bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐80: Effect of CT Truncation Artifacts to Proton Dose Calculation
Authors: Wu R , Amos R , Sahoo N , Kornguth D , Bluett J , Gillin M , Zhu X
Published: July 2008

Purpose: When a patient body part is out side of the CT scan field of view, truncation artifacts generally occur in the images leading to inaccuracy in the CT number (HU) in these affected images. In proton therapy treatment planning, CT numbers are converted to stopping powers to calculate dose, beam range and range compensators for the treatment fields to cover the target volumes. We have evaluated the effects of these artifacts on proton dose calculation accuracy and on range uncertainty for spinal fields used for cranial spinal irradiation. Method and Materials: A thoracic phantom was imaged on a GE 16 slice CT scanner using a standard body protocol. Two RMI bone tissue blocks simulating patient arm/or shoulder was placed outside of the scan field of view. Two sets of scans were obtained with and without the bone tissue blocks. Proton treatment plans were generated using Eclipse treatment planning system. Then, treatment plans were compared to each other to determine the dose and range differences. Results: There is an overall of 20–30 HU difference in the target area due to the image truncation artifacts. This creates a 2–3mm difference in the range of the proton beam at 50% dose line between the plans with and without truncation artifacts. Conclusion: The image artifacts cause uncertainty in dose estimations in the distal edge of the treatment target. The difference between the corrected plan and the truncated plan is on the order of 2–3mm, which is comparable to the distal margin normally used to account for the range uncertainty for the spine field proton therapy treatment planning.
SU‐GG‐J‐81: Efficacy of Patient Setup Correction Procedure in Prostate Radiotherapy
Authors: Zhou S , Das S , Yin F , Yoo S , Lee W , Yan H , Wu Q , Wang Z , Marks L
Published: July 2008

Purpose: Using an on‐board cone‐beam CT (CBCT) based statistical margin model to determine whether a prostate center‐of‐mass (COM) based translation correction procedure can significantly reduce the CTV‐to‐PTV margin required for prostate patients who were first setup based on skin/alpha‐cradle markers (SAM). Method and Materials: A total 110 CBCT scans were performed, daily in the first week of radiotherapy and once weekly afterward, for 10 prostate patients immediately after their clinical setup based on SAM. Soft tissue matching was used to estimate the required translation corrections by matching the COM of the observed prostate volumes on treatment planning CT and CBCTs. Based on the CBCT prostate volumes, a statistical model (Bayesian margin expectation model) provided patient specific optimal margins before and after a prostate COM based translation correction was added to the patient SAM based setup. We compared these margins to determine the efficacy of prostate COM based translation correction when it is added to the SAM based setup. Results: After the 5 daily CBCTs from the first week, all 10 patient prostate uniform margins for 95% tumor geometric coverage were reduced after applying the prostate COM based translation correction to their SAM based setup. However, the percentage reduction varied from patient to patient, ranging from 1% to 60% with a median value of 22%. In 4 of 10 patients, margin reduction greater than 4mm was obtained. In general, patients with more deformable prostates benefited less from COM translation. Beyond the first 5 CBCTs, very little further margin change was obtained. Conclusions: The addition of prostate COM based translation correction to SAM based setup did reduce the uniform margin required to achieve 95% tumor geometric coverage, but the extent of reduction was patient specific. In general, incorporating COM translation in prostate margin determination can help reduce bladder/rectal doses.
SU‐GG‐J‐82: Elastic Scattering of Electrons in Gold: An Event‐By‐Event Simulation Algorithm Based On the NIST Cross‐Section Data
Authors: Vassiliev O , Mohan R
Published: July 2008

Purpose: An increasing number of studies report on new approaches to detection and therapy of cancer based on the use of gold nanoparticles. Interaction of these nanoparticles with ionizing radiation, used either for diagnostic or therapeutic purposes, distorts the radiation field, especially on a microscopic scale. Monte Carlo calculation of dose distributions on such a scale, and microdosimetric analysis require event‐by‐event algorithms. The purpose of this study was to develop an event‐by‐event algorithm for simulation of electron elastic scattering in gold that is based on accurate cross sections from the NIST data base, Version 3.1. Method and Materials: Angular dependencies of the NIST singly differential cross sections were fitted with a linear combination of the Wentzel cross section and Legendre polynomials of up to the 11th order. An algorithm was developed for sampling a scattering angle from the distribution represented by this linear combination. The algorithm is based on a rejection scheme. An angle is sampled from a simple distribution that has three components represented by Wentzel, isotropic, and backscatter (peak at π) terms. The sampled angle is rejected with a probability depending on the ratio of this simple distribution and the desired one. For some applications the three component distribution can be a sufficiently accurate representation of the NIST cross sections. Results: Fitting parameters have been determined for electron energies in the range from 50 eV to 1 keV. Total cross sections calculated with these parameters agreed with the NIST data within 2×10−4 % and transport cross sections agreed within 0.5%. The algorithm has been implemented in a computer code and tested. The probability of accepting an angle in the rejection scheme was in the range of 0.25 to 0.54 depending on electron energy. Conclusion: An algorithm has been developed for accurate simulation of electron elastic scattering in gold.
SU‐GG‐J‐91: Fast, Low‐Dose Patient Localization On TomoTherapy Via Topogram Registration
Authors: Moore KL , Goddu SM , Chaudhari S , Kintzel EJ , Low DA
Published: July 2008

