bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐57: Dosimetric Impact of Segmentation Differences in the Context of Brain IMRT
Authors: Deeley MA , Cai YC , Archambault J , Hard D , Heitkamp H , Milnes P , Reid M , Wallace HJ , Dawant BM
Published: July 2014

Purpose:

To gauge the dosimetric impact of segmentation differences amongst experts and an automated system for intracranial organs at risk in the presence of large space‐occupying lesions being treated with IMRT.

Methods:

Eight expert raters and a single automated system were used to segment normal tissues of the brain using MR and CT for 20 patients. The expert segmentations were used to generate ground truth estimations. One hundred‐eighty IMRT plans were generated to test impact of segmentation differences on three dosimetric end points: target coverage, dose to ground truth, and dose reported versus dose to ground truth. Several dosimetric figures of merit with guidance from QUANTEC were used quantitate these differences: mean/maximum dose, V45, V54, V59, V64 and D1mL for the normal tissues; min, mean, maximum, and V95 for target coverage.

Results:

We found target coverage was not affected by segmentation differences. Inverse‐planning was also generally robust to segmentation differences and not result in marked over doses to the simulated ground truth structures. Dose reporting discrepancies, however, were commonplace and could be large; that is, the dose reported by the plan compared to that which was the best estimate of true dose, were over or under reported by as much as 30 Gy; one third of maximum doses were under‐ or over‐reported by 2 Gy or more.

Conclusion:

This work indicates that inverse‐planning in the context of large brain lesions may be generally robust to segmentation differences in terms of target coverage and true dose to the normal tissues. Discrepancies in dose reporting of maximum dose were large, could impact treatment decisions, and may contribute to lack of consensus regarding toxicity, especially relating to the brainstem and optic pathway. These results indicate using figures of merit for planning other than the maximum dose, such as the mean and volume doses.
SU‐E‐J‐61: Electrodynamics and Nano‐Scale Fluid Dynamics in Protein Localization of Nuclear Pore Complexes
Authors: Cunningham J , Gatenby R
Published: July 2014

Purpose:

To develop a simulation to catalyze a reevaluation of common assumptions about 3 dimensional diffusive processes and help cell biologists gain a more nuanced, intuitive understanding of the true physical hurdles of protein signaling cascades. Furthermore, to discuss the possibility of intracellular electrodynamics as a critical, unrecognized component of cellular biology and protein dynamics that is necessary for optimal information flow from the cell membrane to the nucleus.

Methods:

The Unity 3D gaming physics engine was used to build an accurate virtual scale model of the cytoplasm within a few hundred nanometers of the nuclear membrane. A cloud of simulated pERK proteins is controlled by the physics simulation, where diffusion is based on experimentally measured values and the electrodynamics are based on theoretical nano‐fluid dynamics. The trajectories of pERK within the cytoplasm and through the 1250 nuclear pores on the nuclear surface is recorded and analyzed.

Results:

The simulation quickly demonstrates that pERKs moving solely by diffusion will rarely locate and come within capture distance of a nuclear pore. The addition of intracellular electrodynamics between charges on the nuclear pore complexes and on pERKs increases the number of successful translocations by allowing the electro‐physical attractive effects to draw in pERKs from the cytoplasm. The effects of changes in intracellular shielding ion concentrations allowed for estimation of the “capture radius” under varying conditions.

Conclusion:

The simulation allows a shift in perspective that is paramount in attempting to communicate the scale and dynamics of intracellular protein cascade mechanics. This work has allowed researchers to more fully understand the parameters involved in intracellular electrodynamics, such as shielding anion concentration and protein charge. As these effects are still far below the spatial resolution of currently available measurement technology this simulation is invaluable to researchers to visualize and study current hypotheses concerning protein dynamics.
SU‐E‐J‐62: Estimating Plausible Treatment Course Dose Distributions by Accounting for Registration Uncertainty and Organ Motion
Authors: Thor M , Saleh Z , Oh JH , Apte A , Muren L , Deasy J
Published: July 2014

Purpose:

Dose accumulation following deformable image registration (DIR) is challenging. In this study, we used a statistical sampling approach, which takes into account both DIR uncertainties and patient‐specific organ motion, to study the distribution of possible true dose distributions.

Methods:

The study included ten patients (six CT scans/patient) treated with radiotherapy for prostate cancer. For each patient, the planned dose was re‐calculated on the repeated geometries, following rigid registration based on fiducial markers. The dose re‐calculated on the first CT served as our snapshot dose distribution (D1) and the average of the first five repeat scans as our treatment course reference dose distribution (Dref). Patient‐specific motion and DIR‐uncertainties, at each voxel in CT1, were assessed using a previously developed DIR performance measure, the distance discordance metric (DDM). To sample the distribution of possible true, predicted dose distributions (Dpred), we resampled D1 by perturbing the location of each voxel with the corresponding DDM. The three dose distribution approaches are compared for the rectum and the bladder.

Results:

The bladder generalized equivalent uniform dose (gEUD) from the averaged Dpred was closer to the gEUDref than to the gEUD1 (difference: 0.6 vs. 1.0 Gy). For both structures, the gEUDpred was higher than the gEUDref, and significantly higher (p≤0.05) for the rectum (average: 50.8 Gy vs. 48.0 Gy).

