bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐I‐101: Effects of Gantry Rotation Time On CT Number Accuracy in Single‐Source Dual Energy CT Imaging with Fast‐KVp Switching
Authors: Liu X , Cody D , Rong J
Published: July 2014

Purpose:

To investigate the effects of gantry rotation time on CT number accuracy in dual energy CT imaging with GE Discovery CT750 HD singlesource CT scanner.

Methods:

The CT number linearity section (CTP404) of the Catphan 600 phantom was imaged using the dual energy protocols equipped on a GE Discovery CT750 HD CT scanner. The imaging section of the Catphan phantom was surrounded with a fat‐equivalent oval ring to better approximate an adult body shape during the image acquisition. A series of dual energy (gemstone spectral imaging (GSI)) presets was selected to acquire images at a gantry rotation time of 0.5 – 1.0 second in an increment of 0.1 second. Images were reconstructed using “Standard” algorithm at different monochromatic energies of 40 — 140 keV in an increment of 10 keV. Two sets of phantom image were acquired with the Axial mode and 5 mm slice thickness for each GSI preset. Total eight images were averaged to compute the CT number of each material insert in the CTP404 section. A squared region‐of‐interest (ROI) of approximate 5 x 5 mm was placed at the center of each material insert to measure the CT number and to investigate the effects of gantry rotation time on CT number accuracy.

Results:

For LDPE (−100 HU), the CT number increases with rotation time and starts to decrease at 0.9 s for energies at 80 keV and above; while the CT number decreases with rotation time and starts to increase at 0.8 s for energies at 60 keV and below. For Teflon (990 HU), CT number increases with rotation time and starts to decrease at 0.8 s for energies at 80 keV and above; while the CT number decreases with rotation time and starts to increase at 1.0 s for energies at 60 keV and below. At 50 keV, the average CT numbers were −101 HU and 940 HU with maximum differences of 8.7 HU and 10.7 HU for LDPE and Teflon, respectively. The CT numbers were measured −57 HU for LDPE and 913 HU for Teflon for single energy imaging at 120 kVp.

Conclusion:

Effects of gantry rotation time on CT number accuracy in dual energy CT imaging depends on type of insert material and the monochromatic energy at which the images were reconstructed.
SU‐E‐J‐01: 3D Fluoroscopic Image Estimation From Patient‐Specific 4DCBCT‐Based Motion Models
Authors: Dhou S , Hurwitz M , Mishra P , Lewis J
Published: July 2014

Purpose:

3D motion modeling derived from 4DCT images, taken days or weeks before treatment, cannot reliably represent patient anatomy on the day of treatment. We develop a method to generate motion models based on 4DCBCT acquired at the time of treatment, and apply the model to estimate 3D time‐varying images (referred to as 3D fluoroscopic images).

Methods:

Motion models are derived through deformable registration between each 4DCBCT phase, and principal component analysis (PCA) on the resulting displacement vector fields. 3D fluoroscopic images are estimated based on cone‐beam projections simulating kV treatment imaging. PCA coefficients are optimized iteratively through comparison of these cone‐beam projections and projections estimated based on the motion model. Digital phantoms reproducing ten patient motion trajectories, and a physical phantom with regular and irregular motion derived from measured patient trajectories, are used to evaluate the method in terms of tumor localization, and the global voxel intensity difference compared to ground truth.

Results:

Experiments included: 1) assuming no anatomic or positioning changes between 4DCT and treatment time; and 2) simulating positioning and tumor baseline shifts at the time of treatment compared to 4DCT acquisition. 4DCBCT were reconstructed from the anatomy as seen at treatment time. In case 1) the tumor localization error and the intensity differences in ten patient were smaller using 4DCT‐based motion model, possible due to superior image quality. In case 2) the tumor localization error and intensity differences were 2.85 and 0.15 respectively, using 4DCT‐based motion models, and 1.17 and 0.10 using 4DCBCT‐based models. 4DCBCT performed better due to its ability to reproduce daily anatomical changes.

Conclusion:

The study showed an advantage of 4DCBCT‐based motion models in the context of 3D fluoroscopic images estimation. Positioning and tumor baseline shift uncertainties were mitigated by the 4DCBCT‐based motion models, while they caused errors when using 4DCT‐based motion models.

Partially funded by Varian research grant.
SU‐E‐J‐02: 4D Digital Tomosynthesis Based On Algebraic Image Reconstruction and Total‐Variation Minimization for the Improvement of Image Quality
Authors: Kim D , Kang S , Kim T , Kim S , Suh T
Published: July 2014

Purpose:

In this paper, we implemented the four‐dimensional (4D) digital tomosynthesis (DTS) imaging based on algebraic image reconstruction technique and total‐variation minimization method in order to compensate the undersampled projection data and improve the image quality.

Methods:

The projection data were acquired as supposed the cone‐beam computed tomography system in linear accelerator by the Monte Carlo simulation and the in‐house 4D digital phantom generation program. We performed 4D DTS based upon simultaneous algebraic reconstruction technique (SART) among the iterative image reconstruction technique and total‐variation minimization method (TVMM). To verify the effectiveness of this reconstruction algorithm, we performed systematic simulation studies to investigate the imaging performance.

