Search NASA⌕ Search

SEARCH · Search NASA

Results for “CT SCANNER”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

SU-F-T-215: An Investigation Of Multi-Scanner CT Hounsfield Unit Calibration for Pencil Beam Scanning Proton Therapy Using 3D Gamma Analysis

Purpose: We compare and investigate the dosimetric impacts on pencil beam scanning (PBS) proton treatment plans generated with CT calibration curves from four different CT scanners and one averaged ‘global’ CT calibration curve. Methods: The four CT scanners are located at three different hospital locations within the same health system. CT density calibration curves were collected from these scanners using the same CT calibration phantom and acquisition parameters. Mass density to HU value tables were then commissioned in a commercial treatment planning system. Five disease sites were chosen for dosimetric comparisons at brain, lung, head and neck, adrenal, and prostate. Three types of PBS plans were generated at each treatment site using SFUD, IMPT, and robustness optimized IMPT techniques. 3D dose differences were investigated using 3D Gamma analysis. Results: The CT calibration curves for all four scanners display very similar shapes. Large HU differences were observed at both the high HU and low HU regions of the curves. Large dose differences were generally observed at the distal edges of the beams and they are beam angle dependent. Out of the five treatment sites, lung plans exhibits the most overall range uncertainties and prostate plans have the greatest dose discrepancy. There are no significant differences between the SFUD, IMPT, and the RO-IMPT methods. 3D gamma analysis with 3%, 3 mm criteria showed all plans with greater than 95% passing rate. Two of the scanners with close HU values have negligible dose difference except for lung. Conclusion: Our study shows that there are more than 5% dosimetric differences between different CT calibration curves. PBS treatment plans generated with SFUD, IMPT, and the robustness optimized IMPT has similar sensitivity to the CT density uncertainty. More patient data and tighter gamma criteria based on structure location and size will be used for further investigation.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-T-70: Commissioning a Multislice CT Scanner for X-Ray CT Polymer Gel Dosimetry

Purpose: To commission a multislice computed tomography (CT) scanner for fast and reliable readout of radiation therapy (RT) dose distributions using CT polymer gel dosimetry (PGD). Methods: Commissioning was performed for a 16-slice CT scanner using images acquired through a 1L cylinder filled with water. Additional images were collected using a single slice machine for comparison purposes. The variability in CT number associated with the anode heel effect was evaluated and used to define a new slice-by-slice background image subtraction technique. Image quality was assessed for the multislice system by comparing image noise and uniformity to that of the single slice machine. The consistency in CT number across slices acquired simultaneously using the multislice detector array was also evaluated. Finally, the variability in CT number due to increasing x-ray tube load was measured for the multislice scanner and compared to the tube load effects observed on the single slice machine. Results: Slice-by-slice background subtraction effectively removes the variability in CT number across images acquired simultaneously using the multislice scanner and is the recommended background subtraction method when using a multislice CT system. Image quality for the multislice machine was found to be comparable to that of the single slice scanner. Further study showed CT number was consistent across image slices acquired simultaneously using the multislice detector array for each detector configuration of the slice thickness examined. In addition, the multislice system was found to eliminate variations in CT number due to increasing x-ray tube load and reduce scanning time by a factor of 4 when compared to imaging a large volume using a single slice scanner. Conclusion: A multislice CT scanner has been commissioning for CT PGD, allowing images of an entire dose distribution to be acquired in a matter of minutes. Funding support provided by the Natural Sciences and Engineering Research Council of Canada (NSERC)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

SU-E-I-31: Differences Observed in Radiation Doses Across 2 Similar CT Scanners From Adult Brain-Neck CT Angiography