Conclusion:

We have shown that the bladder gEUD values resulting from our DIR‐uncertainty inclusive dose sampling approach, Dpred, were closer to the gEUD from Dref than the gEUD values from D1. For the rectum, gEUDpred overestimated gEUDref. Theoretically however, gEUDpred values, sampled from DDM uncertainties are more representative of dose uncertainties.
SU‐E‐J‐64: Evaluation of a Commercial EPID‐Based in Vivo Dosimetric System in the Presence of Lung Tissue Heterogeneity
Authors: Gimeno‐Olmos J , Palomo‐Llinares R , Candela‐Juan C , Garcia‐Martinez T , Carmona Meseguer V , Lliso‐Valverde F , Richart‐Sancho J , Ballester F , Perez‐Calatayud J
Published: July 2014

Purpose:

To study the performance of Dosimetry Check (DC), an EPID‐based dosimetry software, which allows performing transit dosimetry, in low density medium, by comparing calculations in‐phantom, and analysing results for 15 lung patients.

Methods:

DC software (v.3.8, pencil beam‐based algorithm) has been tested, for plans (Eclipse v.10.0 TPS) delivered in two Varian Clinac iX equipped with aS1000 EPIDs.In the CIRS lung phantom, comparisons between DC and Eclipse (Acuros) were performed for several plans: (1) four field box; (2) square field delivered in arc mode; (3) RapidArc lung patient plan medially centred; (4) RapidArc lung patient plan centred in one lung. Reference points analysed: P1 (medial point, plans 1–3) and P2 (located inside one lung, plan 4).For fifteen lung patients treated with RapidArc, the isocentre and 9 additional points inside the PTV as well as the gamma passing rate (3%/3mm) for the PTV and at the main planes were studied.

Results:

In‐phantom:P1: Per‐field differences in plan 1: good agreement for AP‐PA fields; discrepancy of 7% for the lateral fields. Global differences (plans 1–3): about 4%, showing a compensating effect of the individual differences.P2: Global difference (plan 4): 15 %. This represents the worst case situation as it is a point surrounded by lung tissue, where the DC pencil beam algorithm is expected to give the greater difference against Acuros.Lung patients: Mean point difference inside the PTV:(5.4±4.2) %. Gamma passing rate inside the PTV:(45±12) %.

Conclusion:

The performance of DC in heterogeneous lung medium was studied with a special phantom and the results for 15 patients were analysed. The found deviations show that even though DC is a highly promising in vivo dosimetry tool, there is a need of incorporating a more accurate algorithm mainly for plans with low density regions involved.
SU‐E‐J‐67: Evaluation of Breathing Patterns for Respiratory‐Gated Radiation Therapy Using Respiration Regularity Index
Authors: Cheong K , Lee M , Kang S , Yoon J , Park S , Hwang T , Kim H , Kim K , Han T , Bae H
Published: July 2014

Purpose:

Despite the importance of accurately estimating the respiration regularity of a patient in motion compensation treatment, an effective and simply applicable method has rarely been reported. The authors propose a simple respiration regularity index based on parameters derived from a correspondingly simplified respiration model.

Methods:

In order to simplify a patient's breathing pattern while preserving the data's intrinsic properties, we defined a respiration model as a power of cosine form with a baseline drift. According to this respiration formula, breathing‐pattern fluctuation could be explained using four factors: sample standard deviation of respiration period, sample standard deviation of amplitude and the results of simple regression of the baseline drift (slope and standard deviation of residuals of a respiration signal. Overall irregularity (δ) was defined as a Euclidean norm of newly derived variable using principal component analysis (PCA) for the four fluctuation parameters. Finally, the proposed respiration regularity index was defined as ρ=ln(1+(1/ δ))/2, a higher ρ indicating a more regular breathing pattern. Subsequently, we applied it to simulated and clinical respiration signals from real‐time position management (RPM; Varian Medical Systems, Palo Alto, CA) and investigated respiration regularity. Moreover, correlations between the regularity of the first session and the remaining fractions were investigated using Pearson's correlation coefficient.

Results:

The respiration regularity was determined based on ρ; patients with ρ<0.3 showed worse regularity than the others, whereas ρ>0.7 was suitable for respiratory‐gated radiation therapy (RGRT). Fluctuations in breathing cycle and amplitude were especially determinative of ρ. If the respiration regularity of a patient's first session was known, it could be estimated through subsequent sessions.

Conclusions:

Respiration regularity could be objectively determined using a respiration regularity index, ρ. Such single‐index testing of respiration regularity can facilitate determination of RGRT availability in clinical settings, especially for free‐breathing cases.

This work was supported by a Korea Science and Engineering Foundation (KOSEF) grant funded by the Korean Ministry of Science, ICT and Future Planning (No. 2013043498).
SU‐E‐J‐70: Feasibility Study of Dynamic Arc and IMRT Treatment Plans Utilizing Vero Treatment Unit and IPlan Planning Computer for SRS/FSRT Brain Cancer Patients
Authors: Huh S , Lee S , Dagan R , Malyapa R , Mendenhall N , Mendenhall W , Ho M , Hough D , Yam M , Li Z
Published: July 2014

Purpose:

To investigate the feasibility of utilizing Dynamic Arc (DA) and IMRT with 5mm MLC leaf of VERO treatment unit for SRS/FSRT brain cancer patients with non‐invasive stereotactic treatments. The DA and IMRT plans using the VERO unit (BrainLab Inc, USA) are compared with cone‐based planning and proton plans to evaluate their dosimetric advantages.