Results:

The 4D DTS algorithm based upon the SART and TVMM seems to give better results than that based upon the existing method, or filtered‐backprojection.

Conclusion:

The advanced image reconstruction algorithm for the 4D DTS would be useful to validate each intra‐fraction motion during radiation therapy. In addition, it will be possible to give advantage to real‐time imaging for the adaptive radiation therapy.

This research was supported by Leading Foreign Research Institute Recruitment Program (Grant No.2009‐00420) and Basic Atomic Energy Research Institute (BAERI); (Grant No. 2009‐0078390) through the National Research Foundation of Korea(NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP).
SU‐E‐J‐03: A Comprehensive Comparison Between Alpha and Beta Emitters for Cancer Radioimmunotherapy
Authors: Huang C.Y. , Guatelli S , Oborn B , Allen B
Published: July 2014

Purpose:

The purpose of this study is to perform a comprehensive comparison of the therapeutic efficacy and cytotoxicity of alpha and beta emitters for Radioimmunotherapy (RIT). For each stage of cancer development, specific models were built for the separate objectives of RIT to be addressed:a) kill isolated cancer cells in transit in the lymphatic and vascular circulation,b) regress avascular cell clusters,c) regress tumor vasculature and tumors.

Methods:

Because of the nature of short range, high LET alpha and long energy beta radiation and heterogeneous antigen expression among cancer cells, the microdosimetric approach is essential for the RIT assessment. Geant4 based microdosimetric models are developed for the three different stages of cancer progression: cancer cells, cell clusters and tumors. The energy deposition, specific energy resulted from different source distribution in the three models was calculated separately for 4 alpha emitting radioisotopes (211At, 213Bi, 223Ra and 225Ac) and 6 beta emitters (32P, 33P, 67Cu, 90Y, 131I and 177Lu). The cell survival, therapeutic efficacy and cytotoxicity are determined and compared between alpha and beta emitters.

Results:

We show that internal targeted alpha radiation has advantages over beta radiation for killing isolated cancer cells, regressing small cell clusters and also solid tumors. Alpha particles have much higher dose specificity and potency than beta particles. They can deposit 3 logs more dose than beta emitters to single cells and solid tumor. Tumor control probability relies on deep penetration of radioisotopes to cancer cell clusters and solid tumors.

Conclusion:

The results of this study provide a quantitative understanding of the efficacy and cytotoxicity of RIT for each stage of cancer development.
SU‐E‐J‐04: A Data‐Driven, Response‐Based, Multi‐Criteria Decision Support System for Personalized Lung Radiation Treatment Planning
Authors: Luo Y , McShan D , Schipper M , Matuszak M , Kong F , Ten Haken R
Published: July 2014

Purpose:

To develop a decision support tool to predict a patient's potential overall survival (OS) and radiation induced toxicity (RIT) based on clinical factors and responses during the course of radiotherapy, and suggest appropriate radiation dose adjustments to improve therapeutic effect.

Methods:

Important relationships between a patient's basic information and their clinical features before and during the radiation treatment are identified from historical clinical data by using statistical learning and data mining approaches. During each treatment period, a data analysis (DA) module predicts radiotherapy features such as time to local progression (TTLP), time to distant metastases (TTDM), radiation toxicity to different organs, etc., under possible future treatment plans based on patient specifics or responses. An information fusion (IF) module estimates intervals for a patient's OS and the probabilities of RIT from a treatment plan by integrating the outcomes of module DA. A decision making (DM) module calculates “satisfaction” with the predicted radiation outcome based on trade‐offs between OS and RIT, and finds the best treatment plan for the next time period via multi‐criteria optimization.

Results:

Using physical and biological data from 130 lung cancer patients as our test bed, we were able to train and implement the 3 modules of our decision support tool. Examples demonstrate how it can help predict a new patient's potential OS and RIT with different radiation dose plans along with how these combinations change with dose, thus presenting a range of satisfaction/utility for use in individualized decision support.

Conclusion:

Although the decision support tool is currently developed from a small patient sample size, it shows the potential for the improvement of each patient's satisfaction in personalized radiation therapy. The radiation treatment outcome prediction and decision making model needs to be evaluated with more patients and demonstrated for use in radiation treatments for other cancers.

P01‐CA59827;R01CA142840
SU‐E‐J‐09: A Monte Carlo Analysis of the Relationship Between Cherenkov Light Emission and Dose for Electrons, Protons, and X‐Ray Photons
Authors: Glaser A , Zhang R , Gladstone D , Pogue B
Published: July 2014

Purpose:

A number of recent studies have proposed that light emitted by the Cherenkov effect may be used for a number of radiation therapy dosimetry applications. Here we investigate the fundamental nature and accuracy of the technique for the first time by using a theoretical and Monte Carlo based analysis.

Methods:

Using the GEANT4 architecture for medically‐oriented simulations (GAMOS) and BEAMnrc for phase space file generation, the light yield, material variability, field size and energy dependence, and overall agreement between the Cherenkov light emission and dose deposition for electron, proton, and flattened, unflattened, and parallel opposed x‐ray photon beams was explored.

