bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐FF‐I‐110: Measurement of X‐Ray Beam and Grid Misalignment in Portable Chest Radiography Using a 3D Test Object
Authors: Fetterly K , Erickson D , Schueler B
Published: July 2007

Purpose: X‐ray beam to grid alignment is crucial for acquiring high‐quality portable chest radiographs. The purpose of this work was to measure x‐ray beam to grid alignment by imaging a custom alignment phantom during routine acquisition of portable chest images acquired using computed radiography (CR). A better understanding of typical beam alignment in the clinical practice is expected to be useful to specify the most appropriate grid ratio and to help foster better in‐room alignment. Materials and Methods: The disk‐shaped phantom was 5 cm in diameter and 1 cm tall. A 2 cm diameter ring of sixteen 2 mm tungsten balls was positioned at the entrance surface of the phantom and a 4 cm ring of twenty‐four balls was positioned at the exit surface. Computer analysis of the phantom on the CR image provided for measurement of the 3D spatial location of the x‐ray focal spot with respect to the image center. Results: Trial measurements using uniform exposure images demonstrated that the (x, y, z) location of the focal spot with respect to the image plane could be measured with error less than 2% of the x‐ray source to image distance. A preliminary clinical trial using 20 portable chest images demonstrated that misalignment of the x‐ray beam to the grid ranged from 0 to 14 cm (average = 6 cm) in the direction perpendicular to the gridlines. Conclusions: A phantom and image analysis application was developed to measure the x‐ray beam to grid misalignment for CR portable chest radiographs. Initial measurements showed that the precision is appropriate for this task. Preliminary clinical studies demonstrated a relatively wide variation in alignment in the clinical practice. The results of this work will be used to foster better alignment and to specify the most appropriate grid ratio for portable chest imaging.
SU‐FF‐I‐122: Multiple Overlapping Low Intensity Focused Ultrasound Fields for Localized Tissue Ablation
Authors: Winey B , Liao L , Yu Y
Published: July 2007

Ultrasound has long been known to cause tissue heating when applied in high intensities. More recently, interest has arisen in the area of High Intensity Focused Ultrasound (HIFU) for localized tissue heating effects, specifically thermal ablation. HIFU is being introduced into clinical settings for localized tissue ablation guided by MRI. All present techniques employ focused traveling high intensity acoustic waves to create a region of elevated temperature, which causes cell death. Such high intensity traveling waves can be damaging to normal tissue in the vicinity of the focal region, and have demonstrated surface burns and caused patient discomfort in certain clinical trials. The focal region is also difficult to determine due to divergence of the beam and elongation of the focus along the direction of propagation. Use of lower intensity ultrasound can minimize the side‐effects presented by HIFU. This paper demonstrates the use of multiple low intensity focused ultrasound beams resulting in stationary acoustic fields which are capable of heating a very small and more precisely located region of tissue. The intensity of the individual ultrasound beams is within FDA diagnostic ultrasound limits (0.720 W/cm2). Temperature elevation that would cause cell death was achieved in tissue‐mimicking phantoms after short exposures to the acoustic field in the region of beam overlap. The technique was tested with excised turkey breast samples. Temperature increases of 30 C above ambient (37 C) were observed after sonication times of 30 seconds. The size of the tissue ablation was a quasi‐sphere of diameter = 1 cm.
SU‐FF‐I‐123: 3‐D Elasticity Imaging with a 2‐D Array
Authors: Fisher T , Hall T , Panda S , Jiang J , Resnick J , Barnes S
Published: July 2007

Purpose: Assess the performance of various motion tracking strategies applied to a 3‐D RF echo data set from an oil‐in‐gelatin phantom with spherical targets for a multi‐step deformation totaling about 15% axial strain. Discuss the prospects and preliminary experience of in vivo motion tracking. Method and Materials: A prototype 9‐MHz 2‐D CMUT array connected to a Siemens SONOLINE Antares was used to acquire RF echo data from a 100‐mm × 100‐mm × 70‐mm oil‐in‐gelatin phantom containing a 10‐mm diameter spherical inclusion that has a 5:1 elastic contrast with the background. This CMUT array images like a 1‐D linear array in generating a 2‐D image in the azimuthal plane, and it acquires a 3‐D volume by electronically stepping the 2‐D imaging plane in the elevational direction. A series of controlled compressions of 1.5–2% axial strain were applied. Phantom motion was tracked with off‐line data processing using different approaches including 2‐D, 2.5‐D and 3‐D axial guidance tracking. The method that performed the best was applied to a 3‐D in vivo data set obtained with the same transducer. Results: The contrast to noise ratios (CNR) and the cross correlation between the motion‐compensated RF and the reference RF for the four motion tracking approaches were used as metrics of performance. The CNR increased with increasingly sophisticated motion tracking with 3‐D axial guidance performing the best. The same trend was observed with the normalized cross correlation. Tracking in vivo data has proved more difficult. Conclusions: These results demonstrate the improvement in motion tracking available through 3‐D tracking. This work also demonstrates that volume data acquisition allows accurate motion tracking and axial strain image formation for an entire target (within the field of view). Volume data acquisition with 2‐D arrays will provide a major advancement in the capabilities of elasticity imaging systems.
SU‐FF‐I‐128: Regional Time Density Curves (R‐TDC) Derived From Angiographic Sequences for Analysis of Aneurysmal Flow Modification Resulting From Endovascular Image‐Guided Interventions
Authors: Dohatcu AC , Ionita CN , Sherman JR , Rangwalla HS , Bednarek DR , Hoffman K , Rudin S
Published: July 2007