Methods:

The Vero treatment has unique features like no rotational or translational movements of the table during treatments, Dynamic Arc/IMRT, tracking of IR markers, limitation of Ring rotation. Accuracies of the image fusions using CBCT, orthogonal x‐rays, and CT are evaluated less than ∼ 0.7mm with a custom‐made target phantom with 18 hidden targets. 1mm margin is given to GTV to determine PTV for planning constraints considering all the uncertainties of planning computer and mechanical uncertainties of the treatment unit. Also, double‐scattering proton plans with 6F to 9F beams and typical clinical parameters, multiple isocenter plans with 6 to 21 isocenters, and DA/IMRT plans are evaluated to investigate the dosimetric advantages of the DA/IMRT for complex shape of targets.

Results:

3 Groups of the patients are divided: (1) Group A (complex target shape), CI's are same for IMRT, and DGI of the proton plan are better by 9.5% than that of the IMRT, (2) Group B, CI of the DA plans (1.91+/−0.4) are better than cone‐based plan, while DGI of the DA plan is 4.60+/−1.1 is better than cone‐based plan (5.32+/−1.4), (3) Group C (small spherical targets), CI of the DA and cone‐based plans are almost the same.

Conclusion:

For small spherical targets, cone‐based plans are superior to other 2 plans: DS proton and DA plans. For complex or irregular plans, dynamic and IMRT plans are comparable to cone‐based and proton plans for complex targets.
SU‐E‐J‐72: Geant4 Simulations of Spot‐Scanned Proton Beam Treatment Plans
Authors: Kanehira T , Sutherland K , Matsuura T , Umegaki K , Shirato H
Published: July 2014

Purpose:

To evaluate density inhomogeneities which can effect dose distributions for real‐time image gated spot‐scanning proton therapy (RGPT), a dose calculation system, using treatment planning system VQA (Hitachi Ltd., Tokyo) spot position data, was developed based on Geant4.

Methods:

A Geant4 application was developed to simulate spot‐scanned proton beams at Hokkaido University Hospital. A CT scan (0.98 × 0.98 × 1.25 mm) was performed for prostate cancer treatment with three or four inserted gold markers (diameter 1.5 mm, volume 1.77 mm3) in or near the target tumor. The CT data was read into VQA. A spot scanning plan was generated and exported to text files, specifying the beam energy and position of each spot. The text files were converted and read into our Geant4‐based software. The spot position was converted into steering magnet field strength (in Tesla) for our beam nozzle. Individual protons were tracked from the vacuum chamber, through the helium chamber, steering magnets, dose monitors, etc., in a straight, horizontal line. The patient CT data was converted into materials with variable density and placed in a parametrized volume at the isocenter. Gold fiducial markers were represented in the CT data by two adjacent voxels (volume 2.38 mm3). 600,000 proton histories were tracked for each target spot. As one beam contained about 1,000 spots, approximately 600 million histories were recorded for each beam on a blade server. Two plans were considered: two beam horizontal opposed (90 and 270 degree) and three beam (0, 90 and 270 degree).

Results:

We are able to convert spot scanning plans from VQA and simulate them with our Geant4‐based code. Our system can be used to evaluate the effect of dose reduction caused by gold markers used for RGPT.

Conclusion:

Our Geant4 application is able to calculate dose distributions for spot scanned proton therapy.
SU‐E‐J‐79: Internal Tumor Volume Motion and Volume Size Assessment Using 4D CT Lung Data
Authors: Jurkovic I , Stathakis S , Li Y , Patel A , Vincent J , Papanikolaou N , Mavroidis P
Published: July 2014

Purpose:

To assess internal tumor volume change through breathing cycle and associated tumor motion using the 4DCT data.

Methods:

Respiration induced volume change through breathing cycle and associated motion was analyzed for nine patients that were scanned during the different respiratory phases. The examined datasets were the maximum and average intensity projections (MIP and AIP) and the 10 phases of the respiratory cycle. The internal target volume (ITV) was delineated on each of the phases and the planning target volume (PTV) was then created by adding setup margins to the ITV. Tumor motion through the phases was assessed using the acquired 4DCT dataset, which was then used to determine if the margins used for the ITV creation successfully encompassed the tumor in three dimensions.

Results:

Results showed that GTV motion along the superior inferior axes was the largest in all the cases independent of the tumor location and/or size or the use of abdomen compression. The extent of the tumor motion was found to be connected with the size of the GTV. The smallest GTVs exhibited largest motion vector independent of the tumor location. The motion vector size varied through the phases depending on the tumor size and location and it was smallest for phases 20 and 30. The smaller the volume of the delineated GTV, the greater its volume difference through the different respiratory phases was. The average GTV volume change was largest for the phases 60 and 70.

Conclusion:

Even if GTV is delineated using both AIP and MIP datasets, its motion extent will exceed the used margins especially for the very small GTV volumes. When the GTV size is less than 10 cc it is recommended to use fusion of the GTVs through all the phases to create the planning ITV.
SU‐E‐J‐84: Is There a Threshold Limit in the Accuracy of Deformable Image Registration (DIR)? A Validation Study Using Deformable Bladder Phantom with Implanted Markers
Authors: Varadhan R , Hui S , Overbeck C
Published: July 2014

Purpose:

To establish the fundamental relationship between deformation and its causative physical force using a deformable bladder phantom. To ascertain if a threshold limit exists for DIR accuracy, beyond which its applicability in deformed anatomy may be clinically inappropriate.

