bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐U‐04: Evaluation of Normal Tissue Toxicity of Drug‐Loaded Nanodroplets Used for Treating Prostate Cancer with MR‐Guided Focused‐Ultrasound
Authors: Gupta R , Cvetkovic D , Wang B , Ma C , Chen L
Published: June 2015

Purpose:

Our prior studies have showed significant prostate tumor growth‐delay when pulsed focused ultrasound (pFUS) is applied under MR‐guidance in combination with docetaxel‐encapsulated nanodroplets (DTX‐ND). The purpose of the present work was to investigate normal tissue toxicity of DTX‐ND in order to study true efficacy of a novel prostate cancer treatment approach combining DTX‐ND injections and pFUS exposures under MR guidance.

Methods:

Poly {ethylene oxide}‐co‐poly {D, L‐lactide} (PDLA) nanodroplets loaded with docetaxel were synthesized in our lab using solid dispersion technique with 0.5% docetaxel, 2% perfluorocarbon and 2% PDLA. The mean diameter of the nanodroplets was 220 ± 30nm. Human prostate cancer, LNCaP cells were implanted orthotopically in prostates of male nude mice. Tumor growth was monitored using MRI. Tumor–bearing mice were randomly divided into 5 groups. Group 1 animals were treated with DTX‐ND and pFUS. Ultrasound treatment parameters were 1MHz, 25W acoustic power, 10% duty cycle and 60 seconds for each sonication. Group 2 mice were treated with pFUS. Group 3 mice were injected with DTX‐ND. Group 4 received free docetaxel and Group 5 mice were used as control (no treatment). Mice weights were monitored for toxicity.

Results:

Docetaxel‐loaded nanodroplets showed no normal tissue toxicity as average mice weights (27.12 ±0.75 g) from group 1 were statistically, no different when compared with average mice weights (24.39 ±0.62 g) from control group (p >0.05). Also, average mice weights from group2 (24.95 ±1.2 g), group3 (26.16 ± 0.66 g) and group4 (27.10 ±0.65 g) showed no significant difference in weights when compared to control group (p >0.05).

Conclusion:

This study demonstrates that our formulation of DTX‐ND shows no normal tissue toxicity in mice. These findings help us in evaluating the true efficacy of our hypothesized prostate cancer treatment strategy using focused‐ultrasound activated drug‐delivery under MR guidance without incurring additional toxicity.
SU‐E‐I‐09: The Impact of X‐Ray Scattering On Image Noise for Dedicated Breast CT
Authors: Yang K , Gazi P , Boone J
Published: June 2015

Purpose:

To quantify the impact of detected x‐ray scatter on image noise in flat panel based dedicated breast CT systems and to determine the optimal scanning geometry given practical trade‐offs between radiation dose and scatter reduction.

Methods:

Four different uniform polyethylene cylinders (104, 131, 156, and 184 mm in diameter) were scanned as the phantoms on a dedicated breast CT scanner developed in our laboratory. Both stationary projection imaging and rotational cone‐beam CT imaging was performed. For each acquisition type, three different x‐ray beam collimations were used (12, 24, and 109 mm measured at isocenter). The aim was to quantify image noise properties (pixel variance, SNR, and image NPS) under different levels of x‐ray scatter, in order to optimize the scanning geometry. For both projection images and reconstructed CT images, individual pixel variance and NPS were determined and compared. Noise measurement from the CT images were also performed with different detector binning modes and reconstruction matrix sizes. Noise propagation was also tracked throughout the intermediate steps of cone‐beam CT reconstruction, including the inverse‐logarithmic process, Fourier‐filtering before backprojection.

Results:

Image noise was lower in the presence of higher scatter levels. For the 184 mm polyethylene phantom, the image noise (measured in pixel variance) was ∼30% lower with full cone‐beam acquisition compared to a narrow (12 mm) fan‐beam acquisition. This trend is consistent across all phantom sizes and throughout all steps of CT image reconstruction.

Conclusion:

From purely a noise perspective, the cone‐beam geometry (i.e. the full cone‐angle acquisition) produces lower image noise compared to the lower‐scatter fan‐beam acquisition for breast CT. While these results are relevant in homogeneous phantoms, the full impact of scatter on noise in bCT should involve contrast‐to‐noise‐ratio measurements in heterogeneous phantoms if the goal is to optimize the scanning geometry for dedicated breast CT.

This work was supported by a grant from the National Institute for Biomedical Imaging and Bioengineering (R01 EB002138).
SU‐E‐I‐12: Flexible Geometry Computed Tomography
Authors: Shaw R
Published: June 2015

Purpose:

The concept separates the mechanical connection between the radiation source and detector. This design allows the trajectory and orientation of the radiation source/detector to be customized to the object that is being imaged. This is in contrast to the formulaic rotation‐translation image acquisition of conventional computed tomography(CT).Background/significance:CT devices that image a full range of: anatomy, patient populations, and imaging procedures are large. The root cause of the expanding size of comprehensive CT is due to the commitment to helical geometry that is hardwired into the image reconstruction. FGCT extends the application of alternative reconstruction techniques, i.e. tomosynthesis, by separating the two main components— radiation source and detector— and allow for 6 degrees of freedom motion for radiation source, detector, or both. The image acquisition geometry is then tailored to how the patient/object is positioned. This provides greater flexibility on the position and location that the patient/object is being imaged. Additionally, removing the need of a rotating gantry reduces the footprint so that CT is more mobile and more available to move to where the patient/object is at, instead of the other way around.

