bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐J‐80: A Simulation Study with Geant4 on the Yields of Positron‐Emitting Nuclei (10C, 11C, and 15O) Induced by Protons and Carbon Ions
Authors: lau A , Chen Y , Ahmad S
Published: June 2012

Purpose: To study the yields and the depth‐distributions of positron‐emitting nuclei (PEN) 10C, 11C, and 15O induced by protons and carbon ions in PMMA. Methods: An application built with various physics packages was constructed with Geant4 Monte Carlo Toolkit. A phantom of 15 cm × 15 cm × 50 cm consisting of PMMA (C5H8O2, density 1.18 g/cm3) was irradiated with 70, 110 MeV protons and 204 A, 212.12 A MeV carbonions. Beam quality of 1 cm FWHM with 0.2% Gaussian energy spread FWHM was used. For each beam energy, simulation of the energy deposited was recorded for every 1 mm increment of depth in the phantom. The resulting PEN and their yields were recorded at the production point and also at the point of decay in increments of 1 mm. Results: The overall percentage yields, depth‐distributions, and total percentages of PEN per incident particle for both protons and carbon ions were obtained. Our results found that the predominant PMMA fragment was 11C irrespective of incident particle type or energy. Conclusions: Our yields of PEN are comparable with other simulations (FLUKA and MCHIT) as well as existing experimental data. The present work however overestimates the percentage of PEN in the simulations of incident carbon ions and the percentage of 10C for incident protons compared to the experimental data. This particular application built within the Geant4 Monte Carlo Toolkit can estimate the amount of PEN as well as the depth‐distributions of these nuclei in hadron induced radiation therapy.
SU‐E‐J‐84: Investigating the Use of Deformable Algorithms to Register and Accumulate Dose to the Spinal Cord for Head‐And‐Neck Radiotherapy Patients
Authors: Ueda U , Chen J , Kirby N , Quivey J , Yom S , Pouliot J
Published: June 2012

Purpose: Mega‐voltage cone‐beam CT (MVCBCT) imaging can be used to monitor changes in neck flexion and calculate the true spinal cord dose during radiotherapy. To sum the dose over multiple fractions and compare with the planned dose requires deformable image registration. This study investigates the accuracy of deformable registration of the spine in kilovoltage CT (kVCT) to MVCBCT images for head‐and‐neck patients. Methods: Head‐and‐neck kVCT and MVCBCT images were selected from five patients who exhibited large changes in neck flexion. The spinal canal was contoured in each image. MVCBCT images were rigidly registered to the kVCT image by aligning the C1–C2 vertebrae. Variations of a commercial deformable registration algorithm using the B‐spline method were applied to a volume of interest surrounding the spine to deform the spinal cord structure from the kVCT to the MVCBCT. The Dice similarity index (DSI) was calculated between rigidly registered structures (DSI1), and compared against the DSI calculated between the MVCBCT structure and the structure deformed from kVCT to MVCBCT (DSI2). The difference between DSI2 and DSI1 was calculated to investigate the ability of the deformation algorithm to match the change in neck flexion. Results: In this data set, a single‐pass B‐spline deformation algorithm was the most effective in deforming the kVCT spinal canal to the MVCBCT spinal canal, with a mean improvement in DSI (DSI2 ‐ DSI1) of 0.134. The mean change in DSI for a single‐pass algorithm with a contrast correction was 0.111; for a multiple‐pass algorithm was 0.105; and for a multiple‐pass algorithm with contrast correction was 0.075. Conclusions: Several versions of a commercially implemented B‐spline deformation algorithm were found to improve the registration of the spinal canal in kVCT and MVCBCT head‐and‐neck images. The resulting accuracy in the calculation of the cumulative dose to the spinal cord is under investigation. We acknowledge Velocity for providing the registration software.
SU‐E‐J‐85: Anthropomorphic Development for Intermodality Deformation Algorithms Validation
Authors: Vincent S D. , Archambault L
Published: June 2012

Purpose: Radiation therapy is often based on a single treatment plan calculated on patient's anatomy at the time of the simulation scan. Deformation algorithms offer the possibility to register initial treatment plan on a daily CBCT. This way, the planning can be adapted to the evolution of patient anatomy. Validation of deformable image registration algorithms (DRA) ideally requires the use of phantoms offering some deformation possibilitiesMethods: An anthropomorphic, pelvic phantom was built to test volume variation (bladder), deformation of contours (prostate) and translation (all organs). Algorithms must be able to perform intermodality registration. Therefore, images were acquired for both CT and CBCT. The phantom has been created in a way to allow total control of the deformation amplitude. Each of the three types of deformations studied were realized independently and scanned in a manner to have the same initial and deformed images set for each modality. Results: Two algorithm systems were use to compare their efficiency; an open‐source software, a toolbox for registration that offers parameter adjustment and a commercial system with limited control for user. The phantom provides us usable images for DRA validation. For a 2 cm mass center organ translation, the first one reduced 98% of the distance while the other only performed 60%. For a 100 ml volume variation, we get 88% and 62%. Conclusions: Comparison of each intermodal deformation registration performed by the two algorithm systems show how control on parameters improves registration quality. DRA allow the initial planning adaptation on different deformations which occur in human body.
SU‐E‐J‐87: Building Deformation Error Histogram and Quality Assurance of Deformable Image Registration
Authors: Park SB , Kim H , Yao M , Ellis R , Machtay M , Sohn JW
Published: June 2012