Methods:

A tissue equivalent deformable bladder phantom with 21 implanted aluminum markers was developed using a viscoelastic polymer with Youngs modulus and physical density properties comparable to human bladder. Applied force on the organ was incrementally varied from 10N to 70N which in turn deforms the organ. DIR accuracy was studied for commercially available algorithms (MIM and Velocity AI) by comparing the centroid (3D vector) of the 21 marker locations at the undeformed CT (ground truth) with synthetically derived marker positions from each target image from DIR.

Results:

The relationship between applied force and both 1D deformation along the axis of applied force (R2 =0.98) and 3D deformation as quantified by the 95 percentile hausdorff distance (R2 =0.96) showed a linear response. The maximum 1D deformation (compression) ranged from 3mm to 28 mm. A threshold limit at 30N (maximum 13mm 1D and 6.8mm 3D deformation) was established beyond which average registration error of 21 markers was ≥ 2mm for all algorithms studied. Utilizing the Reg Refine feature of the MIM software, the marker accuracy beyond 50N improved by 2mm while average marker error using Velocity multipass deformation was ≤3mm up to 50N.

Conclusions:

he accuracy of DIR was evaluated using a tissue equivalent mass and density conserving bladder phantom in the best case scenario using 21 implanted aluminum high contrast markers to improve the accuracy. The limits of applicability of DIR are strongly dependent on the magnitude of deformation. There is a threshold limit beyond which the accuracy of DIR fails for the range of mass and density conserving deformation studied.
SU‐E‐J‐97: Pretreatment Test and Post‐Treatment Evaluation for Iso‐NTCP Dose Guided Adapive Radiotherapy (DGART), Experience with Prostate Cancer Patients Treated with Rectal Balloons
Authors: Yu J , Hardcastle N , Bender E , Jeong K , Xiao Y , Ritter M , Tome' M
Published: July 2014

Purpose:

To explore the feasibility of pretreatment test for iso‐NTCP DGART and to compare the pretreatment test results with post‐treatment evaluations.

Methods:

NTCP here refers to late rectal wall toxicity only and is calculated with the ring rectal wall DVH. Simulation for one time iso‐ NTCP DGART starts after half of the total dose was done for 10 patients to investigate if TCP gains could be achieved. Six patients were treated using a 12‐fraction 4.3Gy technique and four using 16‐fraction 3.63Gy technique. For each of the 12‐fraction cases a VMAT plan was generated in Pinnacle3™ using the daily CT obtained prior to the 6th fraction. A pretreatment simulation was performed using only the first 6 daily CTs. The idea is to add the 6 original plan delivered doses with 6 DGART plan delivered doses by deformable dose accumulation (DDA) on each of the first 6 CTs, resulting in 6 rectal wall doses (RWDs) and NTCPs. The 95% confidence interval (95%CI) for the 6 NTCPs were computed. The posttreatment evaluation was done by: a) copy the DGART plan to 6 CTs for fraction 7–12 and calculate the 6 actual DGART delivered fractional doses; b) sum the 6 actual DGART doses with the 6 original plan delivered doses by DDA on each of the 12 CTs resulting in 12 post‐treatment RWDs and NTCPs; c) boxplot the 12 post‐treatment NTCPs.

Results:

Target dose gain is 0.76–1.93 Gy. The 95%CI widths of the pretreatment tests NTCPs were 1.1–2.7%. For 5 patients, the planned NTCP fell within the 95%CI. For 4 patients, the planned NTCP was lower than the 95%CI lines. Post‐treatment results show that for 7 patients, the upper quartile was within the 95%CI; for 2 patients, the upper quartile were higher than the 95%CI.

Conclusion:

The pretreatment test yields conservative prediction of the actual delivered NTCP.
SU‐E‐J‐98: Radiogenomics: Correspondence Between Imaging and Genetic Features Based On Clustering Analysis
Authors: Harmon S , Wendelberger B , Jeraj R
Published: July 2014

Purpose:

Radiogenomics aims to establish relationships between patient genotypes and imaging phenotypes. An open question remains on how best to integrate information from these distinct datasets. This work investigates if similarities in genetic features across patients correspond to similarities in PET‐imaging features, assessed with various clustering algorithms.

Methods:

[18F]FDG PET data was obtained for 26 NSCLC patients from a public database (TCIA). Tumors were contoured using an in‐house segmentation algorithm combining gradient and region‐growing techniques; resulting ROIs were used to extract 54 PET‐based features. Corresponding genetic microarray data containing 48,778 elements were also obtained for each tumor. Given mismatch in feature sizes, two dimension reduction techniques were also applied to the genetic data: principle component analysis (PCA) and selective filtering of 25 NSCLC‐associated genes‐ofinterest (GOI). Gene datasets (full, PCA, and GOI) and PET feature datasets were independently clustered using K‐means and hierarchical clustering using variable number of clusters (K). Jaccard Index (JI) was used to score similarity of cluster assignments across different datasets.

Results:

Patient clusters from imaging data showed poor similarity to clusters from gene datasets, regardless of clustering algorithms or number of clusters (JImean= 0.3429±0.1623). Notably, we found clustering algorithms had different sensitivities to data reduction techniques. Using hierarchical clustering, the PCA dataset showed perfect cluster agreement to the full‐gene set (JI =1) for all values of K, and the agreement between the GOI set and the full‐gene set decreased as number of clusters increased (JI=0.9231 and 0.5769 for K=2 and 5, respectively). K‐means clustering assignments were highly sensitive to data reduction and showed poor stability for different values of K (JIrange: 0.2301–1).