Methods:

As proof‐of‐principle, a reconstruction algorithm is designed to produce FGCT images. Using simulated detector data, voxels intersecting a line drawn between the radiation source and an individual detector are traced and modified using the detector signal. The detector signal is modified to compensate for changes in the source to detector distance. Adjacent voxels are modified in proportion to the detector signal, providing a simple image filter.

Results:

Image‐quality from the proposed FGCT reconstruction technique is proving to be a challenge, producing hardily recognizable images from limited projections angles.

Conclusion:

Preliminary assessment of the reconstruction technique demonstrates the inevitable tradeoff of producing meaningful image‐quality verses the practicality of how to obtain sufficient image data.
SU‐E‐I‐13: Evaluation of Metal Artifact Reduction (MAR) Software On Computed Tomography (CT) Images
Authors: Huang V , Kohli K
Published: June 2015

Purpose:

A new commercially available metal artifact reduction (MAR) software in computed tomography (CT) imaging was evaluated with phantoms in the presence of metals. The goal was to assess the ability of the software to restore the CT number in the vicinity of the metals without impacting the image quality.

Methods:

A Catphan 504 was scanned with a GE Optima RT 580 CT scanner (GE Healthcare, Milwaukee, WI) and the images were reconstructed with and without the MAR software. Both datasets were analyzed with Image Owl QA software (Image Owl Inc, Greenwich, NY). CT number sensitometry, MTF, low contrast, uniformity, noise and spatial accuracy were compared for scans with and without MAR software. In addition, an in‐house made phantom was scanned with and without a stainless steel insert at three different locations. The accuracy of the CT number and metal insert dimension were investigated as well.

Results:

Comparisons between scans with and without MAR algorithm on the Catphan phantom demonstrate similar results for image quality. However, noise was slightly higher for the MAR algorithm. Evaluation of the CT number at various locations of the in‐house made phantom was also performed. The baseline HU, obtained from the scan without metal insert, was compared to scans with the stainless steel insert at 3 different locations. The HU difference between the baseline scan versus metal scan was improved when the MAR algorithm was applied. In addition, the physical diameter of the stainless steel rod was over‐estimated by the MAR algorithm by 0.9 mm.

Conclusion:

This work indicates with the presence of metal in CT scans, the MAR algorithm is capable of providing a more accurate CT number without compromising the overall image quality. Future work will include the dosimetric impact on the MAR algorithm.
SU‐E‐I‐19: Optimization of Low Contrast Detectability Across Two CT Manufacturers
Authors: Mahmood U , Dauer L , Erdi Y
Published: June 2015

Purpose:

Our goal was to evaluate low contrast detectability (LCD) for abdominal CT protocols across two CT scanner manufacturers, while producing a similar noise texture and CTDIvol for acquired images.

Methods:

A CIRS tissue equivalent LCD phantom containing three columns of 7 spherical targets, ranging from 10 mm to 2.4 mm, that are 5, 10, and 20 HU below the background matrix (HUBB) was scanned using two a GE HD750 64 slice scanner and a Siemens Somatom Definition AS 64 slice scanner. Protocols were designed to deliver a CTDIvol of 12.26 mGy and images were reconstructed with FBP, ASIR and Sapphire. Comparisons were made with those algorithms that had matching noise power spectrum peaks (NPS). NPS information was extracted from a previously published article that matched NPS peak frequencies across manufacturers by calculating the NPS from uniform phantom images reconstructed with several IR algorithms.

Results:

The minimum detectable lesion size in the 20 HUBB and 10 HUBB column was 6.3 mm, and 10 mm in the 5 HUBB column for the GE HD 750 scanner. The minimum detectable lesion size in the 20 HUBB column was 4.8 mm, in the 10 HUBB column, 9.5 mm, and the 5 HUBB column, 10 mm for the Siemens Somatom Definition AS.

Conclusion:

Reducing radiation dose while improving or maintaining LCD is possible with application of IR. However, there are several different IR algorithms, with each generating a different resolution and noise texture. In multi‐manufacturer settings, matching only the CTDIvol between manufacturers may Result in a loss of clinically relevant information.
SU‐E‐I‐21: Dosimetric Characterization and Image Quality Evaluation of the AIRO Mobile CT Scanner
Authors: Weir V , Zhang J , Bruner A
Published: June 2015

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.
SU‐E‐I‐22: A Comprehensive Investigation of Noise Variations Between the GE Discovery CT750 HD and GE LightSpeed VCT
Authors: Bache S , Loyer E , Stauduhar P , Liu X , Rong J
Published: June 2015

Purpose:

To quantify and compare the noise properties between two GE CT models‐the Discovery CT750 HD (aka HD750) and LightSpeed VCT, with the overall goal of assessing the impact in clinical diagnostic practice.

Methods:

Daily QC data from a fleet of 9 CT scanners currently in clinical use were investigated – 5 HD750 and 4 VCT (over 600 total acquisitions for each scanner). A standard GE QC phantom was scanned daily using two sets of scan parameters with each scanner over 1 year. Water CT number and standard deviation were recorded from the image of water section of the QC phantom. The standard GE QC scan parameters (Pitch = 0.516, 120kVp, 0.4s, 335mA, Small Body SFOV, 5mm thickness) and an in‐house developed protocol (Axial, 120kVp, 1.0s, 240mA, Head SFOV, 5mm thickness) were used, with Standard reconstruction algorithm. Noise was measured as the standard deviation in the center of the water phantom image. Inter‐model noise distributions and tube output in mR/mAs were compared to assess any relative differences in noise properties.

