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At least 559 records · Page 31

Throughput Estimation of Data Transport Networks From Digital Twin Measurements

Digital twins of networked infrastructures, known as Virtual Infrastructure Twins (VITs), are increasingly used for software development, pre-deployment testing, and design space exploration. While VITs avoid the costs and potential disruptions associated with experiments on operational networks, their throughput measurements are typically not sufficiently accurate for performance profiling of wide-area networks that they emulate. Here, machine learning (ML) methods are developed to transform these inaccurate VIT network throughput measurements to closely match in peak and overall profile of those from a physical testbed or production network. First, a micro kernel network reflecting a physical network is utilized to collect one-time measurements on a host to support this ML transformation. Then, a generic multi-modal ML method is developed to learn a map that transforms measurements from subsequent VITs on the same host to match past, current and follow-on testbed and cloud networks. ML generalization equations are derived to establish its correctness and probabilistically guarantee its generalization accuracy. Experimental results are presented for a variety of VIT hosts with target testbed and cloud networks; they include a case study of a four-site science ecosystem wherein inaccurate convex VIT measurement profiles are transformed into accurate concave profiles of target networks.

97 MATHEMATICS AND COMPUTING↗

Performance-Aligned LLMs for Generating Fast HPC Code

Optimizing scientific software is a difficult task because codebases are often large and complex, and performance can depend upon several factors including the algorithm, its implementation, and hardware among others. Causes of poor performance can originate from disparate sources and be difficult to diagnose. Recent years have seen a multitude of work that use large language models (LLMs) to assist in software development tasks. However, these tools are trained to model the distribution of code as text, and are not specifically designed to understand performance aspects of code. In this work, we introduce a reinforcement learning based methodology to align the outputs of code LLMs with performance. This allows us to build upon the current code modeling capabilities of LLMs and extend them to generate better performing code. Here, we demonstrate that our fine-tuned model improves the expected speedup of generated code over base models for a set of benchmark tasks from 0.9 to 1.6 for serial code and 1.9 to 4.5 for OpenMP parallel code.

Computer science↗

SU-E-J-11: A New Optical Method to Register Patient External Motion

Purpose: To devise and implement a new system to measure and register the patient motion during radiotherapy treatments. Methods: The system can obtain the position of several points in the 3D-space, through their projections in the 2D-images recorded by two cameras. The algorithm needs a series of constants, that are obtained using the images of a calibrated phantom.To test the system, some adhesive labels were placed on the surface of an object. Two cameras recorded the moving object over time. An in-house developed software localized the labels in each image. In the first pair of images, the program used a first approximation given by the user. In the subsequent images, it used the last position as an approximate location. The final exact coordinates of the point were obtained in a two-step process using the contrast of the images. From the 2D-positions of the point in each frame, the 3D-trajectories of each of these marks were obtained.The system was tested with linear displacements, oscillations of a mechanical oscillator, circular trajectories of a rotating disk, and with respiratory motion of a volunteer. Results: Trajectories of several points were reproduced with sub-millimeter accuracy in the three directions of the space. The system was able to follow periodic motion with amplitudes lower than 0.5mm; and trajectories of rotating points at speeds up to 200mm/s. The software could also track accurately the respiration motion of a person. Conclusion: A new, inexpensive optical tracking system for patient motion has been demonstrated. The system detects motion with high accuracy. Installation and calibration of the system is simple and quick. Data collection is not expected to involve any discomfort for the patient, nor any delay for the treatment. The system could be also used as a method of warning for patient movements, and for gating. We acknowledge financial support from Fundacion Mutua Madrilena, Madrid, Spain.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

SU-E-J-190: Characterization of Radiation Induced CT Number Changes in Tumor and Normal Lung During Radiation Therapy for Lung Cancer