Conclusion:

Using commonly‐used clustering algorithms, we found poor agreement in patient characterization from genomic versus imaging data. Interpretation of radiogenomic associations was found to be dependent on clustering algorithms and sensitive to data reduction techniques.
SU‐E‐J‐99: Reconstruction of Cone Beam CT Image Using Volumetric Modulated Arc Therapy Exit Beams
Authors: Jeong K , Kuo H , Goddard L , Savacool M , Basavatia A , Hong L , Yaparpalvi R , Mynampati D , Godoy Scripes P , Kalnicki S , Tome' W
Published: July 2014

Purpose:

To test the possibility of obtaining an image of the treated volume during volumetric modulated arc therapy (VMAT) with exit beams.

Method:

Using a Varian Clinac 21EX and MVCT detector the following three sets of detector projection data were obtained for cone beam CT reconstruction with and without a Catphan 504 phantom. 1) 72 projection images from 20 × 16 cm^2 open beam with 3 MUs, 2) 72 projection images from 20 × 16 cm^2 MLC closed beam with 14 MUs. 3) 137 projection images from a test RapicArc QA plan. All projection images were obtained in ‘integrated image’ mode. We used OSCaR code to reconstruct the cone beam CT images. No attempts were made to reduce scatter or artifacts.

Results:

With projection set 1) we obtained a good quality MV CBCT image by optimizing the reconstruction parameters. Using projection set 2) we were not able to obtain a CBCT image of the phantom, which was determined to be due to the variation of interleaf leakage with gantry angle. From projection set 3), we were able to obtain a weak but meaningful signal in the image, especially in the target area where open beam signals were dominant. This finding suggests that one might be able to acquire CBCT images with rough body shape and some details inside the irradiated target area.

Conclusion:

Obtaining patient images using the VMAT exit beam is challenging but possible. We were able to determine sources of image degradation such as gantry angle dependent interleaf leakage and beams with a large scatter component. We are actively working on improving image quality.
SU‐E‐J‐100: Reconstruction of Prompt Gamma Ray Three Dimensional SPECT Image From Boron Neutron Capture Therapy(BNCT)
Authors: Yoon D , Jung J , Suh T
Published: July 2014

Purpose:

Purpose of paper is to confirm the feasibility of acquisition of three dimensional single photon emission computed tomography (SPECT) image from boron neutron capture therapy (BNCT) using Monte Carlo simulation.

Methods:

In case of simulation, the pixelated SPECT detector, collimator and phantom were simulated using Monte Carlo n particle extended (MCNPX) simulation tool. A thermal neutron source (<1 eV) was used to react with the boron uptake region (BUR) in the phantom. Each geometry had a spherical pattern, and three different BURs (A, B and C region, density: 2.08 g/cm3) were located in the middle of the brain phantom. The data from 128 projections for each sorting process were used to achieve image reconstruction. The ordered subset expectation maximization (OSEM) reconstruction algorithm was used to obtain a tomographic image with eight subsets and five iterations. The receiver operating characteristic (ROC) curve analysis was used to evaluate the geometric accuracy of reconstructed image.

Results:

The OSEM image was compared with the original phantom pattern image. The area under the curve (AUC) was calculated as the gross area under each ROC curve. The three calculated AUC values were 0.738 (A region), 0.623 (B region), and 0.817 (C region). The differences between length of centers of two boron regions and distance of maximum count points were 0.3 cm, 1.6 cm and 1.4 cm.

Conclusion:

The possibility of extracting a 3D BNCT SPECT image was confirmed using the Monte Carlo simulation and OSEM algorithm. The prospects for obtaining an actual BNCT SPECT image were estimated from the quality of the simulated image and the simulation conditions. When multiple tumor region should be treated using the BNCT, a reasonable model to determine how many useful images can be obtained from the SPECT could be provided to the BNCT facilities.

This research was supported by the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, Information and Communication Technologies (ICT) and Future Planning (MSIP)(Grant No.200900420) and the Radiation Technology Research and Development program (Grant No.2013043498), Republic of Korea.
SU‐E‐J‐118: Verification of Intrafractional Positional Accuracy Using Ultrasound Autoscan Tracking for Prostate Cancer Treatment
Authors: Yu S , Hristov D , Phillips T
Published: July 2014

Purpose:

Transperineal ultrasound imaging is attractive option for imageguided radiation therapy as there is no need to implant fiducials, no extra imaging dose, and real time continuous imaging is possible during treatment. The aim of this study is to verify the tracking accuracy of a commercial ultrasound system under treatment conditions with a male pelvic phantom.

Methods:

A CT and ultrasound scan were acquired for the male pelvic phantom. The phantom was then placed in a treatment mimicking position on a motion platform. The axial and lateral tracking accuracy of the ultrasound system were verified using an independent optical tracking system. The tracking accuracy was evaluated by tracking the phantom position detected by the ultrasound system, and comparing it to the optical tracking system under the conditions of beam on (15 MV), beam off, poor image quality with an acoustic shadow introduced, and different phantom motion cycles (10 and 20 second periods). Additionally, the time lag between the ultrasound‐detected and actual phantom motion was investigated.

Results:

Displacement amplitudes reported by the ultrasound system and optical system were within 0.5 mm of each other for both directions and all conditions. The ultrasound tracking performance in axial direction was better than in lateral direction. Radiation did not interfere with ultrasound tracking while image quality affected tracking accuracy. The tracking accuracy was better for periodic motion with 20 second period. The time delay between the ultrasound tracking system and the phantom motion was clinically acceptable.

