bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐87: Calibrating Cherenkov Emission to Match Superficial Dose in Tissue
Authors: Zhang R , Glaser A , Gladstone D , Pogue B
Published: June 2015

Purpose:

Through Monte Carlo simulations and phantom studies, the dominant factors affecting the calibration of superficial Cherenkov intensity to absolute surface dose was investigated, including tissue optical properties, curvatures, beam properties and imaging angle.

Methods:

The phasespace files for the TrueBeam system from Varian were used in GAMOS (a GEANT4 based Monte Carlo simulation toolkit) to simulate surface emission Cherenkov signals and the correlated deposited dose. The parameters examined were: i) different tissue optical properties (skin color from light to dark), ii) beam types (X‐ray and electron beam), iii) beam energies, iv) thickness of tissues (2.5 cm to 20 cm), v) SSD (80 cm to 120 cm), vi) field sizes (0.5×0.5 cm2 to 20×20 cm2), vii) entrance/exit sides, viii) curvatures (cylinders with diameters from 2.5 cm to 20cm) and ix) imaging angles (0 to 90 degrees). In a specific case, for any Cherenkov photon emitted from the surface, the original position and direction, final position and direction and energy were recorded. Similar experimental measurements were taken in a range of the most pertinent parameters using tissue phantoms.

Results:

Combining the dose distribution and sampling sensitivity of Cherenkov emission, quantitatively accurate calibration factors (the amount of radiation dose represented by a single Cherenkov photon) were calculated. The data showed relatively large dependence upon different optical properties, curvature, entrance/exit and beam types. For a diffusive surface, the calibration factor was insensitive to imaging angles smaller than 60 degrees. Normalization with the reflectance image was experimentally validated as a simple and accurate method for calibrations of different optical properties.

Conclusion:

This study sheds light on how and to what extent different conditions affect the calibration from Cherenkov intensity to absolute superficial dose and provides practical solutions to allow quantitative Cherenkov imaging to be used as a dose surrogate for imaging.
SU‐E‐I‐88: The Effect of System Dead Time On Real‐Time Plastic and GOS Based Fiber‐Optic Dosimetry Systems
Authors: Hoerner M , Hintenlang D
Published: June 2015

Purpose:

A methodology is presented to correct for measurement inaccuracies at high detector count rates using a plastic and GOS scintillation fibers coupled to a photomultiplier tube with digital readout. This system allows temporal acquisition and manipulation of measured data.

Methods:

The detection system used was a plastic scintillator and a separate gadolinium scintillator, both (0.5 diameter) coupled to an optical fiber with a Hamamatsu photon counter with a built‐in microcontroller and digital interface. Count rate performance of the system was evaluated using the nonparalzable detector model. Detector response was investigated across multiple radiation sources including: orthovoltage x‐ray system, colbat‐60 gamma rays, proton therapy beam, and a diagnostic radiography x‐ray tube. The dead time parameter was calculated by measuring the count rate of the system at different exposure rates using a reference detector.

Results:

The system dead time was evaluated for the following sources of radiation used clinically: diagnostic energy x‐rays, cobalt‐60 gamma rays, orthovoltage xrays, particle proton accelerator, and megavoltage x‐rays. It was found that dead time increased significantly when exposing the detector to sources capable of generating Cerenkov radiation, all of the sources sans the diagnostic x‐rays, with increasing prominence at higher photon energies. Percent depth dose curves generated by a dedicated ionization chamber and compared to the detection system demonstrated that correcting for dead time improves accuracy. On most sources, nonparalzable model fit provided an improved system response.

Conclusion:

Overall, the system dead time was variable across the investigated radiation particles and energies. It was demonstrated that the system response accuracy was greatly improved by correcting for dead time effects. Cerenkov radiation plays a significant role in the increase in the system dead time through transient absorption effects attributed to electron hole‐pair creations within the optical waveguide.
SU‐E‐J‐02: Towards Real‐Time PRFS Thermometry Using Simultaneous MultiSlice Acquisitions
Authors: Borman P , Crijns S , Bos C , Moonen C , Raaymakers B
Published: June 2015

Purpose:

To speed up PRFS thermometry using Simultaneous MultiSlice acquisitions (SMS) with a focus on HIFU treatments, where temperatures at multiple locations such as near field, far field and focus need to be monitored in real‐time.

Methods:

The phantom is a 2% agar 2% silica gel. The gel was heated using an ultrasound transducer operating at 1.2MHz with a focus of 8mm, delivering 60W for 60 seconds. The temperature is measured with two optical probes; one at the focus and one 4cm above that. The probes are used to compare the PRFS thermometry results with. The images are made on a 1.5T Philips Achieva scanner with a SMS GRE acquisition using CAIPIRINHA: two slices are excited simultaneously with a Multi‐Band pulse and one slice is shifted one half FOV, resulting in minimal overlap and optimal sensitivity.The images are reconstructed offline in MATLAB using ReconFrame (GyroTools). The temperature is calculated from the PRFS and averaged over an ROI at the focus. The SMS acquisition has acceleration factor 2 and can be combined with SENSE. Results are compared to M2D acquisitions with SENSE factors 1 and 2. Results: The SMS temperature curves are in good qualitative agreement with the temperature curves of the probes. The difference is probably caused by the probes not being exactly at the focus. There is good agreement between the M2D and SMS curves, even though SMS scans have acceleration factor 2. We also showed that SMS can be combined with SENSE to achieve acceleration factor 3.

