bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐G‐206‐15: Effects of Dose Reduction On Emphysema Score
Authors: Lo P , Young S , Hoffman J , Wahi‐Anwar M , Kim H , McNitt‐Gray M
Published: July 2016

Purpose:

The purpose of this study was to investigate the effects of reducing radiation dose levels on emphysema scores from lung cancer screening CT exams.

Methods:

52 cases were selected from the National Lung Screening Trial (NLST) patients for which we had both the image series and the raw CT data. All scans were acquired with fixed effective mAs (25 for standard‐sized patients, 40 for large patients) on a 64‐slice scanner (Sensation 64, Siemens Healthcare) using 120kV, 64×0.6mm collimation and pitch 1.0. All images were reconstructed with 1mm slice thickness, B50 kernel. Based on a previously‐published technique, we added noise to the raw data to simulate reduced‐dose versions at 50% and 25% of the original dose (approximately 1.0‐ and 0.5‐mGy CTDIvol). Lung segmentations were obtained via region growing from manual seed point at a threshold of 600HU followed by manual removal of trachea and major airways. Lung segmentations were only performed on original dose scans, and mapped to simulated reduced‐dose scans. Emphysema scores based on relative area of lung with attenuation values lower than −950HU (RA950) were computed for all cases.

Results:

Average RA950 of all 50 cases were 31.6 (±5.5), 32.5 (±4.9) and 32.8 (±4.6) for 100%, 50% and 25% dose level respectively. The average absolute difference in RA950 between simulated and original dose scans were 1.0 (±0.7) and 1.4 (±1.1) for 50% and 25% dose level respectively.

Conclusion:

RA950 is relatively robust to dose level, with a difference of no more than 5 from the original dose scans. The average RA950 of this population was high for a two reasons: This was a high risk population of patients with substantial smoking history; The use of B50 kernel, which may be biased towards high emphysema scores. Further exploration with smoother kernels will be conducted in the future.

Institutional research agreement, Siemens Healthcare; Past recipient, research grant support, Siemens Healthcare; Consultant, Toshiba America Medical Systems; Consultant, Samsung Electronics; NIH grant support from U01 CA181156
SU‐G‐206‐16: Investigation of Dosimetric Consequence Via Cone‐Beam CT Based Dose Reconstruction in Hepatocellular Carcinoma Radiotherapy
Authors: Huang P , Li H , Chen J , Ma C , Gang Y , Qin S , Yin Y , Li D
Published: July 2016

Purpose:

Many patients with technically unresectable or medically inoperable hepatocellular carcinoma (HCC) had hepatic dosimetric variations as a result of inter‐fraction anatomical deformation. This study was conducted to assess the hepatic dosimetric consequences via reconstructing weekly dose in HCC patients receiving three dimensional conformal radiation therapy.

Methods:

Twenty‐one HCC patients with 21 planning CT (pCT) scans and 63 weekly Cone‐beam CT (CBCT) scans were enrolled in this investigation. Among them, six patients had been diagnosed of radiation induced liver disease (RILD) and the other fifteen patients had good prognosis after treatment. And each patient had three weekly CBCT before re‐planning. In reconstructing CBCT‐based weekly dose, we registered pCT to CBCT to provide the correct Hounsfield units for the CBCT using gradient‐based deformable image registration (DIR), and this modified CBCT (mCBCT) were introduced to enable dose calculation.To obtain the weekly dosimetric consequences, the initial plan beam configurations and dose constraints were re‐applied to mCBCT for performing dose calculation, and the mCBCT were extrapolated to 25 fractions. Besides, the manually delineated contour was propagated automatically onto the mCBCT of the new patient by exploiting the deformation vectors field, and the reconstructed weekly dose was mapped back to pCT to understand the dose distribution difference. Also, weekly dosimetric variations were compared with the hepatic radiation tolerance in terms of D50 and Dmean.

Results:

Among the twenty‐one patients, the three weekly D50 increased by 0.7Gy, 5.1Gy and 6.1Gy, respectively, and Dmean increased by 0.9%, 4.7% and 5.5%, respectively. For patients with RILD, the average values of the third weekly D50 and Dmean were both high than hepatic radiation tolerance, while the values of patients without RILD were below.

Conclusion:

The planned dose on pCT was not a real dose to the liver, and the liver overdose increased the risk of RILD.

The author would like to express great thanks to Lei Xing, Daniel S Kapp and Yong Yang in the Stanford University School of Medicine for their valuable suggestions to this work. This work is supported by NSFC(61471226), China Postdoctoral Science Foundation (2015T80739,2014M551949) and research funding from Shandong Province (JQ201516).
SU‐G‐206‐17: RadShield: Semi‐Automated Shielding Design for CT Using NCRP 147 and Isodose Curves
Authors: DeLorenzo M , Rutel I , Yang K , Wu D
Published: July 2016

Purpose:

Computed tomography (CT) exam rooms are shielded more quickly and accurately compared to manual calculations using RadShield, a semi‐automated diagnostic shielding software package. Last year, we presented RadShield's approach to shielding radiographic and fluoroscopic rooms calculating air kerma rate and barrier thickness at many points on the floor plan and reporting the maximum values for each barrier. RadShield has now been expanded to include CT shielding design using not only NCRP 147 methodology but also by overlaying vendor provided isodose curves onto the floor plan.