Purpose: We present a protocol to efficiently localize patients on TomoTherapy by using a scout imaging (topogram) mode that can be used instead of or in conjunction with 3D MVCT imaging. Method and Materials: To show the feasibility of this method, we scanned anthropomorphic head, thorax, and pelvis phantoms on a kilovoltage CT simulator and subsequently generated digitally reconstructed topograms (DRTs) in the native geometry of the TomoTherapy source/imaging array. The same phantoms were scanned in the imaging mode of the TomoTherapy unit with a moving couch and fixed gantry of 0° and 270°. The raw detector data were read out at the end of these respective “anterior‐posterior” and “right‐lateral” scans, which in turn were compared against DRTs to evaluate the ability of computing shifts and rotations using these images. Results: Using the helical MVCT beam parameters, the time needed to acquire a quality topogram was 12.5 sec for a 50 cm long field. The minimum acquisition time was limited by the maximum couch speed of 4.0 cm/sec. The topogram dose was <1% of that incurred by a MVCT scan. Conclusion: Using topogram images may dramatically reduce the time required to localize the patient for treatment sites that require only bony anatomy imaging. Topograms can be used alternately with MVCT imaging for cases where topograms are useful for positioning, while MVCT is used for monitoring soft tissue response. Where topograms alone can suffice, our protocol boasts a 30‐fold reduction in time and 100‐fold reduction in dose to standard MVCT patient localization.

This work is supported by a grant from TomoTherapy, Inc.
SU‐GG‐J‐99: Geometrical Uncertainty Caused by Prostate Rotation During Radiotherapy
Authors: Jin L , Ma C , Xu Q , Chi Z , Fan J , Li J
Published: July 2008

Purpose: To assess the geometrical uncertainty caused by the prostate rotational motion in radiotherapy and its' effect on the treatment margin calculation. Method and Materials: Prostate rotation angle relative to the position in the planning CT is reported daily by the Calypso 4D Localization System (Calypso Medical, Seattle, WA) based on the detected transponders' locations. The contour for the clinical target volume (CTV) was obtained from the planning CT image and was smoothed first to remove the jitters caused by the uncertainty of the delineation. After the CTV contour was rotated by a Calypso system reported degree around the isocenter, distances from the points on the rotated contour to the original contour were then calculated. The prostate was treated as a rigid body in the calculation and thus the deformation was ignored. After the distances for all the points on the contour were calculated based on the rotation angles of ten treatment fractions for twenty patients, the statistical results of the geometrical uncertainty caused by rotation, such as the mean value and standard deviation of the systematic error and the standard deviation of the random error were then calculated. Results: The prostate rotation detected at the setup time for the twenty prostate patients has a mean value of 6.4 degrees and a standard deviation of 4.4 degrees. The maximum rotation angle is 27 degree. The standard deviations for the systematic error and the random error of the geometrical uncertainty are about 1.3 mm and 1.7 mm, respectively. The mean value of the systematic errors is about zero. Conclusion: Geometrical uncertainty caused by prostate rotational motion was estimated quantitatively based on the detected rotation angles. Its' effect on treatment margin calculation is significant.
SU‐GG‐J‐107: Improvement of the Stability and Reproducibility of Deep‐Inspiration Breath Hold for Left Breast Irradiation Using Video‐Based Visual Coaching and 3D Surface Imaging
Authors: Cerviño L , Yashar C , Jiang S
Published: July 2008

Purpose: To assess and quantify the improvement in stability and reproducibility of Deep‐Inspiration Breath Hold (DIBH) for left breast irradiation when using video‐based visual coaching and 3D surface imaging. Method and Materials: Ten volunteers were asked to perform a series of four 20‐second DIBHs without coaching followed by a series of 4 DIBH with visual coaching. A 3D surface imaging system (Vision RT Ltd, London) was used to track the motion of the breast surface. Visual coaching was performed with the aid of video goggles which displayed the surface‐based respiratory signal tracked by the surface imaging system. During the non‐coached DIBHs a window level was identified for each volunteer at their DIBH level. When coached, the volunteers were asked to maintain their DIBH respiratory signal within the window level identified before. Reproducibility and stability of DIBH were measured for each volunteer. Reproducibility is defined as the standard deviation of the different DIBH levels. Stability is measured as the average standard deviation of the breathing signals within each individual DIBH. Results: With visual coaching all the volunteers improved reproducibility of the DIBH with respect to un‐coached DIBH, and 9 of the volunteers improved stability of the DIBH. The volunteer that did not improve stability had a very stable DIBH even without coaching. On average, reproducibility improved from ±1.6mm to ±0.3mm, while stability improved from ±1.3mm to ±0.6mm. Conclusion: This work indicates that gated radiotherapy of the left‐breast cancer will benefit from visual coaching of the patient. Visual coaching greatly improves reproducibility and stability of the DIBH, both properties that need to be guaranteed for an accurate and efficient treatment. A future study will be performed for left‐breast cancer patients. Conflict of Interests: Research sponsored by Vision RT Ltd.
SU‐GG‐J‐116: Investigation of the Image Quality in Phase‐Sorted 4DCT Data
Authors: Goharian M , Khan R
Published: July 2008