Results:

The SMS temperature curves are in good qualitative agreement with the temperature curves of the probes. The difference is probably caused by the probes not being exactly at the focus. There is good agreement between the M2D and SMS curves, even though SMS scans have acceleration factor 2. We also showed that SMS can be combined withSENSE to achieve acceleration factor 3. Conclusion: This work showsthatPRFSthermometry inmultiple slices can be accelerated by SMS techniques. We demonstrated that the temperature measured using SMS scans is in agreement with the M2D scans, while the dynamic scan time of the former is almost half of that of the latter.

Conclusion:

This work shows that PRFS thermometry in multiple slices can be accelerated by SMS techniques. We demonstrated that the temperature measured using SMS scans is in agreement with the M2D scans, while the dynamic scan time of the former is almost half of that of the latter.

This work was funded by the SoRTS consortium
SU‐E‐J‐03: Characterization of the Precision and Accuracy of a New, Preclinical, MRI‐Guided Focused Ultrasound System for Image‐Guided Interventions in Small‐Bore, High‐Field Magnets
Authors: Ellens N , Farahani K
Published: June 2015

Purpose:

MRI‐guided focused ultrasound (MRgFUS) has many potential and realized applications including controlled heating and localized drug delivery. The development of many of these applications requires extensive preclinical work, much of it in small animal models. The goal of this study is to characterize the spatial targeting accuracy and reproducibility of a preclinical high field MRgFUS system for thermal ablation and drug delivery applications.

Methods:

The RK300 (FUS Instruments, Toronto, Canada) is a motorized, 2‐axis FUS positioning system suitable for small bore (72 mm), high‐field MRI systems. The accuracy of the system was assessed in three ways. First, the precision of the system was assessed by sonicating regular grids of 5 mm squares on polystyrene plates and comparing the resulting focal dimples to the intended pattern, thereby assessing the reproducibility and precision of the motion control alone. Second, the targeting accuracy was assessed by imaging a polystyrene plate with randomly drilled holes and replicating the hole pattern by sonicating the observed hole locations on intact polystyrene plates and comparing the results. Third, the practicallyrealizable accuracy and precision were assessed by comparing the locations of transcranial, FUS‐induced blood‐brain‐barrier disruption (BBBD) (observed through Gadolinium enhancement) to the intended targets in a retrospective analysis of animals sonicated for other experiments.

Results:

The evenly‐spaced grids indicated that the precision was 0.11 +/− 0.05 mm. When image‐guidance was included by targeting random locations, the accuracy was 0.5 +/− 0.2 mm. The effective accuracy in the four rodent brains assessed was 0.8 +/− 0.6 mm. In all cases, the error appeared normally distributed (p<0.05) in both orthogonal axes, though the left/right error was systematically greater than the superior/inferior error. Conclusions: The targeting accuracy of this device is sub‐millimeter, suitable for many preclinical applications including focused drug delivery and thermal therapy.

Funding support provided by Philips Healthcare
SU‐E‐J‐24: Can Fiducial Marker‐Based Setup Using ExacTrac Be An Alternative to Soft Tissue‐Based Setup Using Cone‐Beam CT for Prostate IMRT?
Authors: Tanabe S , Utsunomiya S , Abe E , Satou H , Sakai H , Yamada T , Aoyama H
Published: June 2015

Purpose:

To assess an accuracy of fiducial maker‐based setup using ExacTrac (ExT‐based setup) as compared with soft tissue‐based setup using Cone‐beam CT (CBCT‐based setup) for patients with prostate cancer receiving intensity‐modulated radiation therapy (IMRT) for the purpose of investigating whether ExT‐based setup can be an alternative to CBCT‐based setup.

Methods:

The setup accuracy was analyzed prospectively for 7 prostate cancer patients with implanted three fiducial markers received IMRT. All patients were treated after CBCT‐based setup was performed and corresponding shifts were recorded. ExacTrac images were obtained before and after CBCT‐based setup. The fiducial marker‐based shifts were calculated based on those two images and recorded on the assumption that the setup correction was carried out by fiducial marker‐based auto correction. Mean and standard deviation of absolute differences and the correlation between CBCT and ExT shifts were estimated.

Results:

A total of 178 image dataset were analyzed. On the differences between CBCT and ExT shifts, 133 (75%) of 178 image dataset resulted in smaller differences than 3 mm in all dimensions. Mean differences in the anterior‐posterior (AP), superior‐inferior (SI), and left‐right (LR) dimensions were 1.8 ± 1.9 mm, 0.7 ± 1.9 mm, and 0.6 ± 0.8 mm, respectively. The percentages of shift agreements within ±3 mm were 76% for AP, 90% for SI, and 100% for LR. The Pearson coefficient of correlation for CBCT and ExT shifts were 0.80 for AP, 0.80 for SI, and 0.65 for LR.

Conclusion:

This work showed that the accuracy of ExT‐based setup was correlated with that of CBCT‐based setup, implying that ExT‐based setup has a potential ability to be an alternative to CBCT‐based setup. The further work is to specify the conditions that ExT‐based setup can provide the accuracy comparable to CBCT‐based setup.
SU‐E‐J‐26: A Novel Technique for Markerless Self‐Sorted 4D‐CBCT Using Patient Motion Modeling: A Feasibility Study
Authors: Zhang L , Zhang Y , Harris W , Yin F , Ren L
Published: June 2015

Purpose:

To develop an automatic markerless 4D‐CBCT projection sorting technique by using a patient respiratory motion model extracted from the planning 4D‐CT images.

