bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐J‐47: Assessment of Diaphragm as An Internal Surrogate for Lung Tumor Motion Prediction
Authors: Cerviño L , Jiang Y , Jiang S
Published: April 2010

Purpose: We have previously assessed the use of diaphragm as a surrogate for predicting real‐time tumor position with linear models built with training data extracted from the same treatment fraction. In this study, we evaluate inter‐fraction variability of model parameters and the prediction error for different fractions from the model built on the first fraction. Method and Materials: 21 fluoroscopic sequences from 5 lung cancer patients were used for this study. Each patient has from 2 to 6 fluoroscopic sequences from at least 2 different treatment fractions. Each sequence consists of 352 to 690 frames at 15 frames per second. Superior‐inferior motions of the diaphragm and the tumor were identified in every frame. A model to predict tumor position was built for each sequence, and the parameters from different sequences were compared. Then, the model built from the first fluoroscopic sequence was used to predict tumor position in the subsequent fluoroscopic sets of each patient. Prediction error was calculated for three different ways of registering fluoroscopic sets: manual bony anatomy registration, mean tumor position registration, and mean diaphragm position registration. Results: Average variability of the correlation and slope of linear models built from different fluoroscopic sequences are 1.3% and 8.6% respectively. Prediction based on the model built with data from the first sequence leads to an average mean localization error and average error at a 95% confidence level of 1.2mm and 2.9mm respectively for bony registration, 1.5mm and 3.3mm for mean tumor position registration, and 2.5mm and 4.7mm for mean diaphragm position registration. Conclusion: For the patients studied, diaphragm has shown to be a good surrogate for tumor motion. Variability of model parameters and prediction error from one sequence to another are small. Bony registration seems the most accurate method for patient setup when using diaphragm as a surrogate.
SU‐FF‐J‐48: Localization Accuracy of a Gantry‐Mounted Radioactive Tracking System in the Clinical Radiation Therapy Environment
Authors: Alezra D , Shchory T , Lifshitz I , Pfeffer R
Published: April 2010

Purpose: The submillimeter accuracy of a novel gantry‐mounted radioactive fiducial tracking system has been reported previously in a number of semi‐clinical scenarios. These have included tissue equivalent phantoms without bones, and antomical phantoms including bones, but with measurements being made from a single gantry angle that does not include potential interference from the bones and the patient couch and potential tracking system alignment inaccuracy due to gantry and collimator rotation. In this study the gantry‐mounted tracking system is tested in a more realistic clinical scenario. This study used an anatomical phantom with bones placed at multiple positions about the isocenter and made localization measurements with the gantry and collimator at various angles. Method and Materials: The tracking device was installed on a Varian Trilogy® linac gantry. The radioactive marker was located at the approximate position of the prostate in an anatomical tissue equivalent phantom on the patient couch. Actual marker location was measured using a Microscribe MLX coordinate measuring machine (CMM) arm (certified spatial accuracy of 0.08 mm). The marker was attached to the tip of the CMM arm, which was inserted into a hole in the phantom, and its location was measured simultaneously by the CMM and the tracking system. 102 localization accuracy measurements were made at locations covering a 10cm diameter sphere centered at the linac iso‐center with varying gantry and collimator angles including those that would potentially induce interference due to bones and the patient couch. Results: The mean localization error for all measured positions and gantry and collimator angles was less than 1mm. Conclusion: The gantry‐mounted radioactive tracking system maintains sufficient accuracy for radiation therapy patient localization and monitoring in a real clinical environment even in the presence of bones and patient couch interference. Conflict of Interest: Research sponsored by Navotek Medical Ltd.
SU‐FF‐J‐61: Evaluation of the Need for Simultaneous Orthogonal Gated Setup Imaging
Authors: Berbeco R , Nishioka S , Shirato H
Published: April 2010

Purpose: As many clinics would prefer to use a pair of kV radiographs for gated patient setup, it is important to quantify the possible errors that could occur due to the non‐simultaneity of the acquisitions. Method and Materials: The data set from 11 patients includes internal and external coordinates acquired at 30Hz during multi‐fraction SBRT treatments. We simulated a gated setup procedure which included an AP radiograph, followed by a lateral radiograph. The time interval between the two radiographic acquisitions was set to a minimum of 30 seconds based on our clinical experience. The setup position is derived from a combination of both the initial (AP) and the second (LAT) image in the following way: . The 3D error is then the magnitude of the vector from the initial position to the setup position. The calculation was done for every exhale phase in the data for which there was another one at least 30 seconds later at an amplitude within 2 mm from the first. In all, 1908 data points were analyzed. Results: The 3D error is found to be less than 2 mm for 91% of the data points and less than 3 mm for 97% of the data. The maximum error found was 7.5 mm. 97.5% of the second acquisitions could be completed within 35 seconds of the first. The maximum time interval found was 42 seconds. No correlation was found between the length of the time interval and the 3D error. Conclusion: When acquiring gated radiographs for patient setup, no large setup errors should be expected if those images are not taken simultaneously. Conflict of Interest: This work was sponsored, in part, by a grant from Varian Medical Systems, Inc.
SU‐FF‐J‐68: Evaluation of An IGRT System for Mobile Targets
Authors: Sethi A
Published: April 2010

