bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐73: Investigate the Equivalence of Cone Beam CT (CBCT) versus 4‐Dimensinoal (4D) MIP Images for Internal Target Volume (ITV) Definition
Authors: Wang L , Fan J , Lin T , Jin L , Feigenberg S , Ma C
Published: August 2010

Purpose: Maximum intensity projection (MIP) reconstructed 4‐dimensional (4D) computed tomography (CT) reflects the range of target motion and thus is generally used for internal target volume (ITV) definition in lung stereotactic body radiotherapy treatment planning. During treatment delivery, CBCT is used for image guidance by aligning the visualized target in the CBCT with the MIP‐based ITV. This work investigates whether these two image modalities are equivalent in defining an ITV. Materials and Methods: A ball‐shaped polystyrene phantom with different built‐in objects (cube, cone, and sphere) was attached to a motor‐driven platform, which simulates a sinusoidal movement with changeable motion amplitude and frequency. The motion of the platform was set along patient superior‐inferior direction with 1‐cm peak‐to‐peak amplitude. The Varian on‐board Exact Arms kV CBCT system and the GE LightSpeed 4‐slice CT integrated with Respiratory Position Management 4DCT scanner were used to scan the phantom that moved with three frequencies (e.g. 3.4, 4.5, and 5.8 seconds). MIP images were produced. The objects were contoured in the MIP and CBCT images, respectively, and the volumes of these objects were compared between the two sets of images. Results: It was found that the MIP‐based volumes of these objects increase with the increase of the motion period while the CBCT‐based volumes do not change with the frequency. Even for the fast motion (3.4 sec), the volumes contoured in the MIP images, which are smallest among the volumes of three frequencies, are generally 10% larger than those delineated from CBCT. Conclusions: The delineated volume of an ITV changes as the frequency of target motion changes in the MTP reconstructed 4DCT. The delineated volume of a moving target is not affect by the frequency, but by motion magnitude, in CBCT. In general, CBCT and MIP images are not equivalent in defining an ITV.
SU‐GG‐J‐74: Congruence of Cone‐Beam CT Image Center with the Radiation Isocenter of a Linear Accelerator
Authors: Du W , Yang J , Chang E , Luo D , McAleer M , Shiu A , Martel M
Published: August 2010

Purpose: To develop a quantitative method to evaluate the cone‐beam CT (CBCT) image center congruence with the linac radiation isocenter. Method and Materials: A ball‐bearing (BB) was placed in the proximity of the isocenter of a Varian Trilogy linac. The center of BB served as a static reference point in the space. The BB was imaged with square megavolt (MV) radiation beams at gantry angles of 0, 90, 180, and 270 degrees. The radiation isocenter was localized relative to the BB center based on the four MV EPID images. Then the BB was imaged with the CBCT. The CBCT image center was localized relative to the BB center. Finally, the 3D displacement between the CBCT image center and the radiation isocenter was computed. Results: The CBCT image center was found to have excellent short‐term positional reproducibility, i.e., <0.1 mm wobbling in each of the x(lateral), y(vertical), and z(longitudinal) directions in 10 consecutive acquisitions. Measured in a 7‐month period, the CBCT image center deviated from the radiation isocenter by 0.40 ± 0.12 mm (x), 0.43 ± 0.04 mm (y), and 0.34 ± 0.14 mm (z). Small yet systematic discrepancies were found between the CBCT image center, 2D MV or kV portal image center, and the radiation isocenter. For the linac studied, we detected a 0.8 mm discrepancy between the CBCT image center and the MV EPID image center in the anterior‐posterior direction. This discrepancy was demonstrated in a clinical case study where the patient was positioned with 3D CBCT imaging followed by 2D MV portal imaging verification. Conclusion: The CBCT image center was localized relative to the radiation isocenter using a simple QA procedure. Computerized analysis revealed that the misalignment of CBCT image center was highly reproducible in short term and long term and could be quantified at sub‐millimeter scale.
SU‐GG‐J‐76: Validation of a Proposed Optimal Slow Gantry Rotation Technique for On‐Board Four‐Dimensional Imaging Using Lung Patient Data
Authors: Maurer J , Vergalasova I , Pan T , Yin F
Published: August 2010

Purpose: Substantial efforts have been made in recent years to develop on‐board four‐dimensional (4D) imaging techniques using gantry mounted cone‐beam imaging devices. This study validates a slow gantry rotation 4D imaging protocol using lung patient data. Methods & Materials: The proposed 4D imaging protocol determines optimal gantry rotation speeds and frame rates based on patients' respiratory cycles and desired phase windows to optimize projection distributions in phase bins by reducing numbers of tightly spaced projections and avoiding large gaps between projections. The effect of frame rate on projection distributions was tested using data from three lung patients. Projections were acquired using an on‐board kV imager (OBI)® (Varian Medical Systems, Palo Alto, CA). Gantry rotation speeds and frame rates were 0.59–0.73 °/s and 4.9–7.3 fps. Subsets of data were extracted to represent frame rates that were lower (50% and 75% of the predicted optimal) equal to and higher than (125%, 150%) predicted optimal frame rates. The protocol predicts that large gaps between projections will occur in the low (50 and 75%) frame rate data sets and excessive tightly spaced projections will occur in high (125 and 150%) frame rate data sets. Results: As predicted, large gaps occurred in the 50 and 75% frame rate sets. This effect was worse for the 50% data sets than for the 75%. Up to 23.8% of the intervals between projections in the 50% data sets exhibited large gaps, while up to 1.2% presented in the 75% frame rate sets. Percentages of tightly spaced projections averaged 6, 39 and 61% for 50, 100 and 150% frame rate data sets. Conclusion: A slow gantry rotation protocol for determining optimal acquisition parameters was validated using lung patient data and may serve as a foundation for further on‐board 4D imaging investigations. Conflict of Interest: Research sponsored by Varian Corporation.
SU‐GG‐J‐78: Investigation of Combined MV‐KV Prostate Treatment Dose Planning for Real‐Time MV‐KV IGRT
Authors: Grelewicz Z , Pearson E , Alaei P , Pelizzari C , Wiersma R
Published: August 2010