Methods:

The floor plan image is imported onto the RadShield workspace to serve as a template for drawing barriers, occupied regions and CT locations. SubGUIs are used to set design goals, occupancy factors, workload, and overlay isodose curve files. CTDI and DLP methods are solved following NCRP 147. RadShield's isodose curve method employs radial scanning to extract data point sets to fit kerma to a generalized power law equation of the form K(r) = ar^b. RadShield's semiautomated shielding recommendations were compared against a board certified medical physicist's design using dose length product (DLP) and isodose curves.

Results:

The percentage error found between the physicist's manual calculation and RadShield's semi‐automated calculation of lead barrier thickness was 3.42% and 21.17% for the DLP and isodose curve methods, respectively. The medical physicist's selection of calculation points for recommending lead thickness was roughly the same as those found by RadShield for the DLP method but differed greatly using the isodose method.

Conclusion:

RadShield improves accuracy in calculating air‐kerma rate and barrier thickness over manual calculations using isodose curves. Isodose curves were less intuitive and more prone to error for the physicist than inverse square methods. RadShield can now perform shielding design calculations for general scattering bodies for which isodose curves are provided.
SU‐G‐IeP1‐01: A Novel MRI Post‐Processing Algorithm for Visualization of the Prostate LDR Brachytherapy Seeds and Calcifications Based On B0 Field Inhomogeneity Correction and Hough Transform
Authors: Nosrati R , Soliman A , Owrangi A , Ghugre N , Morton G , Pejovic‐Milic A , Song W
Published: July 2016

Purpose:

This study aims at developing an MRI‐only workflow for post‐implant dosimetry of the prostate LDR brachytherapy seeds. The specific goal here is to develop a post‐processing algorithm to produce positive contrast for the seeds and prostatic calcifications and differentiate between them on MR images.

Methods:

An agar‐based phantom incorporating four dummy seeds (I‐125) and five calcifications of different sizes (from sheep cortical bone) was constructed. Seeds were placed arbitrarily in the coronal plane. The phantom was scanned with 3T Philips Achieva MR scanner using an 8‐channel head coil array. Multi‐echo turbo spin echo (ME‐TSE) and multi‐echo gradient recalled echo (ME‐GRE) sequences were acquired. Due to minimal susceptibility artifacts around seeds, ME‐GRE sequence (flip angle=15; TR/TE=20/2.3/2.3; resolution=0.7×0.7×2mm3) was further processed.The induced field inhomogeneity due to the presence of titaniumencapsulated seeds was corrected using a B0 field map. B0 map was calculated using the ME‐GRE sequence by calculating the phase difference at two different echo times. Initially, the product of the first echo and B0 map was calculated. The features corresponding to the seeds were then extracted in three steps: 1) the edge pixels were isolated using “Prewitt” operator; 2) the Hough transform was employed to detect ellipses approximately matching the dimensions of the seeds and 3) at the position and orientation of the detected ellipses an ellipse was drawn on the B0‐corrected image.

Results:

The proposed B0‐correction process produced positive contrast for the seeds and calcifications. The Hough transform based on Prewitt edge operator successfully identified all the seeds according to their ellipsoidal shape and dimensions in the edge image.

Conclusion:

The proposed post‐processing algorithm successfully visualized the seeds and calcifications with positive contrast and differentiates between them according to their shapes. Further assessments on more realistic phantoms and patient study are required to validate the outcome.
SU‐G‐IeP1‐03: Comparing Arterial Input Function Measurements in DCE‐MRI Using MOLLI and Phase
Authors: Majtenyi N , Gabrani‐Juma H , Klein R , deKemp RA , Cron G , Nguyen TB , Cameron I
Published: July 2016

Purpose:

To compare two different methods for measuring the arterial input function (AIF) in dynamic contrast‐enhanced (DCE)‐MRI.

Methods:

Five DCE‐MRI experiments were performed on an aqueous DCE‐MRI phantom (Shelley Medical) in a Siemens 3T Trio MRI scanner with 32 channel head coil and clinical DCE‐MRI protocol. MRI signal phase (φ) data were saved for offline processing. T1 relaxation measurements, using a Modified Look‐ Locker Inversion Recovery (MOLLI) pulse sequence, were performed preand post‐DCE. The input flow rate was set to 200 mL/min to mimic blood flow in the human body. The AIF of Gd injection was determined with two different methods. 1. “Phase‐only”: Pre‐injection baseline phase (φ0) was subtracted from phase‐vs‐time [φ(t)]. This quantity, φ(t) – φ0, was then used to compute the AIF. 2. “Phase+MOLLI”: The AIF value during the post‐injection steady‐state washout, denoted AIF(w), was calculated from MOLLI T1s and known relaxivity. Phase during washout was denoted φ(w). The quantity φ(t) – φ(w) was used to compute AIF – AIF(w). The final Phase+MOLLI AIF was then calculated by adding the MOLLI AIF(w). A “gold‐standard” AIF(w) was also obtained by sampling liquid in the input tube port of the phantom post‐DCE, then later measuring T1 with standard inversion recovery (IR). AIF(w) values from Phase‐only, MOLLI, and IR were compared using a two‐tailed paired t‐test.

Results:

AIF(w) from Phase‐only and MOLLI were significantly different (p = 0.04). AIF(w) from MOLLI and IR were the same (p = 0.89). The Phase‐only curve therefore incorrectly estimated AIF(w).