Results:

With the in‐house protocols, average noise for the five HD750 scanners was ∼9% higher than the VCT scanners (5.8 vs 5.3). For the GE QC protocol, average noise with the HD750 scanners was ∼11% higher than with the VCT scanners (4.8 vs 4.3). This discrepancy in noise between the two models was found despite the tube output in mR/mAs being comparable with the HD750 scanners only having ∼4% lower output (8.0 vs 8.3 mR/mAs).

Conclusion:

Using identical scan protocols, average noise in images from the HD750 group was higher than that from the VCT group. This confirms feedback from an institutional radiologist's feedback regarding grainier patient images from HD750 scanners. Further investigation is warranted to assess the noise texture and distribution, as well as clinical impact.
SU‐E‐I‐85: Absorbed Dose Estimation for a Commercially Available MicroCT Scanner
Authors: Lau A , Ren L , Liu H , Yang K , Ahmad S , Chen Y
Published: June 2015

Purpose:

To quantify the simulated absorbed dose delivered for a typical scan from a commercially available microCT scanner in order to aid in the dose estimation.

Methods:

The simulations were conducted using the Geant4 Monte Carlo Toolkit (version 10) with the standard electromagnetic classes. The Quantum FX microCT scanner (PerkinElmer, Waltham, MA) was modeled incorporating the energy fluence and angular distributions of generated photons, spatial dimensions of nominal source‐to‐object and source‐to‐detector distances. The energy distribution was measured using a spectrometer (X‐123CdTe, Amptek Inc., Bedford, USA) with a 300 angular spread from the source for the 90 kVp X‐ray beams with no additional filtration. The nominal distances from the source to object consisted of three setups: 154.0 mm, 104.0 mm, and 51.96 mm. Our simulations recorded the dose absorbed in a cylindrical phantom of PMMA with a fixed length of 2 cm and varying radii (10, 20, 30 and 40 mm) using 100 million incident photons. The averaged absorbed dose in the object was then quantified for all setups. An exposure measurement of 417 mR was taken using a Radcal 9095 system utilizing 10×9–180 ion chamber with the given technique of 90 kVp, 63 μA, and 12 s. The exposure rate was also simulated with same setup to calculate the conversion factor of the beam current and the number of incident photons.

Results:

For a typical cone‐beam scan with non‐filtered 90kVp, the dose coefficients (the absorbed dose per mAs) were 2.614, 2.549 and 2.467 μGy/mAs under source to object distance of 104 mm for the object diameters of 10 mm, 20 mm and 30 mm, respectively.

Conclusion:

A look‐up table was developed where an investigator can estimate the delivered dose using this particular microCT given the scanning protocol (kVp and mAs) as well as the size of the scanned object.
SU‐E‐J‐04: Integration of Interstitial High Intensity Therapeutic Ultrasound Applicators On a Clinical MRI‐Guided High Intensity Focused Ultrasound Treatment Planning Software Platform
Authors: Ellens N , Partanen A , Ghoshal G , Burdette E , Farahani K
Published: June 2015

Purpose:

Interstitial high intensity therapeutic ultrasound (HITU) applicators can be used to ablate tissue percutaneously, allowing for minimally‐invasive treatment without ionizing radiation [1,2]. The purpose of this study was to evaluate the feasibility and usability of combining multielement interstitial HITU applicators with a clinical magnetic resonance imaging (MRI)‐guided focused ultrasound software platform.

Methods:

The Sonalleve software platform (Philips Healthcare, Vantaa, Finland) combines anatomical MRI for target selection and multi‐planar MRI thermometry to provide real‐time temperature information. The MRI‐compatible interstitial US applicators (Acoustic MedSystems, Savoy, IL, USA) had 1–4 cylindrical US elements, each 1 cm long with either 180° or 360° of active surface. Each applicator (4 Fr diameter, enclosed within a 13 Fr flexible catheter) was inserted into a tissue‐mimicking agar‐silica phantom. Degassed water was circulated around the transducers for cooling and coupling. Based on the location of the applicator, a virtual transducer overlay was added to the software to assist targeting and to allow automatic thermometry slice placement. The phantom was sonicated at 7 MHz for 5 minutes with 6–8 W of acoustic power for each element. MR thermometry data were collected during and after sonication.

Results:

Preliminary testing indicated that the applicator location could be identified in the planning images and the transducer locations predicted within 1 mm accuracy using the overlay. Ablation zones (thermal dose ≥ 240 CEM43) for 2 active, adjacent US elements ranged from 18 mm × 24 mm (width × length) to 25 mm × 25 mm for the 6 W and 8 W sonications, respectively.

Conclusion:

The combination of interstitial HITU applicators and this software platform holds promise for novel approaches in minimally‐invasive MRI‐guided therapy, especially when bony structures or air‐filled cavities may preclude extracorporeal HIFU.[1] Diederich et al. IEEE UFFFC 46.5 (1999): 1218.[2] Chopra et al. PMB 50.21 (2005): 4957.

Funding support was provided by Philips Healthcare and in‐kind support from Acoustic MedSystems Inc. Ari Partanen is a paid employee of Philips Healthcare. Goutam Ghoshal and Everette Clif Burdette are paid employees of Acoustic MedSystems Inc.
SU‐E‐J‐10: Imaging Dose and Cancer Risk in Image‐Guided Radiotherapy of Cancers
Authors: Zhou L , Bai S , Zhang Y , Deng J
Published: June 2015

Purpose:

To systematically evaluate imaging doses and cancer risks to organs‐at‐risk as a Result of cumulative doses from various radiological imaging procedures in image‐guided radiotherapy (IGRT) in a large cohort of cancer patients.