Methods:

Each phase of onboard 4D‐CBCT is considered as a deformation of one phase of the prior planning 4D‐CT. The deformation field map (DFM) is represented as a linear combination of three major deformation patterns extracted from the planning 4D‐CT using principle component analysis (PCA). The coefficients of the PCA deformation patterns are solved by matching the digitally reconstructed radiograph (DRR) of the deformed volume to the onboard projection acquired. The PCA coefficients are solved for each single projection, and are used for phase sorting. Projections at the peaks of the Z direction coefficient are sorted as phase 1 and other projections are assigned into 10 phase bins by dividing phases equally between peaks. The 4D digital extended‐cardiac‐torso (XCAT) phantom was used to evaluate the proposed technique. Three scenarios were simulated, with different tumor motion amplitude (3cm to 2cm), tumor spatial shift (8mm SI), and tumor body motion phase shift (2 phases) from prior to on‐board images. Projections were simulated over 180 degree scan‐angle for the 4D‐XCAT. The percentage of accurately binned projections across entire dataset was calculated to represent the phase sorting accuracy.

Results:

With a changed tumor motion amplitude from 3cm to 2cm, markerless phase sorting accuracy was 100%. With a tumor phase shift of 2 phases w.r.t. body motion, the phase sorting accuracy was 100%. With a tumor spatial shift of 8mm in SI direction, phase sorting accuracy was 86.1%.

Conclusion:

The XCAT phantom simulation results demonstrated that it is feasible to use prior knowledge and motion modeling technique to achieve markerless 4D‐CBCT phase sorting.

National Institutes of Health Grant No. R01‐CA184173 Varian Medical System
SU‐E‐J‐27: Shifting Multiple EPID Imager Layers to Improve Image Quality and Resolution in MV CBCT
Authors: Chen H , Rottmann J , Yip S , Morf D , Fueglistaller R , Star‐Lack J , Zentai G , Berbeco R
Published: June 2015

Purpose:

Vertical stacking of four conventional EPID layers can improve DQE for MV‐CBCT applications. We hypothesize that shifting each layer laterally by half a pixel relative to the layer above, will improve the contrast‐to‐noise ratio (CNR) and image resolution.

Methods:

For CNR assessment, a 20 cm diameter digital phantom with 8 inserts is created. The attenuation coefficient of the phantom is similar to lung at the average energy of a 6 MV photon beam. The inserts have attenuations 1, 2…8 times of lung. One of the inserts is close to soft tissue, resembling the case of a tumor in lung. For resolution assessment, a digital phantom featuring a bar pattern is created. The phantom has an attenuation coefficient similar to soft tissue and the bars have an attenuation coefficient of calcium sulfate. A 2 MeV photon beam is attenuated through these phantoms and hits each of the four stacked detector layers. Each successive layer is shifted by half a pixel in the × only, y only, and × and y (combined) directions, respectively. Blurring and statistical noise are added to the projections. Projections from one, two, three and four layers are used for reconstruction. CNR and image resolution are evaluated and compared.

Results:

When projections from multiple layers are combined for reconstruction, CNR increases with the number of layers involved. CNR in reconstructions from two, three and four layers are 1.4, 1.7 and 1.99 times that from one layer. The resolution from the shifted four layer detector is also improved from a single layer. In a comparison between one layer versus four layers in this preliminary study, the resolution from four shifted layers is at least 20% better.

Conclusion:

Layer‐shifting in a stacked EPID imager design enhances resolution as well as CNR for half scan MV‐CBCT.

The project described was supported, in part, by a grant from Varian Medical Systems, Inc., and Award No. R01CA188446‐01 from the National Cancer Institute. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Cancer Institute or the National Institutes of Health
SU‐E‐J‐32: Dosimetric Evaluation Based On Pre‐Treatment Cone Beam CT for Spine Stereotactic Body Radiotherapy: Does Region of Interest Focus Matter?
Authors: Magnelli A , Xia P
Published: June 2015

Purpose:

Spine stereotactic body radiotherapy requires very conformal dose distributions and precise delivery. Prior to treatment, a KV cone‐beam CT (KV‐CBCT) is registered to the planning CT to provide image‐guided positional corrections, which depend on selection of the region of interest (ROI) because of imperfect patient positioning and anatomical deformation. Our objective is to determine the dosimetric impact of ROI selections.

Methods:

Twelve patients were selected for this study with the treatment regions varied from C‐spine to T‐spine. For each patient, the KV‐CBCT was registered to the planning CT three times using distinct ROIs: one encompassing the entire patient, a large ROI containing large bony anatomy, and a small target‐focused ROI. Each registered CBCT volume, saved as an aligned dataset, was then sent to the planning system. The treated plan was applied to each dataset and dose was recalculated. The tumor dose coverage (percentage of target volume receiving prescription dose), maximum point dose to 0.03 cc of the spinal cord, and dose to 10% of the spinal cord volume (V10) for each alignment were compared to the original plan.

Results:

The average magnitude of tumor coverage deviation was 3.9%±5.8% with external contour, 1.5%±1.1% with large ROI, 1.3%±1.1% with small ROI. Spinal cord V10 deviation from plan was 6.6%±6.6% with external contour, 3.5%±3.1% with large ROI, and 1.2%±1.0% with small ROI. Spinal cord max point dose deviation from plan was: 12.2%±13.3% with external contour, 8.5%±8.4% with large ROI, and 3.7%±2.8% with small ROI.

Conclusion:

A small ROI focused on the target results in the smallest deviation from planned dose to target and cord although rotations at large distances from the targets were observed. It is recommended that image fusion during CBCT focus narrowly on the target volume to minimize dosimetric error. Improvement in patient setups may further reduce residual errors.
SU‐E‐J‐37: Feasibility of Utilizing Carbon Fiducials to Increase Localization Accuracy of Lumpectomy Cavity for Partial Breast Irradiation
Authors: Zhang Y , Hieken T , Mutter R , Park S , Yan E , Brinkmann D , Pafundi D
Published: June 2015

Purpose

To investigate the feasibility of utilizing carbon fiducials to increase localization accuracy of lumpectomy cavity for partial breast irradiation (PBI).