Purpose: Evaluate accuracy/precision of Novalis (BrainLAB®) IGRT in treating mobile targets. Method and Materials: Novalis IGRT is an automated 6D patient positioning/verification system using infra‐red (IR) markers and stereoscopic X‐ray image guidance. We used two respiratory motion phantoms in end‐to‐end hidden‐target‐test mode. A 2mm diameter marker was placed on high sensitivity Gafchromic film. Phantoms were irradiated with treatment fields collimated by a 10mm cone. Difference between centers of irradiated field and marker location yielded system accuracy. Irradiations were performed with phantom in both static and dynamic modes. Static phantom treatments corrected for known target displacements and established IGRT system baseline. In dynamic mode, the following geometries were considered: (a) Gated setup‐Gated treatment. (b) Gated setup‐Ungated (free‐breathing) treatment. (c) Ungated setup‐Ungated treatment. The last case corresponds to treatments using larger ITV margins derived from end inhale/exhale scans. All X‐ray fusion was based on implanted internal fiducial markers. System accuracy was studied as a function of breathing cycle(1.5–12sec/cycle), amplitude(0–1cm), gate‐level(0–50%) and gate‐window(10–30%). Results: Novalis IGRT gave excellent results for repeat irradiation in the static mode (mean error = 0.22±0.11mm; max = 0.44mm). For mobile targets, best results were obtained for fully gated treatments (gated setup‐gated treatment): mean error = 0.14±0.45mm, max = 0.67mm. However, for gated setups and ungated treatments, system accuracy dropped somewhat with mean error = 0.61 ±1.08mm, max = 2.13mm. Fully ungated treatments had the worst outcome, mean error = 3.78±6.94mm, max = 12.20mm. Here the maximum error is caused by fusion of orthogonal X‐rays taken at opposite phases of breathing cycle (worst‐case scenario). No systematic dependence was noted on the breathing cycle, amplitude, or gate‐level and window. Conclusion: Novalis IGRT offers highly accurate and precise treatments for static and mobile targets. For mobile targets gated IGRT is strongly recommended.
SU‐FF‐J‐139: Cumulative Dose to the Rectal Wall and Implications for Prostate IGRT Treatment Planning
Authors: Foskey M , Tracton G , Lian J , Tang X , Chang S
Published: April 2010

Purpose: To investigate the effect of daily variation in rectal volume and shape on dose to the anterior rectal wall in prostate IMRT. Method and Materials: A patient data set was used, consisting of a planning image and a sequence of treatment images (in‐room CTs) acquired over the course of IGRT. 5‐beam IMRT plans (prescription dose 46 Gy) were generated using three different daily treatment CTs as the planning image, with rectal volumes of 77 cc, 89 cc, and 158 cc. For each plan, the daily treatment dose was computed under optimal prostate alignment on all daily images. Dose to the rectal wall was then accumulated to a single image using a landmark‐registered deformable model to determine correspondence. The planned and cumulative rectal wall dose distributions were displayed in a rendered 3D surface display for comparison. Results: The only substantial change in the peak rectal dose occurred when the treatment was planned on the day with the most distended rectum, when the delivered peak dose was ∼5% less than that planned. For the other two planning images, with a medium or small rectum, the change in dose to the hot spot was less than 2%. Examination of each day showed that the rectal wall was closest to the prostate on the day with the largest rectum, so that, when the rectal constraints were satisfied for that case, the resulting dose distributions had a lower maximum on other days for which there was separation between the two organs. The surface displays indicated some spreading of dose due to organ motion. Conclusion: With growing accuracy of prostate setup, the relative motion of other organs may merit separate consideration in planning. A study extending this work to images from 5 patients is under way.
SU‐FF‐J‐145: Comparsion of Diffusion Weighted Imaging (DWI), T2‐Weighted and Post Contrast T1 Weighted Imaging After MR Guided High Intensity Focused Ultrasound Treatment of Uterine Leiomyomata: Preliminary Results
Authors: Jacobs M , Gultekin D , Kim H
Published: April 2010

Purpose: To investigate the agreement between diffusion weighted imaging (DWI), T2 weighted imaging(T2WI), and contrast T1 weighted imaging (cT1WI) in uterine leiomyoma following treatment by magnetic resonance imaging guided high intensity focused ultrasound surgery (MRg‐HIFUS). Materials and Methods: Twenty‐one patients (45±3.8yrs) with clinical symptoms of uterine leiomyoma were treated by MRg‐HIFUS using an integrated 1.5T MRI‐FUS System. The post MRg‐HIFUS treatment volume in the leiomyoma was assessed by cT1WI and DWI. MRI parameters consisted of DWI, T2WI, and T1 weighted fast spoiled gradient echo (FSPGR) before and after contrast. Trace apparent diffusion coefficient (ADC) maps were constructed for quantitative analysis. The regions of the treated uterine tissue were defined by a semi‐supervised segmentation method called the Eigenimage filter using both cT1WI and DWI. Signal to noise ratios were determined for the T2WI pretreatment images. Segmented regions were tested by similarity index for congruence. Descriptive, regression, and ANOVA statistics were completed. Results: All the patients exhibited heterogeneously increased DWI signal intensity localized in the treated leiomyoma regions and were colocalized with the cT1WI defined area. The mean pretreatment T2WI signal intensity ratios were T2WI/muscle=1.8±0.7 and T2WI/myometrium=0.7±0.4. The congruence between the regions was significant, with a similarity of 84% and a difference of 8% between the regions. Regression analysis of the cT1WI and DWI segmented treatment volumes were found to be significantly correlated (r2=0.94,p<0.05) with the linear equation, (cT1WI)=1.1(DWI)−0.66. Conclusion: Diffusion weighted imaging exhibited excellent correlation and agreement with the cT1WI defined region of treatment in uterine leiomyoma. Therefore, DWI could be useful as an adjunct for assessing treatment of uterine leiomyomata by MRg‐HIFUS.
SU‐FF‐J‐147: Estimation of Thermal Response of Optically Tunable Gold Nanoparticles Embedded in a Tissue‐Like Medium
Authors: Cheong SK , Krishnan S , Cho S
Published: April 2010