Methods:

With IRB approval, imaging procedures (computed tomography, kilo‐voltage portal imaging, megavoltage portal imaging and kilo‐voltage cone‐beam computed tomography) of 4832 cancer patients treated during 4.5 years were collected with their gender, age and circumference. Correlations between patient's circumference and Monte Carlo simulated‐organ dose were applied to estimate organ doses while the cancer risks were reported as 1+ERR using BEIR VII models.

Results:

80 cGy or more doses were deposited to brain, lungs and RBM in 273 patients (maximum 136, 278 and 267 cGy, respectively), due largely to repetitive imaging procedures and non‐personalized imaging settings. Regardless of gender, relative cancer risk estimates for brain, lungs, and RBM were 3.4 (n = 55), 2.6 (n = 49), 1.8 (n = 25) for age group of 0–19; 1.2 (n = 87), 1.4 (n = 98), 1.3 (n = 51) for age group of 20–39; 1.0 (n = 457), 1.1 (n = 880), 1.8 (n=360) for age group of 40–59; 1.0 (n = 646), 1.1 (n = 1400), 2.3 (n = 716) for age group of 60–79 and 1.0 (n = 108),1.1 (n = 305),1.6 (n = 147) for age group of 80–99.

Conclusion:

The cumulative imaging doses and associated cancer risks from multi‐imaging procedures were patient‐specific and site‐dependent, with up to 2.7 Gy imaging dose deposited to critical structures in some pediatric patients. The associated cancer risks in brain and lungs for children of age 0 to 19 were 2–3 times larger than those for adults. This study indicated a pressing need for personalized imaging protocol to maximize its clinical benefits while reducing associated cancer risks.

Sichuan University Scholarship
SU‐E‐J‐12: An Image‐Guided Soft Robotic Patient Positioning System for Maskless Head‐And‐Neck Cancer Radiotherapy: A Proof‐Of‐Concept Study
Authors: Ogunmolu O , Gans N , Jiang S , Gu X
Published: June 2015

Purpose:

We propose a surface‐image‐guided soft robotic patient positioning system for maskless head‐and‐neck radiotherapy. The ultimate goal of this project is to utilize a soft robot to realize non‐rigid patient positioning and real‐time motion compensation. In this proof‐of‐concept study, we design a position‐based visual servoing control system for an air‐bladder‐based soft robot and investigate its performance in controlling the flexion/extension cranial motion on a mannequin head phantom.

Methods:

The current system consists of Microsoft Kinect depth camera, an inflatable air bladder (IAB), pressured air source, pneumatic valve actuators, custom‐built current regulators, and a National Instruments myRIO microcontroller. The performance of the designed system was evaluated on a mannequin head, with a ball joint fixed below its neck to simulate torso‐induced head motion along flexion/extension direction. The IAB is placed beneath the mannequin head. The Kinect camera captures images of the mannequin head, extracts the face, and measures the position of the head relative to the camera. This distance is sent to the myRIO, which runs control algorithms and sends actuation commands to the valves, inflating and deflating the IAB to induce head motion.

Results:

For a step input, i.e. regulation of the head to a constant displacement, the maximum error was a 6% overshoot, which the system then reduces to 0% steady‐state error. In this initial investigation, the settling time to reach the regulated position was approximately 8 seconds, with 2 seconds of delay between the command start of motion due to capacitance of the pneumatics, for a total of 10 seconds to regulate the error.

Conclusion:

The surface image‐guided soft robotic patient positioning system can achieve accurate mannequin head flexion/extension motion. Given this promising initial Result, the extension of the current one‐dimensional soft robot control to multiple IABs for non‐rigid positioning control will be pursued.
SU‐E‐J‐13: Six Degree of Freedom Image Fusion Accuracy for Cranial Target Localization On the Varian Edge Stereotactic Radiosurgery System: Comparison Between 2D/3D and KV CBCT Image Registration
Authors: Xu H , Song K , Chetty I , Wen N , Kim J
Published: June 2015

Purpose:

To determine the 6 degree of freedom systematic deviations between 2D/3D and CBCT image registration with various imaging setups and fusion algorithms on the Varian Edge Linac.

Methods:

An anthropomorphic head phantom with radio opaque targets embedded was scanned with CT slice thicknesses of 0.8, 1, 2, and 3mm. The 6 DOF systematic errors were assessed by comparing 2D/3D (kV/MV with CT) with 3D/3D (CBCT with CT) image registrations with different offset positions, similarity measures, image filters, and CBCT slice thicknesses (1 and 2 mm). The 2D/3D registration accuracy of 51 fractions for 26 cranial SRS patients was also evaluated by analyzing 2D/3D pre‐treatment verification taken after 3D/3D image registrations.

Results:

The systematic deviations of 2D/3D image registration using kV‐ kV, MV‐kV and MV‐MV image pairs were within ±0.3mm and ±0.3° for translations and rotations with 95% confidence interval (CI) for a reference CT with 0.8 mm slice thickness. No significant difference (P>0.05) on target localization was observed between 0.8mm, 1mm, and 2mm CT slice thicknesses with CBCT slice thicknesses of 1mm and 2mm. With 3mm CT slice thickness, both 2D/3D and 3D/3D registrations performed less accurately in longitudinal direction than thinner CT slice thickness (0.60±0.12mm and 0.63±0.07mm off, respectively). Using content filter and using similarity measure of pattern intensity instead of mutual information, improved the 2D/3D registration accuracy significantly (P=0.02 and P=0.01, respectively). For the patient study, means and standard deviations of residual errors were 0.09±0.32mm, −0.22±0.51mm and −0.07±0.32mm in VRT, LNG and LAT directions, respectively, and 0.12°±0.46°, −0.12°±0.39° and 0.06°±0.28° in RTN, PITCH, and ROLL directions, respectively. 95% CI of translational and rotational deviations were comparable to those in phantom study.

