bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐25: Motion Pattern of Electromagnetic Transponders Implanted in the Prostate Gland
Authors: He T , Tanyi J , Laub W , Hung A
Published: August 2010

Purpose: To investigate inter‐transponder motions over the period from implantation to the last treatment. Method and Materials: The inter‐transponder motions were assessed by the changes in the inter‐transponder distances (ITD). ITDs were obtained from simulation CTs, CBCTs and/or the Calypso System. Total 8 patients who were CT‐scanned on the same day of implantation were studied. ITDs obtained from initial CT scans were used as reference to evaluate the changes in ITDs measured at subsequent treatments. ITD variations relative to the day of implantation were plotted versus the number of days post implantation. Results: Over the 8 to 9 weeks long treatment course, most observed ITD variations were negative in values indicating reduction in the ITDs since implantation. Some patients had minimal ITD reductions (< 0.2 cm) over the entire course while some were found to be as large as 1.0 cm. The most rapid and substantial reduction in ITDs, if any, occurred during the first 2 weeks post implantation with a magnitude as large as 0.8 cm. From then on, the ITDs continued to decrease over time in most patients, but the reduction rate appeared to slow down with time. The ITDs eventually varied within a narrow range of ±0.1 cm for the rest of course. This stability, however, was not seen in one patient, where the ITD between RmB and LmB transponders continued to decrease to the last treatment day with no sign of stopping. Conclusion: The ITDs tend to reduce continuously throughout the entire course of treatment but appear to stabilize over time in most patients with few exceptions. The most rapid and substantial changes in ITD occur in the first two weeks post implantation. CT on patients for treatment planning use is preferred at least two weeks post implantation to reduce uncertainties in target delineation and localization.
SU‐GG‐J‐28: Evaluation of Various MIP CT Images for Target Volume Delineation
Authors: Zamora D , Mawlawi O , Balter P , Starkschall G , Pan T
Published: August 2010

Purpose: To compare iGTV delineations of NSCLC with four maximum intensity projection (MIP) CTs with and without respiratory gating. Method and Materials: We identified 26 NSCLC patients whose tumors exhibited respiratory‐induced motion of ≥ 1cm. Each patient had a four‐dimensional computed tomography (4D‐CT) therapy simulation scan on a GE PET/CT scanner with Varian RPM respiratory surrogate. For each patient, we used an in‐house 4D‐CT sorting software to create MIP images using three different binning methods: 1) raw RPM phase‐binned 2) phase‐corrected (PC, force 0% to end inspiration and 50% to end expiration) phase‐binned, and 3) amplitude‐binned. Additionally, we created a MIP from the entire unsorted cine CT image set. All four MIP data sets were sent to Pinnacle 8.1w treatment planning software and visible tumor motion envelope (iGTV, internal gross target volume) was auto‐contoured using a lower threshold of 600. Results: In all cases, the cine iGTV without respiratory gating was the largest. Expressed as a percent of cine iGTV, our 4D‐CT iGTV ranged from 83.8% to 99.1%; the largest average 4D‐CT iGTV was from the PC dataset, followed by the phase‐binned dataset. Expressed as a percentage of cine PTV, the 4D‐CT PTV ranged from 90.0% to 99.9%. In regions of the respiratory waveform corresponding to high time rate of change in phase or amplitude, duplicate image selection can occur; duplication was most frequent with amplitude and PC binning methods. Contrary to previous studies, the image corresponding to the extreme respiratory amplitude did not inherently exhibit the full tumor motion extent, suggesting a phase delay between the internal tumor motion and the external respiratory surrogate. Conclusion: This work identifies quantitative differences and probable causes of the incomplete capture of tumor motion extent when using 4D‐CT based MIPs, and demonstrated a potential application of cine CT MIP without respiratory gating.
SU‐GG‐J‐37: Development of a Quantitative Target Localizing and Tracking Method for IGRT
Authors: Luo W , Young M , Aryal P , Johnson E , Molloy J
Published: August 2010

Purpose: To develop a quantitative target localizing and tracking method based on the contrast‐to‐noise ratio (CNR) that is derived from the images. Methods and materials: The kV, MV, CT and CBCT images for Catphan504, a phantom including high contrast sensitometric objects with different attenuations and CT numbers were included in this study. Contrast‐to‐noise ratio is defined by CNR = (T‐B)/σ, where T is the target and B the background in the surrounding area and determined by the corresponding pixel values; σ is the noise caused by photon scatters and related to the regional standard deviation. A region of interest (ROI) was selected to cover the target, which measured T, and a relative larger ROI encompassing the target and surrounding tissue was defined as the background which provided B. CNRs were calculated for the targets in CT and other images used for target localization, and the correlations between them can be used to localize and track the target. Results: The CNR obtained from CT was 2.91 for air, 2.37 for LDPE, and 2.16 for Delrin, while corresponding CNRs from CBCT were 2.91, 2.36 for, and 2.14, respectively, which were comparable. For a sagittal image, CBCT provided better image quality (CNR 1.18) than kV imaging (1.02) and the quality of MV image (0.37) was poor. The CT and CBCT images for a lung patient were used to test the method. The CNR for the tumor was 0.564 for CT and 0.567 for CBCT, which were comparable. The CNR for the tissue adjacent to the tumor was 0.418 for CT and 0.421 for CBCT. This showed that the target can be distinguished and tracked with CNR. Conclusions: CNR was used to quantify the visibility of the targets in multi‐modality images and can be potentially used for automated target localizing and real‐time tracking.
SU‐GG‐J‐38: Real‐Time MR Tumor Tracking Using a Linac‐MR System
Authors: Yun J , MacKenzie M , Robinson D , Rathee S , Murray B , Fallone B
Published: August 2010