Purpose: Four‐dimensional computed tomography (4DCT) integrated into radiation imaging system is a useful tool for precise delineation of tumor volume. While 4DCT provides excellent reconstruction of respiratory motion, sometimes it may introduce further inaccuracies in the target delineation. In this work, we have studied geometrical stability, image quality, and the artifacts introduced in different phases of the phase resorted 4DCT data. Method and Materials: The 4DCT images were acquired for a Catphan type CT phantom mounted on a moving platform using Philips Brilliance Big Bore (Philips Medical System, Madison, WI). The platform is capable of generating sinusoidal motion up to 2 cm amplitude at different frequencies. Scans were obtained at various amplitudes and frequencies and the 4DCT data was sorted into 10% phase bins. Geometrical stability was calculated by taking the volume ratio of different CT inserts scanned on moving phantom to their static images. Similarly, the Hounsfield Units (HU) variations were also measured. Results: Variation of CT inserts volume from their static volume has been observed to be different at various phases of motion. The biggest volume variation was found to be at 20–30% and 60–70% phases for motion with amplitude up to 2 cm at a frequency of 20 cycles per minute. The CT inserts such as Teflon and air showed up to 50% and 45% increase while low‐density polyethylene (LDPE) and Polystryene up to 35% and 25% reduction in volume. The mean value of HU for CT inserts was within ±5% of the static images. Conclusion: The biggest volume deviations for both high and low density inserts occurred at phases for which the phantom motion is highest. This shows that the magnitude of partial volume effect depends on the phase of respiration. HU constancy means that the 4DCT data can be used for dose calculation.
SU‐GG‐J‐122: Magnitude of Shift of Tumor Position as a Function of Deep Inspiration Breath Hold: An Analysis of Pooled Data of Lung Patients with Active Breath Control in Image Guided Radiotherapy
Authors: Muralidhar K Raja
Published: July 2008

Purpose: To evaluate the reproducibility and magnitude of shift of tumor position by using an active breathing control (ABC) and iView‐GT for tumor targeting in patients with lung cancer with moderate deep inspiration breath hold (mDIBH) for different volumes of air inhaling. Method and Materials: Eight patients with lung cancer were treated with ABC. Planning CT and radiation delivery were done by using mDIBH in active breath control (ABC) system. Digital Reconstructed radiographs (DRR'S) from planning system were compared with the images taken from iView‐GT for tumor position and potential motion during ABC in treatment room using 2D‐2D matching tool. During an ABC procedure, spirometer is utilized to reproducibly apply the same breath‐holding level for each session. The system is configurable to each individual patient or procedure, with variable threshold levels and BH durations possible. For the same value of Threshold, diffent volumes of air inhaling, the shifts in x, y and z directions of target were measured with the help of AP and lateral DRR's. Results: A total of 80 fractions of radiation were delivered using ABC. The maximum shift in x direction is 3mm, 3.1mm in y direction and 3.1mm in the z direction. Indicating a change of tumor position over the course of treatment with breath holds at the same phase of the respiratory cycle (mDIBH) with same value of threshold. Conclusion: Our data demonstrate good intrafraction reproducibility of lung tumor position using ABC with same volume of air inhaling. Patient cannot inhale same amount of air every time even though threshold is same. As the volume of inhalation is different for every time the patient inhales, the maximum shift observed is less than 4mm. For maximum difference of inhaling volume there is a need for observing the shift.
SU‐GG‐J‐126: Markerless Gating for Lung Radiotherapy Based On Machine Learning Algorithms
Authors: Lin T , Tang X , Sandhu A , Jiang S
Published: July 2008

Purpose: To develop computational algorithms based on machine learning techniques that allow high precision respiratory gated lung radiotherapy without implanted fiducial markers. Method and Materials: First, 15 seconds of fluoroscopic images are taken before the treatment. These images serve as training images. We apply machine learning techniques to analyze these training images and classify them into two classes—images corresponding to beam on (ON class) and off (OFF class) based on a preset gating window. From the classified training images, machine learning techniques can learn what features indicate beam on and what features indicate beam off. The trained machine learning technique can therefore analyze the fluoroscopic images obtained during the treatment, classify them, and thus generate correct gating signals. The accuracy of the proposed methods is assessed by comparing the results with the reference gating signals manually determined by an expert observer. Results: Two machine learning techniques are considered—artificial neural network (ANN) and support vector machine (SVM). 12 sequences of fluoroscopic images have been studied retrospectively. Results are reported in terms of precision, which represents the target coverage. For ANN, the precisions vary from 90% to 99%, with mean of 96.5%. For SVM, the range is in 96% and 100%, with mean of 98.8%. SVM achieves higher precisions at the cost of longer training time. For both ANN and SVM, their performances are better than the best method published in the literature—template matching method where the precision is from 88% to 99% with mean of 94.7%. Conclusion: We applied ANN and SVM to classify fluoroscopic images. Based on the classification results, treatment beam can be turned on and off correspondingly. This work provides an important clinical tool for fluoroscopic gating without implanting fiducial markers.
SU‐GG‐J‐128: Modeling of Plasmonic Heating From Individual Gold Nanoshells for Near‐Infrared Laser‐Induced Thermal Therapy
Authors: Cheong S‐K , Krishnan S , Cho S
Published: July 2008