Purpose: To present a recent development on the computational method to estimate thermal response of optically tunable gold nanoparticles such as nanoshells or nanorods embedded in a tissue‐like medium when illuminated by a near‐infrared (NIR) laser. Method and Materials: The light transport theory with diffusion approximation was initially applied to model the temperature rise within a medium without gold nanoshells as a result of the dissipation of the NIR laser power throughout the medium. Subsequently, the heat generated by individual gold nanoshells due to photothermal effect was calculated and combined with the results for the medium without gold nanoshells to estimate the global elevation of temperature within the gold nanoshell‐laden medium. The current computational model was tested for its validity using two different phantom examples, one of which was similar to a previously reported phantom experiment. Results: The test demonstrated the capability of the current model in terms of producing qualitatively reasonable results, while it also revealed a number of potential differences in the assumptions for the current model and previous experiment. After an adjustment in the model parameters to properly take into account such differences, the computational results and the experimental data matched reasonably well within the average percentage difference of 10%. Conclusions: The calculation of temperature distribution from the heat transfer equation is straightforward with the fine element method using the commercial package. However, obtaining the changed optical constant of medium containing gold nanoshells is not an easy task in routine clinical applications. On the other hand, the method with the heat generated by individual gold nanoshell uses the known optical constants of tissue without gold nanoshells, which makes this modeling more practical in a treatment planning for the clinical use.
SU‐FF‐J‐149: Monte Carlo Simulation of Dose Distribution Around 198 Au Nanoparticles: A Preliminary Study for Treatment Quality Criterion
Authors: Marques T , Schwarcke M , Alva‐Sánchez M , Baffa O , Nicolucci P
Published: April 2010

Purpose: To simulate dose distributions around gold‐198 nanoparticles using the Monte Carlo method and study the relation between nanoparticles concentration and dose homogeneity in a tissue. Method and Materials: nanoparticles with 500 nm of radius immersed in a water phantom were simulated with PENELOPE Monte Carlo simulation code. The spatial resolution in the simulations wasset to 0.32 μm. Gold K‐edge decay (80.7 keV), L1‐edge decay (14.7 keV), L2‐edge decay (13.4 keV) and L3‐edge decay (12 keV) energies were simulated individually. A volumetric dose distribution around the Au particle was obtained and percentage depth dose curves and relative 2D and 3D maps were achieved. Using standards for large radiation field treatments, the region of 80% dose was found to define a dose penumbra region. The necessary distance between adjacent nanoparticles distributed in a tissue was studied to result in a homogeous distribution for each energy decay. Results: The percentage depth dose curve related to K‐edge energy showed a buid‐up region of 120 nm (reference to the center of the nanosphere) and 1% dose at a 3.5 cm from the source. To the L1‐edge, L2‐edge and L3‐edge energies the the 1% dose was found at 1.7 cm, 1.6 cm and 1.5 cm respectively. The distances between particles necessary to achieve dose homogeneity in water are 1.0 cm, 0.7 cm, 0.6 cm and 0.5 cm, respectively to K‐edge, L1‐edge, L2‐edge and L3‐edge. The nanoparticles concentration when the L1‐edge is used is 42% grater then when the K‐edge emission is used. The same relations calculated to L2 and L3 relative to the K‐edge are similar. Conclusions: Monte Carlo simulation is an accurate instrument to study dose distributions around nanoparticles and provides data to define a homogeneity criteria for treatments.
SU‐FF‐J‐150: Experimental Demonstration of Dose Enhancement Due to Gold Nanoparticles and Kilovoltage X‐Rays Using Radio‐Sensitive Polymer Gel Dosimeter
Authors: Siddiqi A , Yang Y , Dextraze K , Hu T , Krishnan S , Cho S
Published: April 2010