Purpose: To measure CT number (CTN) changes in tumor and normal lung as a function of radiation therapy (RT) dose during the course of RT delivery for lung cancer using daily IGRT CT images and single respiration phase CT images. Methods: 4D CT acquired during planning simulation and daily 3D CT acquired during daily IGRT for 10 lung cancer cases randomly selected in terms of age, caner type and stage, were analyzed using an in-house developed software tool. All patients were treated in 2 Gy fractions to primary tumors and involved nodal regions. Regions enclosed by a series of isodose surfaces in normal lung were delineated. The obtained contours along with target contours (GTVs) were populated to each singlephase planning CT and daily CT. CTN in term of Hounsfield Unit (HU) of each voxel in these delineated regions were collectively analyzed using histogram, mean, mode and linear correlation. Results: Respiration induced normal lung CTN change, as analyzed from single-phase planning CTs, ranged from 9 to 23 (±2) HU for the patients studied. Normal lung CTN change was as large as 50 (±12) HU over the entire treatment course, was dose and patient dependent and was measurable with dose changes as low as 1.5 Gy. For patients with obvious tumor volume regression, CTN within the GTV drops monotonically as much as 10 (±1) HU during the early fractions with a total dose of 20 Gy delivered. The GTV and CTN reductions are significantly correlated with correlation coefficient >0.95. Conclusion: Significant RT dose induced CTN changes in lung tissue and tumor region can be observed during even the early phase of RT delivery, and may potentially be used for early prediction of radiation response. Single respiration phase CT images have dramatically reduced statistical noise in ROIs, making daily dose response evaluation possible.

60 APPLIED LIFE SCIENCES↗

SU-E-J-227: Breathing Pattern Consistency and Reproducibility: Comparative Analysis for Supine and Prone Body Positioning

Purpose: Evaluate and compare the cycle-to-cycle consistency of breathing patterns and their reproducibility over the course of treatment, for supine and prone positioning. Methods: Respiratory traces from 25 patients were recorded for sequential supine/prone 4DCT scans acquired prior to treatment, and during the course of the treatment (weekly or bi-weekly). For each breathing cycle, the average(AVE), end-of-exhale(EoE) and end-of-inhale( EoI) locations were identified using in-house developed software. In addition, the mean values and variations for the above quantities were computed for each breathing trace. F-tests were used to compare the cycle-to-cycle consistency of all pairs of sequential supine and prone scans. Analysis of variances was also performed using population means for AVE, EoE and EoI to quantify differences between the reproducibility of prone and supine respiration traces over the treatment course. Results: Consistency: Cycle-to-cycle variations are less in prone than supine in the pre-treatment and during-treatment scans for AVE, EoE and EoI points, for the majority of patients (differences significant at p<0.05). The few cases where the respiratory pattern had more variability in prone appeared to be random events. Reproducibility: The reproducibility of breathing patterns (supine and prone) improved as treatment progressed, perhaps due to patients becoming more comfortable with the procedure. However, variability in supine position continued to remain significantly larger than in prone (p<0.05), as indicated by the variance analysis of population means for the pretreatment and subsequent during-treatment scans. Conclusions: Prone positioning stabilizes breathing patterns in most subjects investigated in this study. Importantly, a parallel analysis of the same group of patients revealed a tendency towards increasing motion amplitude of tumor targets in prone position regardless of their size or location; thus, the choice for body positioning during radiation therapy will have to consider the clinical relevance of the two opposing trends - breathing consistency and motion amplitude.

60 APPLIED LIFE SCIENCES↗

SU-E-J-263: Dosimetric Analysis On Breast Brachytherapy Based On Deformable Image Registration