Purpose: To investigate the feasibility of direct (i.e. no surrogates), real‐time MR tumor tracking using a linac‐MR system. Method and Materials: This study is focused primarily on investigating the requirements for lung tumor tracking due to its extreme range of motion. Two MR compatible motion phantoms have been built to simulate tumor motions. Various motion patterns of lung tumors were generated and used to drive our phantoms. Algorithms have been developed to auto‐contour and to track tumor motion in real‐time from 4D MR phantom images and simulated tumor images. Tumor tracking is achieved by controlling an MLC in real‐time. Processing time delays between the completion of MR imaging and the beginning of beam delivery in our tracking system have also been investigated. Results: Both phantoms showed successful MR compatibility. The phantoms were scanned with 3T MRI while in motion. The auto‐contouring algorithm showed successful tumor contouring capabilities. The algorithm was applied to (1) In‐vivo MR images of lung tumor; (2) MR images of healthy lung (coronal, sagittal, transverse) with 10 different tumor shapes inserted; and (3) MR images of motion phantoms. By combining the auto‐contouring algorithm with an MLC controlling system, real‐time MR tumor tracking was demonstrated in principle. Processing time delays of 50∼400 ms were determined for our tracking system. Conclusion: A potential real‐time MR tumor tracking system was studied. Lung tumor motions were simulated using two in‐house built motion phantoms with various tumor motion patterns. Our auto‐contouring algorithm was integrated within a MLC controlling system, and its real‐time tracking capability and processing time delays was evaluated. We have demonstrated the feasibility of (1) real‐time tumor auto‐contouring; (2) real‐time beam conformity to the Beam's Eye view shape of the tumor using 4D MR imaging.
SU‐GG‐J‐40: Accuracy Limits for Projection‐To‐Volume Targeting during Arc Therapy
Authors: Long Y , Fessier J , Balter J
Published: August 2010

Purpose: To investigate the fundamental accuracy limit of estimating local configuration of tumors using projection‐to‐volume alignment between a small spread of radiographs and a reference CT volume. Method and Materials: We used a real thorax CT volume at the inhale state as the reference and synthesized two target volumes at another inhale and exhale state based on two corresponding real volumes of the same patient. The projection radiographs of limited‐angle scans with six arc lengths (12°, 18°, 24°, 36°, 60° and 90°) centered at three angles (0°, 45° and 90°) were generated from these two target volumes. The tested projection‐to‐volume registration method used a nonrigid B‐spline motion model, a cost function composed of a sum of squared difference (SSD) measure and a regularizer to encourage local invertibility, and the conjugate gradient optimization method implemented in a 4‐level multi‐resolution scheme. Registration was also performed on radiographs corrupted by Poisson noise with two different incident intensities simulating 105 and 104 counts per ray. Results: The experiments demonstrated the potential accuracy of limited‐angle projection‐to‐volume registration. Registration accuracy can be sensitive to angular center, tends to be larger along the projection direction, and tends to decrease away from the rotation center, whereas registration accuracy tends to be maintained at different noise levels and extents of deformation. Conclusion: This investigation indicates the potential of position monitoring of high contrast tumors during treatment using a small spread of projections without implanted markers. This investigation may also help optimally design various parameters for position monitoring, such as projection arrangement (hardware configuration), noise/dose tradeoffs, and temporal/spatial accuracy limits. This work was supported in part by NIH grant P01 CA59827.
SU‐GG‐J‐62: Use Winston‐Lutz Test to Check Cone Beam CT Isocenter Accuracy for Imaging Guided Intracranial Stereotactic Radiosurgery
Authors: Wang Z , Chang Z , Chen Q , Yin F
Published: August 2010

Objectives: Cone beam CT (CBCT) opens the era of three dimensional (3D) imaging guided stereotactic radiosurgery (SRS). The CBCT isocenter accuracy is critical for imaging guided SRS guidance. This study analyzes the daily quality assurance (QA) results of using Wiston‐Lutz test to verify CBCT isocenter accuracy. Methods: A Winston‐Lutz phantom (Brainlab AG, Germany) is set up daily to lign up with the isocenter (Novalis TX, Varian Medical Systems, Palo Alto, CA). After the isocenter is verified with Winston‐Lutz ball‐shot films, the couch position is recorded. The couch is then moved away from the isocenter. CBCT of the Winston‐Lutz phantom is then acquired and matched to the planning CT to shift the target ball back to the isocenter. The displacement between the ball‐shot film verified isocenter position and the CBCT determined isocenter position is calculated along anterior‐posterior (AP), cranial‐caudal (CC) and medial‐lateral (ML) directions. This test is performed daily for SRS treatment. The results for the last half a year daily QA since we started this test are analyzed. The 3D vector of the isocenter displacement is also calculated. Results: The mean values and standard deviations of the differences between the Winston‐Lutz ball‐shot film verified isocenter and the CBCT determined isocenter are 0.013 ± 0.044 cm, 0.078 ± 0.061 cm, and 0.016 ± 0.049 cm along AP, CC, and ML direction respectively. The histogram distribution of the difference along three orthogonal directions is shown in Figure 1. The histogram distribution of the 3D vector for the isocenter displacement is shown in Figure 2. The mean value and standard deviation of the 3D vector are 0.11 ± 0.04 cm. Conclusion: Winston‐Lutz test could be used for isocenter checks of both machine and kV imaging system. With proper QA tests, CBCT can provide accurate localization for intracranial SRS treatments.
SU‐GG‐J‐80: Characterization of Cross Scatter in Dual Source CBCT
Authors: Giles W , Bowsher J , Yin F
Published: August 2010