Purpose: As a result of internal organ motion, the ITV used during treatment planning must be larger than the CTV, reducing the benefit of highly conformal RT. In prostate cancer cases, there is no strong correlation between internal organ motion and externally visible motion, so application of IGRT requires internal imaging. Previous work has shown the effectiveness of real‐time 3D fiducial tracking using reduced aperture combined MV‐kV imaging. The aim of this work further advances MV‐kV tracking by incorporation of delivered kV tracking dose at the treatment planning stage through combined MV‐kV beam modeling. Method and Materials: A Monte Carlo scheme was developed to model dose deposition kernels that were imported into Phillips' Pinnacle treatment planning system. The kV source of an on‐board‐imager from a Varian Trilogy LINAC was commissioned in the TPS. Using previously treated 9‐field prostate patients, the TPS was used to calculate dose that would be delivered by the kV beam during real‐time tracking. To provide stereoscopic imaging at each gantry angle during treatment, the kV and MV beam times were matched. Apertures studied included a small 3×3 cm field capable of tracking closely placed fiducials in prostate cases. Results: In the four patients studied, the average prostate dose from a 3×3 cm field was 5 cGy, increasing to 9 cGy per fraction for a CBCT aperture, 2–5% of the prescribed dose. The 3×3 cm aperture spared more tissue, delivering 5 cGy or more per fraction to less than 1% of a patient volume, compared to 80% for the full field. Conclusion: The use of conformal kV apertures shaped to the tracking region of interest can lead to significant reductions in total kV diagnostic radiation delivered. This allows for the kV beam to provide useful tracking information, while simultaneously delivering therapeutic dose to the prostate.
SU‐GG‐J‐79: Experimentally Optimizing Prompt Gamma Detection for Proton Therapy
Authors: Moteabbed M , Binns P , Flanz J , Paganetti H , Riley K
Published: August 2010

Purpose: To model and optimize an experimental setup that could potentially provide in‐situ range verification during proton therapy. The approach relies on measuring the prompt gamma emission profile produced by a beam of protons traversing a medium to provide information on the actual distal dose falloff in real time. Method and Materials: Calculations were performed using the GEANT4 Monte Carlo toolkit and a well‐developed model of a therapy beam line at the Francis Burr Proton Therapy Center. A 150 MeV pencil beam of protons was transported through a cylindrical Lucite phantom and the prompt gammas emitted orthogonal to the beam direction were scored. Measurements were performed under similar conditions with beam intensities of approximately 5 nA using both an HPGe spectrometer and different scintillators. The experimental arrangement was then simulated as part of a design study to investigate a more optimized measuring geometry. Results: The measured and calculated gamma energy spectrum displayed several distinctive emission peaks corresponding to 12C, 16O, and 1H as expected. Depth profiles measured with 150 MeV protons using two different detectors exhibited distal falloffs that correlated with the Bragg peak and agreed well with calculated gamma‐ray emission profiles. Calculations found a significant neutron background that may be effectively reduced by energy deposit or possibly timing discrimination. Conclusion: This study highlights the necessity of performing accurate MC simulations to help interpret and design experiments under realistic conditions. Calculations, once properly correlated with measurements aid the effective and efficient use of beam time and will be used to optimize parameters for experiments such as collimation, shielding and detector media.
SU‐GG‐J‐83: Interplay Study between Respiration Motion and Dynamic MLC Delivery for 4D EMRT Plan
Authors: Zhu J , Liang J , Yan D
Published: August 2010

Purpose Interplay between MLC movement and organ motion can affect treatment dose. The study investigates interplay effect of 4D inverse planning and delivery, and discusses possible ways to reduce it. Method and Materials: Three 4D phantom images were used in this study. Respiratory movement was in S‐I direction with amplitude of 1cm, 2cm and 3cm. 4D inverse planning was accomplished with the prescription dose to the isocenter. The expected (planed) dose is weighted sum over all phases of motion. The delivery dose, however, depends on the starting phase and lasting time of each segment. Starting phase was selected randomly. With the target motion extracted from 4DCT images, we calculated position, phase and dose rate at point of interest for any given time. With an appropriate sampling rate, the dose was accumulated to mimic the treatment delivery in one fraction. Other fractions was simulated the same way. Here we did 100 simulations for each case and compared difference on point dose and equivalent uniform dose (EUD). We also studied time evolution of the delivery dose and its sensitivity on dose rate. Results: The target point dose difference could be 6.3% (the maximum in one fraction). Tumor volume with point dose difference greater than +/−3% was less than 8%. EUD differs from the expected dose by less than 1% for 1cm and 2cm phantom in all simulations. For phantom with 3cm motion amplitude, the mean EUD reduced to 1% difference in 6 fractions. Reducing dose rate makes EUD variance and maximum point dose difference smaller. Conclusion: The result suggests a small interplay effect in our 4D IMRT plans. Limiting number of segments, increasing minimum MU per segment and decreasing dose rate could reduce interplay effect. Conflict of interest: The work is supported by Elekta.
SU‐GG‐J‐87: State Based Motion Tracking and Prediction Using a Hidden Markov Model
Authors: Kalet A , Sandison G , Schmitz R , Wu H
Published: August 2010