Purpose: To quantify the systematic error of a Deformable Image Registration (DIR) system and establish Quality Assurance (QA) procedure. Methods: To address the shortfall of landmark approach which it is only available at the significant visible feature points, we adapted a Deformation Vector Map (DVM) comparison approach. We used two CT image sets (R and T image sets) taken for the same patient at different time and generated a DVM, which includes the DIR systematic error. The DVM was calculated using fine‐tuned B‐Spline DIR and L‐BFGS optimizer. By utilizing this DVM we generated R′ image set to eliminate the systematic error in DVM,. Thus, we have truth data set, R′ and T image sets, and the truth DVM. To test a DIR system, we use R′ and T image sets to a DIR system. We compare the test DVM to the truth DVM. If there is no systematic error, they should be identical. We built Deformation Error Histogram (DEH) for quantitative analysis. The test registration was performed with an in‐house B‐Spline DIR system using a stochastic gradient descent optimizer. Our example data set was generated with a head and neck patient case. We also tested CT to CBCT deformable registration. Results: We found skin regions which interface with the air has relatively larger errors. Also mobile joints such as shoulders had larger errors. Average error for ROIs were as follows; CTV: 0.4mm, Brain stem: 1.4mm, Shoulders: 1.6mm, and Normal tissues: 0.7mm. Conclusions: We succeeded to build DEH approach to quantify the DVM uncertainty. Our data sets are available for testing other systems in our web page. Utilizing DEH, users can decide how much systematic error they would accept. DEH and our data can be a tool for an AAPM task group to compose a DIR system QA guideline. This project is partially supported by the Agency for Healthcare Research and Quality (AHRQ) grant 1R18HS017424‐01A2.
SU‐E‐J‐91: FFT Based Medical Image Registration Using a Graphics Processing Unit (GPU)
Authors: Luce J , Hoggarth M , Lin J , Block A , Roeske J
Published: June 2012

Purpose: To evaluate the efficiency gains obtained from using a Graphics Processing Unit (GPU) to perform a Fourier Transform (FT) based image registration. Methods: Fourier‐based image registration involves obtaining the FT of the component images, and analyzing them in Fourier space to determine the translations and rotations of one image set relative to another. An important property of FT registration is that by enlarging the images (adding additional pixels), one can obtain translations and rotations with sub‐pixel resolution. The expense, however, is an increased computational time. GPUs may decrease the computational time associated with FT image registration by taking advantage of their parallel architecture to perform matrix computations much more efficiently than a Central Processor Unit (CPU). In order to evaluate the computational gains produced by a GPU, images with known translational shifts were utilized. A program was written in the Interactive Data Language (IDL; Exelis, Boulder, CO) to performCPU‐based calculations. Subsequently, the program was modified using GPU bindings (Tech‐X, Boulder, CO) to perform GPU‐based computation on the same system. Multiple image sizes were used, ranging from 256×256 to 2304×2304. The time required to complete the full algorithm by the CPU and GPU were benchmarked and the speed increase was defined as the ratio of the CPU‐to‐GPU computational time. Results: The ratio of the CPU‐to‐ GPU time was greater than 1.0 for all images, which indicates the GPU is performing the algorithm faster than the CPU. The smallest improvement, a 1.21 ratio, was found with the smallest image size of 256×256, and the largest speedup, a 4.25 ratio, was observed with the largest image size of 2304×2304. Conclusions: GPU programming resulted in a significant decrease in computational time associated with a FT image registration algorithm. The inclusion of the GPU may provide near real‐time, sub‐pixel registration capability.
SU‐E‐J‐92: CERR: New Tools to Analyze Image Registration Precision
Authors: Apte A , Wang Y , Oh J , Saleh Z , Deasy J
Published: June 2012

Purpose: To present new tools in CERR (The Computational Environment for Radiotherapy Research) to analyze image registration and other software updates/additions. Methods: CERR continues to be a key environment (cited more than 129 times to date) for numerous RT‐research studies involving outcomes modeling, prototyping algorithms for segmentation, and registration, experiments with phantom dosimetry, IMRT research, etc. Image registration is one of the key technologies required in many research studies. CERR has been interfaced with popular image registration frameworks like Plastimatch and ITK. Once the images have been autoregistered, CERR provides tools to analyze the accuracy of registration using the following innovative approaches (1)Distance Discordance Histograms (DDH), described in detail in a separate paper and (2)‘MirrorScope’, explained as follows: for any view plane the 2‐d image is broken up into a 2d grid of medium‐sized squares. Each square contains a right‐half, which is the reference image, and a left‐half, which is the mirror flipped version of the overlay image. The user can increase or decrease the size of this grid to control the resolution of the analysis. Other updates to CERR include tools to extract image and dosimetric features programmatically and storage in a central database and tools to interface with Statistical analysis software like SPSS and Matlab Statistics toolbox. Results: MirrorScope was compared on various examples, including ‘perfect’ registration examples and ‘artificially translated’ registrations. for ‘perfect’ registration, the patterns obtained within each circles are symmetric, and are easily, visually recognized as aligned. For registrations that are off, the patterns obtained in the circles located in the regions of imperfections show unsymmetrical patterns that are easily recognized. Conclusions: The new updates to CERR further increase its utility for RT‐research. Mirrorscope is a visually intuitive method of monitoring the accuracy of image registration that improves on the visual confusion of standard methods.
SU‐E‐J‐193: Gamma Knife Perfexion End‐To‐End Testing with a Commercial Stereotactic Phantom
Authors: Yount C , Lyons K , Rahnema S , McDonald D , Peng J , Vanek K
Published: June 2012