Purpose: The aim of this study is to evaluate the difference in radiation doses from adult Brain-Neck CT angiography (CTA) between two CT scanners. Methods: We collected CT dose index data (CTDIvol, DLP) from adult Brain-Neck CTA performed with two CT scanners (Sensation 64 (S64) and Definition AS (AS), Siemens Healthcare) performed at two of our facilities from Jan 1st to Dec 31th, 2014. X-ray dose management software (Radmetrics, Bayer Healthcare) was used to mine these data. All exams were performed with Tube Current Modulation (Care Dose 4D), tube voltage of 120 kVp, quality reference mAs of 300, beam collimation of 64*0.6 mm. The rotation time was set to 0.5 sec for S64 and 1.0 sec for AS. We also scanned an anthropomorphic skull and chest phantom under routine Brain-Neck CTA protocol with the two scanners and extracted the tube current values from the raw projection data. Results: The mean CTDIvol and DLP in Brain-Neck CTA was 72 mGy and 2554 mGy*cm for AS, which was substantially larger than the mean values of 46 mGy and 1699 mGy*cm for S64. The maximum tube current was 583 mA for most cases on the S64 while the maximum was 666 mA for AS even though the rotation time set for AS was 1.0 sec. Measurements obtained with the anthropomorphic phantom showed that the tube current reached 583 mA at the shoulder region for S64 while it reached to 666 mA for AS. Conclusion: The results of this study showed that substantially different CT doses can Result from Brain-Neck CTA protocols even when similar scanners and similar settings are used. Though both scanners have a similar maximum mA rating, differences in mA were observed through the shoulders, resulting in substantially different CTDIvol values.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-I-21: Dosimetric Characterization and Image Quality Evaluation of the AIRO Mobile CT Scanner

Purpose: The AIRO Mobile CT system was recently introduced which overcomes the limitations from existing CT, CT fluoroscopy, and intraoperative O-arm. With an integrated table and a large diameter bore, the system is suitable for cranial, spine and trauma procedures, making it a highly versatile intraoperative imaging system. This study is to investigate radiation dose and image quality of the AIRO and compared with those from a routine CT scanner. Methods: Radiation dose was measured using a conventional 100mm pencil ionization chamber and CT polymethylmetacrylate (PMMA) body and head phantoms. Image quality was evaluated with a CATPHAN 500 phantom. Spatial resolution, low contrast resolution (CNR), Modulation Transfer Function (MTF), and Normalized Noise Power Spectrum (NNPS) were analyzed. Results: Under identical technique conditions, radiation dose (mGy/mAs) from the AIRO mobile CT system (AIRO) is higher than that from a 64 slice CT scanner. MTFs show that both Soft and Standard filters of the AIRO system lost resolution quickly compared to the Sensation 64 slice CT. With the Standard kernel, the spatial resolutions of the AIRO system are 3lp/cm and 4lp/cm for the body and head FOVs, respectively. NNPSs show low frequency noise due to ring-like artifacts. Due to a higher dose in terms of mGy/mAs at both head and body FOV, CNR of the AIRO system is higher than that of the Siemens scanner. However detectability of the low contrast objects is poorer in the AIRO due to the presence of ring artifacts in the location of the targets. Conclusion: For image guided surgery applications, the AIRO has some advantages over a routine CT scanner due to its versatility, large bore size, and acceptable image quality. Our evaluation of the physical performance helps its future improvements.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Spectra of clinical CT scanners using a portable Compton spectrometer