Purpose: To evaluate the effectiveness of a probabilistic mathematical model at tracking and predicting respiratory motion gated and motion compensated in radiation therapy. Method and Materials: A previously recorded set of fiducial marker positions were recorded at 30Hz for four patients and modeled into finite states representing the natural breathing states of Exhale, Inhale, and End of Exhale. State sequences and observables representing those sequences were analyzed using a hidden Markov model (HMM) to predict a future set of sequences and new observables. Velocities and other parameters were clustered using a k‐means clustering algorithm to associate each state with a set of observables such that a prediction of state would enable a prediction of velocity. Positional results were then compared to several other published predictive models in terms of their overall RMS errors from actual position. System delay times from 33 to 1000 ms were considered and for additional comparison, a simple time average model which bases future sequence prediction on average past state lengths was also computed. State sequences which are known a priori to fit the data were fed into the hidden Markov model prediction algorithm to set a theoretical limit of the predictive power of the model at ∼20% of the motion amplitude. Results: RMS errors for motion traces modeled by the hidden Markov model show improvement over linear and phase shift type prediction models at latencies higher than 500 ms, but do not reach the target lower limit. RMS errors for the time average model approach the theoretical limit of the HMM, even though their state sequences are poorly correlated with sequences known to fit the data. Conclusion: Hidden Markov models and their simpler probabilistic counterparts show much promise for use in online prediction of tumor motion for improved accuracy of radiation delivery.
SU‐GG‐J‐90: Quantification of the Thorax‐To‐Abdomen Breathing Ratio for Breathing Motion Modeling
Authors: White B , Wuenschel S , Zhao T , Lamb J , Low D
Published: August 2010

Purpose: To develop a methodology to quantitatively measure the thorax‐to‐abdomen breathing ratio for breathing motion modeling and breathing motion studies. Method and Materials: The breathing ratio was quantified by measuring the rate of body volume increase throughout the thorax and abdomen as a function of tidal volume. 15 16‐slice 4DCT patient image data sets from the neck through the pelvis were acquired during quiet respiration using a protocol that acquired 25 ciné scans at each couch position. Tidal volume was used as the breathing‐cycle surrogate, measured using a spirometer and abdominal pneumatic bellows. The volume within the skin contour at each CT slice was compared against the tidal volume, exhibiting a nearly linear relationship. A linear regression analysis was used to determine η(i), defined as the amount of expansion at each slice i per unit tidal volume. The sum Ση(i) throughout all slices was predicted to be the ratio of room air density to internal air density; 1.11. The boundary between the thorax and abdomen was determined by examining the patient anatomy and setting the boundary at the Xiphoid process. The thorax and abdomen regions were individually analyzed to determine the thorax‐to‐abdomen breathing ratios. Results: The average Ση(i) for all data sets was found to be 1.23±0.20, close to the expected value of 1.11. The thorax‐to‐abdomen breathing ratios were 0.22±0.19. The average Ση(i) was 0.20±0.13 in the thorax and 1.04±0.26 in the abdomen. The boundary between the thorax and abdomen was localized using a 50th tidal volume percentile reconstructed CT image. Conclusion: A method to quantify the relationship between abdomen and thoracic breathing was developed and validated. This work supported in part by NIHR01CA116712 and NIHR01CA96679.
SU‐GG‐J‐95: Reproducibility of a Vaginal Dilator Used for Female Anal Cancer Patients
Authors: Briere TM , Das P , Beddar S , Crane CH
Published: August 2010

Purpose: Dysparunia is a major source of post‐treatment morbidity among patients treated with chemoradiation for squamous cell carcinoma of the anal canal. The main goal of IMRT plans in this setting is sparing of the anterior vaginal wall, vulva, and urethra. The daily of reproducibility vaginal dilators was investigated in this study. Method and Materials: Seven patients were included in this study. Patients were placed in a frog‐legged position and immobilized with a vacloc bag. A silicone vaginal dilator measuring 2.9 cm in diameter and 11.4 cm in length (Soul Source Enterprises, Portland, OR) was inserted in each patient before simulation and each treatment fraction. Antero‐posterior (AP) and lateral kV images were used for daily set‐up on bony anatomy. BBs inserted in the dilator improved visibility on kV images. Dilator and bony anatomy positions were compared with the digitally reconstructed radiographs (DRRs) generated from the simulation CT. Results: Within the AP images, the average deviation of bony anatomy from the DRR was 0.3 ± 0.2 cm, while for the lateral images, it was 0.5 ± 0.3 cm. The 3‐dimensional position of the apex of the dilator showed strong variation, with an average deviation of 1.3 ± 0.8 cm. However, the position of the dilator axis near the tumor volume showed less deviation, 0.5 ± 0.3 cm. Variation of the dilator angle was small in the AP images (−2° ± 3°) and slightly larger in the lateral images (−3° ± 9°). Conclusion: The reproducibility of a reference point along the vaginal dilator's longitudinal axis was comparable to that of bony anatomy. While dilator depth was not as reproducible, the reproducibility of the distal dilator was excellent and could allow maximal sparing of the female genitalia in patients undergoing IMRT.
SU‐GG‐J‐96: Statistical Analysis of the Correlation between Breathing Characteristics with Patient Parameters
Authors: Guo B , Vazquez L , Xu X , Shi C
Published: August 2010