Purpose: To quantitatively compare and evaluate the dosimetry difference between breast brachytherapy protocols with different fractionation using deformable image registration. Methods: The accumulative dose distribution for multiple breast brachytherapy patients using four different applicators: Contura, Mammosite, Savi, and interstitial catheters, under two treatment protocols: 340cGy by 10 fractions in 5 days and 825cGy by 3 fractions in 2days has been reconstructed using a two stage deformable image registration approach. For all patients, daily CT was acquired with the same slice thickness (2.5mm). In the first stage, the daily CT images were rigidly registered to the initial planning CT using the registration module in Eclipse (Varian) to align the applicators. In the second stage, the tissues surrounding the applicator in the rigidly registered daily CT image were non-rigidly registered to the initial CT using a combination of image force and the local constraint that enforce zero normal motion on the surface of the applicator, using a software developed in house. We calculated the dose distribution in the daily CTs and deformed them using the final registration to convert into the image domain of the initial planning CT. The accumulative dose distributions were evaluated by dosimetry parameters including D90, V150 and V200, as well as DVH. Results: Dose reconstruction results showed that the two day treatment has a significant dosimetry improvement over the five day protocols. An average daily drop of D90 at 1.3% of the prescription dose has been observed on multiple brachytherapy patients. There is no significant difference on V150 and V200 between those two protocols. Conclusion: Brachytherapy with higher fractional dose and less fractions has an improved performance on being conformal to the dose distribution in the initial plan. Elongated brachytherapy treatments need to consider the dose uncertainty caused by the temporal changes of the soft tissue.

60 APPLIED LIFE SCIENCES↗

SU-E-T-314: The Application of Cloud Computing in Pencil Beam Scanning Proton Therapy Monte Carlo Simulation

Purpose: Monte Carlo simulation plays an important role for proton Pencil Beam Scanning (PBS) technique. However, MC simulation demands high computing power and is limited to few large proton centers that can afford a computer cluster. We study the feasibility of utilizing cloud computing in the MC simulation of PBS beams. Methods: A GATE/GEANT4 based MC simulation software was installed on a commercial cloud computing virtual machine (Linux 64-bits, Amazon EC2). Single spot Integral Depth Dose (IDD) curves and in-air transverse profiles were used to tune the source parameters to simulate an IBA machine. With the use of StarCluster software developed at MIT, a Linux cluster with 2–100 nodes can be conveniently launched in the cloud. A proton PBS plan was then exported to the cloud where the MC simulation was run. Results: The simulated PBS plan has a field size of 10×10cm{sup 2}, 20cm range, 10cm modulation, and contains over 10,000 beam spots. EC2 instance type m1.medium was selected considering the CPU/memory requirement and 40 instances were used to form a Linux cluster. To minimize cost, master node was created with on-demand instance and worker nodes were created with spot-instance. The hourly cost for the 40-node cluster was $0.63 and the projected cost for a 100-node cluster was $1.41. Ten million events were simulated to plot PDD and profile, with each job containing 500k events. The simulation completed within 1 hour and an overall statistical uncertainty of < 2% was achieved. Good agreement between MC simulation and measurement was observed. Conclusion: Cloud computing is a cost-effective and easy to maintain platform to run proton PBS MC simulation. When proton MC packages such as GATE and TOPAS are combined with cloud computing, it will greatly facilitate the pursuing of PBS MC studies, especially for newly established proton centers or individual researchers.

07 ISOTOPE AND RADIATION SOURCES↗

SU-E-CAMPUS-T-05: Validation of High-Resolution 3D Patient QA for Proton Pencil Beam Scanning and IMPT by Polymer Gel Dosimetry

Purpose: Validation of high-resolution 3D patient QA for proton pencil beam scanning and IMPT by polymer gel dosimetry. Methods: Four BANG3Pro polymer gel dosimeters (manufactured by MGS Research Inc, Madison, CT) were used for patient QA at the Robert's Proton Therapy Center (RPTC, Philadelphia, PA). All dosimeters were sealed in identical thin-wall Pyrex glass spheres. Each dosimeter contained a set of markers for 3D registration purposes. The dosimeters were mounted in a consistent and reproducible manner using a custom build holder. Two proton pencil beam scanning plans were designed using Varian Eclipse™ treatment planning system: 1) A two-field intensity modulated proton therapy (IMPT) plan and 2) one single field uniform dose (SFUD) plan. The IMPT fields were evaluated as a composite plan and individual fields, the SFUD plan was delivered as a single field plan.Laser CT scanning was performed using the manufacturer's OCTOPUS-IQ axial transmission laser CT scanner using a 1 mm slice thickness. 3D registration, analysis, and OD/cm to absorbed dose calibrations were perfomed using DICOM RT-Dose and CT files, and software developed by the manufacturer. 3D delta index, a metric equivalent to the gamma tool, was used for dose comparison. Results: Very good agreement with single IMPT fields and with SFUD was obtained. Composite IMPT fields had a less satisfactory agreement. The single fields had 3D delta index passing rates (3% dose difference, 3 mm DTA) of 98.98% and 94.91%. The composite 3D delta index passing rate was 80.80%. The SFUD passing rate was 93.77%. Required shifts of the dose distributions were less than 4 mm. Conclusion: A formulation of the BANG3Pro polymer gel dosimeter, suitable for 3D QA of proton patient plans is established and validated. Likewise, the mailed QA analysis service provided by the manufacturer is a practical option when required resources are unavailable. We fully disclose that the subject of this research regards a production of MGS Research, Inc.