Conclusion:

There is currently no standard method for determining the AIF in DCE‐MRI. This work has shown that a Phase‐only AIF returns incorrect values for the washout portion of the curve. The Phase+MOLLI method could provide a more accurate and reproducible AIF in clinical DCE‐MRI, which could lead to better diagnoses.
SU‐G‐IeP1‐08: MR Geometric Distortion Dependency On Imaging Sequence, Acquisition Orientation and Receiver Bandwidth of a Dedicated 1.5T MR‐Simulator
Authors: Law M , Yuan J , Wong O , Yu S
Published: July 2016

Purpose:

To investigate the 3D geometric distortion of four potential MR sequences for radiotheraptic applications, and its dependency on sequence‐type, acquisition‐orientation and receiver‐bandwidth from a dedicated 1.5T 700mm‐wide bore MR‐simulator (Magnetom‐Aera, Sienmens Healthcare, Erlangen, Germany), using a large customized geometric accuracy phantom.

Methods:

This work studied 3D gradient‐echo (VIBE) and spin‐echo (SPACE) sequences for anatomical imaging; a specific ultra‐short‐TE sequence (PETRA) potentially for bone imaging and MR‐based dosimetry; and a motion‐insensitive sequence (BLADE) for dynamic applications like 4D‐MRI. Integrated geometric‐correction was employed, three orthogonal acquisition‐orientations and up to three receiver‐bandwidths were used, yielding 27 acquisitions for testing (Table 1a).A customized geometric accuracy phantom (polyurethane, MR/CT invisible, W×L×H:55×55×32.5cm3) was constructed and filled with 3892 spherical markers (6mm diameter, MR/CT visible) arranged on a 25mm‐interval 3D isotropic‐grid (Fig.1). The marker positions in MR images were quantitatively calculated and compared against those in the CT‐reference using customized MatLab scripts.

Results:

The average distortion within various diameter‐of‐spherical‐volumes (DSVs) and the usable DSVs under various distortion limits were measured (Tables 1b‐c). It was observed that distortions fluctuated when sequence‐type, acquisition‐orientation or receiver‐bandwidth changed (e.g. within 300mm‐DSV, the lowest/highest average distortions of VIBE were 0.40mm/0.59mm, a 47.5% difference). According to AAPM‐TG66 (<1mm distortion, left‐most column of Table 1c), PETRA (Largest‐DSV:253.9mm) has the potential on brain treatment, while BLADE (Largest‐DSV:207.2mm) may need improvement for thoracic/abdominal applications. The results of VIBE (Largest‐DSVs:294.3mm, the best among tested acquisitions) and SPACE (Largest‐DSVs:267.7mm) suggests their potentials on head and neck applications. These Largest‐DSVs were attained on different acquisition‐orientations and receiver‐bandwidths.

Conclusion:

Geometric distortion was shown to be dependent on sequence‐type, acquisition‐orientation and receiver‐bandwidth. In the experiment, no configuration in any one of these factors could consistently reduce distortion while the others were varying. The distortion analysis result is a valuable guideline for sequence selection and optimization for MR‐aided radiotherapy applications.
SU‐G‐IeP1‐10: Permeability Evaluation of Interstitial Cystitis by DCE‐MRI of the Bladder
Authors: Wu D , Vo J , North J , Towner R , Hurst R
Published: July 2016

Purpose:

Interstitial cystitis (IC) is a chronic and painful condition that can lead to bladder pain syndrome (BPS) in women. IC and BPS have been known to manifest after physiological changes after giving birth. In this project, we pioneered and advanced a new clinical utility using DCE‐MRI to assess bladder permeability. At first IC/BPS perfusion methods were with ratio signal evaluation, we now incorporate pharmacokinetics techniques to allow for further assessment.

Methods:

In this pilot study, female patients and volunteers (IC=4, Control=3) underwent imaging with a clinical GE 3T 750W MRI system. This project was approved by the OUHSC IRB. Multiple TR Images series were acquired. Images were analyzed in the coronal plane at 0‐, 3‐, 6‐, 9‐, 12‐, 15‐, 20‐, 25‐, and 30‐minute intervals. We used a three‐compartmental pharmacokinetic model with these data. The compartments included: a) bladder interior site of injection, b) bladder wall, and c) external psoas muscle. The signal was transformed and corrected for T1‐relaxation based on a multi‐TR exponential regression before pharmacokinetic analysis.

Results:

Significant differences (p<0.05) were detected with relative means for T1 concentration changes (IC/BPS=0.0107, control=0.616) on the outflow between the k13 transfer coefficient, which represents the injection leakage to the external parenchyma. Trend differences (p<0.1) were found in permeability between the bladder injection site to the rim. We also found changes in the kurtosis of the histograms of regional perfusion. No detectable changes were found in the reverse directions for the above compartments (k21, k31).

Conclusion:

We report clinical changes in this pilot study. This study illustrates early detectable evidence for a possible DCE‐MRI tool that can detect permeability differences with pharmacokinetics measurement of k13. These techniques are intended to advance quantitative imaging methods for IC/BPS, per the goals/objectives of the Quantitative Imaging Biomarker Alliance (QIBA) and other AAPM and RSNA initiatives.
SU‐G‐JeP1‐04: Characterization of a High‐Definition Optical Patient Surface Tracking System Across Five Installations
Authors: Smith T , Ayan A , Cochran E , Woollard J , Gupta N
Published: July 2016

Purpose:

To assess the performance of Varian's real‐time, Optical Surface Monitoring System (OSMS) by measuring relative regular and irregular surface detection accuracy in 6 degrees of motion (6DoM), across multiple installations.