Purpose: A dual‐source CBCT imaging system provides an efficient means to perform 3D and 4D imaging, but the addition of the second imaging chain produces additional scattered photons or cross scatter. The purpose of this study is to characterize cross scatter and its effects on uniformity and contrast in dual‐source CBCT imaging system. Method and Materials: An x‐ray imaging system has been developed consisting of two tube/detector pairs mounted orthogonally; each chain includes a 40×30 cm amorphous silicon flat panel detector with anti‐scatter grid. A timing system was developed to offset the exposures of each imaging chain relative to the detector cycle which remained synchronous for both imagers. Cross scatter is directly measured by only firing the orthogonal tube. The magnitude of cross scatter is expressed as the cross scatter fraction (CSF) which is the ratio of the signal attributed to cross scatter to the total detected signal. Contrast measurements were made using the Catphan® 504 and uniformity was measured with the Catphan® 504 as well as in anthropomorphic head and pelvis phantoms. Results: In all cases cross scatter produced a severe cupping artifact in the reconstructions. For the Catphan® the CSF reached 30% at the center of the projections and in excess of 60% for the pelvic phantom. The presence of cross scatter also reduced the contrast in reconstructions by up to 10%. The cross scatter distribution was also observed to have a strong gradient decreasing away from the orthogonal x‐ray tube by as much as 60%. Conclusion: Cross scatter is a degrading factor of both contrast and ct number uniformity in dual source CBCT. Conflict of Interest: This research is supported in part by Varian Medical Systems
SU‐GG‐J‐81: Geometric Accuracy of Imaging Systems on Trilogy MX Using an Automated Geometric Test Tool
Authors: Jeung A , Graf A , Suri R , Munro P
Published: August 2010

Purpose: To characterize the geometric accuracy of the imaging systems of a newly designed accelerator (Trilogy MX, Varian Medical Systems, Palo Alto, CA) using a fully automated, geometric calibration tool. Methods: A geometric calibration tool ‐ consisting of a phantom containing 16 tungsten carbide ball‐bearings and a MV collimator insert with a central pin ‐ has been used to characterize the geometric coincidence of MV and kV imaging equipment with the radiation isocenter of Trilogy MX. Three sets of data are acquired: MV images at multiple MV collimator rotations, and both MV and kV images at multiple gantry angles. The MV collimator images are used to identify the central axis of the MV beam, and the MV images at different gantry angles are then used to identify the MV radiation isocenter. Calculations then determine the corrections needed to move both the MV and kV imagers so that their central pixels exactly align with the projection of the radiation isocenter. The Trilogy MX employs a new control system so corrections can be downloaded to the control system and used to physically correct the imager positions while the gantry is being rotated. The positions of the imagers have been verified using the geometric calibration tool and a Winston‐Lutz test. Results: Coincidence between the MV isocenter ‐ measured using the geometric tool ‐ and the central imager pixels of both imagers was less than ±0.1mm. The coincidence between the central pixels of both imagers and the projection of the Winston‐Lutz BB was better than ±0.3mm. Conclusions: An automated tool for calibrating the geometry of MV and kV imaging equipment has been developed and tested. The tool gives similar results to conventional Winston‐Lutz measurements. The geometric accuracy of the imaging systems of Trilogy MX is better than ±0.3mm.
SU‐GG‐J‐82: Comparison of Positional Accuracy for KVkV, KVMV, and CBCT OBI for Cranial Localization
Authors: Armstrong H , Lamba M , Elson H , Davis M
Published: August 2010

Purpose: To quantify and compare the positional accuracy and precision of an OBI device for use as a localization system for cranial alignment. Quantification of these errors will allow for discussion of the efficacy of OBI as a replacement for invasive head ring systems. Methods and Materials: A 6.5mm BB is placed in an anthropomorphic head phantom at five positions located throughout the head. A treatment planning CT is taken and a simple plan and DRR's are generated to precisely define the isocenter. The phantom is then aligned to isocenter using a traditional three‐point setup and kVkV, kVMV, and CBCT images are acquired. These images are then auto‐fused with either setup DRR's (kVkV & kVMV) or with the planning CT (CBCT). Shifts are applied and 2×2cm port films are taken. Measurement of the displacement of the BB from the center of the field in each direction (A‐P, LAT, Sup‐Inf) indicate residual systematic error. Results: Results for displacement in the A‐P, Sup‐Inf, and Lat directions are −1.3±0.7mm (1.5mm RMS), 0.1±0.8mm (0.8mm RMS), and 0.2±1.1mm (1.1mm RMS) for 2D2D kVkV fusion; −1.5±0.7mm (1.7mm RMS), 0.7±0.8mm (1.1mm RMS), 0.0±1.2mm (1.2mm RMS) for 2D2D kVMV fusion; and −1.5±0.5mm (1.6mm RMS), 0.1±0.7mm (0.7mm RMS), and 0.2±0.9mm (0.9mm RMS) for 3D3D CBCT fusion. For each technique positive values indicate the BB is displaced in the anterior, superior, or patient left direction. The average magnitude of the total displacement from isocenter is 1.3±0.6mm, 1.7±0.5mm, and 1.6±0.3mm for kVkV, kVMV, and CBCT respectively. Conclusion: We have shown that OBI imaging can place the target at isocenter with millimeter accuracy in all directions and for each technique. A large ≥ 1.5mm systematic error is present in the posterior direction for each technique. Further investigation is ongoing to isolate the cause of this error.
SU‐GG‐J‐88: Evaluation of Phase Sampling Methods for 4D Dose Accumulation
Authors: Chi Y , Liang J , Yan D , Wuu C , Chen H , Chao K
Published: August 2010