Purpose: The goal of this study is to propose a new method to estimate thermal response of gold nanoshells presented in a tissue‐like medium induced by near‐infrared laser using a contribution of temperature elevation from the individual gold nanoshell at resonance frequency. Method and Materials: A cube was used for a geometrical model representing a volume of tissue containing gold nanoshells (1.0 × 108 nanoshells/ml). Two different mathematical models were investigated and compared. First, we develop a model based on calculation describing the light distribution from diffusion approximation of the transport theory and the rise in temperature of individual gold nanoshell induced by the photons reached at its site as a consequence of light spreading in the medium. The total increase in temperature at the position of interest is determined by entire contribution of rise in temperature from these individual gold nanoshells. While the same light distribution is used for the second model as for the first one the temperature response was calculated from a heat transfer equation using the finite element method with modified optical properties for the gold nanoshell contained tissue‐like medium. Results: The peak temperatures from the two different methods agree well each other, even though the distributions of change in temperature are slightly different. Conclusion: The calculation of temperature distribution from the heat transfer equation is straightforward with the fine element method using the commercial package (COMSOL). 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‐GG‐J‐131: Motion Assessment Using Phase‐ and Amplitude‐Binned 4D‐CT: Comparison with Cine CT
Authors: Riegel A , Sun X , Pan T
Published: July 2008

Purpose: To determine the accuracy of tumor motion extent measurements derived from phase‐ and amplitude‐binned 4D‐CT maximum intensity projections (MIPs). Method and Materials: Twelve stage I patients (13 lesions) received cine CT scans for 4D‐CT radiotherapy simulation. All lesions were in the middle of the lung parenchyma and not adjacent to surrounding tissue. Two 4D‐CT image sets were constructed: One sorted by phase, the other sorted by amplitude. MIPs were formed from each 4D‐CT image set and from unsorted cine CT data. Lesions were auto‐segmented on each image set using a threshold of −225 HU. Using the auto‐segmented contours as a guide, three‐dimensional motion extent was assessed visually on both 4D‐CT MIPs and compared with motion extent assessed on MIP from cine CT. The cine MIP was considered the reference image set because it includes all images at each couch position and therefore more accurately samples the respiratory pattern. Results: For phase‐binned 4D‐CT, motion extent was accurately identified on 12 of 13 lesions. For amplitude‐binned 4D‐CT, motion extent was accurately identified on 11 of 13 lesions. The two patients whose motion extent was missed on amplitude‐binned 4D‐CT demonstrated a substantial discrepancy near the superior edge of the tumor. Upon further investigation, this discrepancy was found to be caused by lag between the respiratory surrogate and internal anatomy. Conclusion: Both phase binning and amplitude binning were unable to accurately identify the motion extent for all 13 lesions. Though generally regarded as more artifact‐free, amplitude‐binned 4D‐CT demonstrated increased sensitivity to the correlation between respiratory surrogate and internal anatomy which caused inaccurate assessments of motion extent. MIP processed directly from cine CT should be used in place of MIP processed from 4D‐CT (either phase‐ or amplitude‐binned) wherever possible.
SU‐GG‐J‐132: Motion Characterization for Early Stage Non‐Small Cell Lung Cancer
Authors: Yu Z , Liu H , Balter P , Vedam S , Hunjan S , Ikushima H , Zhang L , Mohan R , Dong L
Published: July 2008

Purpose: With the increasing use of conformal radiation therapy methods for lung cancer, it is a necessity to accurately determine respiratory induced tumor motion. The purpose of this study is to analyze the motion characteristics of early stage lung tumors in a large population, and correlate tumor motion with position and other clinical factors. Method and Materials: 113 patients with 119 early stage non‐small cell lung tumors were analyzed. Each patient received a 4DCT scan. To determine tumor motion, a soft‐tissue based rigid registration algorithm was used to track the tumor position in ten respiratory phases. Tumor positions were standardized to correlate with their motion characteristics and other clinical factors, which included the lobe location, TMN staging information and etc. Diaphragm motion was calculated by subtracting the diaphragm position between the expiration and the inspiration phase. Tumor volumes were determined based on the GTV drawn by physicians on the expiration phase. Results: Average tumor motion in the AP, SI, and RL directions were 3.1±2.2mm, 6.3±6mm, and 1.5±1.4mm respectively. Lower lobe tumors showed an average vector motion (±1SD) of 11.6±7mm while upper/mid lobe tumors only averaged 5.3±4mm. To fully cover 95% of the tumors, a margin of 6.8mm, 18.3mm, and 3.9mm was needed in the AP, SI, and RL directions. From two‐tailed Spearman's rho correlations, tumor SI motion was strongly correlated with AP and SI positions of the tumor in the thorax, with correlation coefficients of −0.418 and 0.584 respectively. Diaphragm motion and tumor volume were not correlated with tumor motion. Conclusion: Respiratory induced lung tumor motion is primarily in the SI direction. Tumors in the lower lobe on average double the motion range of upper/mid tumors. Because the magnitude of tumor motion is different in each direction, it is beneficial to use an asymmetrical CTV margin for radiotherapy planning.
SU‐GG‐J‐137: New Prospective Gated CBCT
Authors: Pan T , Lu J , Balter P , Sun X
Published: July 2008