Purpose: To demonstrate the dose enhancement due to gold nanoparticles and kilovoltage x‐rays by experimental measurements using radio‐sensitive gel dosimeters. Method and Materials: The dose enhancement due to gold nanoparticles and kilovoltage x‐rays has been well demonstrated through in‐vitro, in‐vivo, and computational work. However, it has not been clearly shown by any physical measurements over a volume loaded with gold nanoparticles. This study attempted to demonstrate the dose enhancement across the phantom made of radio‐sensitive gel, known as MAGIC gel, uniformly mixed with gold nanoparticles at a concentration of 1 % by weight. Specifically, formaldehyde‐containing MAGIC gel, reportedly more radio‐sensitive than the conventional MAGIC gel, was poured into 2 mL cylindrical plastic containers serving as the phantoms for x‐ray irradiation. Seven of them had MAGIC gel only, while the remaining two were filled with MAGIC gel and gold nanoparticles. Each gel phantom was irradiated using 110 kVp x‐rays entered into the phantom from six different directions separated by 60°. The total dose delivered to the phantom ranged from 0 to 30 Gy. One phantom in each group was unirradiated and taken as the control. All phantoms were read using a 7T small animal MR scanner. The inverse T2 relaxation time (i.e., R2 value) for each phantom was plotted against the delivered dose to obtain the calibration curve. Results: Preliminary results suggest addition of gold nanoparticles to MAGIC gel did not significantly change the R2 value, at least at the currently tested gold concentration level. They also show there was more than 100% dose enhancement across the volume of the phantom. Conclusion: The current investigation provides, probably for the first time, a solid physical evidence for the dose enhancement under the given conditions. It also provides a strong support for the previous estimation of dose enhancement by the Monte Carlo method.
SU‐FF‐J‐154: Computerized Method for Quantifying the Alignment of Mechanical Or Digital Graticules Relative to Radiation Fields Using Electronic Portal Images
Authors: Du W , Yang J , Luo D , Martel M
Published: April 2010

Purpose: Accurate alignment of graticules in MV or kV portal images is important in radiation therapy, especially in sterotactic radiosurgey. A quick computerized method is developed to quantify the small misalignments of the MV and kV graticules, in either mechanical or digital form, from the radiation central axis (CAX) at selected gantry angles. Method and Materials: A metal ball was placed approximately at a Varian linac's isocenter. The center of the ball served as a reference point in space. A pair of MV and kV portal images was taken at each cardinal gantry angle (0, 90, 180, and 270 degrees). A 10×10 cm2 square radiation field was used for MV portal images. The images were processed to obtain the following informaiton: center of ball, radiation CAX, center of mechanical graticule, center of MV digital graticule, center of kV digital graticule. Hough transform was used to detect automatically the linear or circular features in these images. The accuracy of image analysis algorithms was tested with numerically simulated images. Results: On test images, detection error of ⩽ 0.2 pixels (or 0.05 mm for pixel size of 0.26 mm) was achieved in determining the center of ball, the radiation CAX, and the center of mechanical graticule. The centers of MV or kV digital graticules were defined at the center of imager detector array. For the linac studied, the gantry‐averaged displacements of MV mechanical graticule, MV digital graticule, and kV digital graticule were 0.52 mm, 1.07 mm, 0.63 mm, respectively, from the radiation CAX. Conclusions: An efficient method was presented to quantify the small misalignments of mechanical or digital graticules from the radiation CAX. Systematic displacements of the graticules may be compensated either mechanically or digitally. This method is useful in stereotacic radiosurgery programs that require high spatial accuracy in patient setup.
SU‐FF‐J‐156: High Throughput Micro‐CT Scanner Using a Distributed Multi‐Beam Field Emission X‐Ray Source
Authors: Peng R , Zhang J , Calderon‐Colon X , Quan E , Wang S , Sultana S , Chang S , Lalush D , Lu J , Zhou O
Published: April 2010

Purpose: To investigate the feasibility of a stationary gantry‐free micro‐CT scanner using spatially distributed multi‐beam x‐ray source. A prototype multi‐beam micro‐CT (MBμCT) scanner has been developed and its imaging performance characterized. Method and Materials: The MBμCT system consists of a 20‐beam carbon nanotube (CNT) field emission x‐ray source; an object table; a flat panel x‐ray detector; a MOSFET based control circuitry and a control console with a customized software user interface written in LabVIEW for data acquisition and processing. The x‐ray beams are individually controlled and can generate a scanning beam covering an angle span of 36°. It takes merely 9 steps to finish a full rotation in less than 10s. The projection images are acquired and stored for imaging processing and CT reconstruction. Results: The performance (focal spot size, field emission I‐V characteristics and current stability) of the multi‐beam x‐ray source has been characterized. The control circuitry and LabVIEW based control software have been implemented and tested. A mouse carcass has been scanned using the prototype MBμCT system and the acquired projection images showed decent imaging quality. We are currently working on refining the system geometry calibration and developing the corresponding CT reconstruction algorithm for this novel MBμCT imaging system, and some preliminary data will be presented. Conclusion: The feasibility of a stationary gantry‐free MBμCT has been evaluated based on the study of the as‐developed prototype system. Our preliminary results showed that the MBμCT scanner has the potential to deliver fast CT scan speed as a result of its novel scanning configuration. As a prototype system, it will be used to perform various feasibility tests for the future development of a fully stationary multi‐beam micro‐CT scanner. Once fully developed, this system would potentially provide fast screening, image registration and guidance for radiotherapy in pre‐clinical studies as well.
SU‐FF‐J‐157: A Monte Carlo Model for Small Animal Stereotactic Irradiation
Authors: Speiser M , Pidikiti R , Stojadinovic S , Song K , Solberg T
Published: April 2010