Conclusion:

Intrafractional prostate motion is a potential source of treatment error especially in the context of emerging SBRT regimens. It is feasible to use transperineal ultrasound daily to monitor prostate motion during treatment. Our results verify the tracking accuracy of a commercial ultrasound system to be better than 1 mm under typical external beam treatment conditions.
SU‐E‐J‐130: ViewRay Real‐Time Imaging of a Motion Phantom and In‐Vivo Canine Patients
Authors: Saenz D , Bayouth J , Christensen N , Henzler M , Forrest L , Paliwal B
Published: July 2014

Purpose:

To test the sub‐second imaging achieved with ViewRay for accuracy and ability to track real‐time target motion during treatment delivery.

Methods:

A motion phantom incorporating MR compatibility was designed using the QUASAR Respiratory Motion Phantom. A silicon di‐electric gel poured into a cylindrical shape was used as the target, connected to the motor via a rod. The target was driven with a sinusoidal trajectory of 20 mm amplitude. The cycle length was varied from 3 to 9 seconds per cycle. Images were acquired in the sagittal plane every 0.25 seconds and processed in MATLAB. Morphological‐based automatic contouring identified the target through intensity thresholds and smoothing via erosion and dilation on each frame. The trajectory, y(n), was plotted using the centroid of each contour as an estimate of position and was fitted to a sinusoidal curve with four fitting parameters. The resultant amplitude, angular frequency, and cross‐sectional area were compared with the expected quantity. Motion tracking was also tested in canine patients. Both automatic and manual contouring on each frame was used to obtain a trajectory.

Results:

The average measured amplitude over each trajectory was 20.3±0.1mm, within 2% of the known amplitude. The expected angular frequency, calculated from 2 π /T, agreed with the measured value within 2% for each trajectory. The average recorded cross‐sectional area was 3.9±0.2 cm². which matches with the expected 3.9 cm². Finally, the cine images from the canine study had sufficient image quality to quantify motion and track target trajectories.

Conclusion:

Over the range of cycle lengths representing a wide range of breathing rates in patients, very good agreement was observed between the expected and measured target trajectory. Clinically relevant quantitative motion data can be extracted from the cine images.
SU‐E‐J‐140: Availability of Using Diaphragm Matching in Stereotactic Body Radiotherapy (SBRT) at the Time in Breath‐Holding SBRT for Liver Cancer
Authors: Kawahara D , Ozawa S , Nakashima T. , Aita M. , Tsuda S. , Ochi Y. , Okumura T. , Masuda H. , Ohno Y. , Kimura T. , Nagata Y.
Published: July 2014

Purpose:

IGRT based on the bone matching may produce a larger target positioning error in terms of the reproducibility of the expiration breath hold. Therefore, the feasibility of the 3D image matching between planning CT image and pretreatment CBCT image based on the diaphragm matching was investigated.

Methods:

In fifteen‐nine liver SBRT cases, Lipiodol, uptake after TACE was outlined as the marker of the tumor. The relative coordinate of the isocenter obtained by the contrast matching was defined as the reference coordinate. The target positioning difference between diaphragm matching and bone matching were evaluated by the relative coordinate of the isocenter from the reference coordinate obtained by each matching technique. In addition, we evaluated PTV margins by van Herk setup margin formula.

Results:

The target positioning error by the diaphragm matching and the bone matching was 1.31±0.83 and 3.10±2.80 mm in the cranial‐caudal(C‐C) direction, 1.04±0.95 and 1.62±1.02 mm in the anterior‐posterior(A‐P) direction, 0.93±1.19 and 1.12±0.94 mm in the left‐right(L‐R) direction, respectively. The positioning error by the diaphragm matching was significantly smaller than the bone matching in the C‐C direction (p<0.05). The setup margin of diaphragm matching and bone matching that we had calculated based on van Herk margin formula was 4.5mm and 6.2mm(C‐C), and 3.6mm and 6.3mm(A‐P), and 2.6mm and 4.5mm(L‐R), respectively.

Conclusion:

IGRT based on a diaphragm matching could be one alternative image matching technique for the positioning of the patients with liver tumor.
SU‐E‐J‐142: Performance Study of Automatic Image‐Segmentation Algorithms in Motion Tracking Via MR‐IGRT
Authors: Feng Y , Kawrakow I , Olsen J. , Parikh P. , Noel C , Wooten H , Du D , Dempsey J , Mutic S , Hu Y
Published: July 2014

Purpose:

Evaluate commonly used segmentation algorithms on a commercially available real‐time MR image guided radiotherapy (MR‐IGRT) system (ViewRay), compare the strengths and weaknesses of each method, with the purpose of improving motion tracking for more accurate radiotherapy.

Methods:

MR motion images of bladder, kidney, duodenum, and liver tumor were acquired for three patients using a commercial on‐board MR imaging system and an imaging protocol used during MR‐IGRT. A series of 40 frames were selected for each case to cover at least 3 respiratory cycles. Thresholding, Canny edge detection, fuzzy k‐means (FKM), k‐harmonic means (KHM), and reaction‐diffusion level set evolution (RD‐LSE), along with the ViewRay treatment planning and delivery system (TPDS) were included in the comparisons. To evaluate the segmentation results, an expert manual contouring of the organs or tumor from a physician was used as a ground‐truth. Metrics value of sensitivity, specificity, Jaccard similarity, and Dice coefficient were computed for comparison.