Purpose: Spectral information of the output of x-ray tubes in (dual source) computer tomography (CT) scanners can be used to improve the conversion of CT numbers to proton stopping power and can be used to advantage in CT scanner quality assurance. The purpose of this study is to design, validate, and apply a compact portable Compton spectrometer that was constructed to accurately measure x-ray spectra of CT scanners. Methods: In the design of the Compton spectrometer, the shielding materials were carefully chosen and positioned to reduce background by x-ray fluorescence from the materials used. The spectrum of Compton scattered x-rays alters from the original source spectrum due to various physical processes. Reconstruction of the original x-ray spectrum from the Compton scattered spectrum is based on Monte Carlo simulations of the processes involved. This reconstruction is validated by comparing directly and indirectly measured spectra of a mobile x-ray tube. The Compton spectrometer is assessed in a clinical setting by measuring x-ray spectra at various tube voltages of three different medical CT scanner x-ray tubes. Results: The directly and indirectly measured spectra are in good agreement (their ratio being 0.99) thereby validating the reconstruction method. The measured spectra of the medical CT scanners are consistent with theoretical spectra and spectra obtained from the x-ray tube manufacturer. Conclusions: A Compton spectrometer has been successfully designed, constructed, validated, and applied in the measurement of x-ray spectra of CT scanners. These measurements show that our compact Compton spectrometer can be rapidly set-up using the alignment lasers of the CT scanner, thereby enabling its use in commissioning, troubleshooting, and, e.g., annual performance check-ups of CT scanners.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2016

Sci-Fri AM: Quality, Safety, and Professional Issues 03: The Increasing Costs of Shielding Diagnostic CT Scanners in Ontario

Purpose: In Ontario, shielding for all X-ray machines, including CT scanners, must be evaluated according to Safety Code 20A (Health Canada, 1983) which is based on NCRP-49 (NCRP, 1976). NCRP-147 (NCRP, 2004) is the international standard for shielding calculations of CT scanners and is also referenced in Safety Code 35 (Health Canada, 2008) which, was published to supersede SC20A. The goal of this work is to demonstrate the cost effectiveness of NCRP-147 for CT scanner shielding. Methods: CT scanner shielding calculations are performed using SC20A and NCRP-147: A room located on the third floor with the nearest building 75m away A room with high occupancy uncontrolled adjacent spaces Two side by side rooms on the main floor Results: 1. SC20A: The exterior windows required 0.1mm of Pb to protect the public who may occupy the building at 75m. 1. NCRP-147: No additional shielding required. 2. SC20A: Two walls adjacent to high occupancy uncontrolled space required an additional 1.58mm Pb. 2. NCRP-147: No additional shielding required. 3. SC20A: The entire floor and ceiling slabs in both rooms required an additional 0.79mm Pb. In addition, 0.79mm Pb was added to the walls from the ceiling to overlap the existing Pb shielding in the walls. 3. NCRP-147: No additional shielding required. Conclusion: The application of NCRP Report No. 147 affords the required protection to staff and the public, in the true spirit of the ALARA principle, taking into account relevant social and economic factors.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

WE-FG-207B-12: Quantitative Evaluation of a Spectral CT Scanner in a Phantom Study: Results of Spectral Reconstructions

Purpose: To evaluate the quantitative image quality of spectral reconstructions of phantom data from a spectral CT scanner. Methods: The spectral CT scanner (IQon Spectral CT, Philips Healthcare) is equipped with a dual-layer detector and generates conventional 80-140 kVp images and variety of spectral reconstructions, e.g., virtual monochromatic (VM) images, virtual non-contrast (VNC) images, iodine maps, and effective atomic number (Z) images. A cylindrical solid water phantom (Gammex 472, 33 cm diameter and 5 cm thick) with iodine (2.0-20.0 mg I/ml) and calcium (50-600 mg/ml) rod inserts was scanned at 120 kVp and 27 mGy CTDIvol. Spectral reconstructions were evaluated by comparing image measurements with theoretical values calculated from nominal rod compositions provided by the phantom manufacturer. The theoretical VNC was calculated using water and iodine basis material decomposition, and the theoretical Z was calculated using two common methods, the chemical formula method (Z1) and the dual-energy ratio method (Z2). Results: Beam-hardening-like artifacts between high-attenuation calcium rods (≥300 mg/ml, >800 HU) influenced quantitative measurements, so the quantitative analysis was only performed on iodine rods using the images from the scan with all the calcium rods removed. The CT numbers of the iodine rods in the VM images (50∼150 keV) were close to theoretical values with average difference of 2.4±6.9 HU. Compared with theoretical values, the average difference for iodine concentration, VNC CT number and effective Z of iodine rods were −0.10±0.38 mg/ml, −0.1±8.2 HU, 0.25±0.06 (Z1) and −0.23±0.07 (Z2). Conclusion: The results indicate that the spectral CT scanner generates quantitatively accurate spectral reconstructions at clinically relevant iodine concentrations. Beam-hardening-like artifacts still exist when high-attenuation objects are present and their impact on patient images needs further investigation. YY is an employee of Philips Healthcare.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-E-12: Validation of the Implementation of Different CT Scanners in Proton Treatment Planning