Methods

Carbon fiducials were placed intraoperatively in the lumpectomy cavity following resection of breast cancer in 11 patients. The patients were scheduled to receive whole breast irradiation (WBI) with a boost or 3D‐conformal PBI. WBI patients were initially setup to skin tattoos using lasers, followed by orthogonal kV on‐board‐imaging (OBI) matching to bone per clinical practice. Cone beam CT (CBCT) was acquired weekly for offline review. For the boost component of WBI and PBI, patients were setup with lasers, followed by OBI matching to fiducials, with final alignment by CBCT matching to fiducials. Using carbon fiducials as a surrogate for the lumpectomy cavity and CBCT matching to fiducials as the gold standard, setup uncertainties to lasers, OBI bone, OBI fiducials, and CBCT breast were compared.

Results

Minimal imaging artifacts were introduced by fiducials on the planning CT and CBCT. The fiducials were sufficiently visible on OBI for online localization. The mean magnitude and standard deviation of setup errors were 8.4mm ± 5.3 mm (n=84), 7.3mm ± 3.7mm (n=87), 2.2mm ± 1.6mm (n=40) and 4.8mm ± 2.6mm (n=87), for lasers, OBI bone, OBI fiducials and CBCT breast tissue, respectively. Significant migration occurred in one of 39 implanted fiducials in a patient with a large postoperative seroma.

Conclusion

OBI carbon fiducial‐based setup can improve localization accuracy with minimal imaging artifacts. With increased localization accuracy, setup uncertainties can be reduced from 8mm using OBI bone matching to 3mm using OBI fiducial matching for PBI treatment. This work demonstrates the feasibility of utilizing carbon fiducials to increase localization accuracy to the lumpectomy cavity for PBI. This may be particularly attractive for localization in the setting of proton therapy and other scenarios in which metal clips are contraindicated.
SU‐E‐J‐39: Dosimetric Benefit of Implanted Marker‐Based CBCT Setup for Definitive Prostatic Radiotherapy
Authors: Zhen H , Wu Z , Bluemenfeld P , Chu J , Wang D
Published: June 2015

Purpose

Daily setup for definitive prostatic radiotherapy is challenged by suboptimal visibility of the prostate boundary and daily variation of rectum shape and position. For patients with improved bowel preparation, we conducted a dosimetric comparison between prostate implanted marker (IM)‐based daily setup and anterior rectal wall (ARW)‐based setup, with the hypothesis that the former leads to adequate target coverage with better rectal sparing.

Methods

Five IMRT/VMAT prostate cases with implanted markers were selected for analysis. Daily CBCT showed improvement of the rectal volume compared to planning CT. For each patient, the prostate and rectum were contoured on three CBCT images (fraction 5/15/25) with subsequent physician review. The CBCTs were then registered to a planning CT using IM‐based registration. The deviation of ARW positions from planning CT to CBCT were analyzed at various sup‐inf levels (−1.8 cm to 1.8 cm from level of prostate center). To estimate the potential dosimetric impact from ARW‐based setup, the treatment plans were recalculated using A‐P shifts ranging from −1mm to +6mm. Clinically important rectum DVH values including Dmax, D3cc and Dmean were computed.

Results

For the studied patients, we observed on average 32% rectum volume reduction from planning CT to CBCT. As a Results, the ARW on average shifts posteriorly by −1mm to +5mm, depending on the sup‐inf level of observation, with larger shifts observed at more superior levels. Recalculation shows that when ARW shifts 1mm posteriorly, ARW‐based CBCT setup leads to a 1.0%, 4.2%, and 3.2% increase in rectum Dmax, D3cc, and Dmean, respectively, compared to IM‐based setup. The dosimetric deviations increase to 4.7%, 25.8% and 24.7% when ARW shifts 6mm posteriorly. No significant prostate‐only dose difference was observed.

Conclusion

For patients with improved bowel preparation, IM‐based CBCT setup leads to accurate prostate coverage along with significantly lower rectal dose, compared to ARW‐based setup.
SU‐E‐J‐42: Evaluation of Fiducial Markers for Ultrasound and X‐Ray Images Used for Motion Tracking in Pancreas SBRT
Authors: Ng SK , Armour E , Su L , Zhang Y , Iordachita I , Wong J , Sen H Tutkun , Kazanzides P , Bell M Lediju , Ding K
Published: June 2015

Purpose

Ultrasound tracking of target motion relies on visibility of vascular and/or anatomical landmark. However this is challenging when the target is located far from vascular structures or in organs that lack ultrasound landmark structure, such as in the case of pancreas cancer. The purpose of this study is to evaluate visibility, artifacts and distortions of fusion coils and solid gold markers in ultrasound, CT, CBCT and kV images to identify markers suitable for real‐time ultrasound tracking of tumor motion in SBRT pancreas treatment.

Methods

Two fusion coils (1mm × 5mm and 1mm × 10 mm) and a solid gold marker (0.8mm × 10mm) were embedded in a tissue–like ultrasound phantom. The phantom (5cm × 12cm × 20cm) was prepared using water, gelatin and psyllium‐hydrophilic‐mucilloid fiber. Psylliumhydrophilic mucilloid acts as scattering medium to produce echo texture that simulates sonographic appearance of human tissue in ultrasound images while maintaining electron density close to that of water in CT images. Ultrasound images were acquired using 3D‐ultrasound system with markers embedded at 5, 10 and 15mm depth from phantom surface. CT images were acquired using Philips Big Bore CT while CBCT and kV images were acquired with XVI‐system (Elexta). Visual analysis was performed to compare visibility of the markers and visibility score (1 to 3) were assigned.

