bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐J‐36: Combining CBCT Dose Into IMRT Treatment Planning
Authors: Grelewicz Z , Wiersma R 
Published: July 2014

Purpose:Cone beam CT (CBCT) is increasingly used in patient setup for IMRT. Daily CBCT may provide effective localization, however, it introduces concern over excessive imaging dose. Previous studies investigated the calculation of excess CBCT dose, however, no study has yet treated this dose as a source of therapeutic radiation, optimized in consideration of PTV and OARs constrains. Here we present a novel combined MV+kV inverse optimization engine to weave the CBCT and MV dose together such that CBCT dose is used for both imaging and therapeutic purposes. This may mitigate some of the excess imaging dose effects of daily CBCT and allow complete evaluation of the CBCT dose prior to treatment.Methods:The EGSnrc Monte Carlo system was used to model a Varian Trilogy CBCT system and 6 MV treatment beam. Using the model, the dose to patient from treatment beam and imaging beam was calculated for ten patients. The standard IMRT objective function was modified to include CBCT dose. Treatment plan optimization using the MOSEK optimization tool was performed retrospectively with and without assuming kV radiation dose from CBCT, assuming one CBCT per fraction.Results:Across ten patients, the CBCT delivered peaks of between .4% and 3.0% of the prescription dose to the PTV, with average CBCT dose to the PTV between .3% and .8%. By including CBCT dose to skin as a constraint during optimization, peak skin dose is reduced by between 1.9% and 7.4%, and average skin dose is reduced by .2% to 3.3%.Conclusions:Pre‐treatment CBCT may deliver a substantial amount of radiation dose to the target volume. By considering CBCT dose to skin at the point of treatment planning, it is possible to reduce patient skin dose from current clinical levels, and to provide patient treatment with the improved accuracy that daily CBCT provides.
SU‐E‐J‐37: Combining Proton Radiography and X‐Ray CT Information to Better Estimate Relative Proton Stopping Power in a Clinical Environment
Authors: CollinsFekete C , Dias M , Doolan P , Hansen David C , Beaulieu L , Seco J 
Published: July 2014

Purpose:In standard proton therapy clinical practice, proton stopping power uncertainties are in the order of 3.5%, which affects the ability of placing the proton Bragg peak at the edge of the tumor. The innovating idea of this project is to approach the uncertainty problem in RSP by using combined information from X‐ray CT and proton radiography along a few beam angles. In addition, this project aims to quantify the systematic error introduced by the theoretical models (Janni, ICRU49, Bischel) for proton stopping power in media.Methods:A 3D phantom of 36 cm3 composed of 9 materials randomly placed is created. Measured RSP values are obtained using a Gammex phantom with a proton beam. Theoretical RSP values are calculated with Beth‐Block equation in combination with three databases (Janni, ICRU49 and Bischel). Clinical RSP errors are simulated by introducing a systematic (1.5%, 2.5%, 3.5%) and a random error (+/−0.5%) to the theoretical RSP. A ray‐tracing algorithm uses each of these RSP tables to calculate energy loss for proton crossing the phantom through various directions. For each direction, gradient descent (GD) method is done on the clinical RSP table to minimize the residual energy difference between the simulation with clinical RSP and with theoretical RSP. The possibility of a systematic material dependent error is investigated by comparing measured RSP to theoretical RSP as calculated from the three models.Results:Using 10,000 iterations on GD algorithm, RSP differences between theoretical values and clinical RSP have converged (<1%) for each error introduced. Results produced with ICRU49 have the smallest average difference (0.021%) to the measured RSP. Janni (1.168%) and Bischel (−0.372%) database shows larger systematic errors.Conclusion:Based on these results, ray‐tracing optimisation using information from proton radiography and X‐ray CT demonstrates a potential to improve the proton range accuracy in a clinical environment.
SU‐E‐J‐41: Computational and Experimental Analysis of Cancer Cell Mechanics in 3D: Intracellular Viscoelasticity and Internal Stresses
Authors: Mak M , Zaman M , Kamm R 
Published: July 2014

Purpose:We develop an integrated multiscale experimental and computational system to bridge the mechanics and kinetics of motors in crosslinked actin‐networks at the molecular scale with cell‐scaled tensional dynamics in 3D. We investigate the intracellular viscoelastic properties of invasive breast cancer cells in a 3D‐matrix with a tunable microfluidic device that enables the generation of flow and gradients as well as co‐culture conditions.Methods:For computational analyses, we use a custom Brownian dynamics model of F‐actin networks with dynamic crosslinking proteins and active myosin motors to simulate internal stress generation and motor‐induced cytoskeletal remodeling. For experimentation, we develop a system that integrates a highly customizable microfluidic device for 3D cell culture with intracellular particle‐tracking microrheology to study intracellular viscoelasticity of cells in 3D.Results:Our results demonstrate that a balance between crosslinker density, actin polymerization and nucleation dynamics, and motor kinetics and density control intracellular morphology and tension. Experimentally, we show that intracellular viscoelasticity appears to be anisotropic and heterogeneous, and we compare the shear moduli of cells in 2D and 3D. Additionally, we show that altered polymerization dynamics lead to altered cytoskeletal morphologies that appear more aggregated, consistent with our simulations that show motorinduced cytoskeletal remodeling when actin assembly and disassembly rates are not sufficiently high.Conclusion:A multiscale approach that bridges molecular‐scaled dynamics with single and multicellular networks in 3D physiological environments can be an enabling method for understanding the physical and mechanical phenomena that govern cell force generation, migration, and cancer invasion and dissemination. By understanding how molecular mechanical mechanisms translate into metastatic behavior of cells, we can then begin to identify in a rigorous manner new therapeutics that target the functional and physical properties of cancer cells. Specifically, our approach allows for the fundamental elements that give rise to intracellular structure and tension to be investigated.
SU‐E‐J‐44: Design a Platform and Phantom Model for Photoacoustic Imaging in Combination with CT
Authors: Sick J , Alsanea F , Rancilio N , Stantz K 
Published: July 2014

Purpose:Our (long‐term) objective is to develop a US manipulator that will provide in situ radiation response and image‐guided therapy for bladder cancer based on photoacoustic molecular imaging.Methods:A platform was devised to provide a reproducible positional frame of reference for targeting anatomic structure between MDCT and US scans, in lieu of CBCT, and to fuse photoacoustic molecular imaging. US and photoacoustic scans are taken of a patient while in the CT scanner and IRMT. Through co‐registration, based on anatomical positions, we identified a common coordinate system to be used in Eclipse. A bladder phantom was constructed to validate anatomical tracking via US and photoacoustic imaging. We tested the platform using phantom model to demonstrate validity once moved from the CT couch to the linear accelerator couch.Results:This platform interlocks with Varian exact couch index points for reproducibility of positioning. Construction from low Z material and sized appropriately to fit in CT/IMRT gantry. Error in conversion from cylindrical coordinates of the manipulator to X, Y, Z coordinates of the treatment couch was less than 1mm. We measured the bladder size in 3 different directions in both Eclipse from the CT and Acuson from US. The error was less than 2mm in all directions. CT and US images were co‐registered in MATLAB. Co‐registration of photoacoustic images is still being developed.Conclusion:For Linear Accelerators without on board imaging, MV portal images are not a viable option for the localization of soft tissue anatomy. We believe our manipulator provides an alternative using US imaging, which will be examined in an upcoming clinical trial. We plan to examine the value of hypoxia guided treatment through photoacoustic imaging during this trial.
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.