bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐G‐BRA‐15: Dosimetric Evaluation of Dynamic Tumor Tracking Radiation Therapy Using Digital Phantom: A Study On Margin and Desired Accuracy of Tracking
Authors: Uchida T , Kadoya N , Ichiji K , Nakajima Y , Jingu K , Osanai M , Takeda K , Takai Y , Homma N 
Published: July 2016

Purpose:Dynamic tumor tracking radiation therapy can potentially reduce internal margin without prolongation of irradiation time. However, dynamic tumor tracking technique requires an extra margin (tracking margin, TM) for the uncertainty of tumor localization, prediction, and beam repositioning. The purpose of this study was to evaluate a dosimetric impact caused by TM.Methods:We used 4D XCAT to create 9 digital phantom datasets of different tumor size and motion range: tumor diameter TD={1, 3, 5} cm and motion range MR={1, 2, 3} cm. For each dataset, respiratory gating (30%–70% phase) and tumor tracking treatment plans were created using 8‐field 3D‐CRT by 4D dose calculation implemented in RayStation. The dose constraint was based on RTOG0618. For the tracking plan, TMs of {0, 2.5, 5} mm were considered by surrounding a normal setup margin: SM=5 mm. We calculated V20 of normal lung to evaluate the dosimetric impact for each case, and estimated an equivalent TM that affects the same impact on V20 obtained by the gated plan.Results:The equivalent TMs for {TD=1 cm, MR=2 cm}, {TD=1 cm, MR=3 cm}, {TD=5 cm, MR=2 cm}, and {TD=5 cm, MR=3 cm} were estimated as 1.47 mm, 3.95 mm, 1.04 mm, and 2.13 mm, respectively. The larger the tumor size, the equivalent TM became smaller. On the other hand, the larger the motion range, the equivalent TM was found to be increased.Conclusion:Our results showed the equivalent TM changes depending on tumor size and motion range. The tracking plan with TM less than the equivalent TM achieves a dosimetric impact better than the gated plan in less treatment time.This study was partially supported by JSPS Kakenhi and Varian Medical Systems.
SU‐G‐BRA‐17: Tracking Multiple Targets with Independent Motion in Real‐Time Using a Multi‐Leaf Collimator
Authors: Ge Y , Keall P , Poulsen P 
Published: July 2016

Purpose:Multiple targets with large intrafraction independent motion are often involved in advanced prostate, lung, abdominal, and head and neck cancer radiotherapy. Current standard of care treats these with the originally planned fields, jeopardizing the treatment outcomes. A real‐time multi‐leaf collimator (MLC) tracking method has been developed to address this problem for the first time. This study evaluates the geometric uncertainty of the multi‐target tracking method.Methods:Four treatment scenarios are simulated based on a prostate IMAT plan to treat a moving prostate target and static pelvic node target: 1) real‐time multi‐target MLC tracking; 2) real‐time prostate‐only MLC tracking; 3) correcting for prostate interfraction motion at setup only; and 4) no motion correction. The geometric uncertainty of the treatment is assessed by the sum of the erroneously underexposed target area and overexposed healthy tissue areas for each individual target. Two patient‐measured prostate trajectories of average 2 and 5 mm motion magnitude are used for simulations.Results:Real‐time multi‐target tracking accumulates the least uncertainty overall. As expected, it covers the static nodes similarly well as no motion correction treatment and covers the moving prostate similarly well as the real‐time prostate‐only tracking. Multi‐target tracking reduces >90% of uncertainty for the static nodal target compared to the real‐time prostate‐only tracking or interfraction motion correction. For prostate target, depending on the motion trajectory which affects the uncertainty due to leaf‐fitting, multi‐target tracking may or may not perform better than correcting for interfraction prostate motion by shifting patient at setup, but it reduces ∼50% of uncertainty compared to no motion correction.Conclusion:The developed real‐time multi‐target MLC tracking can adapt for the independently moving targets better than other available treatment adaptations. This will enable PTV margin reduction to minimize health tissue toxicity while remain tumor coverage when treating advanced disease with independently moving targets involved.The authors acknowledge funding support from the Australian NHMRC Australia Fellowship and NHMRC Project Grant No. APP1042375.
SU‐G‐206‐05: A Comparison of Head Phantoms Used for Dose Determination in Imaging Procedures
Authors: Xiong Z , Vijayan S , Kilian‐Meneghin J , Rudin S , Bednarek D 
Published: July 2016