Purpose: Design and feasibility of a new prospective gated CBCT for gated treatment IGRT and body SRT treatments. Method and Materials: 4D cone beam CT (4D CBCT) can be used to assess tumor motion for IGRT and body SRT treatments. However, acquisition time for 4D CBCT is normally longer than 3 minutes. For gated treatments, it is sufficient to measure the tumor motion in the range of the gate. We propose using prospective gated CBCT for assessing the tumor motion for the gated treatment to save time in CBCT data acquisition. The same monitoring system (RPM, Varian Medical Systems, Palo Alto, CA) is used to gate the radiotherapy treatment and the CBCT acquisition. Both x‐ray and gantry rotation start when the condition of gating is met such as the breathing amplitude falls in the threshold setting for therapy. The patient can be coached with audio prompting during data acquisition and treatment. The acquisition time is between 1 to 2 min and can be accelerated with a faster gantry rotation. Only one CBCT reconstruction is needed. We applied this approach on a dynamic phantom with 30% duty cycle of beam on time. Results: The gated acquisition was feasible and the image acquired with the gated acquisition of the phantom demonstrated the gated image of the phantom with the specified duty cycle. Conclusion: We have designed a new prospective CBCT and demonstrated its feasibility with a dynamic phantom. This system uses the same thresholds for imaging and treatment demonstrating position and residual motion within the gate on each day. The prospective CBCT is shorter in acquisition time than 4D CBCT. This system can be applied for improving the quality of gated treatment IGRT and body SRT treatments.
SU‐GG‐J‐151: Potential Lung Dose Reduction for Minimally‐Moving Lung Lesions
Authors: Mihaylov I , Corry P , Moros E , Penagaricano J , Ratanatharathorn V
Published: July 2008

Purpose: To evaluate the potential of lung sparing with IMRT for patients whose lung tumor motion range is less than 0.5 cm treated with respiratory gating at inhale. Method and Materials: A retrospective investigation on 8 patients with 4DCT scans was performed. For each patient a maximum intensity projection (MIP) data set, over 10 uniformly distributed breathing phases, was generated. The MIPs were used in contouring of GTVs, heart, and spinal cord. IMRT optimization was performed on a single phase CT data set (Average Phase or APh), representing an average mid‐ventilation phase. An average phase CT data set within 30% gating window (Average Inhale Phase or AInPh) in the proximity of the full inhale was also generated. GTVs, heart and spinal cord contours were kept the same for the APh and AInPh, while the lungs were independently contoured. The IMRT plans consist of 5‐to‐11 coplanar and/or non‐coplanar 6MV and/or 18MV beams. The dose was escalated to the maximum allowed by the organs at risk, which are spinal cord, heart and lungs. The APh optimized plan was transferred to the AInPh and dose was recomputed. Dose indices (DI) and generalized equivalent uniform doses (gEUDs) between APh and AInPh were cross‐compared. The DIs are and , and . Results: All DIs and gEUDs over the APh and AInPh for the targets, the spinal cord, and the heart are within ±1%. The DI differences in the lungs show a dose reduction ranging from 1% to over 9% for the gated plans. Conclusion: A reduction in lung dose of up to 9% is possible when gating at inhale is utilized for treatment of lung tumors with less than 0.5cm motion as seen on 4DCT. Alternatively, 9% target dose escalation shows an increase in TCP in excess of 30%.
SU‐GG‐J‐152: Predictive Capabilities of Thermal Damage Model for Real Time MR Monitored Interstitial Laser Treatment in a Canine Brain Model
Authors: Shetty A , Weinberg J , McNichols R , Gowda A , Klumpp S , Uthamanthil R , Borne A , Elliott A , Hazle J , Stafford R
Published: July 2008

Purpose: A suitable dose predictive capability will improve treatment success of interstitial laser treatment for brain tumors. This study compares the estimation of — Arrhenius damage prediction model (> 1) with the tissue damage measurements from T1 (post‐contrast), T2 and FLAIR images. Method and Materials: Craniotomy holes were created in adult hound dogs (n=4). Imaging was performed on a 1.5T whole body MR scanner (EXCITE HD, GE Healthcare). Under imaging guidance, a 1‐cm diffusing tip laser (980nm, Biotex, Inc, Houston, TX) was used to deliver therapy. A temperature sensitive echo‐planar sequence was used for real‐time monitoring. Applied power was modulated between 6–15W (power times 30–100 seconds), to create ∼1.5cm diameter lesions. Post‐ablation MR assessment was with T1‐weighted and T2‐weighted (with and without FLAIR) sequences. Tissue measurements were made on the vendor supplied workstation (Advantage Windows version 4.1, GE Healthcare). The temperature images were processed and the damage estimation was done, using MATLAB software (Mathworks Inc. MA). Pearson's correlation coefficient and Bland Altman analysis was estimated with SPSS statistical software. Results: The correlation between the damage estimations and T2 measurements was weak R: 0.34 (pval 0.34), moderate with FLAIR R: 0.79 (pval 0.05) and significant with T1 measurements R: 0.87 (pval <0.001). The Bland‐Altman analysis demonstrated fair agreement was between T1 and Arrhenius method. Conclusion: The study demonstrated that thermal damage estimated by Arrhenius damage prediction model correlated significantly with the post‐DCE T1 images, while it was weak to moderate with the T2 and FLAIR areas. Fair agreement was noted between Arrhenius and T1. A reproducible estimation of brain damage will aid the translation of laser ablation from the research setting into the clinical realm.
SU‐GG‐J‐157: Quantitative Feasibility Evaluation of Contrast Enhanced CBCT for IGRT in An In‐Vitro Model
Authors: Chan M , Burman C , Li J , Sim S
Published: July 2008