60 APPLIED LIFE SCIENCES↗

MO-H-19A-03: Patient Specific Bolus with 3D Printing Technology for Electron Radiotherapy

Purpose: Bolus is widely used in electron radiotherapy to achieve desired dose distribution. 3D printing technologies provide clinicians with easy access to fabricate patient specific bolus accommodating patient body surface irregularities and tissue inhomogeneity. This study presents the design and the clinical workflow of 3D printed bolus for patient electron therapy in our clinic. Methods: Patient simulation CT images free of bolus were exported from treatment planning system (TPS) to an in-house developed software package. Bolus with known material properties was designed in the software package and then exported back to the TPS as a structure. Dose calculation was carried out to examine the coverage of the target. After satisfying dose distribution was achieved, the bolus structure was transferred in Standard Tessellation Language (STL) file format for the 3D printer to generate the machine codes for printing. Upon receiving printed bolus, a quick quality assurance was performed with patient resimulated with bolus in place to verify the bolus dosimetric property before treatment started. Results: A patient specific bolus for electron radiotherapy was designed and fabricated in Form 1 3D printer with methacrylate photopolymer resin. Satisfying dose distribution was achieved in patient with bolus setup. Treatment was successfully finished for one patient with the 3D printed bolus. Conclusion: The electron bolus fabrication with 3D printing technology was successfully implemented in clinic practice.

60 APPLIED LIFE SCIENCES↗

TH-C-BRD-05: Reducing Proton Beam Range Uncertainty with Patient-Specific CT HU to RSP Calibrations Based On Single-Detector Proton Radiography

Purpose: Beam range uncertainty in proton treatment comes primarily from converting the patient's X-ray CT (xCT) dataset to relative stopping power (RSP). Current practices use a single curve for this conversion, produced by a stoichiometric calibration based on tissue composition data for average, healthy, adult humans, but not for the individual in question. Proton radiographs produce water-equivalent path length (WEPL) maps, dependent on the RSP of tissues within the specific patient. This work investigates the use of such WEPL maps to optimize patient-specific calibration curves for reducing beam range uncertainty. Methods: The optimization procedure works on the principle of minimizing the difference between the known WEPL map, obtained from a proton radiograph, and a digitally-reconstructed WEPL map (DRWM) through an RSP dataset, by altering the calibration curve that is used to convert the xCT into an RSP dataset. DRWMs were produced with Plastimatch, an in-house developed software, and an optimization procedure was implemented in Matlab. Tests were made on a range of systems including simulated datasets with computed WEPL maps and phantoms (anthropomorphic and real biological tissue) with WEPL maps measured by single detector proton radiography. Results: For the simulated datasets, the optimizer showed excellent results. It was able to either completely eradicate or significantly reduce the root-mean-square-error (RMSE) in the WEPL for the homogeneous phantoms (to zero for individual materials or from 1.5% to 0.2% for the simultaneous optimization of multiple materials). For the heterogeneous phantom the RMSE was reduced from 1.9% to 0.3%. Conclusion: An optimization procedure has been designed to produce patient-specific calibration curves. Test results on a range of systems with different complexities and sizes have been promising for accurate beam range control in patients. This project was funded equally by the Engineering and Physical Sciences Research Council (UK) and Ion Beam Applications (Louvain-La-Neuve, Belgium)