Purpose: To develop a Monte Carlo model of the treatment beam of a small animal stereotactic irradiator. Method and Materials: A Monte Carlo source model has been created for a custom small animal stereotactic irradiation device. X‐ray generation is performed by an XRAD‐320 x‐ray tube (Precision X‐Ray Inc., North Branford, CT) operated at a potential of 250 kVp. Determination of the un‐collimated energy spectrum from the XRAD‐320 at 250 kVp was calculated using the “SpekCalc” GUI program by Poludniowski and Evans. These calculation results were used to form the photon source probability distribution in MCNPX (Los Alamos National Laboratories, Los Alamos, NM). A custom, in‐house field collimation system is used in conjunction with the x‐ray source to collimate the source into 1.0, 3.5, 5.0, 7.5, and 10.0 mm stereotactic beams. This collimation system has been incorporated into the MCNPX beam model. Percent Depth Dose (PDD) curves from the irradiator were measured using radiochromic film (Gafchromic EBT, International Specialty Products, Wayne, NJ) with all collimator apertures and two treatment SSDs of approximately 20 and 25 cm. Results: PDD curves created with film measurements and Monte Carlo simulation results were compared for agreement. Simulated PDD curves were found to agree with measured data for all collimator sizes and source‐to‐surface distances (SSDs) for 2%/2 mm normalization criteria. Conclusion: The agreement between simulated data and repeatedly measured PDD data suggests accuracy in this application of the SpekCalc GUI program. An accurate beam model of this small animal irradiator in conjunction with ongoing micro CT‐based “patient” modeling will provide a system for Monte Carlo‐based clinical and investigational research of small animal stereotactic radiotherapy.
SU‐FF‐J‐158: An Open Source Software Tool for Treatment Planning for Small Animal Conformal Radiotherapy
Authors: Graves E , Nelson G , Rodriguez M , Zhou H , Keall P
Published: April 2010

Purpose: A treatment planning environment for a novel microCT‐based small animal conformal radiotherapy system has been developed. Built on the RT_Image open source package, the software allows planning based on CT data as well as other coregistered image types, and is integrated with a Monte Carlo dose calculation system. Method and Materials: The core RT_Image application allows display, registration, and region‐of‐interest (ROI) analysis of a variety of image types. A set of tools for defining beams was added to this application, matching the specifications of a microCT radiotherapy unit with a variable‐aperture collimator. Beams can be added and configured manually, or can be set to conform to a 3D region of interest. Beam commissioning tissue maximum ratio (TMR) data for the system was incorporated into the application to allow isocenter dose estimation based on its depth. In addition, the software was configured to allow creation of phantom and input files for an EGSnrc Monte Carlo dose calculation engine. The 3ddose files generated by this separate software can then be imported into RT_Image for analysis. Results: Pseudocircular beams of arbitrary geometries can be simulated and viewed from arbitrary directions in RT_Image. Calculation of isocenter depth in tissue is done automatically within 1 second per beam, allowing estimation of isocenter dose using the included TMR data. The interfaces for creating EGSnrc phantom and input files allow flexible specification of phantom materials, Hounsfield and density lookup tables, and simulation parameters. Imported Monte Carlo dose simulations can be analyzed using ROI and dose volume histogram (DVH) techniques, and agree with TMR dose calculations to within 10% at isocenter. Conclusion: An open source tool for planning and simulating small animal radiation treatments has been constructed. Future development of this package will include inverse planning algorithms and control of the microCT hardware to deliver treatments.
SU‐FF‐J‐159: Monte Carlo Simulation for Small Animal Irradiation in Micro CT Settings
Authors: Hsieh H , Tu S
Published: April 2010

Purpose: Report our computer simulation investigation on the small animal irradiator in the hardware settings of a commercial micro CT imaging system. Method and Materials: PENELOPE, a Monte Carlo radiation transport code, was used in our simulation study. Two identical cylinder‐shaped water phantoms were created with diameter of 1.0 cm and length of 3.0 cm. A simulated ball‐shaped tumor with diameter of 1.0 mm was embedded at the center of each phantom. The first tumor model was filled with water and second was filled with a homogeneous mixture of Conray solution. Conray is iodine based sterile aqueous solution and used as the contrast agent in clinical applications. The geometrical irradiation settings of a commercial micro CT (Skyscan 1076) were modeled in the simulation. The distance was 12.1 cm from the irradiation source to rotation center and 5.1 cm from the rotation center to detector. A variety of photon energies were simulated as the irradiation source, including 30, 50, 100, 150, 300, 500 KeV, and 1 MeV. Results: For higher photon energies including 300, 500 KeV and 1 MeV, dose built‐ups and penumbras were observed in the percentage depth dose curves and lateral beam profiles. Maximum dose occurred in the tumor region in the second tumor models for all energies. The lateral beam profiles show that the maximum dose in the second tumor model is greater than the first model. This key finding suggested that iodine based solution can be used as the dose‐enhanced agent for small animal irradiation. Conclusion: Percentage depth dose curves and lateral beam profiles were computed to quantify the various photon beam characteristics. Small animal irradiation facility is a final missing piece in the grant integrative molecular imaging map. Our simulation results can serve as the prior recommendations toward the optimized small animal irradiator hardware development.
SU‐FF‐J‐171: Quantification of Ventilation Imaging From Clinical 4DCT Datasets for Selective Avoidance IMRT in Non‐Small Cell Lung Cancer
Authors: Monroe W , Kim Y , Siochi R , Wu X
Published: April 2010