Results

All markers embedded at various depths are clearly visible (score of 3) in ultrasound images. Good visibility of all markers is observed in CT, CBCT and kV images. The degree of artifact produced by the markers in CT and CBCT images are indistinguishable. No distortion is observed in images from any modalities.

Conclusion

All markers are visible in images across all modalities in this homogenous tissue‐like phantom. Human subject data is necessary to confirm the marker type suitable for real‐time ultrasound tracking of tumor motion in SBRT pancreas treatment.
SU‐E‐J‐46: Evaluation of the Accuracy of a Six Degree of Freedom Robotic Couch Using ConeBeam CT Images of the Isocal Phantom
Authors: Zhang Q , Driewer J , Wang S , Li S , Zheng D , Zhu X , Zhen W , Wahl A , Lin C , Thompson R , Zhou S , Enke C
Published: June 2015

Purpose

The accuracy of Varian PerfectPitch six degree of freedom (DOF) robotic couch was examined using Varian Isocal phantom and cone‐beam CT (CBCT) system.

Methods

CBCT images of the Isocal phantom were taken at different pitch and roll angles. The pitch and roll angles were varied from 357 to 3 degrees in one degree increments by input from service console, generating a total of 49 combinations with couch angle (yaw) zero. The center positions of the 16 tungsten carbide BBs contained in the Isocal were determined with in‐house image processing software. Expected BBs positions at different rotation angles were determined mathematically by applying a combined translation/rotation operator to BB positions at zero pitch and roll values. A least square method was used to minimize the difference between the expected BB positions and their measured positions. In this way rotation angles were obtained and compared with input values from the console.

Results

A total of 49 CBCT images with voxel sizes 0.51 mm × 0.51 mm × 1 mm were used in analysis. Among the 49 calculations, the maximum rotation angle differences were 0.1 degree, 0.15 degree, and 0.09 degree, for pitch, roll, and couch rotation, respectively. The mean ± standard‐deviation angle differences were 0.028±0.001 degree, −0.043±0.003 degree, and −0.009±0.001 degree, for pitch, roll, and couch rotation, respectively. The maximum isocenter shifts were 0.3 mm, 0.5 mm, 0.4 mm in x, y, z direction respectively following IEC6127 convention. The mean isocenter shifts were 0.07±0.02 mm, −0.05±0.06 mm, and −0.12±0.02 mm in x, y and z directions.

Conclusion

The accuracy of the Varian PerfectPitch six DOF couch was studied with CBCTs of the Isocal phantom. The rotational errors were less than 0.15 degree and isocenter shifts were less than 0.5 mm in any direction. This accuracy is sufficient for stereotactic radiotherapy clinical applications.
SU‐E‐J‐49: Design and Fabrication of Custom 3D Printed Phantoms for Radiation Therapy Research and Quality Assurance
Authors: Jenkins C , Xing L
Published: June 2015

Purpose

The rapid proliferation of affordable 3D printing techniques has enabled the custom fabrication of items ranging from paper weights to medical implants. This study investigates the feasibility of utilizing the technology for developing novel phantoms for use in radiation therapy quality assurance (QA) procedures.

Methods

A phantom for measuring the geometric parameters of linear accelerator (LINAC) on‐board imaging (OBI) systems was designed using SolidWorks. The design was transferred to a 3D printer and fabricated using a fused deposition modeling (FDM) technique. Fiducials were embedded in the phantom by placing 1.6 mm diameter steel balls in predefined holes and securing them with silicone. Several MV and kV images of the phantom were collected and the visibility and geometric accuracy were evaluated. A second phantom, for use in the experimental evaluation of a high dose rate (HDR) brachytherapy dosimeter, was designed to secure several applicator needles in water. The applicator was fabricated in the same 3D printer and used for experiments.

Results

The general accuracy of printed parts was determined to be 0.1 mm. The cost of materials for the imaging and QA phantoms were $22 and $5 respectively. Both the plastic structure and fiducial markers of the imaging phantom were visible in MV and kV images. Fiducial marker locations were determined to be within 1mm of desired locations, with the discrepancy being attributed to the fiducial attachment process. The HDR phantom secured the applicators within 0.5 mm of the desired locations.

Conclusion

3D printing offers an inexpensive method for fabricating custom phantoms for use in radiation therapy quality assurance. While the geometric accuracy of such parts is limited compared to more expensive methods, the phantoms are still highly functional and provide a unique opportunity for rapid fabrication of custom phantoms for use in radiation therapy QA and research.
SU‐E‐J‐50: An Evaluation of the Stability of Image Quality Parameters of the Elekta XVI and IView Imaging Systems
Authors: Stanley D , Papanikolaou N , Gutierrez A
Published: June 2015

Introduction

Quality assurance of the image quality for image guided localization systems is crucial to ensure accurate visualization and localization of target volumes. In this study, the long term stability of selected image parameters was assessed and evaluated for CBCT mode, planar radiographic kV mode and MV mode. Methods and Materials: The CATPHAN, QckV‐1 and QC‐3 phantoms were used to evaluate the image quality parameters. The planar radiographic images were analyzed in PIPSpro™ with spatial resolution (f30, f40, f50) being recorded. For XVI CBCT, Head and Neck Small20 (S20) and Pelvis Medium20 (M20) standard acquisition modes were evaluated for Uniformity, Noise, Spatial Resolution and HU constancy. Dose and kVp for the XVI were recorded using the Unfors RaySafe Xi system with the R/F Low Detector for the kV planar radiographic mode.