07 ISOTOPE AND RADIATION SOURCES↗

Time-resolved dosimetry using a pinpoint ionization chamber as quality assurance for IMRT and VMAT

Purpose: To develop a method to verify the dose delivery in relation to the individual control points of intensity modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) using an ionization chamber. In addition to more effective problem solving during patient-specific quality assurance (QA), the aim is to eventually map out the limitations in the treatment chain and enable a targeted improvement of the treatment technique in an efficient way. Methods: Pretreatment verification was carried out for 255 treatment plans that included a broad range of treatment indications in two departments using the equipment of different vendors. In-house developed software was used to enable calculation of the dose delivery for the individual beamlets in the treatment planning system (TPS), for data acquisition, and for analysis of the data. The observed deviations were related to various delivery and measurement parameters such as gantry angle, field size, and the position of the detector with respect to the field edge to distinguish between error sources. Results: The average deviation of the integral fraction dose during pretreatment verification of the planning target volume dose was −2.1% ± 2.2% (1 SD), −1.7% ± 1.7% (1 SD), and 0.0% ± 1.3% (1 SD) for IMRT at the Radboud University Medical Center (RUMC), VMAT (RUMC), and VMAT at the Wellington Blood and Cancer Centre, respectively. Verification of the dose to organs at risk gave very similar results but was generally subject to a larger measurement uncertainty due to the position of the detector at a high dose gradient. The observed deviations could be related to limitations of the TPS beam models, attenuation of the treatment couch, as well as measurement errors. The apparent systematic error of about −2% in the average deviation of the integral fraction dose in the RUMC results could be explained by the limitations of the TPS beam model in the calculation of the beam penumbra. Conclusions: This study showed that time-resolved dosimetry using an ionization chamber is feasible and can be largely automated which limits the required additional time compared to integrated dose measurements. It provides a unique QA method which enables identification and quantification of the contribution of various error sources during IMRT and VMAT delivery.

60 APPLIED LIFE SCIENCES↗

SU-E-J-114: A Practical Hybrid Method for Improving the Quality of CT-CBCT Deformable Image Registration for Head and Neck Radiotherapy

Purpose: Accurate deformable image registration (DIR) between CT and CBCT in H&N is challenging. In this study, we propose a practical hybrid method that uses not only the pixel intensities but also organ physical properties, structure volume of interest (VOI), and interactive local registrations. Methods: Five oropharyngeal cancer patients were selected retrospectively. For each patient, the planning CT was registered to the last fraction CBCT, where the anatomy difference was largest. A three step registration strategy was tested; Step1) DIR using pixel intensity only, Step2) DIR with additional use of structure VOI and rigidity penalty, and Step3) interactive local correction. For Step1, a public-domain open-source DIR algorithm was used (cubic B-spline, mutual information, steepest gradient optimization, and 4-level multi-resolution). For Step2, rigidity penalty was applied on bony anatomies and brain, and a structure VOI was used to handle the body truncation such as the shoulder cut-off on CBCT. Finally, in Step3, the registrations were reviewed on our in-house developed software and the erroneous areas were corrected via a local registration using level-set motion algorithm. Results: After Step1, there were considerable amount of registration errors in soft tissues and unrealistic stretching in the posterior to the neck and near the shoulder due to body truncation. The brain was also found deformed to a measurable extent near the superior border of CBCT. Such errors could be effectively removed by using a structure VOI and rigidity penalty. The rest of the local soft tissue error could be corrected using the interactive software tool. The estimated interactive correction time was approximately 5 minutes. Conclusion: The DIR using only the image pixel intensity was vulnerable to noise and body truncation. A corrective action was inevitable to achieve good quality of registrations. We found the proposed three-step hybrid method efficient and practical for CT/CBCT registrations in H&N. My department receives grant support from Industrial partners: (a) Varian Medical Systems, Palo Alto, CA, and (b) Philips HealthCare, Best, Netherlands.