Purpose: To determine a clinically appropriate ventilation level for selective avoidance IMRT using clinical 4D CT data sets and a small‐deformation inverse‐consistent linear‐elastic (SICLE) registration algorithm Materials/Methods: Using SICLE, the maximum inhalation and expiration phases of 4D CT datasets from 6 NSCLC patients were registered. After registration, smoothing was applied to the input images to account for registration error. A correction was applied to the voxels in the inhalation image to account for lung tissue mass discrepancy due to lung inflation. The ventilation was calculated voxel by voxel as a local volume change, DV/Vex = 1000 (HUin − HUex)/(HUex(1000 + HUin)), where HUex and HUin are the Hounsfield units associated with the expiration and inhalation images, respectively. After this, an additional smoothing filter and a cumulative distribution function were applied to aid segmentation and normalize the data between 0% and 100%. Ventilation volumes were quantified as a function of normalized ventilation level, which can be used as a threshold for delineation of ventilation subregions. Results: Using the inhalation image registered to the expiration image, consistent ventilation images were calculated. The ventilation levels of 90%, 80%, 70%, 60%, and 50% were studied as it was determined that ventilation levels below 50% would not be beneficial as this region would include almost the entirety of the lungs. An exponential relationship between ventilation level and ventilationcompetent volume at a given percentage ventilation was observed. Quantified ventilation data and charts demonstrating these relationships were generated. Conclusions: In selective avoidance IMRT for NSCLC, it is critical to determine the optimal ventilation level to segment within a normal lung region, which would then be used as an avoidance structure in functional image guided IMRT. Our study shows that a 70% ventilation level is promising to be implemented into selective avoidance IMRT techniques for NSCLC.
SU‐FF‐J‐176: Assessing the Impact of Partial Volume Correction On Dose Painting
Authors: Barbee D , Bowen S , Flynn R , Holden J , Jeraj R
Published: April 2010

Purpose: Tumor heterogeneities identified by PET imaging suffer from partial volume effects (PVE) due to the scanner's limited resolution. This study establishes the necessity for including partial volume correction in dose painting prescriptions. Method and Materials: A previously reported iterative partial volume correction (PVC) method, specific to heterogeneous tumors, was applied to 15 tumors exhibiting heterogeneous uptake of [Cu‐61]Cu‐ATSM, a hypoxia surrogate marker. Dose painting prescriptions were generated from PET images using two techniques: a linear transformation converting SUV to dose, and a threshold method creating boost regions for SUVs greater than 3. All prescriptions implemented minimum tumor dose constraints of 50 Gy. Continuous prescriptions linearly redistributed dose about the mean tumor SUV, yielding a mean tumor dose of 70 Gy. Thresholding prescribed an additional 20 Gy to the boost region. Doses were optimized for each prescription using an in‐house helical tomotherapy planning system. Results: PVC images exhibited redistribution of mid‐range SUVs to higher/lower SUVs with heterogeneity uptake differences of ±25–30%. However, average dose differences for linear transformation dose painting were ±5–10%, due to the transform's ratio of base dose to boost dose. The average dose differences for threshold transformation dose painting were dependent on threshold level and the tumor SUV distribution. In cases where the mean tumor SUV was approximately equivalent to the threshold SUV, PVC increased and decreased boost volumes in equal amounts. However, with mean or max tumor SUVs below threshold values, PVC significantly increased boost volumes, creating boost regions where none previously existed. Conclusion: PVC alters the volume and magnitude of regions receiving redistributed boost doses. PVC frequently reveals tumor heterogeneities where none were previously observed due to PVE, which should be included in dose painting prescriptions. Institutions intending to implement PET‐based dose painting should understand and correct for partial volume effects prior to generating prescriptions.
SU‐FF‐J‐177: Effect of Gold Marker Seed On MR Spectroscopy of the Prostate
Authors: Hossain M , Schirmer T , Buyyounouski M , Richardson T , Chen L , Ma C
Published: April 2010

Purpose: Prostate magnetic resonance stereoscopic imaging (MRSI) is an emerging technology that may enhance targeting in radiotherapy. Gold seed fiducial markers are commonly used in prostate radiotherapy to perform daily prostate localization. If MRSI is to be used in targeting prostate cancer, the impact of gold seeds on MRSI must be understood. The purpose of this study is to characterize the local effects of gold seeds on the chemical shift spectra of MRSI. Method and Materials: Two different phantoms are used in this study. One is filled with water and agar containing Choline. A Gold Marker is seed is put in the agar. In the second phantom a cylindrical cavity is filled with liquid Choline and Citrate in water. A gold Marker seed is mounted in the middle of the fluid. Single voxel (SV) and three‐dimensional MR Spectra of the chemical shift (CSI) are taken. Chemical Shift spectra are compared in the presence and absence of gold seed. Spectra close to and near the seed are studied. Results: In general, Choline and Citrate peaks are broadened by the single voxel containing the seed. Local effects on adjacent voxels are seen, mostly by way of a altered baseline drift. This artifact dissipates with distance and is most prominent when the gold seed is aligned perpendicular to the magnetic field. A precise description of the gold seed artifact on prostate MRSI chemical shift spectra will be reported. Conclusion: Gold seeds can cause local artifacts in prostate MRSI. Characterization of this artifact will permit more accurate interpretation of the MRSI spectra.
SU‐FF‐T‐02: Plan Comparison On Magnetic Resonance Image Between Inverse Planning Simulated Annealing and Point A Normalization for High Dose Rate Brachytherapy On a Cervical Cancer Patient
Authors: Huang Y , Rassiah‐Szegedi P , Gaffney D , Salter B
Published: April 2010

