inside the shell (figure 3). The shell with the electronic components yielded severe streaks in the dose distribution (figure 4). Conclusion: It is feasible to use the Flexible Synergy MR body coil for MR guided radiotherapy without any modification to the coil. The rigid HIFU pelvis coil however, is with its current design, unsuitable for MRgRT.
SU‐E‐J‐35: Imaging Dose in Radiotherapy: An Institution‐Based Study
Authors: Maricle S , Mathews B , Yakoubian S
Published: July 2013

Purpose: Image‐guided radiotherapy (IGRT) has become an essential component in comprehensive radiation therapy. However, this method of localization also carries with it increased radiation dose to the patient. As a center with multiple imaging modalities for IGRT, the goal of this research was to quantify the imaging dose received by patients in different treatment and IGRT setups throughout the course of treatment. Methods: At our institution, the IGRT modalities used are MV port films, kV port films, ExacTrac, and kV cone‐beam CT (CBCT). There are currently two different IGRT‐equipped linear accelerators in use at our facilities. Each type of machine was tested for the imaging modalities it utilized. The exposure values for a single image were compared to the AAPM TG‐75 values to see whether the values fell within the previously published data. The exposure values were then converted to dose and multiplied by the conventional fractionation scheme for the associated area of treatment in order to compare the imaging dose to the total treatment dose for that site. Results: The majority of exposures fell within the guidelines of the AAPM TG‐75 report. Imaging doses, as a percentage of treatment dose, were all less than 1%. Conclusion: This study helped to establish baseline values for periodic imaging quality assurance and provided support that imaging doses in our facilities are reasonable in terms of previously published data and the ALARA principle. The exposure values for our institution align well with those listed in TG‐75, and as long as repeat imaging is kept to a minimum, imaging doses will remain only a small percentage of total treatment dose.
SU‐E‐J‐36: Development of a Low Cost, Easily‐Made, Interchangeable, Prostate Brachytherapy Phantom for Multi‐Imaging Guidance Using Ultrasound, CT and MRI
Authors: Julius B , Lin S , Rahmani D , Rockey W , Tracy C , Nixon E , Modrick J , Sander E , Kim Y
Published: July 2013

Purpose: To develop an easily‐made, interchangeable prostate brachytherapy phantom for implant training and/or dummy‐run treatment planning that is feasible for ultrasound (US), CT and MRI guidance. Commercially available phantoms are expensive and not reusable for repeated implant practice. Methods: The phantom consists of two parts: a multiple use lower transrectal‐ultrasound part and an interchangeable upper part. Material composition was iteratively updated based upon each scan of US, CT, and MRI. Image quality on US, CT and MRI was evaluated in terms of the contrasts seen in prostate, urethra, seminal vesicles, and periprostatic tissues. Two dummy‐run needle implants were tested with transrectal‐ultrasound guidance. Results: An interchangeable phantom was developed using soft polyvinyl chloride (PVC) in the lower transrectal‐ultrasound part, the seminal vesicles, and the urethra. The upper interchangeable part consisted of the prostate, urethra, and seminal vesicles, all of which were surrounded by gelatin (2 packets/cup of water). The seminal vesicle (soft PVC) and the prostate (gelatin) were embedded into gelatin. The prostate was made by mixing gelatin (4 packets gelatin and 1.5 tablespoons psyllium/cup of water) into a 50 mL egg shaped mold and then adding the urethra. The first prostate used soft PVC and plasticizer and resulted in poor contrast when using US. After testing with dummy‐run needle implants, the concentration of the upper phantom background (gelatin) was doubled to make it more resistant to wear. The developed phantom produced image quality comparable to those of commercial phantoms but at a cost of only $80 and an 8 hour build time. Conclusion: This study indicates the feasibilities of generating an easily made, interchangeable prostate brachytherapy phantom that is cost‐effective. The developed phantom could be imaged across multiple imaging modalities, thus demonstrating its potential for use in implant practice, dummy‐runs, and planning studies using US, CT, or MRI guidance.
SU‐E‐J‐41: Measurements of CTDI100 and CTDIvol for MVCT Scans On a TomoTherapy System
Authors: Chao E
Published: July 2013