Purpose: To quantify the impact of the relationship of CT number and Relative Stopping Power (RSP) among different CT-scanners in the evaluation of dose distribution, for different tumor sites and proton therapy modalities like Pencil Beam and Uniform Scanning. Methods: The same tissue characterization phantom was used to analyze the difference in the X-rays energy spectra of 2 CT scanners of the same vendor. One CT is for planning and the other for treatment verification. The Hounsfield unit (HU) variations and associated dosimetric uncertainty were investigated in uniform scanning and pencil beam treatment plans of different sites. At the same time comparisons of the CT calibration curve were done using the same acquisition protocols. The phantom was imaged on a 16 multi-row CT scanner, with energies of 120 and 140 kVp,currents of 263 and 245 mA and slice thickness of 2 and 3mm respectively. The dosimetric uncertainty of the plans was evaluated in a homogeneus phantom comparing DVHs, gamma index criteria 3% 3mm, and range between them. Results: The variation of HU was within the standard deviation of the average for each tissue substitute. The curves fitted with a bilinear interpolation show a maximum deviation in high density materials like cortical bone and solid water, where the HU values deviated more than 0,6% for the 120kVp protocol. For the others curves the deviation was more than 2% for low densities materials. The gamma index uncertainty criteria passed in all the cases. Conclusion: The HU variations for the different scanners were ≤3%. Lower than the 3,5% uncertainties considered in our treatment planning system. The dosimetric analysis shows that the X-ray spectrum has a small effect on the HU-RSP curve, allowing the use of a single tissue characterization curve in our proton treatment planning system for plans verifications.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-J-35: Clinical Performance Evaluation of a Phase II Proton CT Scanner

Purpose: To develop the methodology to evaluate the clinical performance of a Phase II Proton CT scanner Methods: Range errors on the order of 3%-5% constitute a major uncertainty in current charged particle treatment planning based on Hounsfield Unit (HU)-relative stopping power (RSP) calibration curves. Within our proton CT collaboration, we previously developed and built a Phase I proton CT scanner that provided a sensitive area of 9 cm (axial) × 18 cm (in-plane). This scanner served to get initial experience with this new treatment planning tool and to incorporate lessons learned into the next generation design. A Phase II scanner was recently completed and is now undergoing initial performance testing. It will increase the proton acquisition rate and provide a larger detection area of 9 cm x 36 cm. We are now designing a comprehensive evaluation program to test the image quality, imaging dose, and range uncertainty associated with this scanner. The testing will be performed along the lines of AAPM TG 66. Results: In our discussion of the evaluation protocol we identified the following priorities. The image quality of proton CT images, in particular spatial resolution and low-density contrast discrimination, will be evaluated with the Catphan600 phantom. Initial testing showed that the Catphan uniformity phantom did not provide sufficient uniformity; it was thus replaced by a cylindrical water phantom. The imaging dose will be tested with a Catphan dose module, and compared to a typical cone beam CT dose for comparable image quality. Lastly, we developed a dedicated dosimetry range phantom based on the CIRS pediatric head phantom HN715. Conclusion: A formal evaluation of proton CT as a new tool for proton treatment planning is an important task. The availability of the new Phase II proton CT scanner will allow us to perform this task. This research is supported by the National Institute of Biomedical Imaging and Bioengineering of the NIH under award number R01EB013118. The content is solely the responsibility of the authors and does not necessarily represent the official views of the NIH.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