Conclusion:

2D/3D image registration provided on the Varian Edge radiosurgery, 6 DOF‐based system provides accurate target positioning for frameless image‐guided cranial stereotactic radiosurgery.
SU‐E‐J‐14: A Comparison of a 2.5MV Imaging Beam to KV and 6MV Imaging Beams
Authors: Nitsch P , Robertson D , Balter P
Published: June 2015

Purpose:

To compare image quality metrics and dose of TrueBeam V2.0's 2.5MV imaging beam and kV and 6MV images.

Methods:

To evaluate the MV image quality, the Standard Imaging QC‐3 and Varian Las Vegas (LV) phantoms were imaged using the ‘quality’ and ‘low dose’ modes and then processed using RIT113 V6.3. The LEEDS phantom was used to evaluate the kV image quality. The signal to noise ratio (SNR) was also evaluated in patient images using Matlab. In addition, dose per image was evaluated at a depth of 5cm using solid water for a 28.6 cm × 28.6 cm field size, which is representative of the largest jaw settings at an SID of 150cm.

Results:

The 2.5MV images had lower dose than the 6 MV images and a contrast to noise ratio (CNR) about 1.4 times higher, when evaluated using the QC‐3. When energy was held constant but dose varied, the different modes, ‘low dose’ and ‘quality’, showed less than an 8% difference in CNR. The ‘quality’ modes demonstrated better spatial resolution than the ‘low dose’; however, even with the ‘low dose’ all line pairs were distinct except for the 0.75lp/mm on the 2.5MV. The LV phantom was used to measure low contrast detectability and showed similar results to the QC‐3. Several patient images all confirmed that SNR were highest in kV images followed by 2.5MV and then 6MV. Qualitatively, for anatomical areas with large variability in thickness, like lateral head and necks, 2.5MV images show more anatomy, such as shoulder position, than kV images.

Conclusions:

The kV images clearly provide the best image metrics per unit dose. The 2.5MV beam showed excellent contrast at a lower dose than 6MV and may be superior to kV for difficult to image areas that include large changes in anatomical thickness.

P Balter: Varian, Sun Nuclear, Philips, CPRIT
SU‐E‐J‐19: An Intra‐Institutional Study of Cone‐Beam CT Dose for Image‐Guided Radiation Therapy
Authors: Knutson N , Rankine L , Reilly M , Li H
Published: June 2015

Purpose:

To determine the variability of Cone‐Beam CT Dose Index (CB‐CTDI) across multiple on‐board imaging (OBI) systems within a single institution, and compare this to manufacturer provided data.

Methods:

The CB‐CTDI was measured on three Trilogy and three TrueBeam Varian OBI systems, for six different clinically used scan protocols. Measurements were taken using a 10 cm long CT ionization chamber in either a 16 cm (head‐simulating) or 32 cm (body‐simulating) diameter, acrylic, cylindrical, 15 cm long CTDI phantom. We assessed the variation in CB‐CTDI between the OBI systems and compared our measured values to the data provided by the manufacturer.

Results:

The standard error in the CB‐CTDI measured for all protocols was found to be within ±2% and ±5% of the mean for TrueBeam and Trilogy, respectively. For all head scan protocols, the measured TrueBeam values were lower than the manufacturer's reported values, with a maximum difference of 13.9% and an average difference of 11%. For the body scan protocols, the TrueBeam measured values were 3% and 13% greater than the manufacturer's reported values for two out of three protocols, and 38% lower than reported for the third protocol. In total, 7/18 CB‐CTDI measurements fell within the manufacturers specified range (±10%). Across all scans the Truebeam machines were found to have a lower CB‐CTDI than Trilogy, particularly the head scan protocols, which show decreases of up to 30% .

Conclusion:

The intra‐institutional variation of CB‐CTDI was found to be clinically acceptable at less than 5%. For the TrueBeam OBI system, over half of the measured scans failed to fall with in the manufactured quoted range of 10%, however, all measured values were within 15% of the manufacturer's reported values. For accurate assessment and reporting of imaging dose to radiotherapy patients, our results indicate a need for standardization in CB‐CTDI measurement technique.
SU‐E‐J‐20: Identifying Predictors for Translational and Rotational Shifts of Liver SBRT Patients
Authors: Powers A , Sheu R , Blacksburg S
Published: June 2015

Purpose:

Identifying predictors of translational and rotational offsets for liver SBRT treatment may be of assistance in determining if the use of a 6D couch is more advantageous for particular patients.

Methods:

From February 2013 to February 2015, 85 patients received liver SBRT for HCC or metastases. CBCT imaging was used for each patient and offsets recorded. There were 399 initial CBCT registrations performed. 184 registrations contained angular offsets. The mean offsets for patients in the superior/inferior, anterior/posterior, and lateral dimension were 4mm, 4mm, and 3mm, respectively. The mean absolute angular yaw, pitch, and roll were 0.2°, 0.3°, and 0.3°, respectively. Mean GTV, PTV, and Liver volume was 46.6, 153.3, and 1435.2cc's. 59 patients were male and the mean body mass index (BMI) was 27.2kg/m2. Hepatic segments were characterized as anterior/posterior left/right, superior/inferior, or lateral/medial by established anatomic classification. Chi‐squared test and Multinomial Logistic Regression were used for univariate (UVA) and multivariate (MVA) analyses.