Purpose: The aim of this work is to evaluate the feasibility of using contrast agent in CBCT and to quantitatively measure the impact of contrast medium on CBCT images. This pilot study seeks to investigate the ability to better visualize radiation targets/tumors utilizing intravenous contrast medium for purpose of targeting with CBCT. Method and Materials: The impact of contrast medium on the CBCT was investigated through comparison of its CT numbers with the conventional CT (CCT) acquired on same object. Two in‐vitro studies were performed with one study using balloons filled with different concentrations of diluted contrast materials (Omnipaque™ (Iohexol Injection 300 mgI/mL), GE Healthcare) and the other using test tubes. Balloons or the test tubes were placed inside a uniform water phantom and were scanned with a conventional CT scanner (Philips Big Bore Brilliance) and a CBCT equipped linear accelerator (Varian Cl‐iX). In‐house image analysis software was used to obtain the mean CT pixel values, standard deviation, and image noise in regions of interest (∼100 pixels/ROI). Electron density calibration was also performed by scanning a Catphan‐504 phantom (Phantom Laboratory) with both CCT and CBCT as a base‐line study. Results: The analysis showed that CT numbers were fairly consistent between CCT and CBCT measurements, namely less than 7% in the mean values of overall contrast media. However, with the test tube study, the CBCT had more scatter artifacts from high density structures nearby and its noise level was about 2.5 times more than that the CCT. Conclusion: This study quantitatively verified that CBCT images are more apt to scatter artifacts from surrounding high density structures. We conclude that contrast enhanced CBCT imaging may be potentially useful for improving target localization in selected cases. Clinical evaluation of contrast enhanced IGRT is warranted.
SU‐GG‐J‐160: Radiation Enclosure Shielding Calculations for a Laboratory‐Based Small Animal Conformal Radiation Therapy Device
Authors: Sharma S , Moros E , Corry P
Published: July 2008

Purpose: Present radiation shielding calculations associated with a new laboratory‐based small animal conformal radiation therapy device (SACRTD). Method and Materials: SACRTD uses a Seifert 225kV X‐ray tube, which produces ∼100 times more penetrating radiation (at maximum tube voltage) than a typical 120kV diagnostic X‐ray imaging tube. Shielding calculations were performed assuming beam energy of 250kV. The Seifert maximum and leakage dose equivalent rates at 1m are ∼13Sv/hr and <10 mSv/hr, respectively. The a 6×6×6ft3 shielded enclosure consist of a steel frame from which two layers of 10lb/ft2 lead blankets are hung (∼½inch lead equivalent). A lead‐lined door (∼½inch lead) was also constructed. The holding structure for all components was constructed using modular framing systems (80/20 Inc). The X‐ray source is mounted ∼40in from the floor, which is a primary barrier. Shielding calculations were performed following the NCRP Report♯49, which is still applicable to sources up to 500kV. Results: Assuming maximum occupancy and use factor, T=U=1, the thickness of the primary barrier required to shield the primary beam at 1m was determined to be ∼0.6inch of lead while for secondary and leakage radiation were ∼0.3inch and 0.17inch of lead, respectively, for a maximum allowed weekly exposure P = 0.08 R / week. The primary beam was shielded with 1 inch of lead while the secondary and leakage barriers consisted of ½ inch of lead equivalent. In addition, the therapy radiation beam is further shielded by a beam collimation attachment. Other radiation safety features (door interlock, radiation monitors and alerts) have been incorporated. A preliminary radiation survey was conducted. Conclusion: A laboratory‐based radiation shielded enclosure for a SACRTD meets or exceeds the requirements of NCRP Report♯49.
SU‐GG‐J‐161: Radiofrequency Interference Between a Linac and MRI
Authors: Carlone M , Burke B , Lamey M , Rathee S , Fallone B
Published: July 2008

Purpose: Modern radiotherapy relies heavily on 3‐D image based guidance to reduce treatment margins and to conform the dose distribution to the target shape. Due to the poor soft‐tissue contrast and non‐real‐time nature of x‐ray and ultrasound based image guidance, several groups are integrating an MRI and linear accelerator. One of several unresolved technical issues is RF interference between the two devices. The purpose of this presentation is to show that LINAC RF correlates with the operation of certain components of its pulsed power modulator (PPM). Method and Materials: Electric (E) and magnetic (H) field temporal patterns (RF signals) were measured using separate E‐field and H‐field probes on three medical LINAC configurations: klystron and PPM in the same room; klystron and PPM in different rooms; and magnetron and PPM in the same room. Time resolved high voltage power supply (HVPS) current, pulse forming network (PFN) voltage, klystron current and klystron voltage, and magnetron current were all measured coinciding with the RF signals. All measured signals were compared in time and frequency domains.