TU-H-207A-01: Development of Conversion Factors to Account for Different CTDI Phantom Setups On a Wide-Beam CT Scanner

Purpose: A fundamental measure performed during an annual physics CT evaluation confirms that system displayed CTDIvol nearly matches the independently measured value in phantom. For wide-beam (z-direction) CT scanners, AAPM Report 111 defined an ideal measurement method; however, the method often lacks practicality. The purpose of this preliminary study is to develop a set of conversion factors for a wide-beam CT scanner, relating the CTDIvol measured with a conventional setup (single CTDI phantom) versus the AAPM Report 111 approach (three abutting CTDI phantoms). Methods: For both the body CTDI and head CTDI, two acquisition setups were used: A) conventional single phantom and B) triple phantom. Of primary concern were the larger nominal beam widths for which a standard CTDI phantom setup would not provide adequate scatter conditions. Nominal beam width (160 or 120 mm) and kVp (100, 120, 140) were modulated based on the underlying clinical protocol. Exposure measurements were taken using a CT pencil ion chamber in the center and 12 o’clock position, and CTDIvol was calculated with ‘nT’ limited to 100 mm. A conversion factor (CF) was calculated as the ratio of CTDIvol measured in setup B versus setup A. Results: For body CTDI, the CF ranged from 1.04 up to 1.10, indicating a 4–10% difference between usage of one and three phantoms. For a nominal beam width of 160 mm, the CF did vary with selected kVp. For head CTDI at nominal beam widths of 120 and 160 mm, the CF was 1.00 and 1.05, respectively, independent of the kVp used (100, 120, and 140). Conclusions: A clear understanding of the manufacturer method of estimating the displayed CTDIvol is important when interpreting annual test results, as the acquisition setup may lead to an error of up to 10%. With appropriately defined CF, single phantom use is feasible.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

A new technique to characterize CT scanner bow-tie filter attenuation and applications in human cadaver dosimetry simulations

Purpose: To present a noninvasive technique for directly measuring the CT bow-tie filter attenuation with a linear array x-ray detector. Methods: A scintillator based x-ray detector of 384 pixels, 307 mm active length, and fast data acquisition (model X-Scan 0.8c4-307, Detection Technology, FI-91100 Ii, Finland) was used to simultaneously detect radiation levels across a scan field-of-view. The sampling time was as short as 0.24 ms. To measure the body bow-tie attenuation on a GE Lightspeed Pro 16 CT scanner, the x-ray tube was parked at the 12 o’clock position, and the detector was centered in the scan field at the isocenter height. Two radiation exposures were made with and without the bow-tie in the beam path. Each readout signal was corrected for the detector background offset and signal-level related nonlinear gain, and the ratio of the two exposures gave the bow-tie attenuation. The results were used in the GEANT4 based simulations of the point doses measured using six thimble chambers placed in a human cadaver with abdomen/pelvis CT scans at 100 or 120 kV, helical pitch at 1.375, constant or variable tube current, and distinct x-ray tube starting angles. Results: Absolute attenuation was measured with the body bow-tie scanned at 80–140 kV. For 24 doses measured in six organs of the cadaver, the median or maximum difference between the simulation results and the measurements on the CT scanner was 8.9% or 25.9%, respectively. Conclusions: The described method allows fast and accurate bow-tie filter characterization.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Technical Note: Measurement of bow tie profiles in CT scanners using radiochromic film