Results:

Due to the exponential attenuation of x‐ray photons, Cherenkov light emission and dose deposition were identical for monoenergetic pencil beams. However, polyenergetic beams exhibited errors with depth due to beam hardening, with the error being inversely related to beam energy. For finite field sizes, the error with depth was inversely proportional to field size, and lateral errors in the umbra were greater for larger field sizes. For opposed beams, the technique was most accurate due to an averaging out of beam hardening in a single beam. The technique was found to be not suitable for measuring electron beams, except for relative dosimetry of a plane at a single depth. Due to a lack of light emission, the technique was found to be unsuitable for proton beams.

Co nclusions:

The results from this exploratory study suggest that optical dosimetry by the Cherenkov effect may be most applicable to near monoenergetic x‐ray photon beams (e.g. Co‐60), dynamic IMRT and VMAT plans, as well as narrow beams used for SRT and SRS. For electron beams, the technique would be best suited for superficial dosimetry, and for protons the technique is not applicable due to a lack of light emission.

NIH R01CA109558 and R21EB017559.
SU‐E‐J‐11: A New Optical Method to Register Patient External Motion
Authors: Barbes B , Foronda J , Azcona J , Moreno M , Prieto E , Burguete J
Published: July 2014

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.
SU‐E‐J‐16: A Review of the Magnitude of Patient Imaging Shifts in Relation to Departmental Policy Changes
Authors: O' Connor M , Sansourekidou P
Published: July 2014

Purpose:

To evaluate how changes in imaging policy affect the magnitude of shifts applied to patients.

Methods:

In June 2012, the department's imaging policy was altered to require that any shifts derived from imaging throughout the course of treatment shall be considered systematic only after they were validated with two data points that are consistent in the same direction. Multiple additions and clarifications to the imaging policy were implemented throughout the course of the data collection, but they were mostly of administrative nature. Entered shifts were documented in MOSAIQ (Elekta AB) through the localization offset. The MOSAIQ database was queried to identify a possible trend. A total of 25,670 entries were analyzed, including four linear accelerators with a combination of MV planar, kV planar and kV three dimensional imaging. The monthly average of the magnitude of the vector was used. Plan relative offsets were excluded. During the evaluated period of time, one of the satellite facilities acquired and implemented Vision RT (AlignRT Inc).

Results:

After the new policy was implemented the shifts variance and standard deviation decreased. The decrease is linear with time elapsed. Vision RT implementation at one satellite facility reduced the number of overall shifts, specifically for breast patients.

Conclusion:

Changes in imaging policy have a significant effect on the magnitude of shifts applied to patients. Using two statistical points before applying a shift as persistent decreased the overall magnitude of the shifts applied to patients.
SU‐E‐J‐23: An Accurate Algorithm to Match Imperfectly Matched Images for Lung Tumor Detection Without Markers
Authors: Rozario T , Bereg S , Chiu T , Liu H , Kearney V , Jiang L , Mao W
Published: July 2014

Purpose:

In order to locate lung tumors on projection images without internal markers, digitally reconstructed radiograph (DRR) is created and compared with projection images. Since lung tumors always move and their locations change on projection images while they are static on DRRs, a special DRR (background DRR) is generated based on modified anatomy from which lung tumors are removed. In addition, global discrepancies exist between DRRs and projections due to their different image originations, scattering, and noises. This adversely affects comparison accuracy. A simple but efficient comparison algorithm is reported.

Methods:

This method divides global images into a matrix of small tiles and similarities will be evaluated by calculating normalized cross correlation (NCC) between corresponding tiles on projections and DRRs. The tile configuration (tile locations) will be automatically optimized to keep the tumor within a single tile which has bad matching with the corresponding DRR tile. A pixel based linear transformation will be determined by linear interpolations of tile transformation results obtained during tile matching. The DRR will be transformed to the projection image level and subtracted from it. The resulting subtracted image now contains only the tumor. A DRR of the tumor is registered to the subtracted image to locate the tumor.

Results:

This method has been successfully applied to kV fluoro images (about 1000 images) acquired on a Vero (Brainlab) for dynamic tumor tracking on phantom studies. Radiation opaque markers are implanted and used as ground truth for tumor positions. Although, other organs and bony structures introduce strong signals superimposed on tumors at some angles, this method accurately locates tumors on every projection over 12 gantry angles. The maximum error is less than 2.6 mm while the total average error is 1.0 mm.

Conclusion:

This algorithm is capable of detecting tumor without markers despite strong background signals.
SU‐E‐J‐24: An Evaluation of the Stability of Image Quality Parameters of Varian On‐Board Imaging (OBI) and EPID Imaging Systems
Authors: Stanley D , Papanikolaou N , Gutierrez A
Published: July 2014

Purpose:

Quality assurance of the image quality for image guided localization systems is crucial to ensure accurate visualization and localization of target volumes. In this study, the long term stability of selected image parameters was assessed and evaluated for CBCT mode, planar radiographic kV mode and the radiographic MV EPID mode.