Purpose: Simplifications and reductions in 4D dose accumulation can be achieved using the motion probability density function (PDF) with properly selected weighting and sampling. One scheme to select phase sampling and weighting scheme is to use k‐means clustering from motion PDF. In this study, we investigated the accuracy and feasibility of this method for 4D dose construction. Method and Materials: Respiration curves from 6 patients and 15 static dose profiles were used in the evaluation. Motion PDFs were constructed from respiration curves for dose convolution and phase sampling. Four sampling schemes were compared: (1) Equal phase sampling; (2) Equal amplitude sampling; (3) K‐means clustering based sampling; (4) PDF and dose profile specific optimal sampling. The cumulative 4D dose from different methods were compared to the expected 4D dose. A digital motion phantom was constructed with dose computed at various displacements for 3D dose evaluation on the above methods. Mid phase dose profile through isocenter was used for optimization in method 4. Results: For dose profiles analysis, the residual errors (normalized to the maximum dose) for the method 1 to 4 are: 1.9+1.4%, 2.2±0.59%, 0.88±0.70%, and 0.55%±0.48%. For phantom study, the maximum residual errors are 7.8%, 3.6%, 2.9%, and 3.5%. The 3D gamma analysis passing rates are (dose difference 2%, distance to agreement 2mm, and dose threshold 30% of maximum dose): 96.1%, 99.6%, 99.7%, and 99.6%. Conclusion: K‐means clustering sampling is effective in 4D dose accumulation. Method 4 will be most accurate sampling method for single dose profile analysis, with all the information included for optimization. K‐means sampling has slightly larger residual error in dose profile approximation, but it applies to multiple dose profiles for a given PDF. In 3D dose analysis, k‐means sampling is the most effective and accurate among the four methods.
SU‐GG‐J‐93: PCA‐Based Lung Motion Model
Authors: Li R , Lewis J , Jia X , Zhao T , Lamb J , Yang D , Low D , Jiang S
Published: August 2010

Purpose: To theoretically study the effectiveness of principal component analysis (PCA) modeling of lung motion, and to investigate its applicability for clinical data. Method and Materials: We first derived an important property which is concerned with the implicit regularization imposed by the PCA lung motion model, i.e., for any two voxels with similar motion, their motion represented by PCA will also be similar. We then introduced two respiratory phantoms based on simple and yet realistic assumptions, where each voxel in the lung moves with cosine motion or an even power of cosine motion, both with arbitrary amplitudes and phases. We then applied the PCA model on two patient 4DCT data sets to test the modeling accuracy. Results: We proved that for respiratory phantoms with cosine and an even power (2n) of cosine motion, 2 and 2n PCA coefficients and eigenvectors will completely represent the lung motion, respectively. Moreover, for the respiratory phantom with cosine motion, we derived the equivalence conditions for the PCA motion model and the physiological 5D lung motion model (Low 2005). When tested on clinical data, the average 3D RMS model error was found to be below 1 mm using only 2 PCA coefficients. Conclusion: We have presented the theoretical analysis and clinical validation of a lung motion model based on PCA. Potential clinical applications include removing motion artifacts in 4DCT, lung motion tracking from implanted markers, surface imaging, or x‐ray projection images.
SU‐GG‐J‐99: Design and Study of In‐House Ultrasound Based Automatic Patient Movement Monitoring Device for Teletherapy Treatment
Authors: Senthilkumar S. , Vinothraj R , Vasanthamalai S
Published: August 2010

Purpose: The purpose of the present study is to fabricate indigenously ultrasonic based automatic patient's movement monitoring device (UPMMD) that immediately halts teletherapy treatment if a patient moves claiming accurate field treatment. This device is an electronic compact device, which is small in size, low‐power, high‐precision, non‐intrusive, low cost, light in weight and reusable. Method and Materials: The UPMMD is an electronic device, which consists of circuit board, magnetic attachment device, LED indicator, speaker, ultrasonic emitter and receiver, which are placed on either side of the treatment table. UPMMD functions based upon the reflection of sound waves. The ultrasonic emitter is emitting the ultrasound waves and the receiver receives the signal from the patient, when a patient moves, the receiver activates the circuit, an audible warning sound will be produced in the treatment console room and thus alerting the technologist to stop the treatment. Simultaneously, the electrical circuit to the teletherapy machine will be interrupted and radiation will be halted. Results: Studies were conducted on phantom and 210 patients with different types of cancers. It shows that among the 210 patients, 89 cancer patients have moved from their positions during the treatment by more than 0.3cm whereas the rest of them received the radiation without movements. During the treatment, the interruption of radiation has occurred due to the patient's movement from 0.5 to 1.5cm laterally from the actual planed field area. Conclusion: This study revealed that the device can prevent the patient's normal tissues from unnecessary radiation exposure and also it is helpful to deliver the radiation to the correct tumor location. The raising sound alerts the radiation technologists. It also enables the technologists to do their work more efficiently. So, this device can potentially be used to monitor and control the patient's movement during External Beam Radiation Treatment.
SU‐GG‐J‐101: Investigation of Intrafractional Prostate Rotation and Its Effect on PTV Margin Evaluation
Authors: Xu Q , Li J , Fan J , Chen Y , Tanyi J , Hossain M , Chen L , Yang B , Ma C
Published: August 2010