Purpose: To provide a noninvasive technique to measure the intensity profile of the fan beam in a computed tomography (CT) scanner that is cost effective and easily implemented without the need to access proprietary scanner information or service modes. Methods: The fabrication of an inexpensive aperture is described, which is used to expose radiochromic film in a rotating CT gantry. A series of exposures is made, each of which is digitized on a personal computer document scanner, and the resulting data set is analyzed to produce a self-consistent calibration of relative radiation exposure. The bow tie profiles were analyzed to determine the precision of the process and were compared to two other measurement techniques, direct measurements from CT gantry detectors and a dynamic dosimeter. Results: The radiochromic film method presented here can measure radiation exposures with a precision of ∼6% root-mean-square relative error. The intensity profiles have a maximum 25% root-mean-square relative error compared with existing techniques. Conclusions: The proposed radiochromic film method for measuring bow tie profiles is an inexpensive (∼$100 USD + film costs), noninvasive method to measure the fan beam intensity profile in CT scanners.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2013

Design and construction of the 1{sup st} proton CT scanner

This paper discusses the design and operation of the 1{sup st} proton CT scanner for 3D imaging. Reduction of proton range uncertainties and improved dose accuracy in the patient for treatment planning are central goals. A central CT slice acquired by reconstruction of 134 million proton tracks through a 14 cm spherical polystyrene phantom with high and low density inserts is presented.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

TH-CD-207B-12: Quantification of Clinical Feedback On Image Quality Differences Between Two CT Scanner Models

Purpose: This work sought to quantify a radiology team’s assessment of image quality differences between two CT scanner models currently in clinical use, with emphasis on noise and low-contrast detectability (LCD). Methods: A water phantom and a Kagaku anthropomorphic body phantom were scanned on GE Discovery CT750 HD and LightSpeed VCT scanners (4 each) with identical scan parameters and reconstructed to 2.5mm/5.0mm thicknesses. Images of water phantom were analyzed at the scanner console with a built-in LCD tool that uses statistical methods to compute requisite CT-number contrast for 95% confidence in detection of a user-defined object size. LCD value was computed for 5mm, 3mm, and 1mm objects. Analysis of standard deviation and LCD values were performed on Kagaku phantom images within liver, stomach, and spleen. LCD value was computed for 4mm, 3mm, and 1mm objects using a benchmarked MATLAB implementation of the GE scanner-console tool. Results: Water LCD values were larger (poorer performance) for all HD scanners compared to VCT scanners. Mean scanner model difference in requisite CT-number contrast for 5mm, 3mm, and 1mm objects for 5.0mm/2.5mm images was 3.0%/3.4% (p=0.02/p=0.10), 5.3%/5.7% (0.00002/0.02), and 8.5%/8.2% (0.0004/0.002), respectively. Mean standard deviations within Kagaku phantom ROIs were greater in HD compared to VCT images, with mean differences for the liver, stomach, and spleen for 5.0mm/2.5mm of 16%/12% (p=0.04/0.10), 8%/12% (0.15/0.11), and 16%/15% (0.05/0.11), respectively. Mean LCD value difference between HD and VCT scanners over all ROIs for 4mm, 3m, and 1mm objects and 5.0mm/2.5mm was 34%/9%, 16%/8%, and 18%/10%, respectively. HD scanners outperformed VCT scanners only for the 4mm stomach object. Conclusion: Using both water and anthropomorphic phantoms, it was shown that HD scanners are outperformed by VCT scanners with respect to noise and LCD in a consistent and in most cases statistically significant manner. The relationship between statistical and clinical significance demands further work.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2016

WE-AB-BRA-11: Improved Imaging of Permanent Prostate Brachytherapy Seed Implants by Combining an Endorectal X-Ray Sensor with a CT Scanner