Methods:

Varian's Intracranial SRS Package includes OSMS, which utilizes 3 HD camera/projector pods to map a patient surface, track intra‐fraction motion, and gate the treatment beam if motion exceeds a threshold. To evaluate motion‐detection accuracy of OSMS, we recorded shifts of a cube‐shaped phantom on a single Varian TrueBeam linear accelerator as known displacements were performed incrementally across 6DoM. A subset of these measurements was repeated on identical OSMS installations. Phantom motion was driven using the TrueBeam treatment couch, and incremented across ±2cm in steps of 0.1mm, 1mm, and 1cm in the cardinal planes, and across ±40° in steps of 0.1°, 1°, and 5° in the rotational (couch kick) direction. Pitch and Roll were evaluated across ±2.5° in steps of 0.1° and 1°. We then repeated this procedure with a frameless SRS setup with a head phantom in a QFix Encompass mask.

Results:

Preliminary data show OSMS is capable of detecting regular‐surfaced phantom displacement within 0.03±0.04mm in the cardinal planes, and within 0.01±0.03° rotation across all planes for multiple installations. In a frameless SRS setup, OSMS is accurate to within 0.10±0.07mm and 0.04±0.07° across 6DoM. Additionally, a reproducible “thermal drift” was observed during the first 15min of monitoring each day, and characterized by recording displacement of a stationary phantom each minute for 25min. Drift settled after 15min to an average delta of 0.26±0.03mm and 0.38±0.03mm from the initial capture in the Y and Z directions, respectively.

Conclusion:

For both regular surfaces and clinical SRS situations, OSMS exceeds quoted detection accuracy. To reduce error, a warm‐up period should be employed to allow camera/projector pod thermal stabilization.
SU‐G‐TeP2‐10: Feasibility of Newly Designed Applicator for High Dose Rate Brachytherapy Treatment of Patients with Vaginal Vault Recurrence
Authors: Lee V , Huang X , Wong M , Chan M , Chui E , Cheung S , Leung R , Lee K , Law G , Leung K , Tung S , Kwong D
Published: July 2016

Purpose:

To compare the dose of an in‐house 3D‐printed gynecology applicator (TMHGA) for vaginal vault recurrence of corpus cancer patients after operation for high dose rate brachytherapy treatment with commercially available applicators.

Methods:

A newly designed applicator is made from 3D‐printing methods using ABSM30i. The isodose of the applicator is compared with Elekta multi‐channel (MC) applicator and titanium Rotterdam applicator with coupling central tube and vaginal cylinder (RC). Three plans are created using three applicators in a CT set of water phantom. The applicators are anchored using the applicator library and implant library in the Elekta Oncentra treatment planning system (ver.4.5). The rectum is mimicked by creating a 2cm diameter cylinder, with a distance 1mm posteriorly away from the high risk CTV (HR‐CTV). Similarly, the bladder is replicated by a 6cm diameter cylinder with distance 1mm anteriorly from the HR‐CTV. Three plans are all normalized 1.5cm superior, 0.5cm anterior and 0.5cm posterior of the applicator surface. By fixing D90 of HR‐CTV to 6Gy, the D2cc of rectum and bladder of three plans are compared.

Results:

The D2cc of the bladder for using TMHGA is lower than MC and RC by 14.0% and 11.9% respectively. While the D2cc of the rectum for using TMHGA is lower than MC and RC by 18.9% and 12.4% respectively. The total treatment time of TMHGA plan is shorter than MC and RC by 11.2% and 12.9%.

Conclusion:

The applicator created via 3D printing delivers a lower dose to the bladder and the rectum while keeping the same coverage to HR‐CTV as other commercially available applicators. Additionally, the new applicator resulted in a reduction of treatment time, which is always welcome.
SU‐G‐TeP2‐11: Initial Evaluation of a Novel Split‐Filter Dual‐Energy CT for Use in Radiation Oncology
Authors: Miller J , Huang J , Szczykutowicz T , Bayouth J
Published: July 2016

Purpose:

To perform an initial evaluation of a novel split‐filter dual‐energy CT (DECT) system with the goal of understanding the clinical utility and limitations of the system for radiation therapy.

Methods:

Several phantoms were imaged using the split‐filter DECT technique on the Siemens Edge CT scanner using a range of clinically‐relevant doses. The optimum‐contrast reconstruction, the mixed reconstruction, and the monoenergetic reconstructions (ranging from 40 keV to 190 keV) were evaluated. Each image was analyzed for CT number accuracy, uniformity, noise, low‐contrast visibility (LCV), spatial resolution and geometric distortion. For comparison purposes, all parameters were evaluated on 120 kVp single‐energy CT (SECT) scans used for treatment planning, as well as, a sequential‐scan DECT technique for corresponding doses.

Results:

For all DECT reconstructions no observable geometric distortion was found. Both the optimal‐contrast and mixed images demonstrated slight improvements in LCV and noise when compared to the SECT, and slight reductions in CT number accuracy and spatial resolution. The CT numbers trended as expected for the monoenergetic reconstructions, with CT number accuracy within 50 HU for materials of density <2 g/cm3. Spatial resolution increased with energy, and for monoenergetic reconstructions >70 keV the spatial resolution exceeded that of the SECT. The noise in the monoenergetic reconstructions increased with decreasing energy. Thus, the image uniformity, signal‐to‐noise ratio and LCV were diminished at lower energies (70 keV). Applying iterative reconstruction techniques to the low‐energy images reduced noise and improved LCV. The signal‐to‐noise ratio was stable for energies >100 keV.