Purpose: To investigate the use of the Lucy ® Stereotactic Phantom (Standard Imaging, Inc.) for Gamma Knife Perfexion radiosurgery quality assurance of the imaging, treatment planning, and dose delivery processes. End‐to‐end testing of the Perfexion and Gamma Plan version 10.1 has not been previously examined in literature. Methods: The phantom was imaged using both the CT and T1‐ and T2‐weighted MR sequences used for treatment planning. For imaging, the isocentric volume insert and fiducial markers were positioned within the phantom. Scans were transferred to the Gamma Plan treatment planning system and were evaluated for geometric and fusion accuracy. A plan was created to deliver 12Gy to the 50% isodose line to the 5.25cm3 volume. During dose delivery, Gafchromic EBT2 film was positioned in the film insert to replicate the position of the target volume. Dose results were analyzed using RIT software (Radiologic Imaging Technology, Inc.). Results: Image fusion integrity was inspected by overlaying the MR and CT markers (5 fiducial markers spaced 5mm apart) and visually examining the resulting volume insert overlap between the three scans. Geometric accuracy was evaluated by contouring three volumes using Gamma Plan contouring tools. Agreement within 1.1%, 6.7% and 12.2% of the actual volumes was seen with the T1‐weighted, T2‐weighted, and CT images, respectively. The volume‐based acquisition and 1mm slice thickness of the T1‐weighted sequence resulted in the most accurate measurement. Geometric measurements along two dimensions showed acceptable accuracy for all imaging modalities within 1.6%. Dosimetry results agreed well with the planned dose. The EBT2 film was calibrated for absolute dose measurements using a dose calibration curve for 0.1–30 Gy and the calibration curve was verified to have <3% error above 1Gy. Conclusions: The Lucy phantom allows for comprehensive quality assurance testing of the Gamma Knife Perfexion radiosurgery process.
SU‐E‐J‐194: The Impact of Different Imaging Measures on Treatment Response Assessment of Bone Metastases
Authors: Morrison C , Liu G , Jeraj R
Published: June 2012

Purpose: Several treatment response metrics, such as RECIST and PERCIST, have been established for assessing individual solid tumors. However, metastatic prostate cancer poses a unique challenge to these metrics because bone lesions are often numerous and non‐measureable. This study investigated the impact of using different imaging measures for treatment response assessment in patients with metastatic prostate cancer. Methods: Six patients with metastatic prostate cancer were treated with molecular targeted therapy and received whole body [18F]NaF PET/CT scans pre‐, mid‐, and post‐treatment. Lesions were segmented using a threshold of 20% the maximum SUV in bone and then manually adjusted with physician guidance. For each patient, SUVmax, SUVmean, SUVpeak, SUVtotal, number of lesions, and total volume of bone lesions were determined. For each measure, treatment response was calculated as the percent change relative to pre‐treatment. The range of the different responses was calculated for each patient at each response time point. The population average of the patient ranges was calculated. Results: The patient responses varied greatly for different imaging measures. The population‐averaged range for all response measures was 50%. In general, SUVmax, SUVmean, and SUVpeak responses were negative, indicating good response to treatment, but the number of lesions, volume, and SUVtotal responses were positive, indicating disease progression. When the measures were separated into these two groups, the population‐averaged range was only 25% among the number of lesions, volume, and SUVtotal responses and 10% among the SUVmax, SUVmean, and SUVpeak responses. Conclusions: Several treatment response metrics, such as RECIST and PERCIST, have been established for assessing individual solid tumors. However, metastatic prostate cancer poses a unique challenge to these metrics because bone lesions are often numerous and non‐measureable. This study investigated the impact of using different imaging measures for treatment response assessment in patients with metastatic prostate cancer.
SU‐E‐J‐195: Dosimetric Consequences of Metal Prosthesis in Prostate 3D CRT by Using Monte Carlo Dose Calculation Method
Authors: Chen Y , Hong L , Yaparpalvi R , Verhaegen F
Published: June 2012

Purpose: To investigate dosimetric consequences of patient metal prosthesis in prostate radiotherapy, considering the body heterogeneity, metal artifacts, prostate daily displacements and target delineation. Methods: Three prostate patients with metal prosthesis were simulated with CT images and 3D ultrasound images. Conformal RT treatment plans were generated based on target volumes delineated on CT images without artifact correction (PTVa). The patients' treatments were aided with an ultrasound (US) localization system for daily PTV setup correction. We retrospectively reevaluated the delineation of PTVs by 1) using simulation CT images artifact‐corrected by using an algorithm developed by M. Bazalova et al (2007) (PTVc) and 2) using the 3D ultrasound simulation images as guide (PTVus). Daily setup corrections to the PTVs were incorporated to calculate composite delivered dose by using XVMC simulation on the patient phantom derived from the artifact‐corrected CT images. DVHs and dose distributions for different PTVs were then compared with the reference treatment plans (XVMC‐calculated on the artifact‐degraded CT images). Results: The PTVa volume was the largest, about 1.3% larger than artifact‐corrected PTVc and 5.2% larger than PTVus. Adapting artifact‐corrected CT images can improve the DVH curves of PTVc and increase the D95% and V95% for PTVc by more than 5% while D50% and V50% for rectum and bladder are raised by up to 41.6%. DVH analysis on PTVa and PTVus shows a small difference in the changes of their DVH indices, less than 4% for the studied cases. Conclusions: The strike artifacts from metal prosthesis will increase the volume of PTVa, and affect the patient dose calculation. Original patient plan did not accurately predict the dose degradation. Artifact correction may be necessary for some cases having severe metal artifacts. Using US images to help delineating PTV makes a negligible clinical significance.
SU‐E‐J‐196: In‐Vivo Tumor Blood‐Oxygen Content Measurement via Interstitial Optical Transmission Spectroscopy
Authors: Campos D , Yan Y , Zhao D , Kissick M , Jacques S , van der Kogel A , Kimple R
Published: June 2012