Purpose: To test feasibility of the use of a digital endorectal x-ray sensor for improved image resolution of permanent brachytherapy seed implants compared to conventional CT. Methods: Two phantoms simulating the male pelvic region were used to test the capabilities of a digital endorectal x-ray sensor for imaging permanent brachytherapy seed implants. Phantom 1 was constructed from acrylic plastic with cavities milled in the locations of the prostate and the rectum. The prostate cavity was filled a Styrofoam plug implanted with 10 training seeds. Phantom 2 was constructed from tissue-equivalent gelatins and contained a prostate phantom implanted with 18 strands of training seeds. For both phantoms, an intraoral digital dental x-ray sensor was placed in the rectum within 2 cm of the seed implants. Scout scans were taken of the phantoms over a limited arc angle using a CT scanner (80 kV, 120–200 mA). The dental sensor was removed from the phantoms and normal helical CT and scout (0 degree) scans using typical parameters for pelvic CT (120 kV, auto-mA) were collected. A shift-and add tomosynthesis algorithm was developed to localize seed plane location normal to detector face. Results: The endorectal sensor produced images with improved resolution compared to CT scans. Seed clusters and individual seed geometry were more discernable using the endorectal sensor. Seed 3D locations, including seeds that were not located in every projection image, were discernable using the shift and add algorithm. Conclusion: This work shows that digital endorectal x-ray sensors are a feasible method for improving imaging of permanent brachytherapy seed implants. Future work will consist of optimizing the tomosynthesis technique to produce higher resolution, lower dose images of 1) permanent brachytherapy seed implants for post-implant dosimetry and 2) fine anatomic details for imaging and managing prostatic disease compared to CT images. Funding: LSU Faculty Start-up Funding. Disclosure: XDR Radiography has loaned our research group the digital x-ray detector used in this work. CoI: None.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2014

SU-E-I-18: CT Scanner QA Using Normalized CTDI Ratio

Purpose: To create a ratio of weighted computed tomography dose index (CTDIw) data normalized to in-air measurements (CTDIair) as a function of beam quality to create a look-up table for frequent, rapid quality assurance (QA) checks of CTDI. Methods: The CTDIw values were measured according to TG-63 protocol using a pencil ionization chamber (Unfors Xi CT detector) and head and body Polymethyl methacrylate (PMMA) phantoms (16 and 32 cm diameter, respectively). Single scan dose profiles were measured at each clinically available energy (80,100,120,140 kVp) on three different CT scanners (two Siemens SOMATOM Definition Flash and one GE Optima), using a tube current of 400 mA, a one second rotation time, and the widest available beam width (32 × 0.6 mm and 16 × 1.25 mm, respectively). These values were normalized to CTDIair measurements using the same conditions as CTDIw. The ratios (expressed in cGy/R) were assessed for each scanner as a function of each energy's half value layer (HVL) paired with the phantom's appropriate bow tie filter measured in mmAl. Results: Normalized CTDI values vary linearly with HVL for both the head and body phantoms. The ratios for the two Siemens machines are very similar at each energy. Compared to the GE scanner, these values vary between 10–20% for each kVp setting. Differences in CTDIair contribute most to the deviation of the ratios across machines. Ratios are independent of both mAs and collimation. Conclusion: Look-up tables constructed of normalized CTDI values as a function of HVL can be used to derive CTDIw data from only three in-air measurements (one for CTDIair and two with added filtration for HVL) to allow for simple, frequent QA checks without CT phantom setup. Future investigations will involve comparing results with Monte Carlo simulations for validation.

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2014

Pilot study for compact microbeam radiation therapy using a carbon nanotube field emission micro-CT scanner