Methods:

The CATPHAN, QckV‐1 and QC‐3 phantoms were used to evaluate the image quality parameters. The planar radiographic images were analyzed in PIPSpro™ with spatial resolution (f30, f40, f50) being recorded. For OBI CBCT, High quality head Full‐Fan acquisition and Pelvis Half‐Fan acquisition modes were evaluated for Uniformity, Noise, Spatial Resolution, HU constancy and geometric distortion. Dose and kVp for the OBI were recorded using the Unfors RaySafe Xi system with the R/F High Detector for planar kV and the CT detector for CBCT. Dose for the MV EPID was recorded using a PTW975 Semiflex Ion Chamber, PTW Unidos electrometer and SolidWater™.

Results:

For each metric, values were normalized to the mean and the standard deviations were recorded. For the planar radiographic spatial resolution the f30, f40, f50 were 0.015, 0.008, 0.004 and 0.006, 0.009, 0.018 for the kV and MV, respectively. The standard deviation of the dose for kV was 0.010 and 0.005 for the MV. The standard deviations for Full and half fan were averaged together and the following standard deviations for each metric were recorded: 0.075(uniformity), 0.071(noise), 0.006(AP‐Geometric Distortion), 0.005(LAT‐Geometric Distortion), 0.058(mean slice thickness), 0.098(f30),0.101(f40),0.124(f50), 0.031(Lung/PMP‐HU constancy), 0.063(Water/poly‐HU constancy), 0.015(Bone/Derlin‐HU constancy),0.006(Dose‐Center), 0.004(Dose‐Periphery). Using these, tolerances can be reported as a warning and action threshold of 1σ and 2σ.

Conclusion:

A study was performed to assess the stability of the basic image quality parameters recommended by TG‐142 for the Varian OBI and EPID Imaging systems. The two systems show consistent imaging and dosimetric properties over the evaluated time frame.
SU‐E‐J‐27: Appropriateness Criteria for Deformable Image Registration and Dose Propagation
Authors: Papanikolaou P , Tuohy Rachel , Mavroidis P , Eng T , Gutierrez A , Stathakis S
Published: July 2014

Purpose:

Several commercial software packages have been recently released that allow the user to apply deformable registration algorithms (DRA) for image fusion and dose propagation. Although the idea of anatomically tracking the daily patient dose in the context of adaptive radiotherapy or merely adding the dose from prior treatment to the current one is very intuitive, the accuracy and applicability of such algorithms needs to be investigated as it remains somewhat subjective. In our study, we used true anatomical data where we introduced changes in the density, volume and location of segmented structures to test the DRA for its sensitivity and accuracy.

Methods:

The CT scan of a prostate patient was selected for this study. The CT images were first segmented to define structure such as the PTV, bladder, rectum, intestines and pelvic bone anatomy. To perform our study, we introduced anatomical changes in the reference patient image set in three different ways: (i) we kept the segmented volumes constant and changed the density of rectum and bladder in increments of 5% (ii) we changed the volume of rectum and bladder in increments of 5% and (iii) we kept the segmented volumes constant but changed their location by moving their COM in increments of 3mm. Using the Velocity software, we evaluated the accuracy of the DRA for each incremental change in all three scenarios.

Results:

The DRA performs reasonably well when the differential density difference against the background is more than 5%. For the volume change study, the DRA results became unreliable for relative volume changes greater than 10%. Finally for the location study, the DRA performance was acceptable for shifts below 9mm.

Conclusion:

Site specific and patient specific QA for DRA is an important step to evaluate such algorithms prior to their use for dose propagation.
SU‐E‐J‐30: Benchmark Image‐Based TCP Calculation for Evaluation of PTV Margins for Lung SBRT Patients
Authors: Li M , Chetty I , Zhong H
Published: July 2014

Purpose:

Tumor control probability (TCP) calculated with accumulated radiation doses may help design appropriate treatment margins. Image registration errors, however, may compromise the calculated TCP. The purpose of this study is to develop benchmark CT images to quantify registration‐induced errors in the accumulated doses and their corresponding TCP.

Methods:

4DCT images were registered from end‐inhale (EI) to end‐exhale (EE) using a “demons” algorithm. The demons DVFs were corrected by an FEM model to get realistic deformation fields. The FEM DVFs were used to warp the EI images to create the FEM‐simulated images. The two images combined with the FEM DVF formed a benchmark model. Maximum intensity projection (MIP) images, created from the EI and simulated images, were used to develop IMRT plans. Two plans with 3 and 5 mm margins were developed for each patient. With these plans, radiation doses were recalculated on the simulated images and warped back to the EI images using the FEM DVFs to get the accumulated doses. The Elastix software was used to register the FEM‐simulated images to the EI images. TCPs calculated with the Elastix‐accumulated doses were compared with those generated by the FEM to get the TCP error of the Elastix registrations.

Results:

For six lung patients, the mean Elastix registration error ranged from 0.93 to 1.98 mm. Their relative dose errors in PTV were between 0.28% and 6.8% for 3mm margin plans, and between 0.29% and 6.3% for 5mm‐margin plans. As the PTV margin reduced from 5 to 3 mm, the mean TCP error of the Elastix‐reconstructed doses increased from 2.0% to 2.9%, and the mean NTCP errors decreased from 1.2% to 1.1%.