Results:

In the segmentation of single image frame, all methods successfully segmented the bladder and kidney, but only FKM, KHM and TPDS were able to segment the liver tumor and the duodenum. For segmenting motion image series, the TPDS method had the highest sensitivity, Jarccard, and Dice coefficients in segmenting bladder and kidney, while FKM and KHM had a slightly higher specificity. A similar pattern was observed when segmenting the liver tumor and the duodenum. The Canny method is not suitable for consistently segmenting motion frames in an automated process, while thresholding and RD‐LSE cannot consistently segment a liver tumor and the duodenum.

Conclusion:

The study compared six different segmentation methods and showed the effectiveness of the ViewRay TPDS algorithm in segmenting motion images during MR‐IGRT. Future studies include a selection of conformal segmentation methods based on image/organ‐specific information, different filtering methods and their influences on the segmentation results.

Parag Parikh receives research grant from ViewRay.

Sasa Mutic has consulting and research agreements with ViewRay.

Yanle Hu receives travel reimbursement from ViewRay.

Iwan Kawrakow and James Dempsey are ViewRay employees.
SU‐E‐J‐150: Impact of Intrafractional Prostate Motion On the Accuracy and Efficiency of Prostate SBRT Delivery: A Retrospective Analysis of Prostate Tracking Log Files
Authors: Xiang H , Qureshi M , De Armas R , Hirsch A , Katz M , Nicholas B , Keohan S , Lu H , Efstathiou J , Zietman A , Willins J , Kachnic J
Published: July 2014

Purpose:

To measure intrafractional prostate motion by time‐based stereotactic x‐ray imaging and investigate the impact on the accuracy and efficiency of prostate SBRT delivery.

Methods:

Prostate tracking log files with 1,892 x‐ray image registrations from 18 SBRT fractions for 6 patients were retrospectively analyzed. Patient setup and beam delivery sessions were reviewed to identify extended periods of large prostate motion that caused delays in setup or interruptions in beam delivery. The 6D prostate motions were compared to the clinically used PTV margin of 3–5 mm (3 mm posterior, 5 mm all other directions), a hypothetical PTV margin of 2–3 mm (2 mm posterior, 3 mm all other directions), and the rotation correction limits (roll ±2°, pitch ±5° and yaw ±3°) of CyberKnife to quantify beam delivery accuracy.

Results:

Significant incidents of treatment start delay and beam delivery interruption were observed, mostly related to large pitch rotations of ≥±5°. Optimal setup time of 5–15 minutes was recorded in 61% of the fractions, and optimal beam delivery time of 30–40 minutes in 67% of the fractions. At a default imaging interval of 15 seconds, the percentage of prostate motion beyond PTV margin of 3–5 mm varied among patients, with a mean at 12.8% (range 0.0%–31.1%); and the percentage beyond PTV margin of 2–3 mm was at a mean of 36.0% (range 3.3%–83.1%). These timely detected offsets were all corrected real‐time by the robotic manipulator or by operator intervention at the time of treatment interruptions.

Conclusion:

The durations of patient setup and beam delivery were directly affected by the occurrence of large prostate motion. Frequent imaging of down to 15 second interval is necessary for certain patients. Techniques for reducing prostate motion, such as using endorectal balloon, can be considered to assure consistently higher accuracy and efficiency of prostate SBRT delivery.
SU‐E‐J‐158: Experimental Investigation of Proton Radiography Based On Time‐Resolved Dose Measurements
Authors: Testa M , Doolan P , H Bentefour E , Paganetti H , Lu H‐M
Published: July 2014

Purpose:

To use proton radiography for i) in‐vivo range verification of the brain fields of medulloblastoma patients in order to reduce the exit dose to the cranial skin and thus the risk of permanent alopecia; ii) for performing patient specific optimization of the calibration from CT‐Hounsfield units to proton relative stopping power in order to minimize uncertainties of proton rang

Methods:

We developed and tested a prototype proton radiography system based on a single‐plane scintillation screen coupled with a fast CCD camera (1ms sampling rate, 0.29×0.29 mm2 pixel size, 30×30 cm2 field of view). The method is based on the principle that, for passively scattered beams, the radiological depth of any point in the plateau of a spread‐out Bragg‐Peak (SOBP) can be inferred from the time‐pattern of the dose rate measurements. We performed detector characterization measurements using complex‐shape homogeneous phantoms and an Alderson phanto

Results:

Detector characterization tests confirmed the robustness of the technique. The results of the phantom measurements are encouraging in terms of achievable accuracy of the water equivalent thickness. A technique to minimize the degradation of spatial resolution due to multiple Coulomb scattering is discussed. Our novel radiographic technique is rapid (100 ms) and simultaneous over the whole field. The dose required to produce one radiograph, with the current settings, is ∼3 cG

Conclusion:

The results obtained with this simple and innovative radiography method are promising and motivate further development of technique. The system requires only a single‐plane 2D dosimeter and it uses the clinical beam for a fraction of second with low dose to the patient
SU‐E‐J‐159: Intra‐Patient Deformable Image Registration Uncertainties Quantified Using the Distance Discordance Metric
Authors: Saleh Z , Thor M , Apte A , Sharp G , Muren L , Deasy J
Published: July 2014

Purpose:

The quantitative evaluation of deformable image registration (DIR) is currently challenging due to lack of a ground truth. In this study we test a new method proposed for quantifying multiple‐image based DIRrelated uncertainties, for DIR of pelvic images.