Purpose: Breathing curve of lung patient is an important feature for tumor tracking and 4D delivery. The correlation of external breathing curve characteristics with internal tumor location and with the biological features of the patient is of large interest. In this study, we are aiming to propose a method for analyzing the parameters of breathing curves and study the correlation of breathing characteristics with features of patients. Method and Materials: Piecewise cosine functions were used to fit breathing curves and determine the amplitude, period and baseline of each breathing cycle. Mean value and standard deviation of amplitude, period and baseline over the breathing curves were determined as the “characteristics” of a breathing curve. Statistical analysis was performed to correlate these characteristics with patient parameters including age, gender and tumor site base on a total of 305 breathing curves from 158 patients acquired from Real‐time Position Management (RPM) system. Pearson correlation method was used to determine the correlation of age with breathing parameters. Two‐sided unpaired t‐test was used to study whether gender or presence of tumor in lung affect the breathing characteristics significantly. Results: Age has no correlation with breathing characteristics studied. Gender affects both the mean (p = 0.971) and standard deviation (p = 0.425) of breathing period. The effect of gender on breathing amplitude or baseline variation was insignificant. Presence of lung tumor affects the mean amplitude (p = 0.317) and period (p = 0.384). The baseline variation was also affected slightly (p = 0.860). But the irregularity of amplitude and period was irrelevant to the tumor locations. Conclusion: Statistical analysis of large number of breathing curves revealed that parameters of patient may affect the breathing curve statistics thus affecting the management of tumor motion in radiation therapy.

Conflict of interest: Research supported by grant NIH/NLM R01LM009362
SU‐GG‐J‐100: A Comparison of the Effect of Intra‐Fraction Motion on Tomotherapy and IMRT Delivery Systems
Authors: Kallenberg P , Langner U , Waite‐Jones C
Published: August 2010

Purpose: To illustrate the variation in dose distribution caused by a moving target volume that can be expected from a Tomotherapy treatment plan and a conventional step and shoot intensity modulated radiation therapy (IMRT) plan. Method and Materials: A two‐dimensional Motionsim platform was used with Mapcheck2 to obtain the measurements. Tumor motion with a superior‐inferior amplitude of 1cm and lateral amplitude of 0.2cm was used. Similar IMRT treatment plans were created for a volume vertically centered on the diode array using Tomotherapy and CMS Xio, respectively. A planned dose of 2Gy per fraction was delivered onto both a stationary Mapcheck2 diode array, as well as on the array when the tumor motion was simulated. The process was then repeated using a 9 beam step and shoot IMRT plan on a conventional Linac. Results: When compared to the plan with a stationary target, the motion file introduced single fraction dose variation at the superior and inferior borders of the field of up to 20%. This was the case for both the helical Tomotherapy and co‐planar IMRT scenarios. Detectors inferior of the target volume received more dose than planned, while superior detectors received up to 20% less dose than planned. The penumbra for these resulting hot/cold spots for the Tomotherapy plan was larger than for the IMRT plan. Conclusion: The results reiterate the need for tumor motion management when IMRT is used during treatment. Motion effects may even be more pronounced for helical tomotherapy treatments than for conventional IMRT.
SU‐GG‐J‐103: Development of Statistical/Mathematical Predictive Model for Lung Tumor Motion
Authors: Verma P , Wu H , Langer M , Das I
Published: August 2010

Introduction: Predicting tumor respiratory motion for image‐guided radiation treatment, especially in the thoracic and abdominal regions of the body is essential, since the effectiveness of radiation therapy is degraded by respiratory motion. To minimize the radiation dose to the surrounding tissues and critical structures, precise tumor localization and dose delivery during treatment is crucial. The objective of this project is to develop a Hidden Markov Model (HMM) predictive model for precise lung tumor motion prediction under free breathing. Method and Materials: A finite state model (FSM) for respiratory motion representation using line segments is used to develop a statistical/mathematical predictive model to predict tumor motion based on historical motion information of the same patient, or data collected from a group of patients. De‐identified and previously acquired tumor motion data from the real‐time tumor‐tracking radiation therapy (RTRT) system and Cyber‐Knife data will be used in the study. Results: Two probability distributions are built to determine the current motion state and state transition which can be dynamically built and adjusted and are used in real‐time motion prediction. These probabilities can be derived for any parameters such as velocity, time or amplitude. These dynamic probability distributions can aid in predicting the current state and future state transitions of a tumor. An algorithm to process raw motion signal consisting unrecoverable and recoverable error has been implemented which will facilitate and improve motion prediction. HMM and FSM based predictive model is expected to predict more accurately than current prediction methods and models and to provide reliable results for different imaging rates (from 30Hz to 1Hz) and different system latency (from 33ms to 2 seconds). Conclusion: A HMM predictive model based on FSM for future tumor positions using the previous motion patterns is under investigation for real‐time radiation treatment.
SU‐GG‐J‐105: An Analysis of CyberKnife Prediction Accuracy
Authors: Pepin E , Wu H , Zhang Y , Lord B
Published: August 2010