Purpose: The intrafractional prostate rotation has been rarely studied due to the limitation of real‐time imaging of the prostate during treatment. The Calypso 4D Localization System provides the capability of real‐time tracking of implanted transponders for prostate patients. Based on the transponder locations, intrafractional prostate rotation can be investigated to facilitate prostate PTV margin evaluation.Method and Materials: With three transponders implanted in the prostate, the system log file recorded intrafractional 3D coordinates of transponders for 10 fractions of 5 patients enrolled in the study. To minimize noise, the 3D coordinates were first downsampled following a size of 5 median filtering. Based on the transponder positions in the planning CT, the rotational and translational motion of the prostate was calculated using a point‐based algorithm. To check the CTV coverage for a particular fraction we overlapped the rotated prostate CTV with the PTV. Results: For 9 fractions, the maximum rotation angles around x (Lateral), y (SI) and z (AP) were 7°, 6° and 3°, respectively. Although the prostate may not rotate around all 3 axes simultaneously we tested this worst case scenario and found that the CTV was still covered by the PTV when the prostate rotated by the maximum angles. For one fraction, large rotational angles were observed (39.4°, −22° and 12° in x, y and z) along with large transponder distance variations (>1cm). In this case, 20.5% of the CTV was outside of the PTV. The rotational angles for this patient need further investigation since large transponder migration may affect the rotation calculation significantly as we reported before. Conclusion: For most cases, the prostate exhibits relatively small intrafractional rotations and the CTV is covered by the PTV. For patients with larger transponder migration, a CBCT or other imaging modality is recommended for further investigation.
SU‐GG‐J‐111: Evaluation of Reproducibility of Immobilization Device for Head‐And‐Neck Radiotherapy
Authors: Chen Y , Rosenthal D , Kry S , Wong P , Harrelson S , Hayden S , Garden A , Schwartz D , Dong L
Published: August 2010

Purpose: To evaluate two commercially available Head‐and‐Neck immobilization devices for daily treatment setup and their correlations to anatomy changes. The study represents an early implementation experience with the Orfit mask, which was new to our clinic. Method and Materials: Twenty‐one patients enrolled in an in‐house adaptive radiotherapy protocol 3171 using daily CT guided treatment were randomly assigned to one of two different thermoplastic masks: 5‐Point Efficast mask from Orfit (ORFIT Industries, Jericho, NY) or the extended S‐Board mask from Civco (CIVCO/MedTec, Orange City, IA). The daily setup displacements in each of the antero‐posterior(AP), supero‐inferior(SI), and medio‐lateral(ML) direction were determined using a 3D rigid image registration technique with the C2 vertebral body as the bony landmark. Systematic and random setup errors were computed for each group. The Pearson product‐moment correlation coefficient was used to determine the correlation between parotid shrinkage and the magnitudes of 3D displacements. Results: The random errors in AP, SI, and ML directions for Orfit mask (10 patients) were 0.13, 0.12, 0.11cm, and 0.12, 0.16, 0.11cm for the Civco mask (11 patients), respectively. The systematic errors were 0.20, 0.12, 0.16 cm for the Orfit mask, and 0.16, 0.16, 0.13 cm for the Civco mask, respectively. The Orfit mask significantly reduced the setup error in SI direction. However, in the AP and ML directions the systematic error increased with the Orfit mask, although the random errors were similar. The magnitude of the total (3D) shift was found to be correlated with the percent of parotid shrinkage for the Civco mask (p=0.026), but not for the Orfit mask. Conclusion: Although the Orfit mask reduced setup error in SI direction due to its head rest design, setup errors in AP and ML directions increased mainly due to increased systematic mask preparation errors. User training may be important.
SU‐GG‐J‐112: A Retrospective Single Institution Patient Population Study of I.G.R.T. Shifts and Their Implications for Non‐IGRT Treatment Set‐Up Margins, as Both an Internal and External Q.A. Tool
Authors: Clouser E
Published: August 2010