Conclusion:

Patient‐specific benchmark images can be used to evaluate the impact of registration errors on the computed TCPs, and may help select appropriate PTV margins for lung SBRT patients.
SU‐E‐J‐43: Deformed Planning CT as An Electron Density Substitute for Cone‐Beam CT
Authors: Mishra K , Godley A
Published: July 2014

Purpose:

To confirm that deforming the planning CT to the daily Cone‐Beam CTs (CBCT) can provide suitable electron density for adaptive planning. We quantify the dosimetric difference between plans calculated on deformed planning CTs (DPCT) and daily CT‐on‐rails images (CTOR). CTOR is used as a test of the method as CTOR already contains accurate electron density to compare against.

Methods:

Five prostate only IMRT patients, each with five CTOR images, were selected and re‐planned on Panther (Prowess Inc.) with a uniform 5 mm PTV expansion, prescribed 78 Gy. The planning CT was deformed to match each CTOR using ABAS (Elekta Inc.). Contours were drawn on the CTOR, and copied to the DPCT. The original treatment plan was copied to both the CTOR and DPCT, keeping the center of the prostate as the isocenter. The plans were then calculated using the collapsed cone heterogeneous dose engine of Prowess and typical DVH planning parameters used to compare them.

Results:

Each DPCT was visually compared to its CTOR with no differences observed. The agreement of the copied CTOR contours with the DPCT anatomy further demonstrated the deformation accuracy. The plans calculated using CTOR and DPCT were compared. Over the 25 plan pairs, the average difference between them for prostate D100, D98 and D95 were 0.5%, 0.2%, and 0.2%; PTV D98, D95 and mean dose: 0.3%, 0.2% and 0.3%; bladder V70, V60 and mean dose: 1.1%, 0.7%, and 0.2%; and rectum mean dose: 0.3%. (D100 is the dose covering 100% of the target; V70 is the volume of the organ receiving 70 Gy).

Conclusion:

We observe negligible difference between the dose calculated on the DPCT and the CTOR, implying that deformed planning CTs are a suitable substitute for electron density. The method can now be applied to CBCTs.

Research version of Panther provided by Prowess Inc. Research version of ABAS provided by Elekta Inc.
SU‐E‐J‐45: Design and Study of An In‐House Respiratory Gating Phantom Platform for Gated Radiotherapy
Authors: Senthilkumar S
Published: July 2014

Purpose:

The main purpose of this work was to develop an in‐house low cost respiratory motion phantom platform for testing the accuracy of the gated radiotherapy system and analyze the dosimetric difference during gated radiotherapy.

Methods:

An in‐house respiratory motion platform(RMP) was designed and constructed for testing the targeting accuracy of respiratory tracking system. The RMP consist of acrylic Chest Wall Platform, 2 DC motors, 4 IR sensors, speed controller circuit, 2 LED and 2 moving rods inside the RMP. The velocity of the movement can be varied from 0 to 30 cycles per minute. The platform mounted to a base using precision linear bearings. The base and platform are made of clear, 15mm thick polycarbonate plastic and the linear ball bearings are oriented to restrict the platform to a movement of approximately 50mm up and down with very little friction.

Results:

The targeting accuracy of the respiratory tracking system was evaluated using phantom with and without respiratory movement with varied amplitude. We have found the 5% dose difference to the PTV during the movement in comparison with stable PTV. The RMP can perform sinusoidal motion in 1D with fixed peak to peak motion of 5 to 50mm and cycle interval from 2 to 6 seconds. The RMP was designed to be able to simulate the gross anatomical anterior posterior motion attributable to respiration‐induced motion of the thoracic region.

Conclusion:

The unique RMP simulates breathing providing the means to create a comprehensive program for commissioning, training, quality assurance and dose verification of gated radiotherapy treatments. Create the anterior/posterior movement of a target over a 5 to 50 mm distance to replicate tumor movement. The targeting error of the respiratory tracking system is less than 1.0 mm which shows suitable for clinical treatment with highly performance.
SU‐E‐J‐47: Development of a High‐Precision, Image‐Guided Radiotherapy, Multi‐ Purpose Radiation Isocenter Quality‐Assurance Calibration and Checking System
Authors: Liu C , Yan G , Helmig R , Lebron S , Kahler D
Published: July 2014

Purpose:

To develop a system that can define the radiation isocenter and correlate this information with couch coordinates, laser alignment, optical distance indicator (ODI) settings, optical tracking system (OTS) calibrations, and mechanical isocenter walkout.

Methods:

Our team developed a multi‐adapter, multi‐purpose quality assurance (QA) and calibration device that uses an electronic portal imaging device (EPID) and in‐house image‐processing software to define the radiation isocenter, thereby allowing linear accelerator (Linac) components to be verified and calibrated. Motivated by the concept that each Linac component related to patient setup for image‐guided radiotherapy based on cone‐beam CT should be calibrated with respect to the radiation isocenter, we designed multiple concentric adapters of various materials and shapes to meet the needs of MV and KV radiation isocenter definition, laser alignment, and OTS calibration. The phantom's ability to accurately define the radiation isocenter was validated on 4 Elekta Linacs using a commercial ball bearing (BB) phantom as a reference. Radiation isocenter walkout and the accuracy of couch coordinates, ODI, and OTS were then quantified with the device.