Purpose: To demonstrate the application of in‐vivo diffuse optical transmission spectroscopy in quantifying oxygen saturation in interstitial tissue, and to use this technique to examine reoxygenation dynamics in real‐time as tumors responds to radiotherapy. Methods: Two 200 micron core fiber optics were threaded through two 21 gauge hypodermic needles: one coupled to an OceanOptics QE65000 spectrometer, and the other to an Ocean Optics HL‐2000‐HP 20W light source. These needles were fixed approximately 3 mm apart, and inserted into nude mice with human head‐ and‐neck tumor xenografts. The oxygen saturation was then measured as a function of time after irradiation at intervals of 0.5, 1, 2, 6, 12, and 24, to measure the tumors' prompt oxygen saturation response to radiation. Results: Blood volume, deoxy and oxy‐hemoglobin concentrations were measured through least‐squares fitting of transmission spectra. Furthermore, various configurations of interstitial fiber optic probes were explored to optimize signal strength. Improvement of the optical coupling to the biological system and a concurrent increase in source intensity are the main two focuses for boosting signal strength. Conclusions: This work has the potential to give an understanding of the time‐scales of hypoxia and reoxygenation in vivo as tumors respond to radiation injury. This technique is of particular interest for hypofractionated therapies particularly treatments of only two or three treatments, where optimizing treatment timing can increase the tumorcidal effect of the remaining fractions.
SU‐E‐J‐197: A Novel Optical Interstitial Fiber Spectroscopic System for Real‐Time Tissue Micro‐Vascular Hemodynamics Monitoring
Authors: Zhao D , Campos D , Yan Y , Kimple R , Jacques S , van der Kogel A , Kissick M
Published: June 2012

Purpose: To demonstrate a novel interstitial optical fiber spectroscopic system, based on diffuse optical spectroscopies with spectral fitting, for the simultaneous monitoring of tumor blood volume and oxygen tension. The technique provides real‐time, minimally‐invasive and quantification of tissue micro‐vascular hemodynamics. Methods: An optical fiber prototype probe characterizesthe optical transport in tissue between two large Numerical Aperture (NA) fibers of 200μm core diameter (BFH37‐200, ThorLabs) spaced 3‐mm apart. Two 21‐Ga medical needles are used to protect fiber ends and to facilitate tissue penetration with minimum local blunt trauma in nude mice with xenografts. A 20W white light source (HL‐2000‐HP, Ocean Optics) is coupled to one fiber with SMA adapter. The other fiber is used to collect light, which is coupled into the spectrometer (QE65000 with Spectrasuite Operating software and OmniDriver, Ocean Optics). The wavelength response of the probe depends on the wavelength dependence of the light source, and of the light signal collection that includes considerable scatter, modeled with Monte‐Carlo techniques (S. Jacques 2010 J. of Innov. Opt. Health Sci. 2 123–9). Measured spectra of tissue are normalized by a measured spectrum of a white standard, yielding the transmission spectrum. A head‐and‐neck xenograft on the flank of a live mouse is used for development. Results: The optical fiber probe delivers and collects light at an arbitrary depth in the tumor. By spectral fitting of the measured transmission spectrum, an analysis of blood volume and oxygen tension is obtained from the fitting parameters in real time. Conclusions: A newly developed optical fiber spectroscopic system with an optical fiber probe takes spectroscopic techniques to a much deeper level in a tumor, which has potential applications for real‐time monitoring hypoxic cell population dynamics for an eventual adaptive therapy metric of particular use in hypofractionated radiotherapy.
SU‐E‐J‐202: Treatment Dose Assessment with the Consideration of Radiation Dose Inducible Organ Shrinkage/Deformation
Authors: Nie X , Yan D
Published: June 2012

Purpose: For asymmetric organ shrinkage caused by heterogeneity dose distribution, tissue elasticity based deformable organ registration cannot be directly applied to the treatment image to construct the treatment dose. A novel approach is proposed to include radiation dose inducible organ shrinkage/deformation in the consideration of treatment dose assessment. Methods: A model and algorithm were developed to include dose inducible organ shrinkage in the deformable image registration. In the model, we assume that the logarithm of tissue‐element volume shrinkage ratio is proportional to the LQ survival function, and the tissue‐element displacement field is the gradient of a scalar potential function. The derived Poisson equation of the potential was solved using a finite element method. Two steps registration was implemented to determine the tissue‐element volume and displacement. The first is the conventional deformable image registration to determine the organ surface. The second is to map the element volume/position in the shrinking organ with using the dose inducible shrinkage model. Treatment dose was constructed by applying both the conventional deformable registration and the shrinkage model on CBCT images obtained from h&n treatment. The dose distribution in the patient parotid was evaluated. Results: Treatment dose‐volume, V30, constructed including the dose inducible parotid shrinkage was 11% higher than the one from the conventional deformable image registration and dose construction. Tissue elements in the high dose region shrink more than those in a low dose region which results in extra tissue elements in the organ move into the high dose area during the treatment course and an unfavorable dose‐volume relationship in the organ. Conclusions: Without including dose inducible organ shrinkage, treatment dose in a shrinking organ could be underestimated. On the other hand, including this effect in the treatment evaluation and adaptive planning optimization will minimize the potential detriment of the effect.
SU‐E‐J‐203: Determination of PTV Margin for Lung Tumor Using In‐Treatment 4D CBCT
Authors: Haga A , Nakagawa K , Yamashita H , Takahashi W , Sakumi A , Masutani Y , Kida S , Saotome N , Itoh S , Shiraki T , Ohtomo K
Published: June 2012