Conclusion:

The initial commissioning of the novel split‐filter DECT technology demonstrated favorable results for clinical implementation. The mixed reconstruction showed potential as a replacement for the treatment planning SECT. The image parameters for the monoenergetic reconstructions varied appropriately with energy. This work provides an initial understanding of the limitations and potential applications for monoenergetic imaging.
SU‐G‐TeP2‐13: Patient‐Specific Reduction of Range Uncertainties in Proton Therapy by Proton Radiography with a Multi‐Layer Ionization Chamber
Authors: Deffet S , Farace P , Righetto R , Macq B , Vander Stappen F
Published: July 2016

Purpose:

The conversion from Hounsfield units (HU) to stopping powers is a major source of range uncertainty in proton therapy (PT). Our contribution shows how proton radiographs (PR) acquired with a multi‐layer ionization chamber in a PT center can be used for accurate patient positioning and subsequently for patient‐specific optimization of the conversion from HU to stopping powers.

Methods:

A multi‐layer ionization chamber was used to measure the integral depth‐dose (IDD) of 220 MeV pencil beam spots passing through several anthropomorphic phantoms. The whole area of interest was imaged by repositioning the couch and by acquiring a 45×45 mm2 frame for each position. A rigid registration algorithm was implemented to correct the positioning error between the proton radiographs and the planning CT. After registration, the stopping power map obtained from the planning CT with the calibration curve of the treatment planning system was used together with the water equivalent thickness gained from two proton radiographs to generate a phantom‐specific stopping power map.

Results:

Our results show that it is possible to make a registration with submillimeter accuracy from proton radiography obtained by sending beamlets separated by more than 1 mm. This was made possible by the complex shape of the IDD due to the presence of lateral heterogeneities along the path of the beam. Submillimeter positioning was still possible with a 5 mm spot spacing. Phantom specific stopping power maps obtained by minimizing the range error were cross‐verified by the acquisition of an additional proton radiography where the phantom was positioned in a random but known manner.

Conclusion:

Our results indicate that a CT‐PR registration algorithm together with range‐error based optimization can be used to produce a patient‐specific stopping power map.

Sylvain Deffet reports financial funding of its PhD thesis by Ion Beam Applications (IBA) during the confines of the study and outside the submitted work.

Francois Vander Stappen reports being employed by Ion Beam Applications (IBA) during the confines of the study and outside the submitted work.
SU‐G‐TeP2‐14: Universal Function Form for Photon Open Field In‐Water Output Ratio
Authors: Zhou S , Wu Q , Fan Q , Lei Y , Li S , Li X , Ma R , Wang S , Wang X , Zheng D , Zhu X , Enke C
Published: July 2016

Purpose:

In‐Water‐Output‐Ratio (IWOR) plays a significant role in linac‐based radiotherapy treatment planning, linking MUs to delivered radiation dose. For an open rectangular field, IWOR depends on both its width and length, and changes rapidly when one of them becomes small. In this study, a universal functional form is proposed to fit the open field IWOR tables in Varian TrueBeam representative datasets for all photon energies.

Methods:

A novel Generalized Mean formula is first used to estimate the Equivalent Square (ES) for a rectangular field. The formula's weighting factor and power index are determined by collapsing all data points as much as possible onto a single curve in IWOR vs. ES plot. The result is then fitted with a novel universal function IWOR=1+b*Log(ES/10cm)/(ES/10cm)^c via a least‐square procedure to determine the optimal values for parameters b and c. The maximum relative residual error in IWOR over the entire two‐dimensional measurement table with field sizes between 3cm and 40cm is used to evaluate the quality of fit for the function.

Results:

The two‐step fitting strategy works very well in determining the optimal parameter values for open field IWOR of each photon energies in the Varian data‐set. Relative residual error ≤0.71% is achieved for all photon energies (including Flattening‐Filter‐Free modes) with field sizes between 3cm and 40cm. The optimal parameter values change smoothly with regular photon beam quality.

Conclusion:

The universal functional form fits the Varian TrueBeam open field IWOR measurement tables accurately with small relative residual errors for all photon energies. Therefore, it can be an excellent choice to represent IWOR in absolute dose and MU calculations. The functional form can also be used as a QA/commissioning tool to verify the measured data quality and consistency by checking the IWOR data behavior against the function for new photon energies with arbitrary beam quality.
SU‐G‐IeP3‐07: High‐Resolution, High‐Sensitivity Imaging and Quantification of Intratumoral Distributions of Gold Nanoparticles Using a Benchtop L‐Shell XRF Imaging System
Authors: Manohar N , Reynoso F , Diagaradjane P , Krishnan S , Cho S
Published: July 2016

Purpose:

To demonstrate the ability to perform high‐resolution imaging and quantification of sparse distributions of gold nanoparticles (GNPs) within ex vivo tumor samples using a highly‐sensitive benchtop L‐shell x‐ray fluorescence (XRF) imaging system.

Methods:

An optimized L‐shell XRF imaging system was assembled using a tungsten‐target x‐ray source (operated at 62 kVp and 45 mA). The x‐rays were filtered (copper: 0.08 mm & aluminum: 0.04 mm) and collimated (lead: 5 cm thickness, 3 cm aperture diameter) into a cone‐beam in order to irradiate small samples or objects. A collimated (stainless steel: 4 cm thickness, 2 mm aperture diameter) silicon drift detector, capable of 2D translation, was placed at 90° with respect to the beam to acquire XRF/scatter spectra from regions of interest. Spectral processing involved extracting XRF signal from background, followed by attenuation correction using a Compton scatter‐based normalization algorithm. Calibration phantoms with water/GNPs (0 and 0.00001–10 mg/cm3) were used to determine the detection limit of the system at a 10‐second acquisition time. The system was then used to map the distribution of GNPs within a 12×11×2 mm3 slice excised from the center of a GNP‐loaded ex vivo murine tumor sample; a total of 110 voxels (2.65×10−3 cm3) were imaged with 1.3‐mm spatial resolution.