Results:

The device was able to define the radiation isocenter within 0.3 mm. Radiation isocenter walkout was within ±1 mm at 4 cardinal angles. By switching adapters, we identified that the accuracy of the couch position digital readout, ODI, OTS, and mechanical isocenter walkout was within sub‐mm.

Conclusion:

This multi‐adapter, multi‐purpose isocenter phantom can be used to accurately define the radiation isocenter and represents a potential paradigm shift in Linac QA. Moreover, multiple concentric adapters allowed for sub‐mm accuracy for the other relevant components. This intuitive and user‐friendly design is currently patent pending.
SU‐E‐J‐48: Development of An Abdominal Compression Device for Respiratory Correlated Radiation Therapy
Authors: Kim T , Kang S , Kim D , Kim S , Suh T
Published: July 2014

Purpose:

The aim of this study is to develop the abdominal compression device which could control pressure level according to the abdominal respiratory motion and evaluate its feasibility.

Methods:

In this study, we focused on developing the abdominal compression device which could control pressure level at any point of time so the developed device is possible to use a variety of purpose (gating technique or respiratory training system) while maintaining the merit of the existing commercial device. The compression device (air pad form) was designed to be able to compress the front and side of abdomen and the pressure level of the abdomen is controlled by air flow. Pressure level of abdomen (air flow) was determined using correlation data between external abdominal motion and respiratory volume signal measured by spirometer. In order to verify the feasibility of the device, it was necessary to confirm the correlation between the abdominal respiratory motion and respiratory volume signal and cooperation with respiratory training system also checked.

Results:

In the previous study, we could find that the correlation coefficient ratio between diaphragm and respiratory volume signal measured by spirometer was 0.95. In this study, we confirmed the correlation between the respiratory volume signal and the external abdominal motion measured by belt‐transducer (correlation coefficient ratio was 0.92) and used the correlated respiratory volume data as an abdominal pressure level. It was possible to control the pressure level with negligible time delay and respiratory volume data based guiding waveforms could be properly inserted into the respiratory training system.

Conclusion:

Through this feasibility study, we confirmed the correlation between the respiratory volume signal and the external abdominal motion. Also initial assessment of the device and its compatibility with the respiratory training system were verified. Further study on application in respiratory gated therapy and respiratory training system will be investigated.

This work was supported by Radiation Technology R&D program (No. 2013M2A2A7043498)and Basic Atomic Energy Research Institute (BAERI)(No. NRF‐2009‐0078390) through the National Research Foundation of Korea funded by the Ministry of Science, ICT&Future Planning.
SU‐E‐J‐51: Dose Response of Common Solid State Detectors in Homogeneous Transverse and Longitudinal Magnetic Fields
Authors: Reynolds M , Fallone B , Rathee S
Published: July 2014

Purpose:

Solid state radiation detectors are often used for dose profiles and percent depth dose measurements. The dose response of selected solid state detectors is evaluated in varying transverse and longitudinal magnetic fields for eventual use in MR‐Linac devices.

Methods:

A PTW 60003 and IBA PFD detector were modeled in the Monte Carlo code PENELOPE, incorporating a magnetic field which was varied in strength and oriented both transversely and longitudinally with respect to the incident photon beam. The detectors' long axis was in turn oriented either parallel or perpendicular to the photon beam. Dose to the active volume of each detector was scored, and its ratio to dose with zero magnetic field strength (dose response) was determined. Accuracy of the simulations was evaluated by measurements using both chambers taken at low field with a small electromagnet. Simulations were also performed in a water phantom to compare to the in air results.

Results:

Significant dose response was found in transverse field geometries, nearing 20% at 1.5T. The response is highly dependent on relative orientations to the magnetic field and photon beam, and on detector composition. Low field measurements confirm these results. In the presence of longitudinal magnetic fields, the detectors exhibit little dose response, reaching 0.5–1% at 1.5T regardless of detector orientation. Water tank simulations compared well to the in air simulations when not at the beam periphery, where in transverse magnetic fields only, the water tank simulations differed from the in air results.

Conclusion:

Transverse magnetic fields can cause large deviations in dose response, and are highly position orientation dependent. Comparatively, longitudinal magnetic fields exhibit little to no dose response in each detector as a function of magnetic field strength. Water tank simulations show longitudinal fields are generally easier to work with, but each detector must be evaluated separately.
SU‐E‐J‐63: Estimating the Effects of Respiratory Motion On Dose Heterogeneity for ITV‐Based Treatments
Authors: Williams C , Lewis J
Published: July 2014

Purpose:

To quantify the relationship between the amount of dose heterogeneity in a treatment plan that uses an internal target volume (ITV) to account for respiratory motion and the true amount of heterogeneity in the dose delivered to the tumor contained within that ITV.

Methods:

We develop a convolution‐based framework for calculating dose delivered to a tumor moving inside an ITV according to a common sinusoid‐based breathing model including asymmetry. We model the planned ITV dose distribution as a centrally peaked analytic function approximating the profile of clinical stereotactic body radiotherapy treatments. Expressions for the minimum and maximum dose received by the tumor are derived and evaluated for a range of clinically relevant parameters. Results of the model are validated with phantom measurements using an ion chamber array.