Purpose: To determine a planning target volume (PTV) margin for lung cancer patients using a four‐dimensional cone‐beam CT (4D CBCT) acquired during volumetric modulated arc therapy (VMAT) treatment. Methods: A VMAT plan for lung cancer patients was created by Pinnacle v9.0 (Philips) treatment planning system (TPS), where the gross target volume (GTVs) in each breathing phase was delineated by using 4D‐planning CT scan (TOSHIBA and ANZAI). The VMAT treatment was performed with a stereotactic body frame after the registration using Elekta X‐ray volume imaging (XVI) unit. Simultaneous cone‐beam projection images were acquired for 3 or 4 fractions of 10 patients. The in‐treatment 4D CBCT was reconstructed by dividing into four breathing phase bins. A total of 38 in‐treatment 4D‐CBCT sets were exported to Pinnacle TPS. The isocenter of in‐treatment 4D CBCT was matched with that of 4D‐planning CT. The tumor motion during treatment was manually tracked on in‐treatment 4D CBCT, and the center‐of‐mass (COM) location of the tumor was estimated. Analyzing the tumor regions observed by in‐treatment 4D CBCT, a PTV margin in our system was derived. Results: The average difference in COM location of the tumor was less than 1mm for all directions, while the standard deviations (SD's) were about 1.3mm, 1.6mm, and 2.1mm for the lateral, the vertical, and the longitudinal directions, respectively. The large discrepancy more than 3mm was observed for one patient. The required PTV margin was about 3‐4mm for the lateral and the vertical directions, whereas it was about 5mm for the longitudinal direction. Conclusions: The uncertainties of the tumor motion caused by respiration were observed by in‐treatment 4D CBCT images. It was feasible to determine the PTV margin from 4D volume images. K. Nakagawa receives research funding from Elekta.
SU‐E‐J‐207: Compensation of Target Distortion of Pancreatic Tumor in Free‐Breathing CT Using 4D Contour Propagation
Authors: Yang X , Reese A , Mutaf Y , Yi B
Published: June 2012

Purpose: Due to lack of soft‐tissue contrast, target distortion for the upper‐abdomen targets such as pancreatic tumors is complicated and requiring sufficient remedy. By applying automatic contour propagation, the authors use the information obtained from 4D CT to test if the deformable image registration compensates the respiration‐induced distortion of pancreatic tumor in free breathing (FB) CT images. Methods: Ten patients with unresected pancreatic cancer treated with either preoperative or definitive chemoradiation were studied. Pancreas GTVs were delineated on the FB CT. Using deformable image registration, the FB GTV contours were propagated to each phase of the 4D CT images taken right after the FB CT, and were compared with the FB GTV to see difference in tumor volume and tumor size along individual dimensions. A one‐dimensional tumor motion in proportion to cos4(ωt) was simulated to calculate the probability distribution function for different magnitude of distortions during FB CT scans, and a binary classification test was conducted to analyze the observed results. Results: The probability distribution function predicted that four out of the ten cases would have substantial target distortion given the variation in target motion amplitudes. Three of these four cases show substantial difference in the superior‐inferior size of FB GTV compared to the average 4D GTV, taking into account the uncertainties caused by motions perpendicular to the scanning axis and resolution of the CT scanner. The binary classification test yielded a precision of 75% and an accuracy of 90%. Conclusions: Pancreatic GTV distorted due to respiration‐induced tumor motion is effectively compensated by contour propagation from free‐breathing CT to 4D CT using DIR. Union of GTVs of all breathing phases or IGTV can be genreated from 4D set of GTVs propagated from that of free breathing. This study is partially supported by NIH grant 1R01CA133539‐01A2. I do not have conflict of interest.
SU‐E‐J‐209: A Simple Method to Minimize Uncertainty in ITV Delineation: Phantom Verification
Authors: Turner K , Cai J , Yin F , Zhang Y , Vergalasova I
Published: June 2012