Purpose: To evaluate the prediction model used by the CyberKnife radiation therapy system in marginal terms. Method and Materials: The CyberKnife uses an online prediction model to improve radiation delivery. Modeler points indicate the tracked position of the tumor and Predictor points predict the position ≈115 ms in the future. The discrepancy between Predictor points and their corresponding Modeler points was investigated. For 100 data sets from 23 de‐identified lung patients, margins were determined in each anatomic direction about the Predictor points so as to minimally increase coverage to an arbitrary percentage of Modeler points. Each data set had about 30 minutes of motion data, of which about 10 minutes constituted treatment time; only these 10 minutes were used in the analysis. The frequencies of margin sizes were analyzed and truncated Gaussian normal functions were fit to each direction's distribution. The standard deviation of each Gaussian distribution was then used to describe the necessary margin expansions in each signed dimension in order to achieve the desired coverage. In this study 95% coverage was compared to 99% coverage. Results: Considering the magnitude of 2 from the mean of the Gaussian in each signed dimension, the margin expansions needed for 95% coverage were 1.2 mm in the lateral directions and 1.7 mm in the AP directions. For the SI directions the fit was poor; but empirically, the expansions were 3.5 mm. For 99% coverage, the AP margin was 3.6 mm and the lateral margin was 2.9 mm. The SI margins for 99% coverage were highly variable. Conclusion: The Predictor points follow the Modeler points closely. Margins were found in each clinical direction that would provide 95% coverage for 95% of the fractions reviewed in this study. Similar margins were found in two clinical directions for 99% coverage in 95% of fractions.
SU‐GG‐J‐106: Prostate and Pelvic Lymph Node PTV Margins for Treatment of Pelvic IMRT Followed by Proton Prostate Boost
Authors: Su Z , Edwards A , Li Z
Published: August 2010

Purpose: To evaluate the PTV margins for both prostate and pelvic nodes for patients treated with initial Pelvic‐IMRT and prostate proton boost. Method and Materials: Total 15 prostate patients were treated with IMRT and proton therapy with rectal balloons. CBCT and 2D x‐ray were used for pre‐treatment alignments for IMRT and proton treatment, respectively. Shifts and rotations from bone‐matching, seed‐matching and seed‐bone differences were obtained from CBCT with translation only, translation and rotation. Pre‐treatment and post‐treatment 2D x‐ray images were analyzed for residual setup errors and intra‐fraction organ motion. Translation‐only Pelvic‐LN PTV margins were calculated from bone‐seed shift differences. Translation‐only prostate margins were calculated from x‐ray data. Similarly, PTV margins for bone‐matching were also obtained. Bone to skin‐mark rotations and prostate to bone rotations were also presented and evaluated for margin impact. Results: PTV Margin was calculated using 2.5*Σ&+0.7*σ. For seed‐matching, prostate margins are 1.5, 3.5, 2.7 mm for LR, SI, AP, respectively; Similarly, the margins are 2.3, 7.1, 7.0 mm for pelvic‐LN. For bone‐matching, prostate margins are 2.7, 7.8, 7.5 mm for LR, SI, AP, respectively; The margins are 0.7, 1.5, 1.3 mm for pelvic‐LN. For skin‐mark setup, prostate margins are 7.6, 13.5, 11.5 mm and pelvic LN margins are 8.3, 12.7, 12.5 mm. The bone to skin‐mark rotations are 1.3±1.4, −0.5±1.1, −0.2±0.7 mm for LR, SI, AP axes, respectively. The seeds to skin‐mark rotations are −0.2±3.4, −0.8±3.1, 0.2±1.5 mm for LR, SI, AP axes, respectively. Conclusion: Prostate and pelvic LN PTV margins were both obtained from translation only setup using 2D and 3D x‐ray imaging data. Seed‐matching reduced prostate margins, which may reduce dose to bladder and rectum compared to bone‐matching. However, pelvic‐LN margins increased because of the inter‐fraction prostate motion relative to pelvic bones. Rotations of bone and prostate will increase both prostate and pelvic‐LN margins.
SU‐GG‐J‐107: Monte Carlo Modelling the Effect of Translational Shifts and Rotations on Prostate Dose‐Population Histograms ‐ What Margins Are Required for IGRT?
Authors: Cowen M , Thomas S
Published: August 2010

Purpose: To investigate the effect of geometric uncertainties on prostate dose coverage based on population statistics and to determine the most appropriate margins for prostate IGRT. Method and Materials: Monte Carlo based software has been written using Matlab in order to implement Dose Volume Population Histograms (DVPH) for modeling geometric uncertainties. Whereas previously published work utilizing the DVPH concept has only accounted for translational uncertainties, this study has expanded this to include rotational uncertainties also. In this modeling, estimated values for systematic and random geometric uncertainties in 3‐dimensions for both translational and rotational shifts are entered into the software. Presented in this study are the results of modeling prostate motion using translational uncertainties of Σ = σ =1.5mm and Σ = σ= 3mm (representing IGRT and non‐IGRT treatment), these are combined with rotational uncertainties of Σ = σ = 1.5° and Σ = σ = 3° for IGRT and non‐IGRT. This modeling has been applied to six plans for a prostate treatment, based on margins around the prostate body of 0, 2, 4, 6, 8 and 10mm. Results: For the modeled non‐IGRT treatment, results show that a full 10mm margin is required in order to achieve 95% prescribed dose coverage of the CTV to 90% of the population. For the IGRT treatment modeling, 95% prescribed dose coverage to >90% of the population was achieved by all plans — including that with 0mm margin. Conclusion: This work demonstrates the effect of geometric uncertainties (including rotations) and margin size on tumor coverage probability. Currently, these Monte Carlo calculations take several hours to complete on a desktop PC, work is in progress to use a distributed computing server in order to minimize the time taken for calculation.
SU‐GG‐J‐108: Validation Study of a Software Tool for Consensus Analysis of Experts' Contours for Generating Atlases of Radiotherapy Target and Normal Structures
Authors: Al‐Lozi R , Li X , White J , Apte A , Tai A , Michalski J , Bosch W , El Naqa I
Published: August 2010