Purpose: The availabilities of CT/MRI compatible tandem and ovoid (TNO) applicators in recent years have improved the visibility of the tumor and organs at risk (OAR) in the treatment of cervical cancer using HDR brachytherapy. The purpose of this study was to observe the dose differences between different optimization methods shown on MRI. Method and Materials: A stage IIIB cervical cancer patient was treated with HDR brachytherapy using CT/MRI compatible TNO applicator. CT and MRI images were taken for the first fraction. The patient was carefully transferred between the two image modalities to prevent applicator movements. Catheter reconstructions on the MRI were performed based on CT/MRI registration focusing mainly on the applicator and the soft tissue surrounding the applicator. Two plans using different optimization methods were generated on MRI images, inverse planning simulated annealing (IPSA) and point A normalization. Dose distribution on each image slices were reviewed and DVHs for two plan protocols were compared. Results: The IPSA method showed better dose coverage to the target area(s) when compared with point A method. For the organs at risk (OAR), lower bladder dose (−16.5% for D2cm3) and higher rectal dose (10.9% for D2cm3) were found in IPSA plan. The rectal dose was increased due to better conformity at the ovoid level. Both plans have similar dose homogeneity index. Conclusion: Better target coverage was achieved with an IPSA plan compared to point A prescription plan. In this study, MRI provided superior soft tissue resolution and CT offered better image quality for catheter and source dwell position definition. It is advantageous to use both CT and MRI for HDR TNO brachytherapy planning.
SU‐FF‐T‐03: Accurate Surface Dose Determination for Electronic Brachytherapy Applicators
Authors: Segala J , Cardarelli G , Hiatt J , Curran B , Sternick E
Published: April 2010

Purpose: To describe the use of experimental and numerical methods for the accurate determination of dose distributions along surface boundaries of applicators used to deliver electronic brachytherapy. Method and Materials: Numerical models for several sizes of an electronic brachytherapy breast balloon applicator and a vaginal applicator were generated and dose distributions calculated using a general purpose multi particle transport code (FLUKA). The numerical data were compared to experimental measurements obtained with a parallel plate extrapolation ionization chamber and with dose distributions generated by a commercial treatment planning system Results: Close agreement between the numerical model and measured doses were found. Comparison with doses computed using the treatment planning system showed good agreement at a prescription depth of 1.0 cm. Dose deviations as great as 150%, however, were observed at the surface‐tissue interface of the applicators. Conclusions: Using both experimental and numerical methods to determine dose distributions for electronic brachytherapy applicators offers a verifiable, comprehensive procedure in the determination of accurate surface doses. It has been demonstrated that treatment planning systems based on AAPM TG‐43 guidelines, as currently configured do not estimate surface doses accurately when attenuating material is interposed between an electronic brachytherapy x‐ray source and irradiated tissue.
SU‐FF‐T‐09: Integral Target Dose Comparison for MammoSite Brachytherapy and Axxent Electronic Brachytherapy Systems
Authors: Li Texin , Gong Jason , Tong Shidong , Fountain Betty , Duffy Edward
Published: April 2010

Purpose: Compare the integral target dose to further understand their clinical suitability. Materials /Methods: Dose rate for MammoSite and Axxent S700 source due to an isotropic point source can be calculated by: . The dose is the products of D(r) and Δt, where Δt is the dwell time. Δt is obtained from PLATO planning system using 40820 U (10 Ci) source strength. Assuming Axxent S700 produces comparable air kerma strength with that of a 10 Ci Ir‐192 source, the same treatment time is used. Target for both systems is a 1.0 cm thickness spherical shell from the surface of the balloon; the integral target dose is obtained by integrating the point source model over this spherical shell. Dosimteric parameters for MammoSite are obtained from AAPM TG43. For Axxent S700, data are obtained from published data1. Radial dose function for Axxent S700 (50 keV) is curve‐fitted with a polynomial to facilitate calculation. Results: For a treatment of 340 cGy, MammoSite delivers 3.80 joules for balloon radius of 2.0 cm, increases to 6.66 joules for balloon radius of 3.0 cm, while Axxent S700 delivers 0.98 joules and 1.32 joules respectively. MammoSite delivers 3.9 times more than Axxent S700 at balloon radius of 2.0 cm. This number increases to 5.0 for balloon radius of 3.0 cm. Conclusion: The integral target dose increases with balloon size for both systems. So is the integral target dose difference between the two. The difference in energy deposition is attributed to the differences in physical characteristics, such as, dose rate constant and radial dose function. Non‐target integral dose evaluations for both systems are underway. Further, equivalent uniform dose (EUD) for both systems can be calculated, when air cavities are present.
SU‐FF‐T‐13: Clinical Use of Multi‐Lumen Catheter for Accelerated Partial Breast Irradiation
Authors: Lee J , Chan R
Published: April 2010