Purpose: Irregular breathing causes variation in delineation of internal target volume (ITV), which is typically generated in the maximum intensity projection (MIP) images [1]. Previous studies have shown that MIP‐based ITV can underestimate true tumor range [2]. This study examines a simple method to reduce such errors by combining the GTV of 3D‐CT with the ITV of MIP. Methods: The Computerized Imaging Reference Systems (CIRS) Dynamic Thorax Phantom Model 008A (CIRS, Norfolk, VA) with CIRS motion control software was used to model 4 irregular patient respiratory profiles and one regular respiratory profile (sine wave). A 3 cm tumor insert was used as target. For each breathing profile, a 3D‐CT and 3 repeated 4D‐CT scans with random intervals within the breathing profile were performed on a 4‐slice clinical scanner (Lightspeed, GE, WI). The RPM system (Varian, Palo Alto, CA) was used to track the respiratory profiles. GTV was contoured on 3D‐CT, and ITV was contoured on each MIP (ITVMIP) using a consistent lung window by the same person. The new method of creating ITV was to combine the GTV and ITVMIP, namely ITVCOMB. To evaluate which ITV is more accurate, ITVCOMB and ITVMIP were compared to a ‘ground truth’ ITV (ITVGT) which was generated by combining the three ITVMIPs. Results: For the regular profile, both ITVMIP (27.25 cm3) and ITVCOMB (28.12 cm3) were comparable to ITVGT (27.25 cm3). For irregular profiles, the mean absolute difference between ITVCOMB and ITVGT (6.3%±4.9) was significantly (p‐value=0.0078) smaller than that between ITVMIP and ITVGT (18.1%±12.3). Conclusions: The results suggest that combining GTV of the 3D‐CT with the ITV of the MIP is more accurate than the ITV of the MIP alone, and thus would be a simple method to reduce breathing irregularity induced errors in ITV delineation for treatment planning of lung cancer.
SU‐E‐T‐01: Applications of 6MV FFF Photon Beams in Optimizing Radiobiological Response for Respiratory‐Gated Liver SBRT
Authors: Karan T , Moiseenko V , Gill B , Horwood R , Minchinton A
Published: June 2012

Purpose: To establish a radiobiological basis for gated stereotactic body radiotherapy of primary and metastatic liver cancers using volumetric arc radiotherapy in a flattening filter free (FFF) mode. Methods: Human cervical carcinoma, SiHa, non‐small cell lung carcinoma, H460, and Chinese hamster V79 cells were irradiated in a water bath with 6MV photons from a Varian TrueBeam linear accelerator. To establish dose‐response and its sensitivity to dose rate following acute irradiation, doses of 2, 4, 6, 8 and 10 Gy were delivered in FFF mode at 400 and 1200 MU/min. To investigate whether removal of the flattening filter affects cell response, doses of 5 and 10 Gy were delivered to SiHa and H460 cells in FFF and filtered modes at 400 MU/min. Finally, to assess the effect of protracting dose delivery by gating, a dose of 10 Gy was delivered to SiHa and H460 cells acutely and also over 15, 30 and 60 min. Results: Dose‐response over doses examined was independent of dose rate in FFF mode. Differences in cell survival following irradiation in FFF and filtered modes were not significant. However a significant increase in survival for both H460 and SiHa cells was observed for 15 min split‐dose irradiation compared to acute irradiation but further increase in irradiation time to 60 min did not affect cell survival. Conclusions: Dose rate and presence of a flattening filter showed no effect on cell survival, however, survival was significantly affected when dose delivery time was protracted to that typical of conformal field therapy. Volumetric arc based gated SBRT may be beneficial for tumor cell kill, though the gating window and duty cycle have to be balanced against the effect of dose delivery protraction. Research Support (Varian Medical Systems)
SU‐E‐T‐02: Radiobiological Comparison of Two Treatment Schemas in IMRT Prostate Radiotherapy
Authors: Hernández T García , González A Vicedo , Cabañero D Granero , González L Brualla , Ferrando J Rosello , Peidro J Pastor , Torrecilla J Lopez
Published: June 2012

Purpose: Different fractionation schemas are used for the treatment of prostate with IMRT. Due to the low α/β of prostate hypofractionated schemas are achieving more importance. The purpose of this study is to compare two IMRT techniques from a radiobiological point of view in the treatment of high risk prostate cancer, the sequential IMRT technique (SIMRT) and a simultaneous integrated boost IMRT treatment (SIBIMRT). Methods: 20 patients were selected and planned using both treatment strategies to give an EQD2 of 82 Gy to prostate, 70 Gy to vesicles and 46 Gy to lymph nodes, using the linear quadratic model LQ supposing an α/β prostate=1.5 Gy. Dose volume histograms of prostate, rectum and bladder were calculated. Tumour Control Probabilities (TCP) and Normal Tissue Complication Probabilities (NTCP) were also calculated. As the prostate α/β is not known exactly the TCP has been calculated for different a/bprostate values ranging from 1.5 to 10 Gy. NTCPs of bladder and rectum were calculated also for α/β oar values ranging between 1 to 15 Gy. Results: Both treatment strategies were found to be equivalent in terms of prostate ptv TCP and EQD2 for low α/β prostate=1.5 Gy. In the case of high α/β prostate values, 3 Gy and 10 Gy, EQD2 and TCP for prostate ptv are lower for the SIBIMRT technique. For rectum and bladder, if a/boar ranges between 2 and 15 Gy EQD2 values are higher for the SIMRT treatment schema. NTCP for bladder and rectum is higher for the SIMRT technique when α/β OAR >= 2 −3 Gy. Conclusions: In this study a comparison between two treatments strategies have been done. Our results show that a hypofractionated technique for high risk prostate cancer reduces, or equals, EQD2 and NTCP for bladder and rectum while maintaining the TCP of prostate for the typical α/β values in use.
SU‐E‐T‐03: Justification and Feasibility of Neural Stem Cell Sparing in Whole Brain Irradiation Using VMAT
Authors: Phillips T , Martin L , Kornblum H , Xing L
Published: June 2012