Results

A total of 20 and 10 measurements were acquired for the planar radiographic and CBCT systems respectively over a two month period. Values were normalized to the mean and the standard deviations (STD) were recorded. For the planar radiographic spatial resolution, the STD for f30, f40, f50 were 0.004, 0.002, 0.002 and 0.005, 0.007, 0.008 for the kV and MV, respectively. The average recorded dose for kV was 38.7±2.7 μGy. The STD of the evaluated metrics for the S20 acquisition were: 0.444(f30), 0.067(f40), 0.062(f50), 0.018(Water/poly‐HU constancy), 0.028(uniformity) and 0.106(noise). The standard deviations for the M20 acquisition were: 0.108(f30), 0.073(f40), 0.091(f50), 0.008(Water/poly‐HU constancy), 0.005(uniformity) and 0.005(noise). Using these, tolerances can be reported as a warning and action threshold of 1σ and 2σ.

Conclusion

A study was performed to assess the stability of the basic image quality parameters recommended by TG‐142 for the Elekta XVI and iView imaging systems. Consistent imaging and dosimetric properties over the evaluated time frame were noted.

This work was funded in part by the Cancer Prevention Research Institute of Texas Pre doctoral fellowship training grant (RP140105) to Dennis N. Stanley M.Sc.
SU‐E‐J‐114: A Practical Hybrid Method for Improving the Quality of CT‐CBCT Deformable Image Registration for Head and Neck Radiotherapy
Authors: Liu C , Kumarasiri A , Chetvertkov M , Gordon J , Chetty I , Siddiqui F , Kim J
Published: June 2015

Purpose:

Accurate deformable image registration (DIR) between CT and CBCT in H&N is challenging. In this study, we propose a practical hybrid method that uses not only the pixel intensities but also organ physical properties, structure volume of interest (VOI), and interactive local registrations.

Methods:

Five oropharyngeal cancer patients were selected retrospectively. For each patient, the planning CT was registered to the last fraction CBCT, where the anatomy difference was largest. A three step registration strategy was tested; Step1) DIR using pixel intensity only, Step2) DIR with additional use of structure VOI and rigidity penalty, and Step3) interactive local correction. For Step1, a public‐domain open‐source DIR algorithm was used (cubic B‐spline, mutual information, steepest gradient optimization, and 4‐level multi‐resolution). For Step2, rigidity penalty was applied on bony anatomies and brain, and a structure VOI was used to handle the body truncation such as the shoulder cut‐off on CBCT. Finally, in Step3, the registrations were reviewed on our in‐house developed software and the erroneous areas were corrected via a local registration using level‐set motion algorithm.

Results:

After Step1, there were considerable amount of registration errors in soft tissues and unrealistic stretching in the posterior to the neck and near the shoulder due to body truncation. The brain was also found deformed to a measurable extent near the superior border of CBCT. Such errors could be effectively removed by using a structure VOI and rigidity penalty. The rest of the local soft tissue error could be corrected using the interactive software tool. The estimated interactive correction time was approximately 5 minutes.

Conclusion:

The DIR using only the image pixel intensity was vulnerable to noise and body truncation. A corrective action was inevitable to achieve good quality of registrations. We found the proposed three‐step hybrid method efficient and practical for CT/CBCT registrations in H&N.

My department receives grant support from Industrial partners: (a) Varian Medical Systems, Palo Alto, CA, and (b) Philips HealthCare, Best, Netherlands
SU‐E‐J‐118: A Systematic Analysis of Rigid Image Registration Using Patient CTs and Simulated Setup Images with a Unique Gold Standard Registration
Authors: Kieselmann J , Rosselet A , Scheib S , Thieme‐Marti S
Published: June 2015

Purpose:

To quantify the reliability of fully automated image registration (IR) of planning CTs with 2D MV/kV projections or kV‐CBCTs in terms of its failure rate, and to investigate the influence of algorithmic and external parameters on registration quality.

Methods:

A gold standard registration is necessary to evaluate the failure rate. We develop a novel framework to obtain unique gold standards for MV imaging: we simulate setup images from 50 patient CTs (5 anatomic sites), using HU mapping, simple raytracing, a semi‐empirical scatter model and noise addition. Comparing simulated and acquired images yields excellent agreement. We introduce translations (≤2cm) and rotations (≤2°) with respect to the planned isocenter between planning CTs and setup images according to reported setup‐errors in the literature, followed by using the clinically available IR software from Varian Medical Systems (Palo Alto). Application of this simulation framework to 2D/3D kV imaging is work in progress.

Results:

We investigate the dependence of the registration failure rate on the field size of MV projection images (square, centered at planned isocenter, detected shift >2mm from known shift). The results suggest a minimum field size of 10×10 cm2 to achieve reasonably small failure rates (<10%). We define an optimized parameter set for 2D/3D MV IR, which outperforms the default one of the IR software with respect to the failure rate (<3%), while not significantly (<50%) increasing computation time.