Purpose: Microbeam radiation therapy (MRT) is defined as the use of parallel, microplanar x-ray beams with an energy spectrum between 50 and 300 keV for cancer treatment and brain radiosurgery. Up until now, the possibilities of MRT have mainly been studied using synchrotron sources due to their high flux (100s Gy/s) and approximately parallel x-ray paths. The authors have proposed a compact x-ray based MRT system capable of delivering MRT dose distributions at a high dose rate. This system would employ carbon nanotube (CNT) field emission technology to create an x-ray source array that surrounds the target of irradiation. Using such a geometry, multiple collimators would shape the irradiation from this array into multiple microbeams that would then overlap or interlace in the target region. This pilot study demonstrates the feasibility of attaining a high dose rate and parallel microbeam beams using such a system. Methods: The microbeam dose distribution was generated by our CNT micro-CT scanner (100μm focal spot) and a custom-made microbeam collimator. An alignment assembly was fabricated and attached to the scanner in order to collimate and superimpose beams coming from different gantry positions. The MRT dose distribution was measured using two orthogonal radiochromic films embedded inside a cylindrical phantom. This target was irradiated with microbeams incident from 44 different gantry angles to simulate an array of x-ray sources as in the proposed compact CNT-based MRT system. Finally, phantom translation in a direction perpendicular to the microplanar beams was used to simulate the use of multiple parallel microbeams. Results: Microbeams delivered from 44 gantry angles were superimposed to form a single microbeam dose distribution in the phantom with a FWHM of 300μm (calculated value was 290 μm). Also, during the multiple beam simulation, a peak to valley dose ratio of ∼10 was found when the phantom translation distance was roughly 4x the beam width. The first prototype CNT-based x-ray tube dedicated to the development of compact MRT technology development was proposed and planned based on the preliminary experimental results presented here and the previous corresponding Monte Carlo simulations. Conclusions: The authors have demonstrated the feasibility of creating microbeam dose distributions at a high dose rate using a proposed compact MRT system. The flexibility of CNT field emission x-ray sources could possibly bring compact and low cost MRT devices to the larger research community and assist in the translational research of this promising new approach to radiation therapy.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
DOE OSTI2013

A prototype fan-beam optical CT scanner for 3D dosimetry

Purpose: The objective of this work is to introduce a prototype fan-beam optical computed tomography scanner for three-dimensional (3D) radiation dosimetry. Methods: Two techniques of fan-beam creation were evaluated: a helium-neon laser (HeNe, {lambda} = 543 nm) with line-generating lens, and a laser diode module (LDM, {lambda} = 635 nm) with line-creating head module. Two physical collimator designs were assessed: a single-slot collimator and a multihole collimator. Optimal collimator depth was determined by observing the signal of a single photodiode with varying collimator depths. A method of extending the dynamic range of the system is presented. Two sample types were used for evaluations: nondosimetric absorbent solutions and irradiated polymer gel dosimeters, each housed in 1 liter cylindrical plastic flasks. Imaging protocol investigations were performed to address ring artefacts and image noise. Two image artefact removal techniques were performed in sinogram space. Collimator efficacy was evaluated by imaging highly opaque samples of scatter-based and absorption-based solutions. A noise-based flask registration technique was developed. Two protocols for gel manufacture were examined. Results: The LDM proved advantageous over the HeNe laser due to its reduced noise. Also, the LDM uses a wavelength more suitable for the PRESAGE{sup TM} dosimeter. Collimator depth of 1.5 cm was found to be an optimal balance between scatter rejection, signal strength, and manufacture ease. The multihole collimator is capable of maintaining accurate scatter-rejection to high levels of opacity with scatter-based solutions (T < 0.015%). Imaging protocol investigations support the need for preirradiation and postirradiation scanning to reduce reflection-based ring artefacts and to accommodate flask imperfections and gel inhomogeneities. Artefact removal techniques in sinogram space eliminate streaking artefacts and reduce ring artefacts of up to {approx}40% in magnitude. The flask registration technique was shown to achieve submillimetre and subdegree placement accuracy. Dosimetry protocol investigations emphasize the need to allow gel dosimeters to cool gradually and to be scanned while at room temperature. Preliminary tests show that considerable noise reduction can be achieved with sinogram filtering and by binning image pixels into more clinically relevant grid sizes. Conclusions: This paper describes a new optical CT scanner for 3D radiation dosimetry. Tests demonstrate that it is capable of imaging both absorption-based and scatter-based samples of high opacities. Imaging protocol and gel dosimeter manufacture techniques have been adapted to produce optimal reconstruction results. These optimal results will require suitable filtering and binning techniques for noise reduction purposes.

62 RADIOLOGY AND NUCLEAR MEDICINE↗