Purpose: To establish a population based set of margins from I.G.R.T. patients to account for set‐up uncertainties based on published formulas for use with non‐I.G.R.T. patients locally and potentially for QA purposes outside of our institution; as well as potentially identify any systematic errors in the patient treatment chain. Method and Materials: All kV and C.B.C.T. based I.G.R.T. patient's shifts were recorded over a 3+ year period and divided into general anatomy based categories. The set‐up uncertainty margin formula proposed by Van Herk et al of 2.5Σ +0.7σ was applied to each category. In addition, all averages and block check sessions were analyzed for systematic problems. Results: Thorax set‐up margins: 0.84 cm vertical, 1.21 cm Longitudinal, 0.89 cm Lateral; Pelvis: 0.94 cm vert., 0.87 cm long., 0.69 cm lat.; Abdomen: 0.94 cm vert., 1.3 cm long., 0.82 cm lat; Head/Neck: 0.34 cm vert., 0.49 cm long, 0.39 cm lat.; extremities: 0.62 cm vert, 0.69 cm long, 0.68 cm lat; and Spine: 1.10 cm vert., 1.25 cm long, 0.87 cm lat. Conclusion: Population based margins can be used as a portion of a total PTV margin formula when designing a treatment plan. If margins the size of those calculated would be clinically unacceptable, I.G.R.T. would be indicated and the patient set up uncertainty would be reduced to the uncertainty of the IGRT process only. Since this population of patients is large and represents a wide variety of diseases, it should also have Q.A. value to other institutions that either do not have I.G.R.T. or are just starting a program as a baseline with which to compare. Machine uncertainties, imaging uncertainties (mostly longitudinal), block edge/penumbra margins and other patient or case specific uncertainties should also be considered when designing margins.
SU‐GG‐J‐115: IGRT with Megavoltage Cone Beam CT for Prostate Patients with Fiducial Markers: Action Levels and Population Margins
Authors: Neves‐Junior WFP , Hanna SA , Mancini A , Pelosi EL , Haddad CMK
Published: August 2010

Purpose: To present and evaluate the results of the use of Image Guided Radiotherapy (IGRT) using Megavoltage Cone Beam CT (MVCBCT) in prostate patients with fiducial markers. Method and Materials: 14 patients with 3 gold seed markers each were treated. The treatment unit was a Siemens Primus. The MVCBCT images were acquired using 3 MU, after skin mark alignment, prior to the treatment and registered manually with the planning CT using the seeds as surrogates. The resulting table coordinates shift in each direction (Lateral, Longitudinal and Vertical) to align the prostate in respect to the isocenter was stored. Different action levels (AL) were simulated and population margins (2.5∑+0.7σ) calculated for each scenario considering a residual error of 2 mm for intra‐fraction and observer errors; as well as the fraction of the days that would need table corrections. Results: 335 MVCBCT images were generated. The average prostate localization errors detected prior to the treatment were: 2±2 mm (Lateral), 3±2 mm (Longitudinal), 3±3 mm (Vertical). The population margins calculation for a non‐AL and for ALs from 8 to 2 mm, indicates that the margins for the non‐AL scenario of 5, 7 and 6 mm, in the Lateral, Longitudinal and Vertical directions respectively, can be reduced to 3 mm in all directions, applying IGRT daily with an AL of 3 mm, and thus acting in 84% of the days. Conclusion: The technique enables a fast and precise prostate localization with low dose. The AL is an important choice and will have a direct impact in the CTV to PTV margin that can be used for the procedure. The simulations indicate that with a 3 mm action level, a 3 mm margin could be used and thus reducing toxicity without compromising the local control.
SU‐GG‐J‐118: Geometrically Targeted Radiation Enhancer Using Semiconductive Nanoparticles
Authors: Sheng K , Wang L , Rzigalinski B , Read P , Larner J , Yang W
Published: August 2010

Purposes: Photo‐emitting semiconductive nanoparticles conjugated with photosensitizer molecules are a promising enhancer for radiation therapy. The purposes are to study toxicity, biodistribution, and in vivo efficacy of the nano‐conjugate. Methods and materials: The toxicity of the conjugate was evaluated by propidium iodide uptake of both 3T3 fibroblast and normal organotypic brain cells 5 to 10 days post exposure to drug with a concentration from 24fM to 24μM. H460 cancer cells were used as the xenograft model in nude mice and the tumors were grown for 1 week. To investigate the biodistribution, tail vein injection of 42nM QDs with or without conjugated folic acid were administered in 2 doses at 24 hours and 16 hours prior to dissection. Tissue samples were taken from the liver, the kidney and the tumor. To measure the efficacy, QDs conjugated with Photofrin and (or) folic acid were injected with the same total dose. 8 Gy of radiation were delivered in a single fraction. The tumor size was measured twice a week and compared with the control group. Results: There was no detectable toxicity for QD concentration up to 24 pM. Cell death was observed at 24nM but remained at a very low level. Less than 2% positively labeled tumor cells were observed under fluorescent microscope with QDs alone. However, the percentage of positively labeled cells increased 38 folds with folate. The in vivo efficacy study is consistent with the biodistribution, with no detectable tumor growth delay from QD/Photofrin alone but a significant growth delay of 3 days (p=0.05) was observed with QDs conjugated to both Photofrin and folate.

Conclusions: Toxicity of the conjugate to normal tissue is low at the level for radiation enhancement. Effectiveness is demonstrated for the first time on an animal model. Methods of drug delivery play critical roles in the efficacy.
SU‐GG‐J‐119: Induction of Plasmonic Heating Inside Breast Tumor Phantom Using Gold Nanorods and Near‐Infrared Laser
Authors: Cho S , Siddiqi A , Manohar N
Published: August 2010