Purpose:To determine similarities and differences between various head phantoms that might be used for dose measurements in diagnostic imaging procedures.Methods:We chose four frequently used anthropomorphic head phantoms (SK‐150, PBU‐50, RS‐240T and Alderson Rando), a computational patient phantom (Zubal) and the CTDI head phantom for comparison in our study. We did a CT scan of the head phantoms using the same protocol and compared their dimensions and CT numbers. The scan data was used to calculate dose values for each of the phantoms using EGSnrc Monte Carlo software. An .egsphant file was constructed to describe these phantoms using a Visual C++ program for DOSXYZnrc/EGSnrc simulation. The lens dose was calculated for a simulated CBCT scan using DOSXYZnrc/EGSnrc and the calculated doses were validated with measurements using Gafchromic film and an ionization chamber. Similar calculations and measurements were made for PA radiography to investigate the attenuation and backscatter differences between these phantoms. We used the Zubal phantom as the standard for comparison since it was developed based on a CT scan of a patient.Results:The lens dose for the Alderson Rando phantom is around 9% different than the Zubal phantom, while the lens dose for the PBU‐50 phantom was about 50% higher, possibly because its skull thickness and the density of bone and soft tissue are lower than anthropometric values. The lens dose for the CTDI phantom is about 500% higher because of its totally different structure. The entrance dose profiles are similar for the five anthropomorphic phantoms, while that for the CTDI phantom was distinctly different.Conclusion:The CTDI and PBU‐50 head phantoms have substantially larger lens dose estimates in CBCT. The other four head phantoms have similar entrance dose with backscatter hence should be preferred for dose measurement in imaging procedures of the head.Partial support from NIH Grant R01‐EB002873 and Toshiba Medical Systems Corp.
SU‐G‐206‐11: The Effect of Table Height On CTDIvol and SSDE in CT Scanning: A Phantom Study
Authors: Marsh R , Silosky M 
Published: July 2016

Purpose:Localizer projection radiographs acquired prior to CT scans are used to estimate patient size, affecting the function of Automatic Tube Current Modulation (ATCM) and calculation of the Size Specific Dose Estimate (SSDE). Due to geometric effects, the projected patient size varies with scanner table height and with the orientation of the localizer (AP versus PA). Consequently, variations in scanner table height may affect both CTDIvol and the calculated size‐corrected dose index (SSDE). This study sought to characterize these effects.Methods:An anthropomorphic phantom was imaged using an AP localizer, followed by a diagnostic scan using ATCM and our institution's routine abdomen protocol. This was repeated at various scanner table heights, recording the scanner‐reported CTDIvol for each diagnostic scan. The width of the phantom was measured from the localizer and diagnostic images using in‐house software. The measured phantom width and scanner‐reported CTDIvol were used to calculate SSDE. This was repeated using PA localizers followed by diagnostic scans.Results:1) The localizer‐based phantom width varied by up to 54% of the nominal phantom width between minimum and maximum table heights. 2) Changing the table height caused a variation in scanner‐reported CTDIvol of a factor greater than 4.6 when using a PA localizer and almost 2 when using an AP localizer. 3) SSDE, calculated from measured phantom size and scanner‐reported CTDIvol, varied by a factor of more than 2.8 when using a PA localizer and almost 1.5 when using an AP localizer.Conclusion:Our study demonstrates that off‐center patient positioning affects the efficacy of ATCM, more severely when localizers are acquired in the PA rather than AP projection. Further, patient positioning errors can cause a large variation in the calculated SSDE. This hinders interpretation of SSDE for individual patients and aggregate SSDE data when evaluating CT protocols and clinical practices.
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.