Results: For a klystron powered LINAC, correlation between the HVPS current, and E and H field signals were observed in both the time and frequency domains. No correlation was observed between RF signals and the klystron current pulse. For a magnetron powered LINAC, correlation among HVPS current, magnetron current and RF signals was observed. RF signals coincided in time with the magnetron current, but the frequency spectrum were dissimilar. Conclusion: The results suggest that charging of the PFN by the HVPS current is a mechanism of RF noise generation in the klystron based LINAC operation. For magnetron based PPMs the results further suggest the magnetron current pulse generates RF noise, however dissimilar frequency spectrum indicates an indirect and more complicateds mechanism requiring further investigation.
SU‐GG‐J‐162: Radiosensitization by Gold Nanoparticles in Superficial Radiotherapy Techniques
Authors: Rahman W , Bishara N , He C , Ackerly T , Jackson P , Wong C , Davidson R , Geso M
Published: July 2008

Purpose: To investigate the radiosensitization of superficial kilovoltage range of x‐ray energy and megavoltage electron beams due to the presence of gold nanoparticles (AuNps) using cell survival curves and normoxic polyacrymide gel (nPAG). Method and Materials: Bovine aortic endothelial cells (BAECs) with and without AuNps were irradiated with kilovoltage superficial x‐ray beams and megavoltage electron beams. Cell survival at various concentrations of AuNps (0.25mMol–1mMol) was measured using colorimetric assay. Level of dose enhancement for x‐ray and electron beams was also quantified using AuNps doped nPAG. Results: AuNps enhanced the cells killing up to 21 fold for 1mMol of AuNps irradiated with 80 kVp x‐ray beams. Maximum dose enhancement factor (DEF) of 4.63 was measured for 12 MeV electron beams in the presence of 1mMol AuNps. 80 kVp which represents effective beam energy of around 40 keV was the optimum energy found that yield highest enhancement ratio. Measurements using AuNps doped nPAG also exhibit higher polymerization resulting from increased photoelectric interactions, Auger electrons and characteristic x‐ray generation. The experimental dose enhancements obtained were also in agreement with theoretical calculation and those previously documented for iodine atoms. Conclusion: Both experiments with cell culture and nPAG confirm that AuNps are able to enhance the radiation dose for x‐ray and electron superficial therapy. Lower doses from external sources are required to produce the same radiation effect with AuNps compared without application of AuNps. This will lead to improvement in superficial radiotherapy techniques of both x‐ray and electron. The use of this technique with microbeam radiotherapy technique and kilovoltage type intraoperative radiotherapy techniques are now under investigation in our group.
SU‐GG‐J‐164: Real‐Time Magnetic Resonance Imaging (MRI) Guidance and Thermal Modeling to Focus Hyperthermia Delivery
Authors: Stakhursky V , Cheng K , MacFall J , Maccarini P , Stauffer P , Das S
Published: July 2008

Purpose: Hyperthermia is an effective adjuvant modality for treatment of locally advanced cancer. However, focusing heat in the tumor using an external microwave applicator can be difficult, due to electromagnetic wave reflections at tissue interfaces. We present a methodology to steer heating towards the desired focus in real‐time, using MR thermal images for feedback. Method and Materials: The treatment control platform is based on repeated MR proton resonance frequency shift thermal imaging of the treatment volume over the course of the treatment. A cylindrical applicator with 4 independent pairs of dipole patch antennas (140MHz) is used as a heat source. The control process consists of iteratively constructing and updating a model for the heated object. At each iteration, the current model is employed to compute the optimal antenna settings (settings that the model predicts to focus heating in the target). These settings are applied to obtain the next thermal image, which is utilized in the next iteration to update the model. Thus, the algorithm progressively steers focusing while updating the model. We report on the convergence efficiency of the algorithm and importance of prior system knowledge (pretreatment simulations). Results: The experiments conducted on a cylindrical muscle‐equivalent phantom demonstrated that, for the 4‐antenna applicator, 16 iterations were sufficient to converge to the optimal thermal coverage of tumor. If prior knowledge was used, only 12 iterations were necessary to reach convergence from a starting focus that is positionally rotated 90° with respect to the desired focus. For a smaller positional rotation of 50°, 3 iterations were sufficient for convergence. The ratio of tumor to normal tissue heating after convergence improved by a factor of 3–6, compared to the initial ratio. Conclusion: Real‐time adaptive thermal modeling enables fast convergence to the optimal treatment of the patient and corrects for dynamic system changes.
SU‐GG‐J‐171: Stability and Visibility of a Novel Non‐Migrating Radiographic/radioactive Fiducial Marker: Implications for External Beam Treatment of Prostate Cancer
Authors: Neustadter D , Tune M , Zaretsky A , Shofti R , Kushnir A , Corn B
Published: July 2008