Purpose: To demonstrate and quantify gold nanorods (GNRs)‐induced plasmonic heating inside breast tumor phantom during near‐infrared (NIR) laser illumination. Method and Materials: GNRs were fabricated using published procedures. Two types of breast gel phantoms were fabricated. The first phantom was nearly water‐equivalent as it was fabricated using 1.5% agar gel (98.5% water). The second phantom, on the other hand, was fabricated using a more turbid intralipid‐based gel (2% agar, 2% intralipid, and 96% water). Both phantoms contained an identical GNR‐filled cavity with 4 mm inner diameter. The cavity was filled with approximately 0.1 weight percent GNRs and located at the center of a quadrant of hemispherical phantom at 2.5 cm depth measured from the base of the phantom. Both phantoms were illuminated with an 808 nm NIR laser at 1 W power under the identical geometry. Thermocouples were used to measure the temperature changes within the cavity and surrounding medium. Results: There was significant difference between the two gel phantoms in terms of achievable temperature rise within a GNR‐filled cavity. For a 60 second illumination, the cavity inside an agar‐based gel phantom was heated up to 15°C above the background temperature, while there was a temperature change of only about 1.5°C within the cavity inside an intralipid‐based gel phantom. Conclusion: The current results suggest tumors inside breast tissue with high water content may be easily heated up to a few degrees above the surrounding body temperature within a short time interval (e.g., on the order of 10 seconds) without much difficulty. According to the current results, however, it might be difficult to achieve such a temperature change for tumors inside breast tissue similar to intralipid‐based gel in terms of its optical property.

This work has been supported by the US Department of Defense, Breast Cancer Research Program, Concept Award, W81XWH‐08‐1‐0686.
SU‐GG‐J‐124: On the Search of the Ideal Radiation Source for Gold Nano‐Particle Enhanced Radiation Treatment
Authors: Van den Heuvel F , Locquet J , Nuyts S
Published: August 2010

Purpose: The efficacy of the dose deposition from X‐rays due to the use of high‐Z materials is dependent on the energy of the radiation used. This paper attempts to select the optimal source for a gold nano‐particles. Methods: A general purpose monte carlo code (MCNPX2.7b) is combined with a code describing radiobiological damage (MCDS) yielding densities of double and single strandbreaks in cellular material. Using different external sources with a minimal energy spread, the densities of radiobiological damage is determined. In addition the energy spectrum and source of depositing electrons is determined, differentiating between fluorescent, Compton, knock‐on, and Auger electrons. Particular interest is focused on the K‐edge of gold. Results: Efficiency at very low energies (10–20keV) seem to be the highest. Contrary to expectations the K‐edge only yields limited increase in radiobiological efficiency. Some increase is found relative to energies just below the K‐edge. A relatively large dose enhancement is noticed, which is seen to be highly dependent on the concentration of the contrast agent. Seeing that lower energies have an increased enhancement and biological effect, the effect of low energy sources like Iodine‐125 and the Xoft electronic brachytherapy source spectra were used to provide the same information. Conclusions: Xoft and I125 brachytherapy sources have a relatively high yield in Auger electrons compared to external sources, while having a comparable dose enhancement. The calculations however, were hampered due to the lack of good modelling for low‐energy electrons, yielding large uncertainties.
SU‐GG‐J‐125: Monte Carlo Simulation of Dose Enhancement in Tumors Using Gold Nanoparticles
Authors: Quinn M , Gao M , Albuquerque K , Roeske J
Published: August 2010

Purpose: In the radiation oncology setting, high atomic number (Z) nanoparticles may provide a local dose enhancement in tumors when combined with low energy x‐rays. At energies near the K‐shell edges of these materials, the mass energy absorption coefficient (μen/ρ) may be significantly higher than that of tissue. For materials such as gold, the K‐shell edge falls in the lower energy spectrum of a conventional CT scanner. Irradiating nanoparticles inside tumor with a CT scanner may provide a high dose to the tumor while sparing healthy surrounding tissue. As a first step, a simulation of gold nanoparticles in a phantom can quantify the magnitude of this effect. Methods: Monte Carlo simulations were performed for different concentrations of gold using the program MCNPX. Simulations were performed using a cylindrical phantom with a tumor having various concentrations of gold nanoparticles. Four concentrations of nanoparticles were used: no gold, 1mg/g, 5mg/g, 10mg/g. The source of radiation was modeled using the spectrum of a 140kVP CT scanner. Each scenario was run using 109 particles. Results: For all cases, the total energy deposited in the target was determined. These calculations indicate that using nanoparticles provides a sizeable increase in the energy deposited inside the target. For 1mg/g, 5mg/g, and 10mg/g nanoparticle concentration the increases were 1.13, 1.78, and 2.58 times relative to no gold. Conclusions: Monte Carlo simulations of a phantom with different concentrations of gold nanoparticles irradiated by an x‐ray source reveal a dose enhancement relative to no nanoparticle presence. Dose enhancements of over 2.5 times for nanoparticle concentrations of up to 10mg/g indicate that localizing nanoparticles in tumor may be effective at providing an improved therapeutic ratio. The results of this simulation can be used to guide measurements for confirmation of this effect. Supported by Dept of the Army — USAMRRA W91ZSQ9081N608.
Benefits of Radiotherapy Added Nanoparticle Assessed by a Quantitative Analysis of Dose‐Gradient: An Evaluation in Soft and Lung Tissues by Monte Carlo
Authors: Marques T , Schwarcke M , Garrido C , Baffa O , Nicolucci P
Published: August 2010