Purpose: To measure the computed tomography dose index (CTDI) for MVCT scans on the TomoTherapy™ System. Methods: The CTDI100 and CTDIvol were measured using a Standard Imaging A17 ion chamber inserted into a standard CTDI phantom (32 cm diameter and 16 cm diameter acrylic cylinders for body or head CTDI measurements, respectively). Dose measurements were performed using both a ‘Fine’ pitch helical scan with a scan range of ±2 cm, as well as an equivalent axial scan generated using a calibration procedure. The two methods yielded identical results, indicating the scattered radiation is well contained within the A17 ion chamber's active length. The A17 ion chamber has a non‐standard active length for CTDI measurements of 11.0 cm. However, since the scattered dose is well contained within the A17's active length, the non‐standard length can be accounted for in the CTDI calculation. Finally, the CTDI100 calculation requires a choice of a nominal axial slice thickness that is not well defined for the TomoTherapy™ System since axial scans are not an available imaging mode. A 4 mm nominal slice thickness was chosen. For the CTDIvol calculations, this choice of nominal slice thickness results in a convenient pitch of 1, 2, and 3 for the Fine, Normal, and Coarse imaging modes, respectively. Results: On the 32 cm body phantom, the center CTDI 100 was 2.18 cGy and the average of the peripheral measurements was 2.72 cGy. The volume CTDI values are calculated to be CTDIvol (Fine) = 2.54 cGy, CTDIvol (Normal) = 1.27 cGy, and CTDIvol (Coarse) = 0.85 cGy. On the 16cm head phantom, the volume CTDI values are calculated to be CTDIvol (Fine) = 3.48 cGy, CTDIvol (Normal) = 1.74 cGy, and CTDIvol (Coarse) = 1.16 cGy. Conclusion: The CTDI values described here provide a reference measured on one representative TomoTherapy™ System.
SU‐E‐J‐50: Maximum a Posteriori Proton CT Reconstruction Using Anatomic Prior
Authors: Li H , Lin Y , Hansen Od , Seco J , Li Q
Published: July 2013

Purpose: It has been demonstrated that the information in one image modality can be used to significantly help the reconstruction of another image modality. Here we develop and evaluate a novel Maximum a Posteriori (MAP) approach to apply anatomical information in MRI or x‐ray CT image to facilitate the estimate of Proton CT (pCT) image. Method: To incorporate anatomical information of MRI or x‐ray CT into the reconstruction of pCT images through priors based on information theoretic similarity measures, we formulate a MAP optimization problem, which includes a least‐square data‐fitting term to account for the noise in the measurement and a penalty term to maximize the joint density of feature vectors extracted from the pCT image and anatomical image. We defined feature vectors that emphasize prominent boundaries in anatomical and functional images, and attach less importance to detail and noise that is less likely to be correlated in the two images. We use a non‐parametric, FFT‐based Parzen window approach to speed up the computation of the density function of the feature vector, the joint density of feature vector, and the gradients of joint entropy. The optimization problem is solved using conjugate gradient and Armijo‐backtracking line search. We performed realistic simulations using anthropomorphic phantom to validate our approach and compare its performance to MAP approach with a quadratic smoothness penalty function (without anatomic information from x‐ray). Results: The Preliminary results demonstrate the proposed MAP approach with MRI or x‐ray CT as prior can achieve better contrast recovery and biasvariance trade‐off curves compared with MAP approach without anatomical prior. Conclusions: The proposed MAP approach can achieve superior image quality by using anatomical information in the MRI/x‐ray CT image. In the future we will investigate how much data reduction we can achieve using the proposed method while maintain the same image quality.