Purpose: To analyze and validate the ability of a newly developed software tool to estimate and analyze consensus contours from manually delineated structures by panel of expert radiation oncologists for building reference atlases for radiotherapy and dosimetry practitioners. Method and Materials: Several statistical methods and a graphical user interface were developed as an integral part of an in‐house research treatment planning system. For evaluation purposes, we used three breast cancer CT scans from the RTOG Breast Cancer Atlas Project labeled A, B, and C. All participating physicians contoured specific structures before and after the consensus panel met without the software aid. Differences in the contours were analyzed qualitatively and quantitatively using metrics based on apparent agreement, kappa statistics, and STAPLE estimates by the developed consensus software tool. Estimates of the consensus contours were analyzed for the different structures before consensus and compared with the experts' manual consensus contour. Dice similarity coefficient (DSC) was used for comparative evaluation between the software and the experts' results. Results: Dice similarity calculations for all pre‐consensus STAPLE estimates and the final consensus panel structures reached 0.80 or greater for the heart, left breast, right breast, case A lumpectomy, case B lumpectomy, and the chest wall. The heart, case A lumpectomy, left breast, and right breast all exhibited a DSC greater than 0.90. The highest Dice coefficients were seen in the comparison of the STAPLE estimated left breast contours, which almost reached 0.96 at 100% confidence level. DSCs were in the range of .70 to .79 for the supraclavicular and internal mammary nodes. Conclusion: Using the consensus software tool incorporating several statistical methods allowed excellent ability to create contours similar to the ones generated by expert physicians and provided metrics for the confidence levels of agreement.
SU‐GG‐J‐110: The Use of 4D Dose Calculations to Evaluate Whether the ITV Can Be Created Using a Reduced Set of 4DCT Phases
Authors: Giakoumakis N , Winey B , Killoran J , Lingos T , Court L
Published: August 2010

Purpose: To investigate whether it is possible to create the ITV using a reduced set of 4DCT phases Methods: Target contours were drawn on the exhale phase of a 4DCT image set for 10 lung cancer patients. Each target volume was mapped to all 10 phases of the 4DCT using deformable registration. An ITV was created as the union of the target volumes for the N phases closest to exhale, where N≤10 (10 indicates the full envelope of motion). VMAT plans were created for each ITV using the exhale phase CT (3D dose calculation). Doses were calculated on each of the 10 phases, and the cumulative dose calculated by deformable mapping of the doses to the exhale phase (4D dose calculation). For each plan, the dose received by 95% of the target (D95) on the exhale phase from the 4D dose calculation was compared with that calculated for N=10. The 4D and 3D dose calculations were also compared. Results: Average tumor motion was 0.7cm (range 0.5 – 1.5cm), 0.9cm (0.5 – 1.5cm) and 0.8cm (0.5 – 1.0cm) in the AP, SI and RL directions, respectively. For all patients, reducing N from 10 to 8 reduced D95 by less than 5%, but the average reduction in ITV volume was only 5±3% (range: 1–10%). For N=7, there was up to a 13% reduction in D95. One patient was an exception: For this patient reducing N from 10 to 6 reduced D95 by just 4%, and reduced the ITV volume by 18% (10 c.c.) Conclusions: For the majority of patients, it is not possible to reduce the size of the ITV appreciably without reducing coverage. There may be a subset of patients for whom the ITV could be further reduced, but they cannot be identified without 4D dose calculations.
SU‐GG‐J‐116: Simplified Method for Acquiring CTN to RLSP Conversion Function
Authors: Moyers M F
Published: August 2010

Purpose: A major uncertainty that affects the margins in light ion beam planning is the conversion of x ray computed tomography numbers (XCTNs) to relative linear stopping powers (RLSPs). Determination of this conversion function has been difficult in the past because of several reasons. This work developed a simplified method of determining this function. Method and Materials: The new method was based on the premise that all scanners have their XCTNs for air and water calibrated daily. The XCTNs for high density / high atomic number materials are variable, however, for different scanning conditions. On the other hand, most previous conversion functions have been linear above an XCTN/RLSP of 1050/1.05. A function can therefore be established using a phantom consisting only of water and a single high density / high atomic number material. XCTNs and RLSPs were calculated for various tissues and aluminum 6061 alloy for various effective x ray energies and compared to literature values. A parameter derived from the scaled XCTN (SXCTN) of aluminum was determined that defines the slope of the function for different scanning conditions. A phantom was constructed and used to test the new method with different scanners at a variety of kVps. Results: The RLSP for an SXCTN of 4095 is given by: RLSP4095 = 16.616 − (1.0323×10−2 * SXCTNA1) + (2.5181×10−6 * SXCTNAL2) − (2.1339×10−10 * SXCTNAL3) For soft tissues, the RLSPs calculated using the aluminum calibration method were between 0 and ± 1.5% of the values determined by different investigators on different scanners using traditional methods; deviations as great as 2.6% were found for hard bone. Due to difficulties with previous methods, it is not clear which values are most appropriate. Conclusion: The new method greatly simplifies acquisition of the conversion function, reduces ambiguity, maintains accuracy, and could promote standardization between facilities.
SU‐GG‐J‐117: Nanoparticle Assembled Capsules for Target Drug Delivery, Controllled Release and Hyperthermia
Authors: McGary J , Kadali S , Wong M
Published: August 2010