Methods:

19 patients were analyzed, each with 6 CT scans, who previously had radiotherapy for prostate cancer. Manually delineated structures for rectum and bladder, which served as ground truth structures, were delineated on the planning CT and each subsequent scan. For each patient, voxel‐by‐voxel DIR‐related uncertainties were evaluated, following B‐spline based DIR, by applying a previously developed metric, the distance discordance metric (DDM; Saleh et al., PMB (2014) 59:733). The DDM map was superimposed on the first acquired CT scan and DDM statistics were assessed, also relative to two metrics estimating the agreement between the propagated and the manually delineated structures.

Results:

The highest DDM values which correspond to greatest spatial uncertainties were observed near the body surface and in the bowel due to the presence of gas. The mean rectal and bladder DDM values ranged from 1.1–11.1 mm and 1.5–12.7 mm, respectively. There was a strong correlation in the DDMs between the rectum and bladder (Pearson R = 0.68 for the max DDM). For both structures, DDM was correlated with the ratio between the DIR‐propagated and manually delineated volumes (R = 0.74 for the max rectal DDM). The maximum rectal DDM was negatively correlated with the Dice Similarity Coefficient between the propagated and the manually delineated volumes (R= −0.52).

Conclusion:

The multipleimage based DDM map quantified considerable DIR variability across different structures and among patients. Besides using the DDM for quantifying DIR‐related uncertainties it could potentially be used to adjust for uncertainties in DIR‐based accumulated dose distributions.
SU‐E‐J‐163: Suppressing Motion Related Artifacts in 4D‐CT Or 4D‐CBCT Reconstruction Using Projections and Digitally Reconstructed Projections: Proof of Principle
Authors: Yi B , Lasio G , Liu Y , Yu C , Mistry N
Published: July 2014

Purpose:

It has been always challenging to reconstruct good quality 4D‐CT or 4D‐CBCT when the data are under‐sampled for each individual phase. For example, CBCT data is often acquired with limited number of projections and while it is sufficient to reconstruct decent motion averaged images; reconstructing a 4D image from this limited data leads to motion induced artifacts. However, inherent in the projection data are both components that capture the moving and non‐moving parts of the image. In this work, we test the feasibility of using such a dataset to separate out the moving and non‐moving components and then reconstruct individual phase images to acquire a complete 4D reconstruction with reduced artifacts.

Methods:

To test our theory, we simulated a simple 2D+time respiratory phantom, and demonstrated the feasibility using a simple filtered backprojection algorithm along with the proposed motion suppression technique to reconstruct 2D+time images. However, the concepts can be expanded to 3D+time (i.e. 4D) datasets both using conventional CT or CBCT acquisition. The core of the technique rests on separating out the motion components from individual projection data by selecting the minimum intensity between projections and digitally reconstructed projections. This information is then later added back into the final images reconstructed at each individual phase to suppress motion artifacts.

Results:

Initial results on a 2D+time simulated phantom proves that severe under‐sampling artifacts can be eliminated and individual phase images can be reconstructed with high fidelity when compared to standard under‐sampled filtered backprojection.

Conclusion:

The technique is successfully demonstrated using simple backprojection, and hence computational complexity is comparable to standard backprojection (for CT) or FDK (for CBCT). Computational complexity will be significantly better when compared to traditional iterative methods that use regularization and penalty functions.

NIH R01CA133539
SU‐E‐J‐164: An Investigation of a Low‐Cost ‘dry’ Optical‐CT Scanning System for 3D Dosimetry
Authors: Bache S , Malcolm J , Adamovics J , Oldham M
Published: July 2014

Purpose:

To characterize and explore the efficacy of a novel low‐cost, lowfluid, broad‐beam optical‐CT system for 3D‐dosimetry in radiochromic Presage dosimeters. Leading current optical‐CT systems incorporate expensive glass‐based telecentric lens technology, and a fluid bath with substantial amounts of fluid (which introduces an inconvenience factor) to minimize refraction artifacts. Here we introduce a novel system which addresses both these limitations by: (1) the use of Fresnel lenses in a telecentric arrangement, and (2) a ‘solid’ fluid bath which dramatically reduces the amount of fluid required for refractive‐index (RI) matching. Materials

Methods:

A fresnel based telecentric optical‐CT system was constructed which expands light from a single red LED source into a nominally parallel beam into which a cubic ‘dry‐tank’ is placed. The drytank consists of a solid polyurethane cube (with the same RI as Presage) but containing a cylindrical cavity (11.5cm diameter × 11cm) into which the dosimeter is placed for imaging. A narrow (1‐3mm) gap between the walls of the dosimeter and dry‐tank is filled with a fluid of similar RI. This arrangement reduces the amount of RI fluid from about 1000cc to 75cc, yielding substantial practical benefit in convenience and cost. The new system was evaluated in direct comparison against Eclipse planning system from a 4‐field parallel‐opposed treatmen

Results:

Gamma calculations of dose from DFOS‐dry system versus Eclipse showed 92% and 97% agreement with 4mm/4% and 5mm/5% criteria, respectively, in the central 80% of dose distribution. Reconstructions showed some edge artifacts, as well as some dose underestimation towards the dosimeter edge.

Conclusion:

The implementation of Fresnel based ‘dry’ optical‐CT for 3Ddosimetry would represent an important advance enhancing costeffectiveness and practical viability. The performance of the prototype presented here is not yet comparable to the state‐of‐the‐art, but shows sufficient promise for further investigation to elevate image quality to match gold‐standard optical‐CT systems.

This work was supported by NIH R01CA100835