Conclusion:

The developed framework demonstrates the possibility of systematic tests of automated IR for arbitrarily large patient datasets. To our current knowledge this is a novel strategy. We are able to define optimized default parameter sets for registration algorithms and to estimate the influence of parameters, such as imaging dose, on the quality of IR. The improvements made for MV IR in this work look promising. Similar studies for kV based IR are work in progress.
SU‐E‐J‐120: Comparing 4D CT Computed Ventilation to Lung Function Measured with Hyperpolarized Xenon‐129 MRI
Authors: Neal B , Chen Q
Published: June 2015

Purpose:

To correlate ventilation parameters computed from 4D CT to ventilation, profusion, and gas exchange measured with hyperpolarized Xenon‐129 MRI for a set of lung cancer patients.

Methods:

Hyperpolarized Xe‐129 MRI lung scans were acquired for lung cancer patients, before and after radiation therapy, measuring ventilation, perfusion, and gas exchange. In the standard clinical workflow, these patients also received 4D CT scans before treatment. Ventilation was computed from 4D CT using deformable image registration (DIR). All phases of the 4D CT scan were registered using a B‐spline deformable registration. Ventilation at the voxel level was then computed for each phase based on a Jacobian volume expansion metric, yielding phase sorted ventilation images. Ventilation based upon 4D CT and Xe‐129 MRI were co‐registered, allowing qualitative visual comparison and qualitative comparison via the Pearson correlation coefficient.

Results:

Analysis shows a weak correlation between hyperpolarized Xe‐129 MRI and 4D CT DIR ventilation, with a Pearson correlation coefficient of 0.17 to 0.22. Further work will refine the DIR parameters to optimize the correlation. The weak correlation could be due to the limitations of 4D CT, registration algorithms, or the Xe‐129 MRI imaging. Continued development will refine parameters to optimize correlation.

Conclusion:

Current analysis yields a minimal correlation between 4D CT DIR and Xe‐129 MRI ventilation.

Funding provided by the 2014 George Amorino Pilot Grant in Radiation Oncology at the University of Virginia.
SU‐E‐J‐122: The CBCT Dose Calculation Using a Patient Specific CBCT Number to Mass Density Conversion Curve Based On a Novel Image Registration and Organ Mapping Method in Head‐And‐Neck Radiation Therapy
Authors: Zhou J , Lasio G , Yi B , Huang J , Chen S , Zhang B , Langen K , Prado K , D'souza W
Published: June 2015

Purpose:

To develop a CBCT HU correction method using a patient specific HU to mass density conversion curve based on a novel image registration and organ mapping method for head‐and‐neck radiation therapy.

Methods:

There are three steps to generate a patient specific CBCT HU to mass density conversion curve. First, we developed a novel robust image registration method based on sparseness analysis to register the planning CT (PCT) and the CBCT. Second, a novel organ mapping method was developed to transfer the organs at risk (OAR) contours from the PCT to the CBCT and corresponding mean HU values of each OAR were measured in both the PCT and CBCT volumes. Third, a set of PCT and CBCT HU to mass density conversion curves were created based on the mean HU values of OARs and the corresponding mass density of the OAR in the PCT. Then, we compared our proposed conversion curve with the traditional Catphan phantom based CBCT HU to mass density calibration curve. Both curves were input into the treatment planning system (TPS) for dose calculation. Last, the PTV and OAR doses, DVH and dose distributions of CBCT plans are compared to the original treatment plan.

Results:

One head‐and‐neck cases which contained a pair of PCT and CBCT was used. The dose differences between the PCT and CBCT plans using the proposed method are −1.33% for the mean PTV, 0.06% for PTV D95%, and −0.56% for the left neck. The dose differences between plans of PCT and CBCT corrected using the CATPhan based method are −4.39% for mean PTV, 4.07% for PTV D95%, and −2.01% for the left neck.

Conclusion:

The proposed CBCT HU correction method achieves better agreement with the original treatment plan compared to the traditional CATPhan based calibration method.
SU‐E‐J‐123: Assessing Segmentation Accuracy of Internal Volumes and Sub‐Volumes in 4D PET/CT of Lung Tumors Using a Novel 3D Printed Phantom
Authors: Soultan D , Murphy J , James C , Hoh C , Gill B , Moiseenko V , Cervino L
Published: June 2015

Purpose:

To assess the accuracy of internal target volume (ITV) segmentation of lung tumors for treatment planning of simultaneous integrated boost (SIB) radiotherapy as seen in 4D PET/CT images, using a novel 3D‐printed phantom.

Methods:

The insert mimics high PET tracer uptake in the core and 50% uptake in the periphery, by using a porous design at the periphery. A lung phantom with the insert was placed on a programmable moving platform. Seven breathing waveforms of ideal and patient‐specific respiratory motion patterns were fed to the platform, and 4D PET/CT scans were acquired of each of them. CT images were binned into 10 phases, and PET images were binned into 5 phases following the clinical protocol. Two scenarios were investigated for segmentation: a gate 30–70 window, and no gating. The radiation oncologist contoured the outer ITV of the porous insert with on CT images, while the internal void volume with 100% uptake was contoured on PET images for being indistinguishable from the outer volume in CT images. Segmented ITVs were compared to the expected volumes based on known target size and motion.

Results:

3 ideal breathing patterns, 2 regular‐breathing patient waveforms, and 2 irregular‐breathing patient waveforms were used for this study. 18F‐FDG was used as the PET tracer. The segmented ITVs from CT closely matched the expected motion for both no gating and gate 30–70 window, with disagreement of contoured ITV with respect to the expected volume not exceeding 13%. PET contours were seen to overestimate volumes in all the cases, up to more than 40%.