Purpose: To develop a combined targeted, drug release and hyperthermia delivery system for simultaneous multimodality therapy with radiation therapy. Method and Materials: The system is based on nanoparticle‐assembled capsules (NACs) where a polymer, multivalent ion, and a nanoparticle are the only constituents required for self‐assembly formation. Poly(allylamine hydrochloride), disodium phosphate, and citrate bound magnetite nanoparticles were used to create the exterior NAC nanoshell, which encapsulates doxorubicin in the microcapsule core. An alternating magnetic field (AMF) of 20 A/m at 267 kHz was used to release the doxorubicin and heat the NAC solution. Three different nanoparticle sizes were used for these studies; 10, 30, and 50 nm to study heating rates and release profiles. Results: Magnetic nanoparticle NACs, with doxorubicin cores, were created with dimensions of ∼ 1 m capsule diameter and a ∼ 200 nm shell thickness. Heating rates of the NAC‐solution as a function of particle size were measured. Doxorubicin release profiles were measured as a function of time, nanoparticle size, and concentration. Heating rates were substantially larger for the 50 nm nanoparticles than the 10 nm particles, where temperatures in excess of 90° C over 15 minutes were measured as compared to 70° for the smaller particles. Release rate measurements show that rate is proportional to particle size. Radiation in excess of 100 Gy delivered to the NACs showed no behavioral or morphology change. Conclusion: We developed a magnetic, nanoparticle‐assembled capsule, which is a multifunctional device that can be used simultaneously for both controlled drug release and hyperthermia. The system is controlled externally through magnetic heat loss processes. These devices have many advantages; their surface can be functionalized for molecular targeting in conjunction with external magnetic field gradients and these capsules can easily be scaled up for pharmaceutical production.
SU‐GG‐J‐120: Silver Nanoparticle Added to Nuclear Medicine: A Preliminary Evaluation of Dose Increase in Iodine Therapy Assessed by Monte Carlo
Authors: Schwarcke M , Marques T , Nicolucci P , Baffa O
Published: August 2010

Purpose: Investigate physical aspects of silver nanoparticle (AgNp) application in iodine therapy aiming increase dose conformality in Nuclear Medicine treatments of thyroid disease. Material and Methods: AgNp (2–3nm size) were considered uniformly embedded in thyroid tissue in 1% mass concentration. PENELOPE‐2008 Monte Carlo code was used to perform the simulations. A faithful neck geometry was described in PENGEOM‐2008 code, considering air cavity, spinal cord and all relevant tissues present in clinical cases. Iodine‐131 radioactive events inside thyroid volume were simulated considering beta and photon energy spectrums. Monte Carlo spectrometry was applied inside thyroid volume to identify components with high probability of interaction with silver atoms that increase dose locally due to AgNP presence. Dose increase in thyroid volume was calculated as the ratio between total dose deposited with and without AgNp (DEF = Dwithout AgNp/Dwith AgNp) and comparing total doses deposited in studied volumes. Dose conformality increase was evaluated from changes in dose‐profiles and isodose curves inside the neck. Results: The DEF was 1.19 to thyroid volume (target) and 0.40, 0.56, 0.77 and 0.63 to spinal cord, spinal bone, parotids and sublingual base, respectively. In non‐target regions, DEF lower than 1 indicate that the dose decrease, resultant from high absorptions of fluency that occurs locally in target volume. Total dose in thyroid volume increases from 32.43Gy to 38.40Gy due to AgNp presence, representing 18.4%. In axial and longitudinal profiles is possible to observe that the doses not only increase in target region, but also decrease in healthy volumes, contributing to more conformai treatment. Conclusions: Silver nanoparticle added to Iodine therapy can contribute to dose increase changing dose conformality in benefic therapeutic levels. Monte Carlo simulation is a powerful tool to investigate metal nanoparticle applications in Nuclear Medicine cases. Future investigations will asses nanoparticle atomic number and concentration variations.
SU‐GG‐J‐121: Targeted Gold Nanoparticles as Contrast Agents in Pancreatic Cancer
Authors: Boote E , Kannan R , Shukla R , Chanda N , Zambre A , Viator J , Katti K
Published: August 2010

Circulating tumor cells are hallmarks of metastatic cancer. The presence of circulating tumor cells in blood stream often correlates with the severity of disease. Photoacoustic imaging (PA) of tumor cells is an attractive technique for potential applications in diagnostic imaging of circulating tumor cells. However, the sensitivity of photoacoustic imaging of tumor cells depends on their photon absorption characteristics. In this context, gold nanoparticle embedded tumor cells offer significant advantages for diagnostic PA of single cells. As the PA absorption is directly proportional to the number of nanoparticles embedded within tumor cells, the propensity of nanoparticles to internalize within tumor cells will dictate the sensitivity for single cell detection. We are developing biocompatible gold nanoparticles to use them as probes as part of our ongoing effort toward the application of X ray CT Imaging, Ultra Sound (US) and photoacoustic imaging of circulating breast, pancreatic and prostate tumor cells. We, herein report our latest results demonstrating that epigallocatechin gallate (EGCG)‐conjugated gold nanoparticles (EGCG‐AuNPs) internalize selectively within cancer cells and thus provide threshold concentrations required for photo acoustic signals. In this presentation, we will describe, our recent results on the synthesis and characterization of EGCG gold nanoparticles, their cellular internalization and photo acoustic imaging of PC‐3 prostate cancer cells and PANC‐1 pancreatic cancer cells.
SU‐GG‐J‐122: Therapeutic Efficacy of 198Au Nanoparticles Using a Canine Model of Prostate Cancer
Authors: Kannan R , Boote E , Khan P , Cutler C , Jurisson S , Katti K , Chanda N , Shukla R , Axiak S , Lattimer J , Henry C , Zambre A , Katti K
Published: August 2010