Purpose: Evaluate the volume fraction enclosed by maximum isodose (isodosemax) within a structure as a quantitative criterion for assessing the benefits of using nanoparticles in Radiotherapy. Material and Methods: Dose enhancement can be evaluated in a volume with and without nanoparticles by the ratio between mean doses, defining an average‐dose‐enhancement‐factor (DEF). Decompounding DEF in multiplicative terms is possible to define a maximum‐dose‐enhancement‐factor(DEFmax) and a dose‐gradient‐factor(GF). GF express what fraction of volume is enclosed by the isodosemax present in the analyzed structure. GF close to 1 express that the isodosemax present in the analyzed volume increase its value. GF close to 0 indicates that the isodosemax decrease its value. Soft and lung targets with 3×3×1cm3 containing and not containing 0.11mM concentration of gold nanoparticles (AuNP) were considered to Monte Carlo simulations, performed with PENELOPE‐2008. Adjacent‐volumes were delimited as tissues 1cm far from the target in all directions. A 120kV x‐ray beam was considered to simulate Intra‐Operative‐Radiotherapy situations. Results: Dose distributions visually revels changes in dose‐gradient and depth dose curves presents it quantitatively. In target soft tissue: To adjacent‐volume It indicates that in target isodose max changes not so much, presenting almost the same values in situations with and without AuNP; However in adjacent‐volume isodosemax had its value increased. In target lung tissue: These parameters indicate that the isodosemax changes its value not so much in lung‐target but radically in lung‐adjacent‐tissue. This behavior is expressed in each corresponding GF of these structures: Coclusions: AuNP increase the mean dose in target and decrease radically the maximum isodose in adjacent tissues. The GF express quantitatively how attenuation and dose‐contribution effects are balanced providing information to guide clinical cases of nanoparticle added to Radiotherapy.
SU‐GG‐J‐128: Comparison of Dose Distributions for Small Animal Radiotherapy Using a MicroCT Scanner and a Single‐Field Irradiator
Authors: Bazalova M , Nelson G , Noll J , Graves E
Published: August 2010

Purpose: To compare dose distributions for small animal radiotherapy performed on a microCT scanner with multiple 120kV beams and a single‐field irradiator with a 200kV beam. Materials and Methods: A microCT scanner with a maximum x‐ray tube potential of 120kV and a single‐field irradiator operating at 200kV were modeled in the EGSnrc/BEAMnrc Monte Carlo code. The models were validated using dose in air and depth dose curves in solid water for various beam sizes measured with an ionization chamber and gafchromic films. Treatment plans for a mouse with subcutaneous teratoma and a mouse with a spontaneous lung tumor were created for both the microCT scanner and the single‐field irradiator. On the microCT, the teratoma treatment was prescribed as tangential 80° and 180° beams and lung tumor treatment consisted of eighteen beams equally spaced between 90° and 270°. On the single‐field irradiator, the mice were planned with a left lateral beam and an anterior posterior beam, respectively. The 5Gy dose to the PTV and the dose to critical structures were calculated in the EGSnrc/DOSXYZnrc code. Results: In both cases, the dose distributions achieved with the microCT scanner using a 120kV beam were superior to the dose calculated for a single 200kV beam. The teratoma case showed 4Gy dose to 30% of the left lung whereas the dose to all critical structures on the microCT scanner was below 0.2Gy. In the case of the lung tumor, the dose to the spinal cord and right lung is considerably larger for the single‐field irradiator plan. Left lung and heart are completely spared in the single‐field treatment, however, the dose to these structures is below 1.5Gy in the microCT plan. Conclusions: This work demonstrates that small animal radiotherapy on a microCT scanner yields better critical organ sparing and is therefore preferred over single‐field irradiator radiotherapy.
SU‐GG‐J‐129: Dosimetric Correction for Lung Aperature Used in Mouse Irradiation Experiments for a 250 KVp Orthovoltage Unit
Authors: Arndt C , Wang Z , Saito N , Podgorsak M
Published: August 2010

Purpose: Mouse lung irradiation experiments are being carried out to investigate radiation induced pulmonary fibrosis. The irradiation setup involves a mouse pie cage device to irradiate 10 mice simultaneously with concentric radiation shields to protect critical organs and a plastic bag containing anesthetic isoflurane gas. The objective is to provide accurate dosimetric evaluation for irradiating mouse lungs with the above setup. Method and Materials: The irradiator is a Philips RT‐250 orthovoltage unit. A 12.5 cm diameter cone and 250 kVp X‐rays were used for irradiation. The procedure for evaluating dose rate consists of: dose calibration for the open cone as per standard protocol, output factor measurement of the shielded field, and percentage depth dose (PDD) comparison of the concentric aperture versus the open cone. The actual mouse irradiation setup also involves a ∼1.0 cm airgap, off‐axis prescription point, and the plastic bag. These dosimetric effects were accounted for as correction factors in the formulism for irradiation time calculation. Dose enhancement at the surface caused by photoelectrons and Compton electrons from the shielding material was also studied. Results: Results showed a cumulative 21.3% drop of dose rate due to attenuation from the bag (1.2%), inverse square law fall‐off (6.3%), and output ratio of the narrow aperture contributing the remaining 13.8% drop. The off‐axis effect found was minimal. Also there was a drop in PDD due to the reduced field size. An increased surface dose from electrons scattered off the shield was noticed from the surface dose profile. This extra surface dose was reduced by the airgap and plastic bag, thereby providing skin sparing for small animal irradiation. Conclusion: More accurate dose delivery will be achieved when the correction factors are applied. By adding a thin attenuating material and airgap, surface dose due to Compton electrons and photoelectrons can be reduced.