60 APPLIED LIFE SCIENCES↗

SU-E-T-02: 90Y Microspheres Dosimetry Calculation with Voxel-S-Value Method: A Simple Use in the Clinic

Purpose: To present a simple and feasible method of voxel-S-value (VSV) dosimetry calculation for daily clinical use in radioembolization (RE) with {sup 90}Y microspheres. Dose distributions are obtained and visualized over CT images. Methods: Spatial dose distributions and dose in liver and tumor are calculated for RE patients treated with Sirtex Medical miscrospheres at our center. Data obtained from the previous simulation of treatment were the basis for calculations: Tc-99m maggregated albumin SPECT-CT study in a gammacamera (Infinia, General Electric Healthcare.). Attenuation correction and ordered-subsets expectation maximization (OSEM) algorithm were applied.For VSV calculations, both SPECT and CT were exported from the gammacamera workstation and registered with the radiotherapy treatment planning system (Eclipse, Varian Medical systems). Convolution of activity matrix and local dose deposition kernel (S values) was implemented with an in-house developed software based on Python code. The kernel was downloaded from www.medphys.it. Final dose distribution was evaluated with the free software Dicompyler. Results: Liver mean dose is consistent with Partition method calculations (accepted as a good standard). Tumor dose has not been evaluated due to the high dependence on its contouring. Small lesion size, hot spots in health tissue and blurred limits can affect a lot the dose distribution in tumors. Extra work includes: export and import of images and other dicom files, create and calculate a dummy plan of external radiotherapy, convolution calculation and evaluation of the dose distribution with dicompyler. Total time spent is less than 2 hours. Conclusion: VSV calculations do not require any extra appointment or any uncomfortable process for patient. The total process is short enough to carry it out the same day of simulation and to contribute to prescription decisions prior to treatment. Three-dimensional dose knowledge provides much more information than other methods of dose calculation usually applied in the clinic.

60 APPLIED LIFE SCIENCES↗

SU-E-T-67: A Quality Assurance Procedure for VMAT Delivery Technique with Multiple Verification Metric Using TG-119 Protocol

Purpose: A successful VMAT plan delivery includes precise modulations of dose rate, gantry rotational and multi-leaf collimator shapes. The purpose of this research is to construct routine QA protocol which focuses on VMAT delivery technique and to obtain a baseline including dose error, fluence distribution and mechanical accuracy during VMAT. Methods: The mock prostate, head and neck (HN) cases supplied from AAPM were used in this study. A VMAT plans were generated in Monaco TPS according to TG-119 protocol. Plans were created using 6 MV and 10 MV photon beams for each case. The phantom based measurement, fluence measurement and log files analysis were performed. The dose measurement was performed using 0.6 cc ion chamber, which located at isocenter. The fluence distribution were acquired using the MapCHECK2 mounted in the MapPHAN. The trajectory log files recorded inner 20 leaf pairs and gantry angle positions at every 0.25 sec interval were exported to in-house software developed by MATLAB and determined those RMS values. Results: The dose difference is expressed as a ratio of the difference between measured and planned doses. The dose difference for 6 MV was 0.91%, for 10 MV was 0.67%. In turn, the fluence distribution using gamma criteria of 2%/2 mm with a 50% minimum dose threshold for 6 MV was 98.8%, for 10 MV was 97.5%, respectively. The RMS values of MLC for 6 MV and 10 MV were 0.32 mm and 0.37 mm, of gantry were 0.33 degree and 0.31 degree. Conclusion: In this study, QA protocol to assess VMAT delivery accuracy is constructed and results acquired in this study are used as a baseline of VMAT delivery performance verification.