Purpose: To determine the impact of radiation on neural stem cells and examine the feasibility of neural stem cell sparing using volumetric modulated arc therapy (VMAT) for whole brain irradiation. Methods: Murine neural stem cells were harvested from the sub‐ventricular zone (SVZ), cultured and assessed for radio‐sensitivity and differentiation potential in response to radiation (0–6Gy). Clonogenic survival of these cells was compared to that of tumor cells derived from the murine PTEN−/−/Kras+ spontaneous brain tumor model. The differentiation potential of neural stem cells surviving irradiation was examined by allowing the cells to differentiate for five days and analyzing cell types. In order to address the feasibility of neural stem cell sparing, a typical 3D whole brain treatment was compared to VMAT, in which the neural stem cell compartment, designated and contoured as the lateral ventricles with a 3–5mm margin, was spared. Whole brain dose coverage was maintained similarly to conventional 3D treatment, while minimizing the dose to the stem cell compartment. Results: Neural stem cells are significantly more radio‐sensitive than their tumor counterparts (2Gy, p=0.018), and the neuronal differentiation capacity of stem cells that survive radiation treatment is markedly diminished. Compared to conventional 3D treatment, VMAT reduces radiation dose to the stem cell SVZ compartment while maintaining adequate coverage of the whole brain. Conclusions: Radiation‐induced cognitive decline from whole brain irradiation is of particular clinical relevance. Cognitive functions are strongly influenced by the activity of neural stem cells, thus stem cell sparing may help mitigate radiation‐induced cognitive decline. To our knowledge, this is the first study to confirm that radiation induces impaired neuronal differentiation at clinically relevant doses, and that improved stem cell sparing of the lateral ventricles (SVZ) is feasible using VMAT. Thus our studies confirm that VMAT should be examined further for clinical relevance in whole brain irradiation.
SU‐E‐T‐10: Monte Carlo Study of the Dose Enhancement Factor (DEF) for Gold Nano‐Particle (GNP) on the Cellular Level
Authors: Zhang M , Qin S , Haffty B , Yue N
Published: June 2012

Purpose: In megavoltage external beam radiotherapy, in vivo cell experiments suggest GNP could be used as a radiosensitizer by having radiation dose enhancement factor (DEF) significantly larger than 1. However, Monte Carlo (MC) simulations published in the literature failed to give prove, in which most of them only simulated the interactions between the radiation beams and a single GNP. In this study, we built a multi‐GNPs model considering possible spatial arrangements of GNPs relative to a cell to calculate the DEFs of GNPs. Methods: Geant4 MC code with G4DNA physics model which can trace electrons down to eV level was used. Two types of geometry models representing different GNP‐cell binding were created with each GNP modeled individually: (1) shell model with GNPs randomly and sparsely distributed in a shell in water mimicking when the GNPs were binding to the cell membrane, and (2) sphere model with GNPs randomly and sparsely distributed in a sphere in water mimicking when GNPs were floating inside the cytoplasm. Photon and electron spectrum at 5 cm in depth in water from a Varian 6MV beam was used as the radiation source. Dose to water inside the shell or the sphere representing cytoplasm were scored and compared to situations without GNPs to calculate the DEF. We also looked into the variation of DEFs due to different GNP sizes and concentrations. Results: A 35 um water cubic were successfully built in Geant4 with spatial resolution of 100 nm. Preliminary results shown under 200 keV electron irradiation, 100 nm GNPs in the shell model shown increased dose to cell at the beam entrance (DEF = 1.08). Conclusions: The computation is undergoing for different GNP sizes and concentrations. Meaningful results are expected on the completion of this study.
SU‐E‐T‐12: Radiation Detector Responses to Applied Homogeneous Transverse and Parallel Magnetic Fields
Authors: Reynolds M , Rathee S , Vidakovic S , Fallone B
Published: June 2012

Purpose: To determine the relative dose response of a diamond detector and a ion chamber in a clinical photon beam within uniform magnetic fields, endeavoring to evaluate and refine reference dosimetry techniques for use in integrated MR‐linac systems. Methods: The Monte Carlo code PENELOPE was used to model the structure and materials of the PTW60003 diamond detector and PR06 ion chamber in a 6MV beam in the presence of a homogeneous magnetic field. The magnetic field strength was varied from 0 to 1.5T, and both the parallel and transverse magnetic field orientations with respect to the beam central axis were simulated. The long axes of the detectors were oriented both perpendicular and parallel to the radiation beam direction for each magnetic field orientation. All simulations determined the detectors' signal in air. A small electromagnet was used to experimentally determine the detectors' response in transverse magnetic fields up to 0.2T to validate the simulations. Results: The simulated response of both detectors matched to the experimental data within the estimation error. The relative response of PR06 and diamond detector varied up to ±8.5% (depending on chamber orientation) and >9% respectively with increasing transverse magnetic field strength. In contrast, both detectors were found to be relatively insensitive to the increasing magnetic fields irrespective of the detector orientation in parallel magnetic field. A maximum change of 2% in PR06 response was observed at 1.5T parallel magnetic field and in the parallel orientation of chamber. Conclusion: This work has significant impact on dosimetry protocols for integrated MR‐linac systems, where detector response may be altered by the presence of a magnetic field. The need for a magnetic field dependent correction factor is strongly indicated for the transverse magnetic field cases, while such changes in detector response can be largely ignored in parallel magnetic fields < 1T. CIHR (Canadian Institutes of Health Research) ‐ funding support Faculty of Medicine and Dentistry, University of Alberta ‐ funding support
SU‐E‐T‐16: Statistical Variability and Confidence Intervals for Planar Dose QA Pass Rates
Authors: Bailey D , Nelms B , Kumaraswamy L , Attwood K , Podgorsak M
Published: June 2012