Results:

Offsets ≥ 2mm, 5mm, and 10mm occurred 82.5%, 49.4%, and 9.5% of the time, respectively. While kV imaging prior to CBCT decreased the frequency of 2 and 5mm offsets on UVA, on MVA BMI's >20 predicted for offsets. On UVA and MVA, lateral lesions were more likely to have ≥ 10mm shift. Offsets ≥ 0.2°, 0.5°, and 1° occurred 76.1%, 68.5%, and 42.9% of the time, respectively. Lateral lesions were more likely on MVA to experience ≥ 0.2° and 0.5° shifts, while previous kV images were the only variable that predicted for shift < 1°. No dosimetric parameter predicted for translation or rotation offsets on MVA.

Conclusion:

BMIs <20 predict for smaller translations during liver SBRT, while lateral lesions predict for greater translation and rotation offsets. Patients treated with lateral lesions might benefit more from the angular capability of a 6D couch.
SU‐E‐J‐25: End‐To‐End (E2E) Testing On TomoHDA System Using a Real Pig Head for Intracranial Radiosurgery
Authors: Corradini N , Leick M , Bonetti M , Negretti L
Published: June 2015

Purpose:

To determine the MVCT imaging uncertainty on the TomoHDA system for intracranial radiosurgery treatments. To determine the end‐to‐end (E2E) overall accuracy of the TomoHDA system for intracranial radiosurgery.

Methods:

A pig head was obtained from the butcher, cut coronally through the brain, and preserved in formaldehyde. The base of the head was fixed to a positioning plate allowing precise movement, i.e. translation and rotation, in all 6 axes. A repeatability test was performed on the pig head to determine uncertainty in the image bone registration algorithm. Furthermore, the test studied images with MVCT slice thicknesses of 1 and 3 mm in unison with differing scan lengths. A sensitivity test was performed to determine the registration algorithm's ability to find the absolute position of known translations/rotations of the pig head. The algorithm's ability to determine absolute position was compared against that of manual operators, i.e. a radiation therapist and radiation oncologist. Finally, E2E tests for intracranial radiosurgery were performed by measuring the delivered dose distributions within the pig head using Gafchromic films.

Results:

The repeatability test uncertainty was lowest for the MVCTs of 1‐mm slice thickness, which measured less than 0.10 mm and 0.12 deg for all axes. For the sensitivity tests, the bone registration algorithm performed better than human eyes and a maximum difference of 0.3 mm and 0.4 deg was observed for the axes. E2E test results in absolute position difference measured 0.03 ± 0.21 mm in x‐axis and 0.28 ± 0.18 mm in y‐axis. A maximum difference of 0.32 and 0.66 mm was observed in × and y, respectively. The average peak dose difference between measured and calculated dose was 2.7 cGy or 0.4%.

Conclusion:

Our tests using a pig head phantom estimate the TomoHDA system to have a submillimeter overall accuracy for intracranial radiosurgery.
SU‐E‐J‐34: Setup Accuracy in Spine SBRT Using CBCT 6D Image Guidance in Comparison with 6D ExacTrac
Authors: Han Z , Yip S , Lewis J , Mannarino E , Friesen S , Wagar M , Hacker F
Published: June 2015

Purpose

Volumetric information of the spine captured on CBCT can potentially improve the accuracy in spine SBRT setup that has been commonly performed through 2D radiographs. This work evaluates the setup accuracy in spine SBRT using 6D CBCT image guidance that recently became available on Varian systems.

Methods

ExacTrac radiographs have been commonly used for Spine SBRT setup. The setup process involves first positioning patients with lasers followed by localization imaging, registration, and repositioning. Verification images are then taken providing the residual errors (ExacTracRE) before beam on. CBCT verification is also acquired in our institute. The availability of both ExacTrac and CBCT verifications allows a comparison study. 41 verification CBCT of 16 patients were retrospectively registered with the planning CT enabling 6D corrections, giving CBCT residual errors (CBCTRE) which were compared with ExacTracRE.

Results

The RMS discrepancies between CBCTRE and ExacTracRE are 1.70mm, 1.66mm, 1.56mm in vertical, longitudinal and lateral directions and 0.27°, 0.49°, 0.35° in yaw, roll and pitch respectively. The corresponding mean discrepancies (and standard deviation) are 0.62mm (1.60mm), 0.00mm (1.68mm), −0.80mm (1.36mm) and 0.05° (0.58°), 0.11° (0.48°), −0.16° (0.32°). Of the 41 CBCT, 17 had high‐Z surgical implants. No significant difference in ExacTrac‐to‐CBCT discrepancy was observed between patients with and without the implants.

Conclusion

Multiple factors can contribute to the discrepancies between CBCT and ExacTrac: 1) the imaging iso‐centers of the two systems, while calibrated to coincide, can be different; 2) the ROI used for registration can be different especially if ribs were included in ExacTrac images; 3) small patient motion can occur between the two verification image acquisitions; 4) the algorithms can be different between CBCT (volumetric) and ExacTrac (radiographic) registrations.
SU‐E‐J‐35: Using CBCT as the Alternative Method of Assessing ITV Volume
Authors: Liao Y , Turian J , Templeton A , Redler G , Chu J
Published: June 2015

Purpose

To study the accuracy of Internal Target Volumes (ITVs) created on cone beam CT (CBCT) by comparing the visible target volume on CBCT to volumes (GTV, ITV, and PTV) outlined on free breathing (FB) CT and 4DCT.

Methods

A Quasar Cylindrical Motion Phantom with a 3cm diameter ball (14.14 cc) embedded within a cork insert was set up to simulate respiratory motion with a period of 4 seconds and amplitude of 2cm superioinferiorly and 1cm anterioposteriorly. FBCT and 4DCT images were acquired. A PTV‐4D was created on the 4DCT by applying a uniform margin of 5mm to the ITV‐CT. PTV‐FB was created by applying a margin of the motion range plus 5mm, i.e. total of 1.5cm laterally and 2.5cm superioinferiorly to the GTV outlined on the FBCT. A dynamic conformal arc was planned to treat the PTV‐FB with 1mm margin. A CBCT was acquired before the treatment, on which the target was delineated. During the treatment, the position of the target was monitored using the EPID in cine mode.