Results:

An analytic expression is presented for the maximum and minimum doses received by the tumor relative to the planned ITV dose. The tumor dose heterogeneity depends solely on the ratio of tumor size to ITV size, the peak dose in the planned ITV dose distribution, and the respiratory asymmetry parameter. Under the assumptions of this model, using a typical breathing asymmetry parameter and a dose distribution with a fixed size ITV covered by the 100% line and with a 130% hotspot, the maximum dose to the tumor varies between 113%–130%, and the minimum dose varies between 100%–116% depending on the amount of tumor motion.

Conclusion:

This modeling exercise demonstrates the interplay between motion and dose heterogeneity. Tumors that exhibit large amounts of respiratory motion relative to their size will receive a more homogeneous dose and a larger minimum dose than would be inferred from the ITV dose distribution. This effect is not captured in current clinical treatment planning methods unless 4D dose calculation techniques are used.

This work was partially supported by a Varian Medical Systems research grant
SU‐E‐J‐65: Evaluation of a Radiation‐Induced Cell Proliferation Probability Formula Using Monte Carlo Simulation
Authors: Watanabe Y , Dahlman E
Published: July 2014

Purpose:

To evaluate the analytic formula of the cell death probability after single fraction dose.

Methods:

Cancer cells endlessly divide, but radiation causes the cancer cells to die. Not all cells die right away after irradiation. Instead, they continue dividing for next few cell cycles before they stop dividing and die. At the end of every cell cycle, the cell decides if it undertakes the mitotic process with a certain probability, Pdiv, which is altered by the radiation. Previously, by using a simple analytic model of radiobiology experiments, we obtained a formula of Pdeath (= 1 − Pdiv). A question is if the proposed probability can reproduce the well‐known survival data of the LQ model. In this study, we evaluated the formula by doing a Monte Carlo simulation of the cell proliferation process. Starting with Ns seed cells, the cell proliferation process was simulated for N generations or until all cells die. We counted the number of living cells at the end. Assuming that the cell colony survived when more than Nc cells were still alive, the surviving fraction S was estimated. We compared the S vs. dose, or S‐D curve, with the LQ model.

Results:

The results indicated that our formula does not reproduce the experimentally observed S‐D curve without selecting appropriate α and α/β. With parameter optimization, there was a fair agreement between the MC result and the LQ curve of dose lower than 20Gy. However, the survival fraction of MC decreased much faster in comparison to the LQ data for doses higher than 20 Gy.

Conclusion:

This study showed that the previously derived probability of cell death per cell cycle is not sufficiently accurate to replicate common radiobiological experiments. The formula must be modified by considering its cell cycle dependence and some other unknown effects.
SU‐E‐J‐66: Evaluation of a Real‐Time Positioning Assistance Simulator System for Skull Radiography Using the Microsoft Kinect
Authors: Kurata T , Ono M , Kozono K , Fukuyoshi R , Sato S , Toyofuku F
Published: July 2014

Purpose:

The purpose of this study is to investigate the feasibility of a low cost, small size positioning assistance simulator system for skull radiography using the Microsoft Kinect sensor. A conventional radiographic simulator system can only measure the three‐dimensional coordinates of an x‐ray tube using angle sensors, but not measure the movement of the subject. Therefore, in this study, we developed a real‐time simulator system using the Microsoft Kinect to measure both the x‐ray tube and the subject, and evaluated its accuracy and feasibility by comparing the simulated and the measured x‐ray images.

Methods:

This system can track a head phantom by using Face Tracking, which is one of the functions of the Kinect. The relative relationship between the Kinect and the head phantom was measured and the projection image was calculated by using the ray casting method, and by using three‐dimensional CT head data with 220 slices at 512 × 512 pixels. X‐ray images were thus obtained by using a computed radiography (CR) system. We could then compare the simulated projection images with the measured x‐ray images from 0 degrees to 45 degrees at increments of 15 degrees by calculating the cross correlation coefficient C.

Results:

The calculation time of the simulated projection images was almost real‐time (within 1 second) by using the Graphics Processing Unit(GPU). The cross‐correlation coefficients C are: 0.916; 0.909; 0.891; and, 0.886 at 0, 15, 30, and 45 degrees, respectively. As a result, there were strong correlations between the simulated and measured images.

Conclusion:

This system can be used to perform head positioning more easily and accurately. It is expected that this system will be useful for learning radiographic techniques by students. Moreover, it could also be used for predicting the actual x‐ray image prior to x‐ray exposure in clinical environments.
SU‐E‐J‐69: Evaluation of the Lens Dose On the Cone Beam IGRT Procedures
Authors: Palomo‐Llinares R , Pujades M , Gimeno‐Olmos J , Carmona Meseguer V , Lliso‐Valverde F , Candela‐Juan C , Ballester F , Perez‐Calatayud J
Published: July 2014

Purpose:

With the establishment of the IGRT as a standard technique, the extra dose that is given to the patients should be taken into account. Furthermore, it has been a recent decrease of the dose threshold in the lens, reduced to 0.5 Gy (ICRP ref 4825‐3093‐1464 on 21st April, 2011). The purpose of this work was to evaluate the extra dose that the lens is receive due to the Cone‐Beam (CBCT) location systems in Head‐and‐Neck treatments.