Purpose: The most common metric for comparing measured to calculated dose planes is a pass rate generated using percent difference, distance‐to‐agreement (DTA), or some combination of the two (e.g. gamma evaluation). The grid of analyzed points often corresponds to a dosimeter array with low areal‐density of point detectors. This work examines the statistical uncertainty of planar dose comparison pass rates and proposes methods for establishing confidence intervals for pass rates obtained with low detector‐density arrays. Methods: Absolute dose planes were acquired via EPID for twenty intensity‐modulated fields of varying complexity. Matching calculated dose planes were created via treatment planning system. Pass rates for each dose plane pair (centered to CAX) were calculated with various %/DTA composite analysis techniques. Software was designed to selectively sample the high‐density EPID matrix to simulate many low‐density measured grids, each representing a different alignment with respect to CAX. Simulations were repeated (100 positional iterations per field) using grids of varying detector‐densities and both random and orthogonal point‐detector orientation. For each simulation, pass rates were calculated with various composite analysis techniques. Results: Repositioning simulated low‐density grids leads to a distribution of possible pass rates for each measured/calculated dose plane pair, independent of whether the detector grid is random or uniform. Distributions can be predicted using a binomial distribution by which a confidence interval (function of sampling density and observed pass rate) is approximated for each pass rate. For example, 95% confidence intervals for IMRT pass rates (2%,2mm) average +/−5.3% and +/−3.8% with 1‐detector/cm2 and 2‐detector/cm2 grids, respectively. Conclusions: Pass rates for low‐density array measurements are not absolute and should be reported with both a full description of calculation method and confidence intervals quantifying their uncertainty. Results extend to 3D detector arrays. The concept of fixed ‘action levels' for pass rates must be reexamined for low‐density array measurements.
SU‐E‐T‐17: Comparison of MCNP5 Calculations in the Buildup Region with Plane Parallel Ionization Chamber Measurements for 6 and 18 MV Photon Beams
Authors: Abbas H , Satti J , MacDonald C
Published: June 2012

Purpose: Cylindrical ion chambers are known to overestimate the dose in the buildup region, where gradients are high. The potential for MCNP5 to produce accurate calculations in this region, even when benchmarked with a large volume chamber, was tested. Methods: MCNP5 was used to model 6 and 18 MV photon beams for a Varian accelerator using vendor geometry with the collimator corrections of Chibani and Ma. Modeling was benchmarked by adjusting electron beam energy and diameter to match calculations with ionization chamber (with 0.125 cm3 sensitive volume) measurements of percent depth doses (PDDs) beyond dmax and cross dose profiles for 5×5, 10×10 and 30×30 cm2 field sizes. For comparison in the buildup region, the MCNP5 voxel was reduced to 1 mm, with extrapolation to find surface dose. In this region a plane parallel chamber (with 0.055 cm3 sensitive volume) was used to measure PDDs at 0, 2 and 4 mm depths for the three field sizes, using the Khan over‐response correction. Results: Calculations and cylindrical chamber measurements for PDDs beyond dmax agree within 2% for all field sizes and energies. Dose profiles at dmax (1.5 cm and 3.3 cm for 6 and 18 MV) and at 10 cm agree within 2% in the flat region and within 10% in the penumbra. In the buildup region, the MCNP5 calculations agree with plane parallel PDD measurements within 3% at 2 and 4 mm depths. The extrapolation of the MCNP5 PDD overestimates the surface dose for the 18 MV beam for the 30×30 cm2 field, and is within 4.2% for the smaller fields and for all field sizes at 6 MV. Improved extrapolation techniques may yield better surface dose agreement. Conclusions: Accurate dose in the buildup region can be calculated by MCNP5
SU‐E‐T‐22: Is the Residual Range a Universal Quantity to Specify the Quality of Modulated Proton Beams?
Authors: Granville D , Chequers M , Sawakuchi G
Published: June 2012

Purpose: To investigate the validity of using the residual range as a universal quantity to specify the quality of modulated proton beams. Methods: We used TOPAS (Tool for Particle Simulation), an application of the Geant4 toolkit, to simulate absorbed dose and stopping‐power distributions from a commercial passive scattering nozzle. We used the standard physics lists from Geant4 in the simulations. All particles were included, as well as physics models for nuclear interactions. No variance reduction techniques were used. Dose and averaged stopping‐power as functions of depth were scored in a water box with 320 scoring volumes of 15 × 15 × 0.1 cm3. Stopping‐power spectra were scored in a15 × 15 × 0.1 cm3 volume located in the middle of SOBPs. All particles were considered in the dose scoring. Only protons (primary and secondary) were considered in the scoring of stopping‐power. Results: For the same residual range, differences in averaged stopping‐power values of up to 13% were observed for a 200 MeV beam with modulations of 4 cm and 8 cm, respectively. Simulations of four modulated proton energies with the same SOBP of 8 cm showed differences of up to 13% in the averaged stopping‐power values even in the SOBP region. We also simulated stopping power spectra in the middle of 8 cm SOBPs for four modulated proton energies. The averaged stopping‐power values calculated from the spectra were within 3%, however, their distributions were very different with full width at half‐maximum 150% larger for the 250 MeV beam compared to that of the 140 MeV beam. Conclusion: Large differences in the averaged stopping‐power values and stopping‐power spectra were observed for the same residual range. Determining whether these differences have a significant effect on the response of radiation detectors exposed to proton beams requires further investigation. Natural Sciences and Engineering Research Council of Canada and Ontario Graduate Scholarship Program, Ontario Ministry of Training, Colleges and Universities