60 APPLIED LIFE SCIENCES↗

SU-E-T-444: Gravity Effect On Maximum Leaf Speed in Dynamic IMRT Treatments

Purpose: A leaf sequencing algorithm has been recently developed in our department. Our purpose is to utilize this algorithm to reduce treatment time by studying the feasibility of using several maximum leaf speeds depending on gantry angle and leaf thickness (0.5 or 1 cm at isocenter). To do so, the gravity effect on MLC performance has been examined by means of analysing the dynalog files. Methods: Leaf position errors has been ascertained according to gantry angle and leaf speed in MLC Millenium120 (Varian). In order to do this, the following test has been designed: all leaves move in synchrony, with same speed and 1 cm gap between opposite leaves. This test is implemented for 18 different speeds: 0.25-0.5-0.75-1-1.25-1.5-1.75-2-2.1-2.2-2.3-2.4-2.5-2.6-2.7-2.8-2.9-3.0 cm/s and 8 gantry angles: 0-45-90-135-180-225-270-315. Collimator angle is 2 degrees in all cases since it is the most usual one in IMRT treatments in our department. Dynamic tolerance is 2 mm. Dynalogs files of 10 repetitions of the test are analysed with a Mathlab in-house developed software and RMS error and 95th percentiles are calculated. Varian recommends 2.5 cm/s as the maximum leaf speed for its segmentation algorithm. In our case, we accept this speed in the most restrictive situation: gantry angle 270 and 1 cm leaf thickness. Maximum speeds for the rest of the cases are calculated by keeping the difference between 95th percentile and dynamic tolerance. In this way, beam hold-off probability does not increase. Results: Maximum speeds every 45 degrees of gantry rotation have been calculated for both leaf thickness. These results are 2.9-2.9-2.9-2.9-2.7-2.6-2.6-2.7 cm/s for 0.5 cm leaf thickness and 2.7-2.7-2.7-2.7-2.6-2.5-2.5-2.6 cm/s for 1 cm leaf thickness. Conclusion: Gravity effect on MLC positioning has been studied. Maximum leaf speed according to leaf thickness and gantry angle have been calculated which reduces treatment time.

60 APPLIED LIFE SCIENCES↗

SU-F-R-25: Automatic Identification of Suspicious Recurrent/residual Disease Regions After Prostatectomy

Purpose: To automatically identify and outline suspicious regions of recurrent or residual disease in the prostate bed using Dynamic Contrast Enhanced-MRI (DCE-MRI) in patients after prostatectomy. Methods: Twenty-two patients presenting for salvage radiotherapy and with identified Gross Tumor Volume (GTV) in the prostate bed were retrospectively analyzed. The MRI data consisted of Axial T2weighted-MRI (T2w) of the pelvis: resolution 1.25×1.25×2.5 mm; Field of View (FOV): 320×320 mm; slice thickness=2.5mm; 72 slices; and Dynamic Contrast Enhanced MRI (DCE-MRI)–12 series of T1w with identical spatial resolution to T2w and at 30–34s temporal resolution. Unsupervised pattern recognition was used to decompose the 4D DCE data as the product W.H of weights W of k patterns H. A well-perfused pattern Hwp was identified and the weight map Wwp associated to Hwp was used to delineate suspicious volumes. Threshold of Wwp set at mean(Wwp)+S*std(Wwp), S=1,1.5,2 and 2.5 defined four volumes labeled as DCE1.0 to DCE2.5. These volumes were displayed on T2w and, along with GTV, were correlated with the highest pre-treatment PSA values, and with pharmacokinetic analysis constants. Results: GTV was significantly correlated with DCE2.0(ρ= 0.60, p<0.003), and DCE 2.5 (ρ=0.58, p=0.004)). Significant correlation was found between highest pre-treatment PSA and GTV(ρ=0.42, p<0.049), DCE2.0(ρ= 0.52, p<0.012), and DCE 2.5 (ρ=0.67, p<<0.01)). Kruskal-Wallis analysis showed that Ktrans median value was statistically different between non-specific prostate bed tissue NSPBT and both GTV (p<<0.001) and DCE2.5 (p<<0.001), but while median Ve was statistically different between DCE2.5 and NSPBT (p=0.002), it was not statistically different between GTV and NSPBT (p=0.054), suggesting that automatic volumes capture more accurately the area of malignancy. Conclusion: Software developed for identification and visualization of suspicions regions in DCE-MRI from post-prostatectomy patients has been validated by PSA and pharmacokinetic constants analysis showing that it generates clinically relevant volumes.