Results

ITV‐CBCT and ITV‐CT were measured to be 56.6 and 62.7cc, respectively, with a Dice Coefficient (DC) of 0.94 and disagreement in center of mass (COM) of 0.59 mm. On the other hand, GTV‐FB was 11.47cc, 19% less than the known volume of the ball. PTV‐FB and PTV‐4D were 149 and 116 cc, with a DC of 0.71. Part of the ITV‐CT was not enclosed by the PTV‐FB despite the large margin. The cine EPID images have confirmed geometrical misses of the target. Similar under‐coverage was observed in one clinical case and captured by the CBCT, where the implanted fiducials moved outside PTV‐FB.

Conclusion

ITV‐CBCT is in good agreement with ITV‐CT. When 4DCT was not available, CBCT can be an effective alternative in determining and verifying the PTV margin.
SU‐E‐J‐41: Is There An Optimal X‐Ray Technique for Prostate Treatment On CyberKnife?
Authors: Henderson E , Compuesto M , Gratton‐Liimatainen J
Published: June 2015

Purpose

To establish guidelines for setting X‐ray technique for CyberKnife (Accuray) prostate treatments to keep imaging dose as low as reasonably achievable while maintaining consistent fiducial identification.

Methods

Four gold seed fiducial markers were inserted into the prostate region of a Rando anthropomorphic phantom, following guidelines for fiducial placement provided by Accuray. A CT scan of the phantom was obtained using our standard clinical protocol and a treatment plan (Fiducial Tracking) was created. In order to simulate prostate treatment on the CyberKnife G4 (TDS v9.6), the phantom was aligned to within 0.2 degrees and 0.2mm of the planned position using X‐ray technique settings of 140kVp, 320mA and 100ms. The phantom was then shifted and rotated to 8 different positions. At each of these 8 positions, 5 orthogonal X‐ray image pairs were acquired at combinations of 3 kVp settings (110kVp, 125kVp, 140kVp), and 5 mAs settings (5mAs, 10mAs, 20mAs, 32mAs), and the frequency of the tracking software correctly identifying all four fiducials per technique setting was recorded. The experiment was repeated for three different simulated patient sizes by wrapping the phantom in layers of bolus.

Results

Regardless of phantom size, there were clear trends toward increased reliability of fiducial detection with increased X‐ray technique (both kVp and mAs), however gains achieved by increasing technique beyond 125kVp and 10mAs are modest. An increase in technique was increasingly ineffective in improving fiducial detection as the phantom was rotated away from the planned position (eg with increasing pitch). A dependence of tracking reliability on the planning DRRs was also noted.

Conclusion

This method is a useful training tool for evaluating the effect of X‐ray technique on fiducial tracking. When fiducial tracking results are not reproducible, we recommend interventions such as eliminating an unreliable fiducial from tracking or adjusting patient position before increasing X‐ray technique.
SU‐E‐J‐45: The Correlation Between CBCT Flat Panel Misalignment and 3D Image Guidance Accuracy
Authors: Kenton O , Valdes G , Brousmiche S , Wikler D , Yin L , Teo B
Published: June 2015

Purpose

To simulate the impact of CBCT flat panel misalignment on the image quality, the calculated correction vectors in 3D image guided proton therapy and to determine if these calibration errors can be caught in our QA process.

Methods

The X‐ray source and detector geometrical calibration (flexmap) file of the CBCT system in the AdaPTinsight software (IBA proton therapy) was edited to induce known changes in the rotational and translational calibrations of the imaging panel. Translations of up to ±10 mm in the x, y and z directions (see supplemental) and rotational errors of up to ±3° were induced. The calibration files were then used to reconstruct the CBCT image of a pancreatic patient and CatPhan phantom. Correction vectors were calculated for the patient using the software's auto match system and compared to baseline values. The CatPhan CBCT images were used for quantitative evaluation of image quality for each type of induced error.

Results

Translations of 1 to 3 mm in the × and y calibration resulted in corresponding correction vector errors of equal magnitude. Similar 10mm shifts were seen in the y‐direction; however, in the x‐direction, the image quality was too degraded for a match. These translational errors can be identified through differences in isocenter from orthogonal kV images taken during routine QA. Errors in the z‐direction had no effect on the correction vector and image quality.Rotations of the imaging panel calibration resulted in corresponding correction vector rotations of the patient images. These rotations also resulted in degraded image quality which can be identified through quantitative image quality metrics.

Conclusion

Misalignment of CBCT geometry can lead to incorrect translational and rotational patient correction vectors. These errors can be identified through QA of the imaging isocenter as compared to orthogonal images combined with monitoring of CBCT image quality.
SU‐E‐J‐47: Comparison of Online Image Registrations of Varian TrueBeam Cone‐Beam CT and BrainLab ExacTrac Imaging Systems
Authors: Li J , Shi W , Andrews D , Werner‐Wasik M , Yu Y , Liu H
Published: June 2015

Purpose

To compare online image registrations of TrueBeam cone‐beam CT (CBCT) and BrainLab ExacTrac imaging systems.