Purpose: To evaluate the effectiveness of using multi‐lumen balloon brachytherapy for early‐stage breast cancer. Method and Materials: Five patients treated with HDR brachytherapy using the Contura™ applicator (SenoRx, Inc.) were investigated in this study. Patients were underwent CT scanning with 2mm/2mm cut. The inverse planning optimization was used for the plan using multi‐lumen catheter. A single dwell at central channel was applied to simulate the plan applying MammoSite® catheter. The resulting isodose distributions and DVH were computed and compared. Results: The mean minimum skin and rib spacing were 1.0 cm and 1.6 cm with a range of 0.25 to 2.7 cm and 0.6 to 4.4 cm, respectively. The mean V100, V150, V200 for the MammoSite® plan were 91.9%±3.5%, 30.4c.c.±4.1c.c. and 4.2c.c.±1.8c.c., respectively. When the patient was implanted under suboptimal conditions, the coverage for PTV can be maintained or improved for multi‐lumen plan. The mean V100, V150, V200 for the multi‐lumen plan were 94.8% (S.D.±0.9%), 32.8c.c. (S.D.±2.9c.c.) and 6.1c.c. (S.D.±2.2c.c.), respectively; however, the dose to skin surface and ribs were reduced significantly. Careful alignment of the catheter right before the treatment is important. The Contura™ catheter tends to rotate +/− 90° between each treatment for our patients. Without proper alignment, an unexpected high dose may be delivered to critical organs. Conclusions: The use of the multi‐lumen applicator appears to deliver a dose to the target with greater coverage while minimizing the skin surface and rib dose at the same time as compared to MammoSite® plan. For patients with suboptimal implantation, who are not qualified for MammoSite® brachytherapy, they still could benefit from accelerated partial breast irradiation using multi‐lumen catheter. It is expected to result in better cosmesis and minimizing late effects. However, it is important to align the catheter precisely prior to each treatment and avoid the rotation during the treatment.
SU‐FF‐T‐14: Skin Dose Evaluation for HDR Accelerated Partial Breast Irradiation
Authors: Xu Y , Watchman C , Krafft S , Jang S , Haddad K , Ganapol B , Hamilton R
Published: April 2010

Purpose: Although the physical consideration of minimum skin distance has been well established for partial breast irradiation HDR treatment, there are uncertainties about the actual calculated skin dose. Usually the calculated dose is based on infinite homogenous media. Thus, the actual skin dose will be less than calculated dose due to lack of backscattering. This study confirms this conclusion by using MOSFET dosimeters and Monte Carlo 3D simulation. Materials & Methods: The MOSFET detector was first calibrated as a function of distance from HDR source. The calibration factors were obtained by recording the voltage variation after delivering exactly 1 Gy. A Contura balloon filled with water was embedded off center in a cylindrical tissue equivalent gel phantom. Four locations along the surface were selected for MOSFET placement. Two plans, one with single dwell position and the other with three dwells, were delivered with the MOSFET at different positions, with and without extra bolus for backscattering. Monte Carlo simulation was validated by simple plans with single source dwell in different catheters of the Contura balloon. Results: The measurements with bolus matched well with the TPS calculated dose, while the data acquired without bolus had dose discrepancies from 12% to 27%, corresponding to the source to detector distance ranging from 2.8cm to 3.9cm. Conclusion: MOSFET measurements have proved that the actual skin dose is much less than the calculated dose, which indicates that the minimum skin distance used as selecting criteria may be less than currently established standard.
SU‐FF‐T‐18: On the Determination of the Absolute Dose for a 192Ir HDR Source Using a Fricke Dosimeter: Correction Factors for Several Radii Using MC Calculation
Authors: Benhabib S , Mota H , Austerlitz C , Ferreira M , Allison R , Sibata C
Published: April 2010

Purpose: To determine the absolute dose at the reference point using measurement with Fricke dosimeter at various transverse bisector distances. Method and Materials: In a previous work we showed how the absolute dose from a source can be measured using a Fricke dosimeter. Ring shaped fricke volume of 1 mm width and 3 mm height was used to determine the absolute dose. AlphaOmega HDR source was located at the center of the ring which was 1 cm away from the source, the uncertainty at this point was too high (k=7%). In another second study we demonstrated that there is a size detector dependence and source positioning uncertainty when doing the measurement. We did dose profile measurements along and away from a source using four different detectors (two ionization chambers and two diodes). We showed that the detector size effect goes from 1.3% at 1 cm to 0.2% at 2.5 cm. Therefore PENELOPE Monte Carlo simulations for several radii have been used to determine conversion factors to the reference point. Results: We show in this work that the absorbed dose at various distances away from the source does not have an inverse square law behavior. Therefore, factors have been determined to convert the dose at measured point to the dose at the reference point recommended by AAPM TG‐43. These conversion factors are 4.454, 7.609, 11.288 and 16.003 for the distances 1.5, 2.0, 2.5, and 3.0 cm respectively. Conclusion: Feasibility of determining the absorbed dose using a Fricke dosimeter at the reference point (1 cm distance) was demonstrated in a previous work, however the uncertainty was too high (7%). Measurement at distances greater than 1 cm was demonstrated to lower the uncertainty. PENELOPE MC code was used to obtain the conversion factors at various radii to the reference point.