Results:

The detection limit of the current cone‐beam benchtop L‐shell XRF system was 0.003 mg/cm3 (3 ppm). Intratumoral GNP concentrations ranging from 0.003 mg/cm3 (3 ppm) to a maximum of 0.055 mg/cm3 (55 ppm) and average of 0.0093 mg/cm3 (9.3 ppm) were imaged successfully within the ex vivo tumor slice.

Conclusion:

The developed cone‐beam benchtop L‐shell XRF imaging system can immediately be used for imaging of ex vivo tumor samples containing low concentrations of GNPs. With minor finetuning/optimization, the system can be directly adapted for performing routine preclinical in vivo imaging tasks. Supported by NIH/NCI grant R01CA155446

This investigation was supported by NIH/NCI grant R01CA155446.
SU‐G‐IeP3‐08: Image Reconstruction for Scanning Imaging System Based On Shape‐Modulated Point Spreading Function
Authors: Wang Ruixing , Yang LV , Xu Kele , Zhu Li
Published: July 2016

Purpose:

Deconvolution is a widely used tool in the field of image reconstruction algorithm when the linear imaging system has been blurred by the imperfect system transfer function. However, due to the nature of Gaussian‐liked distribution for point spread function (PSF), the components with coherent high frequency in the image are hard to restored in most of the previous scanning imaging system, even the relatively accurate PSF is acquired. We propose a novel method for deconvolution of images which are obtained by using shape‐modulated PSF.

Methods:

We use two different types of PSF ‐ Gaussian shape and donut shape ‐ to convolute the original image in order to simulate the process of scanning imaging. By employing deconvolution of the two images with corresponding given priors, the image quality of the deblurred images are compared. Then we find the critical size of the donut shape compared with the Gaussian shape which has similar deconvolution results. Through calculation of tightened focusing process using radially polarized beam, such size of donut is achievable under same conditions.

Results:

The effects of different relative size of donut and Gaussian shapes are investigated. When the full width at half maximum (FWHM) ratio of donut and Gaussian shape is set about 1.83, similar resolution results are obtained through our deconvolution method. Decreasing the size of donut will favor the deconvolution method. A mask with both amplitude and phase modulation is used to create a donut‐shaped PSF compared with the non‐modulated Gaussian PSF. Donut with size smaller than our critical value is obtained.

Conclusion:

The utility of donutshaped PSF are proved useful and achievable in the imaging and deconvolution processing, which is expected to have potential practical applications in high resolution imaging for biological samples.
SU‐G‐IeP3‐12: Preliminary Report On the Experience of Patient Radiation Dose Monitoring and Tracking Systems; PEMNET, Radimetrics and DoseWatch
Authors: Lin P , Corwin F , Ghita M
Published: July 2016

Purpose:

Three patient radiation dose monitoring and tracking (PRDMT) systems have been in operation at this institution for the past 6 months. There are useful information that should be disseminated to those who are considering installation of PRDMT programs. In addition, there are “problems” uncovered in the process of estimating fluoroscopic “peak” skin dose (PSD), especially, for those patients who received interventional angiographic studies and in conjunction with surgical procedures.

Methods:

Upon exporting the PRDMT data to Microsoft Excel program, the peak skin dose can be estimated by applying various correction factors including; attenuation due to the tabletop and examination mattress, table height, tabletop translation, backscatter, etc. A procedure was established to screen and divide the PRDMT reported radiation dose and estimated PSD to three different levels of threshold to assess the potential skin injuries, to assist patient follow‐up, risk management and provide radiation dosimetry information in case of “Sentinel Event”.

Results:

The Radiation Dose Structured Report (RDSR) was found to be the prerequisite for the PRDMT systems to work seamlessly. And, the geometrical parameters (gantry and table orientation) displayed by the equipment are not necessarily implemented in the “patient centric” manner which could result in a large error in the PSD estimation. Since, the PRDMT systems obtain their pertinent data from the DICOM tags including the polarity (+ and − signs), the geometrical parameters need to be verified.

Conclusion:

PRDMT systems provide a more accurate PSD estimation than previously possible as the air‐kerma‐area dose meter become widely implemented. However, care should be exercised to correctly apply the geometrical parameters in estimating the patient dose. In addition, further refinement is necessary for these software programs to account for all geometrical parameters such as the tabletop translation in the z‐direction in particular.
SU‐G‐IeP3‐13: Real‐Time Patient and Staff Dose Monitoring in Fluoroscopy Guided Interventions
Authors: Vergoossen L , Sailer A , Paulis L , Wildberger J , Jeukens C
Published: July 2016

Purpose:

Interventional radiology procedures involve the use of X‐rays, which can pose a large radiation burden on both patients and staff. Although some reports on radiation dose are available, most studies focus on limited types of procedures and only report patient dose. In our cathlabs a dedicated real‐time patient and staff monitoring system was installed in November 2015. The aim of this study was to investigate the patient and staff dose exposure for different types of interventions.