Conclusion:

4DPET images of a novel 3D printed phantom designed to mimic different uptake values were obtained. 4DPET contours overestimated ITV volumes in all cases, while 4DCT contours matched expected ITV volume values. Investigation of the cause and effects of the discrepancies is undergoing.
SU‐E‐J‐126: An Online Replanning Method for FFF Beams Without Couch Shift
Authors: Ahunbay E , Ates O , Li X
Published: June 2015

Purpose:

In a situation that couch shift for patient positioning is not preferred or prohibited (e.g., MR‐Linac), segment aperture morphing (SAM) can address target dislocation and deformation. For IMRT/VMAT with flattening filter free (FFF) beams, however, SAM method would lead to an adverse translational dose effect due to the beam unflattening. Here we propose a new 2‐step process to address both the translational effect of FFF beams and the target deformation.

Methods:

The replanning method consists of an offline and an online steps. The offline step is to create a series of pre‐shifted plans (PSP) obtained by a so called “warm start” optimization (starting optimization from the original plan, rather from scratch) at a series of isocenter shifts with fixed distance (e.g. 2 cm, at x,y,z = 2,0,0; 2,2,0; 0,2,0; …;− 2,0,0). The PSPs all have the same number of segments with very similar shapes, since the warm‐start optimization only adjusts the MLC positions instead of regenerating them. In the online step, a new plan is obtained by linearly interpolating the MLC positions and the monitor units of the closest PSPs for the shift determined from the image of the day. This two‐step process is completely automated, and instantaneously fast (no optimization or dose calculation needed). The previously‐developed SAM algorithm is then applied for daily deformation. We tested the method on sample prostate and pancreas cases.

Results:

The two‐step interpolation method can account for the adverse dose effects from FFF beams, while SAM corrects for the target deformation. The whole process takes the same time as the previously reported SAM process (5–10 min).

Conclusion:

The new two‐step method plus SAM can address both the translation effects of FFF beams and target deformation, and can be executed in full automation requiring no additional time from the SAM process.

This research was supported by Elekta inc. (Crawley, UK)
SU‐E‐J‐131: Augmenting Atlas‐Based Segmentation by Incorporating Image Features Proximal to the Atlas Contours
Authors: Li Dengwang , Liu Li , Kapp Daniel S. , Xing Lei
Published: June 2015

Purpose:

For facilitating the current automatic segmentation, in this work we propose a narrow‐shell strategy to enhance the information of each contour in the library and to improve the accuracy of the exiting atlas‐based approach.

Methods:

In setting up an atlas‐based library, we include not only the coordinates of contour points, but also the image features adjacent to the contour. 139 planning CT scans with normal appearing livers obtained during their radiotherapy treatment planning were used to construct the library. The CT images within the library were registered each other using affine registration. A nonlinear narrow shell with the regional thickness determined by the distance between two vertices alongside the contour. The narrow shell was automatically constructed both inside and outside of the liver contours. The common image features within narrow shell between a new case and a library case were first selected by a Speed‐up Robust Features (SURF) strategy. A deformable registration was then performed using a thin plate splines (TPS) technique. The contour associated with the library case was propagated automatically onto the images of the new patient by exploiting the deformation field vectors. The liver contour was finally obtained by employing level set based energy function within the narrow shell. The performance of the proposed method was evaluated by comparing quantitatively the auto‐segmentation results with that delineated by a physician.

Results:

Application of the technique to 30 liver cases suggested that the technique was capable of reliably segment organs such as the liver with little human intervention. Compared with the manual segmentation results by a physician, the average and discrepancies of the volumetric overlap percentage (VOP) was found to be 92.43%+2.14%.

Conclusion:

Incorporation of image features into the library contours improves the currently available atlas‐based auto‐contouring techniques and provides a clinically practical solution for auto‐segmentation.

This work is supported by NIH/NIBIB (1R01‐EB016777), National Natural Science Foundation of China (No.61471226 and No.61201441), Research funding from Shandong Province (No.BS2012DX038 and No.J12LN23), and Research funding from Jinan City (No.201401221 and No.20120109).
SU‐E‐J‐132: Automated Segmentation with Post‐Registration Atlas Selection Based On Mutual Information
Authors: Ren X , Sharp G , Gao H
Published: June 2015

Purpose:

The delineation of targets and organs‐at‐risk is a critical step during image‐guided radiation therapy, for which manual contouring is the gold standard. However, it is often time‐consuming and may suffer from intra‐ and inter‐rater variability. The purpose of this work is to investigate the automated segmentation.

Methods:

The automatic segmentation here is based on mutual information (MI), with the atlas from Public Domain Database for Computational Anatomy (PDDCA) with manually drawn contours.Using dice coefficient (DC) as the quantitative measure of segmentation accuracy, we perform leave‐one‐out cross‐validations for all PDDCA images sequentially, during which other images are registered to each chosen image and DC is computed between registered contour and ground truth. Meanwhile, six strategies, including MI, are selected to measure the image similarity, with MI to be the best. Then given a target image to be segmented and an atlas, automatic segmentation consists of: (a) the affine registration step for image positioning; (b) the active demons registration method to register the atlas to the target image; (c) the computation of MI values between the deformed atlas and the target image; (d) the weighted image fusion of three deformed atlas images with highest MI values to form the segmented contour.

Results:

MI was found to be the best among six studied strategies in the sense that it had the highest positive correlation between similarity measure (e.g., MI values) and DC. For automated segmentation, the weighted image fusion of three deformed atlas images with highest MI values provided the highest DC among four proposed strategies.

Conclusion:

MI has the highest correlation with DC, and therefore is an appropriate choice for post‐registration atlas selection in atlas‐based segmentation.

Xuhua Ren and Hao Gao were partially supported by the NSFC (#11405105), the 973 Program (#2015CB856000) and the Shanghai Pujiang Talent Program (#14PJ1404500).