Methods:

The On‐Board Imaging (OBI) v 1.5 of the two Varian accelerators, one Clinac iX and one True Beam, were used to obtain the dose that this OBI version give to the lens in the Head‐and‐Neck location treatments. All CBCT scans were acquired with the Standard Dose Head protocol (100 kVp, 80 mA, 8 ms and 200 degree of rotation). The measurements were taken with thermoluminescence (TLD) EXTRAD (Harshaw) dosimeters placed in an anthropomorphic phantom over the eye and under 3 mm of bolus material to mimic the lens position. The center of the head was placed at the isocenter. To reduce TLD energy dependence, they were calibrated at the used beam quality.

Results:

The average lens dose at the lens in the OBI v 1.5 systems of the Clinac iX and the True Beam is 0.071 and 0.076 cGy/CBCT, respectively.

Conclusions:

The extra absorbed doses that receive the eye lenses due to one CBCT acquisition with the studied protocol is far below the new ICRP recommended threshold for the lens. However, the addition effect of several CBCT acquisition during the whole treatment should be taken into account.
SU‐E‐J‐71: Feasibility Study On MRI‐Based BANG3 Gel Dosimetry Using Dual‐Source Parallel RF Transmission System
Authors: Kim S , Baek H , Lee J , Lee D , Lee S , Choe B
Published: July 2014

Purpose:

In this work, we present the feasibility of use of the parallel RF transmission with multiple RF source (MultiTransmit) imaging in MRI‐based polymer gel dosimetry.

Methods:

The commercially available BANG3 gel was used for gel dosimetry. Spin‐spin relaxation rate R2 was used to quantify the absorbed dose. The image quality (signal‐to‐noise ratio, SNR; image uniformity) and B1 field inhomogeneity between conventional single‐source and MultiTransmit MR imaging were compared. Finally, the estimated R2 uncertainty σ(R2) and dosimetric performance (i.e., dose resolution) between conventional single‐source and MultiTransmit MR imaging were compared.

Results:

Image quality and B1 field homogeneity within each calibration vial and large phantom was statistically better in MultiTransmit imaging than in conventional single‐source RF transmission imaging (P < 0.005 for all calibration vials). In particular, σ(R2) (defined as the standard uncertainty of R2) was lower on the MultiTransmit images than on the conventional single‐source images. Furthermore, the MultiTransmit measurement gives a lower than that obtained using the conventional single‐source method.

Conclusion:

The improved image quality and B1 homogeneity resulted in reduced dose uncertainty (i.e., σ(R2) and dose resolution) in MRI‐based polymer gel dosimetry, suggesting that MultiTransmit MR imaging has potential benefits for use in clinical 3D gel dosimetry without the need for the complicated B1 field correction method.
SU‐E‐J‐74: Impact of Respiration‐Correlated Image Quality On Tumor Motion Reconstruction in 4D‐CBCT: A Phantom Study
Authors: Lee S , Lu B , Samant S
Published: July 2014

Purpose:

To investigate the effects of scanning parameters and respiratory patterns on the image quality for 4‐dimensional cone‐beam computed tomography(4D‐CBCT) imaging, and assess the accuracy of computed tumor trajectory for lung imaging using registration of phased 4D‐CBCT imaging with treatment planning‐CT.

Methods:

We simulated a periodic and non‐sinusoidal respirations with various breathing periods and amplitudes using a respiratory phantom(Quasar, Modus Medical Devices Inc) to acquire respiration‐correlated 4D‐CBCT images. 4D‐CBCT scans(Elekta Oncology Systems Ltd) were performed with different scanning parameters for collimation size(e.g., small and medium field‐of‐views) and scanning speed(e.g., slow 50°·min−1, fast 100°·min−1). Using a standard CBCT‐QA phantom(Catphan500, The Phantom Laboratory), the image qualities of all phases in 4D‐CBCT were evaluated with contrast‐to‐noise ratio(CNR) for lung tissue and uniformity in each module. Using a respiratory phantom, the target imaging in 4D‐CBCT was compared to 3D‐CBCT target image. The target trajectory from 10‐respiratory phases in 4D‐CBCT was extracted using an automatic image registration and subsequently assessed the accuracy by comparing with actual motion of the target.

Results:

Image analysis indicated that a short respiration with a small amplitude resulted in superior CNR and uniformity. Smaller variation of CNR and uniformity was present amongst different respiratory phases. The small field‐of‐view with a partial scan using slow scan can improve CNR, but degraded uniformity. Large amplitude of respiration can degrade image quality. RMS of voxel densities in tumor area of 4D‐CBCT images between sinusoidal and non‐sinusoidal motion exhibited no significant difference. The maximum displacement errors of motion trajectories were less than 1.0 mm and 13.5 mm, for sinusoidal and non‐sinusoidal breathings, respectively. The accuracy of motion reconstruction showed good overall agreement with the 4D‐CBCT image quality results only using sinusoidal breathings.

Conclusion:

This information can be used to determine the appropriate acquisition parameters of 4D‐CBCT imaging for registration accuracy and target trajectory measurements in a clinical setting.