Methods:

Radiologists involved in fluoroscopy guided interventional radiology procedures wore personal dose meters (PDM, DoseAware, Philips) on their lead‐apron that measured the personal dose equivalent Hp(10), a measure for the effective dose (E). Furthermore, reference PDMs were installed in the C‐arms of the fluoroscopy system (Allura XPer, Philips). Patient dose‐area‐product (DAP) and PDM doses were retrieved from the monitoring system (DoseWise, Philips) for each procedure. A total of 399 procedures performed between November 2015 and February 2016 were analyzed with respect to the type of intervention. Interventions were grouped by anatomy and radiologist position.

Results:

The mean DAP for the different types of interventions ranged from 2.86±2.96 Gycm2 (percutaneous gastrostomy) to 147±178 Gycm2 (aortic repair procedures). The radiologist dose (E) ranged from 5.39±7.38 µSv (cerebral interventions) to 84.7±106 µSv (abdominal interventions) and strongly correlated with DAP (R2=0.83). The E normalized to DAP showed that the relative radiologist dose was higher for interventions in larger body parts (e.g. abdomen) compared to smaller body parts (e.g. head).

Conclusion:

Using a real‐time dose monitoring system we were able to assess the staff and patient dose revealing that the relative staff dose strongly depended on the type of procedure and patient anatomy. This could be explained by the position of the radiologist with respect to the patient and X‐ray tube.

To facilitate this study L Vergoossen received a scholarship from Philips Medical Systems.
SU‐G‐IeP3‐14: Updating Tools for Radiographic Technique Charts
Authors: Walz‐Flannigan A , Lucas J , Buchanan K , Schueler B
Published: July 2016

Purpose:

Manual technique selection in radiography is needed for imaging situations where there is difficulty in proper positioning for AEC, prosthesis, for non‐bucky imaging, or for guiding image repeats. Basic information about how to provide consistent image signal and contrast for various kV and tissue thickness is needed to create manual technique charts, and relevant for physicists involved in technique chart optimization. Guidance on technique combinations and rules‐of‐thumb to provide consistent image signal still in use today are based on measurements with optical density of screen‐film combinations and older generation x‐ray systems. Tools such as a kV‐scale chart can be useful to know how to modify mAs when kV is changed in order to maintain consistent image receptor signal level. We evaluate these tools for modern equipment for use in optimizing proper size scaled techniques.

Methods:

We used a water phantom to measure calibrated signal change for CR and DR (with grid) for various beam energies. Tube current values were calculated that would yield a consistent image signal response. Data was fit to provide sufficient granularity of detail to compose technique‐scale chart. Tissue thickness approximated equivalence to 80% of water depth.

Results:

We created updated technique‐scale charts, providing mAs and kV combinations to achieve consistent signal for CR and DR for various tissue equivalent thicknesses. We show how this information can be used to create properly scaled size‐based manual technique charts.

Conclusion:

Relative scaling of mAs and kV for constant signal (i.e. the shape of the curve) appears substantially similar between film‐screen and CR/DR. This supports the notion that image receptor related differences are minor factors for relative (not absolute) changes in mAs with varying kV. However, as demonstrated creation of these difficult to find detailed technique‐scales are useful tools for manual chart optimization.
SU‐G‐JeP3‐04: Estimating 4D CBCT from Prior Information and Extremely Limited Angle Projections Using Structural PCA and Weighted Free‐Form Deformation
Authors: Harris W , Yin F , Zhang Y , Ren L
Published: July 2016

Purpose:

To investigate the feasibility of using structure‐based principal component analysis (PCA) motion‐modeling and weighted free‐form deformation to estimate on‐board 4D‐CBCT using prior information and extremely limited angle projections for potential 4D target verification of lung radiotherapy.

Methods:

A technique for lung 4D‐CBCT reconstruction has been previously developed using a deformation field map (DFM)‐based strategy. In the previous method, each phase of the 4D‐CBCT was generated by deforming a prior CT volume. The DFM was solved by a motion‐model extracted by global PCA and a free‐form deformation (GMM‐FD) technique, using data fidelity constraint and the deformation energy minimization. In this study, a new structural‐PCA method was developed to build a structural motion‐model (SMM) by accounting for potential relative motion pattern changes between different anatomical structures from simulation to treatment. The motion model extracted from planning 4DCT was divided into two structures: tumor and body excluding tumor, and the parameters of both structures were optimized together. Weighted free‐form deformation (WFD) was employed afterwards to introduce flexibility in adjusting the weightings of different structures in the data fidelity constraint based on clinical interests. XCAT (computerized patient model) simulation with a 30 mm diameter lesion was simulated with various anatomical and respirational changes from planning 4D‐CT to onboard volume. The estimation accuracy was evaluated by the Volume‐Percent‐Difference (VPD)/Center‐of‐Mass‐Shift (COMS) between lesions in the estimated and “ground‐truth” on board 4D‐CBCT.

Results:

Among 6 different XCAT scenarios corresponding to respirational and anatomical changes from planning CT to on‐board using single 30° on‐board projections, the VPD/COMS for SMM‐WFD was reduced to 10.64±3.04%/1.20±0.45mm from 21.72±9.24%/1.80±0.53mm for GMM‐FD. Using 15° orthogonal projections, the VPD/COMS was further reduced to 1.91±0.86%/0.31±0.42mm based on SMM‐WFD.

Conclusion:

Compared to GMM‐FD technique, the SMM‐WFD technique can substantially improve the 4D‐CBCT estimation accuracy using extremely small scan angles to provide ultra‐fast 4D verification.