Methods

Tests were performed on a Varian TrueBeam STx linear accelerator (Version 2.0), which is integrated with a BrainLab ExacTrac imaging system (Version 6.0.5). The study was focused on comparing the online image registrations for translational shifts. A Rando head phantom was placed on treatment couch and immobilized with a BrainLab mask. The phantom was shifted by moving the couch translationally for 8 mm with a step size of 1 mm, in vertical, longitudinal, and lateral directions, respectively. At each location, the phantom was imaged with CBCT and ExacTrac x‐ray. CBCT images were registered with TrueBeam and ExacTrac online registration algorithms, respectively. And ExacTrac x‐ray image registrations were performed. Shifts calculated from different registrations were compared with nominal couch shifts.

Results

The averages and ranges of absolute differences between couch shifts and calculated phantom shifts obtained from ExacTrac x‐ray registration, ExacTrac CBCT registration with default window, ExaxTrac CBCT registration with adjusted window (bone), Truebeam CBCT registration with bone window, and Truebeam CBCT registration with soft tissue window, were: 0.07 (0.02–0.14), 0.14 (0.01–0.35), 0.12 (0.02–0.28), 0.09 (0–0.20), and 0.06 (0–0.10) mm, in vertical direction; 0.06 (0.01–0.12), 0.27 (0.07–0.57), 0.23 (0.02–0.48), 0.04 (0–0.10), and 0.08 (0– 0.20) mm, in longitudinal direction; 0.05 (0.01–0.21), 0.35 (0.14–0.80), 0.25 (0.01–0.56), 0.19 (0–0.40), and 0.20 (0–0.40) mm, in lateral direction.

Conclusion

The shifts calculated from ExacTrac x‐ray and TrueBeam CBCT registrations were close to each other (the differences between were less than 0.40 mm in any direction), and had better agreements with couch shifts than those from ExacTrac CBCT registrations. There were no significant differences between TrueBeam CBCT registrations using different windows. In ExacTrac CBCT registrations, using bone window led to better agreements than using default window.
SU‐E‐J‐144: Low Activity Studies of Carbon 11 Activation Via GATE Monte Carlo
Authors: Elmekawy A , Butuceanu C , Qu L , Ewell L
Published: June 2015

Purpose:

To investigate the behavior of a Monte Carlo simulation code with low levels of activity (∼1,000Bq). Such activity levels are expected from phantoms and patients activated via a proton therapy beam.

Methods:

Three different ranges for a therapeutic proton radiation beam were examined in a Monte Carlo simulation code: 13.5, 17.0 and 21.0cm. For each range, the decay of an equivalent length11C source and additional sources of length plus or minus one cm was studied in a benchmark PET simulation for activities of 1000, 2000 and 3000Bq. The ranges were chosen to coincide with a previous activation study, and the activities were chosen to coincide with the approximate level of isotope creation expected in a phantom or patient irradiated by a therapeutic proton beam. The GATE 7.0 simulation was completed on a cluster node, running Scientific Linux Carbon 6 (Red Hat©). The resulting Monte Carlo data were investigated with the ROOT (CERN) analysis tool. The half‐life of11C was extracted via a histogram fit to the number of simulated PET events vs. time.

Results:

The average slope of the deviation of the extracted carbon half life from the expected/nominal value vs. activity showed a generally positive value. This was unexpected, as the deviation should, in principal, decrease with increased activity and lower statistical uncertainty.

Conclusion:

For activity levels on the order of 1,000Bq, the behavior of a benchmark PET test was somewhat unexpected. It is important to be aware of the limitations of low activity PET images, and low activity Monte Carlo simulations.

This work was funded in part by the Philips corporation.
SU‐E‐J‐175: Comparison of the Treatment Reproducibility of Tumors Affected by Breathing Motion
Authors: Adamczyk M , Piotrowski T , Adamczyk S
Published: June 2015

Purpose:

The aim of the dose distribution simulations was to form a global idea of intensity‐modulated radiation therapy (IMRT) realization, by its comparison to three‐dimensional conformal radiation therapy (3DCRT) delivery for tumors affected by respiratory motion.

Methods:

In the group of 10patients both 3DCRT and IMRT plans were prepared.For each field the motion kernel was generated with the largest movement amplitude of 4;6 and 8mm.Additionally,the sets of reference measurements were made in no motion conditions(0 mm).The evaluation of plan delivery,using a diode array placed on moving platform,was based on the Gamma Index analysis with distance to agreement of 3mm and dose difference of 3%.

Results:

IMRT plans tended to spare doses delivered to lungs compared to 3DCRT.Nonetheless,analyzed volumes showed no significant difference between the static and dynamic techniques,except for the volumes of both lungs receiving 10 and 15Gy.After adding the components associated with the respiratory movement,all IMRT lung parameters evaluated for the ipsilateral,contralateral and both lungs together,revealed considerable differences between the 0vs.6, 0vs.8 and 4vs.8‐mm amplitudes.Similar results were obtained for the 3DCRT lung measurements,but without significance between the 0vs.6‐mm amplitude.Taking into account the CTV score parameter in 3DCRT and IMRT plans,there was no statistically significant difference between the motion patterns with the smallest amplitudes.The differences were found for the 8‐mm amplitude when it was compared both with static conditions and 4‐mm amplitude (for 3DCRT) and between 0vs.6, 0vs.8 and 4vs.8‐mm amplitudes (for IMRT).All accepted and measured 3DCRT and IMRT doses to spinal cord,esophagus and heart were always below the QUANTEC limits.

Conclusion:

The application of IMRT technique in lung radiotherapy affords possibilities for reducing the lung doses.For maximal amplitudes of breathing trajectory below 4mm,the disagreement between CTV planned and delivered dose distribution can be neglected.Whereas respiratory motion with an amplitude above 5mm leads to significant changes in IMRT delivery.