Purpose: A novel Platinum/Iridium implantable soft tissue marker is being developed for radiographic and/or radioactive target localization to optimize external beam radiation therapy. In this study, non‐radioactive and radioactive versions of the marker were implanted in the prostate of 1 dog and the liver of 19 rabbits to assess marker stability and visibility. Method and Materials: In the canine prostate and each rabbit liver, 3–4 markers were implanted. A total of 34 non‐radioactive markers and 35 radioactive markers were implanted. Stability was assessed by measuring intermarker distance (IMD) variation relative to IMDs measured at the time of implantation. IMDs were measured on a weekly basis for 3 months in the dog and a biweekly basis for 2–4 weeks in the rabbits. Ultrasound and X‐ray imaging were performed on all subjects. CT and MRI were performed on the dog. Results: No differences in marker migration or visibility were found between non‐radioactive and radioactive versions of the marker. A total of 139 IMD variation measurements made in 1 dog and 16 rabbits had a mean absolute variation (+/− SD) of 1.1 +/− 1.1mm. These IMD variations are consistent with those reported in the literature due to random organ deformation. The markers were visible, identifiable, and induced minimal or no image artifacts in all tested imaging modalities. Conclusion: The observed stability of the markers from the time of implantation suggests that these markers may allow the immediate onset of treatment without the 1–2 week post‐implantation stabilization period required with most implanted fiducials. The markers were found to be compatible with all common medical imaging modalities. With respect to marker stability and visibility these implanted fiducials are appropriate for target positioning in the radiation treatment of cancers of the prostate and other mobile organs.

Conflict of Interest: Research sponsored by Navotek Medical Ltd.
SU‐GG‐J‐174: Study On the Correlation of Diaphragm Motion and Lung Tumor Motion
Authors: Cerviño L , Lin T , Tang X , Sandhu A , Jiang S
Published: July 2008

Purpose: To assess the correlation of diaphragm motion and lung tumor motion as seen in anterior‐to‐posterior (AP) fluoroscopic sequences. Method and Materials: Fluoroscopic sequences of 7 different lung cancer patients were used for this study. Each sequence consists of 500 to 700 frames at 15 frames per second. Diaphragm position was identified in every frame by an intensity gradient method and tumor positions were manually marked as the ground truth by an expert observer. A Principal Component Analysis model based on 225 (15sec) training frames was built for each patient for tumor tracking based on surrogates. Surrogates included the current diaphragm position alone or an optimal combination of the current diaphragm position plus the diaphragm position temporal history. This optimal set was obtained by the Sequential Forward Floating Search method for feature selection. The error of each model was computed by using the rest of each sequence as testing data. Results: Results show that, in most of the patients, the diaphragm position alone is a good surrogate of the tumor motion, with an average localization error ē of 1.6mm and average error at a 95% confidence level e95 of 3.9mm. The model is improved in most of the patients by adding new surrogates from the diaphragm position history (ē=1.3mm, e95=3.5mm). However, some patients, especially patients with irregular breathing, do not show a good correlation. Conclusion: Gated radiotherapy of the lung relies on the correlation of the tumor motion with respect to the diaphragm. It has been observed that although this correlation is in general good, and can be improved with more sophisticated correlation models, some patients do not show a good correlation regardless of how sophisticated the model is. In future work, new surrogates which better correlate with the tumor motion will be explored for use in gated treatment.
SU‐GG‐J‐179: The Errors in Determining Lung Tumor ITV From Time Resolved Image Reconstruction
Authors: Cai J , Read P , Wijesooriya K , Benedict S , Sheng K
Published: July 2008

Purpose: We have reported that the maximum intensity projection (MIP) of lung tumor determined from time resolved image modalities, such as 4DCT, may be inaccurate because of the patient breathing variability. Nevertheless, the MIP is often regarded as an overestimation of the internal target volume (ITV) and average intensity projection (AIP) is used for contouring. We created AIPs and their colorized presentation, color intensity projections (CIP), from dynamic MRIs and determined their dependency on respiratory variability and tumor size. Method and Materials: Low temporal resolution images in the superior/inferior direction were reconstructed from dynamic MRIs with high temporal resolution in the same direction. The reconstruction, referred as redCAM, used 4D‐CT time resolving methods with synchronizing to the internal region of interest (ROI). CIP and AIP were reconstructed based on the probability of a certain position being occupied by the tumor. These two parameters of redCAM were analyzed as a function of respiratory variability, which was defined as the average of the standard deviation in the maximal and minimal amplitude displacements. Results:_The error between AIP, MIP and CIP are strongly dependent on the percentage of CIP. Smaller errors were observed with lower percentage CIPs. The MIP derived from redCAM is closer to the 10% CIP instead of the MIP of the real time image, which is 0% CIP. The error of AIP and MIP is fit well as a quadratic function of the respiratory variability for given tumor size, indicating accelerated increase in the error with variability. Conclusion: AIP and MIP are commonly used in lung radiation therapy with 4DCT simulation. However, their accuracy is affected by the patient respiratory variability and tumor size. Our study provides a formula to include these uncertainties into the PTV.