This work was supported by the National Institutes of Health under Grant No. R01‐CA184173 and a research grant from Varian Medical Systems
SU‐G‐JeP3‐05: Geometry Based Transperineal Ultrasound Probe Positioning for Image Guided Radiotherapy
Authors: Camps S , Verhaegen F , de With P , Fontanarosa D
Published: July 2016

Purpose:

The use of ultrasound (US) imaging in radiotherapy is not widespread, primarily due to the need for skilled operators performing the scans. Automation of probe positioning has the potential to remove this need and minimize operator dependence. We introduce an algorithm for obtaining a US probe position that allows good anatomical structure visualization based on clinical requirements. The first application is on 4D transperineal US images of prostate cancer patients.

Methods:

The algorithm calculates the probe position and orientation using anatomical information provided by a reference CT scan, always available in radiotherapy workflows. As initial test, we apply the algorithm on a CIRS pelvic US phantom to obtain a set of possible probe positions. Subsequently, five of these positions are randomly chosen and used to acquire actual US volumes of the phantom. Visual inspection of these volumes reveal if the whole prostate, and adjacent edges of bladder and rectum are fully visualized, as clinically required. In addition, structure positions on the acquired US volumes are compared to predictions of the algorithm.

Results:

All acquired volumes fulfill the clinical requirements as specified in the previous section. Preliminary quantitative evaluation was performed on thirty consecutive slices of two volumes, on which the structures are easily recognizable. The mean absolute distances (MAD) between actual anatomical structure positions and positions predicted by the algorithm were calculated. This resulted in MAD of 2.4±0.4 mm for prostate, 3.2±0.9 mm for bladder and 3.3±1.3 mm for rectum.

Conclusion:

Visual inspection and quantitative evaluation show that the algorithm is able to propose probe positions that fulfill all clinical requirements. The obtained MAD is on average 2.9 mm. However, during evaluation we assumed no errors in structure segmentation and probe positioning. In future steps, accurate estimation of these errors will allow for better evaluation of the achieved accuracy.
SU‐G‐JeP3‐08: Robotic System for Ultrasound Tracking in Radiation Therapy
Authors: Kuhlemann I , Jauer P , Schweikard A , Ernst F
Published: July 2016

Purpose:

For safe and accurate real‐time tracking of tumors for IGRT using 4D ultrasound, it is necessary to make use of novel, high‐end force‐sensitive lightweight robots designed for human‐machine interaction. Such a robot will be integrated into an existing robotized ultrasound system for non‐invasive 4D live tracking, using a newly developed real‐time control and communication framework.

Methods:

The new KUKA LWR iiwa robot is used for robotized ultrasound real‐time tumor tracking. Besides more precise probe contact pressure detection, this robot provides an additional 7th link, enhancing the dexterity of the kinematic and the mounted transducer. Several integrated, certified safety features create a safe environment for the patients during treatment. However, to remotely control the robot for the ultrasound application, a real‐time control and communication framework has to be developed. Based on a client/server concept, client‐side control commands are received and processed by a central server unit and are implemented by a client module running directly on the robot's controller. Several special functionalities for robotized ultrasound applications are integrated and the robot can now be used for real‐time control of the image quality by adjusting the transducer position, and contact pressure. The framework was evaluated looking at overall real‐time capability for communication and processing of three different standard commands.

Results:

Due to inherent, certified safety modules, the new robot ensures a safe environment for patients during tumor tracking. Furthermore, the developed framework shows overall real‐time capability with a maximum average latency of 3.6 ms (Minimum 2.5 ms; 5000 trials).

Conclusion:

The novel KUKA LBR iiwa robot will advance the current robotized ultrasound tracking system with important features. With the developed framework, it is now possible to remotely control this robot and use it for robotized ultrasound tracking applications, including image quality control and target tracking.
SU‐G‐JeP3‐12: Use of Cone Beam CT and Deformable Image Registration for Assessing Geometrical and Dosimetric Variations During Lung Radiotherapy
Authors: Jurkovic I , Stathakis S , Markovic M , Papanikolaou N , Mavroidis P
Published: July 2016

Purpose:

To assess the value of cone beam CT (CBCT) combined with deformable image registration in estimating the accuracy of the delivered treatment and the suitability of the applied target margins.

Methods:

Two patients with lung tumor were selected. Using their CT images intensity modulated radiation therapy (IMRT) treatment plans were developed to deliver 66Gy to the 95% of the PTV in 2Gy fractions. Using the Velocity AI software, the planning CT of each patient was registered with the fractional CBCT images that were obtained through the course of the treatment. After a CT to CBCT deformable image registration (DIR), the same fractional deformation matrix was used for the deformation of the planned dose distributions, as well as of all the contoured volumes, to each CBCT dataset. The dosimetric differences between the planning target volume (PTV) and various organs at risk (OARs) were recorded and compared.

Results:

CBCT data such as CTV volume change and PTV coverage was analyzed. There was a moderate relationship between volume changes and contouring method (automatic contouring using the DIR transformation vs. manual contouring on each CBCT) for patient #1 (r = 0.49), and a strong relationship for patient #2 (r = 0.83). The average PTV volume coverage from all the CBCT datasets was 91.2% for patient #1 and 95.6% for patient #2.

Conclusion:

Daily setup variations, tumor volume motion and lung deformation due to breathing yield differences in the actual delivered dose distributions versus the planned ones. The results presented indicate that these differences are apparent even with the use of daily IGRT. In certain fractions, the margins used seem to be insufficient to ensure acceptable lung tumor coverage. The observed differences notably depend on the tumor volume size and location. A larger cohort of patient is under investigation to verify those findings.