60 APPLIED LIFE SCIENCES↗

SU-F-R-45: The Prognostic Value of Radiotherapy Based On the Changes of Texture Features Between Pre-Treatment and Post-Treatment FDG PET Image for NSCLC Patients

Purpose: The purpose of this research is investigating which texture features extracted from FDG-PET images by gray-level co-occurrence matrix(GLCM) have a higher prognostic value than the other texture features. Methods: 21 non-small cell lung cancer(NSCLC) patients were approved in the study. Patients underwent 18F-FDG PET/CT scans with both pre-treatment and post-treatment. Firstly, the tumors were extracted by our house developed software. Secondly, the clinical features including the maximum SUV and tumor volume were extracted by MIM vista software, and texture features including angular second moment, contrast, inverse different moment, entropy and correlation were extracted using MATLAB.The differences can be calculated by using post-treatment features to subtract pre-treatment features. Finally, the SPSS software was used to get the Pearson correlation coefficients and Spearman rank correlation coefficients between the change ratios of texture features and change ratios of clinical features. Results: The Pearson and Spearman rank correlation coefficient between contrast and SUV maximum is 0.785 and 0.709. The P and S value between inverse difference moment and tumor volume is 0.953 and 0.942. Conclusion: This preliminary study showed that the relationships between different texture features and the same clinical feature are different. Finding the prognostic value of contrast and inverse difference moment were higher than the other three textures extracted by GLCM.

60 APPLIED LIFE SCIENCES↗

SU-G-BRB-17: Dosimetric Evaluation of the Respiratory Interplay Effect During VMAT Delivery Using IPAGAT Polymer Gel Dosimeter

Purpose: To evaluate the dosimetric impact of the interplay effect between multileaf collimator (MLC) movement and tumor respiratory motion during delivery of volumetric modulate arc therapy (VMAT) by using customized polymer gel dosimeter. Methods: Polyacrylamide-based gel dosimeter contained magnesium chloride as a sensitizer (iPAGAT) was used in this study. An excellent gas barrier PAN (BAREX) techno bottle (φ8 cm, 650 mL) filled with iPAGAT was set to the QUASAR™ respiratory motion phantom, and was moved with motion amplitudes of 1 and 2 cm with a 4 second period during VMAT delivery by the Novalis Tx linear accelerator (Varian/BrainLAB). Two spherical tumors with a 2 cm diameter (GTV1 and GTV2) were defined, and ITV1 (GTV1+1 cm) and ITV2 (GTV2+2 cm) with expansion in the superior-inferior (S-I) direction were also defined with simulated respiratory motion. PTV margin was 2 mm around the ITV considering the setup uncertainty. Two single arc VMAT plans with 30 Gy at 3 Gy per fraction (GTV: D98>100%, PTV: D95=100%) were generated by the Varian Eclipse treatment planning system. Three-dimensional dose distribution in iPAGAT was read out by the Signa 1.5T MRI system (GE), and was evaluated by dose-volume histogram (DVH) using in-house developed software. Results: According to DVH analysis by iPAGAT, D98 of GTV1 and GTV2 were more than 100% of the prescribed dose. In contrast, D95 of PTV1 and PTV2 were about 85% and 65%, respectively. Furthermore, low-to-intermediate dose was widespread with motion amplitude of 2 cm. Conclusion: DVH analysis using iPAGAT polymer gel dosimeter was performed in this study. As a result, interplay effect was negligible, since dose coverage of GTV was sufficient during VMAT delivery with simulated respiratory motion. However, the dose reduction of PTV and the spread of low-to-intermediate dose compared to the planned dose require scrupulous attention for large tumor respiratory motion.

60 APPLIED LIFE SCIENCES↗