As part of our efforts toward clinical translation of GA‐198AuNP, our studies are focused on therapeutic efficacy of nanoparticulate GA198AuNP agent in dogs with prostatic carcinoma. The overall goal is to gain clinical insights on therapeutic efficacy of GA198AuNP in a large animal model. We have performed a phase I clinical trial using GA‐AuNP administered intravenously or intra‐tumoral injection or infusion. CT scans were performed prior to injection and 24 hours post injection in 3 of the 4 dogs. Following injections, dogs were allowed further treatment as recommended by the primary attending clinician. Four dogs have been treated to date. Complications related to GA‐AuNP treatment were not observed, and all 4 dogs received adjunctive treatment with radiation therapy and/ or chemotherapy. These preliminary studies have clearly provided compelling evidence on the therapeutic potential of biocompatible GA‐AuNP for their utility as novel therapeutic agents in treating various types of inoperable solid tumors. Intra‐tumoral and intravenous administration of GA‐AuNP is safe in dogs with spontaneously occurring tumors. As further therapeutic efficacy studies continue, the outcome of this clinical trial in a large animal model will generate therapeutic efficacy data which will be used for filing IND application for Phase I clinical trial studies. This clinical translation effort provides significant advances in terms to deliver optimum therapeutic payloads into prostate cancers with subsequent reduction in tumor volume, thus may effectively reduce/eliminate the need for surgical resection. This presentation will include details of clinical translation of GA198AuNP in prostate tumor bearing dogs.
SU‐GG‐J‐127: Monte Carlo Calculation of Secondary Electron Production from Gold Nanoparticles in Proton Beam Irradiation
Authors: Gao J , Ding X , Sun W
Published: August 2010

Purpose: We examined the production efficiency and average kinetic energy of secondary electrons produced from a single gold NP upon proton irradiation Method and Materials: The production efficiency and average kinetic energy were investigated by using the Geant4 Monte Carlo simulation toolkit. The proton energy range corresponding to the 250‐MeV pristine Bragg peak is from 100 MeV to 0 MeV. We investigated proton beams with energies of 100 MeV, 50 MeV, and 20 MeV to represent the scope from 100 MeV to 0 MeV. Upon biological uptake efficiency, we chose gold NPs with diameters of 35 nm, 50 nm, 70 nm, and 100 nm. Results: We found that for a NP with a diameter of 70 nm, the secondary electron production efficiency increased as the proton energy decreased from 100 MeV to 50 MeV and then 20 MeV. The average kinetic energy of the secondary electrons increased with proton energy. We found that the larger the NP size, the higher the production efficiency and average kinetic energy of the secondary electrons. Finally, we found that among the samples we tested the smallest NP was the one with a diameter of 70 nm. Conclusion: Collectively, the secondary electron production efficiency and average kinetic energy from the NPs should also be taken into account when considering the potential use of NPs in proton radiotherapy.
SU‐GG‐J‐130: Recent Development of a Carbon Nanotube Field Emission Based X‐Ray Micro‐Radiotherapy System for Small Animal Radiotherapy
Authors: Wang S , Peng R , Zhang J , Schreiber E , Zhou O , Chang S
Published: August 2010

Purpose: To develop a novel multi‐pixel x‐ray beam micro‐radiotherapy (micro‐RT) system for high‐resolution small animal image‐guided radiotherapy (IGRT) using carbon nanotube (CNT) field emission technology. Materials and Methods: We have developed a prototype multi‐pixel x‐ray beam micro‐RT device for feasibility demonstration. The micro‐RT design uses a pixel beam array which consists of fifty individually addressable x‐ray pixel beams, each beam is ∼2 mm in size. The pixel beam array can form a maximum field size of 1 cm × 2 cm with arbitrary field shapes and intensity modulation patterns. Potential advantages of the multi‐pixel micro‐RT system over the single source micro‐RT systems are stationary flexibility and real‐time nature of the electronic field shaping. CNT field emission based imaging and irradiation systems have also ultrahigh temporal resolution, which can be very important for small animal IGRT. Previously we have demonstrated the feasibility of the system using lower beam energy and here we report the recent progress in CNT FE based micro‐RT development with higher energy beams. Results: A 100 kV prototype CNT field emission based micro‐RT system is developed. The prototype device can generate 75 individual addressable multi‐pixel x‐ray beams. Each beam is expected to produce a dose rate on the order of >1 Gy/min at the center of the irradiated object. We also integrated our CNT field emission based micro‐RT and micro‐CT devices for small animal IGRT. Conclusions: We have made significant progress in developing the novel multi‐pixel micro‐RT system using CNT field emission technology. It remains to be a challenge to achieve high voltage (>100 kV) and high dose rate using this highly original prototype device in an academic research laboratory environment. The CNT‐based micro‐RT can be integrated with the CNT field emission based micro‐CT already developed for real time small animal IGRT.