Purpose: Digital subtraction angiography (DSA) is currently used to evaluate the result of endovascular treatments, either visually or using time‐density curves (TDC) which quantitate the change of contrast as a function of time for the entire aneurysm. Regional analysis (R‐TDCs) of flow patterns in sub‐volumes of an aneurysm was employed in this study to extract local flow information to determine the result of treatment with a partially‐occluding asymmetric vascular stent (AVS). Method and Materials: A patient‐specific, elastomer aneurysm phantom was placed in an in‐vitro pulsatile flow loop containing a glycerin‐water (25/75) solution simulating blood. One cc volumes of iodinated contrast were delivered 20 cm from the aneurysm entrance through a 6‐Fr catheter with an automatic injector. DSA sequences were acquired at 30 frames/sec using a 5‐inch II mode. The neck of the aneurysm was partially covered by a polyurethane‐patch AVS positioned to occlude either the proximal or the distal portion of the orifice. R‐TDCs were obtained for untreated and treated cases. Results: Differences in R‐TDC parameters for untreated, proximally covered, and distally covered cases indicate important modifications of flow occurred in different areas inside the aneurysm that are not evident from the total volume TDC. For example, in one sub‐region with the proximal patch, we measured a 2.3 times increase in peak density compared to the untreated case and a residence time 3.9 times longer, whereas the total aneurysm measurement showed the peak density to be reduced to 0.8 times and the residence time to be increased by a factor of only 1.9 compared to the untreated case. Conclusion: R‐TDC parameters derived from angiographic sequences present a great potential for quantitative in‐vivo assessment of local hemodynamic effects. This approach may provide a valuable, minimally invasive tool for assessing endovascular treatments during the procedure.

Support: NIH R01‐NS43924, R01‐EB002873, Toshiba‐Corp.
SU‐FF‐J‐02: A Cone Beam CT—guided Online Plan Modification Technique to Correct Interfractional Anatomic Changes for Prostate Cancer IMRT Treatment
Authors: Fu W , Yang Y , Yue N , Heron D , Huq M
Published: July 2007

Purpose: To develop an online plan modification technique to compensate for the interfractional anatomic changes for prostate cancer IMRT treatment based on the daily cone beam CT (CBCT). Methods and Materials: Pre‐treatment CBCT were acquired after patients were set up using skin marks. Instead of moving the couch to rigidly align the target, or performing re‐planning, we modified the leaf sequence in the original IMRT plan to account for the interfractional target motion and deformation based on the daily CBCT. The MLC leaf positions for each subfield were automatically adjusted based on the position and shape change of target projection in the beam's‐eye‐view (BEV). Three prostate cases were adapted to evaluate the proposed method and the results were compared with those obtained with bony‐structure‐based correction (Strategy1), prostate‐based correction (Strategy2) and CBCT‐based re‐planning (Strategy3) strategies. Results: For case 1, there was a large prostate deformation. With our MLC modification method, the prostate coverage was improved to 94.0% from 85.3% with Strategy1 and 88.7% with Strategy2, the seminal vesicle (SV) coverage was improved to 93.9% from 60.7% with Strategy1 and 75.4% with Strategy2. For the other two cases, the prostate interfractional target deformation was insignificant, and the prostate coverage using our method was comparable to Strategy2, Strategy3 but was better than Strategy1. The SV coverage was significantly improved with our method compared with Strategy1 and Strategy2 and was similar to that with Strategy3. The DVHs for OARs with our method were similar to those with Strategy3. Conclusions: The proposed method is superior to the bony‐structure‐based and prostate‐based correction techniques, especially when large interfractional target deformation exists. Its dosimetric performance is similar to that of the re‐planning strategy, but with much higher efficiency. This method may be used clinically to compensate for the inter‐fractional target position and shape changes in prostate IMRT.
SU‐FF‐J‐04: Uncertainties in Respiratory Gating for Lung Tumors
Authors: Nelson C , Balter P , Lindsay P , Briere T , Vedam S , Morice R , Komaki R , Starkschall G
Published: July 2007

Purpose: The purpose of this work is to quantify the uncertainties in tumor location during respiratory‐gated radiation delivery when using implanted fiducial‐based setups and respiratory gating to deliver the treatment. Method and Materials: A patient treated for non‐small‐cell lung cancer was set up daily based on a fiducial implanted in the tumor. The fiducial was visualized using AP and Lateral kilovoltage x‐rays gated on end expiration. Audio prompting was used to ensure regular breathing. Following alignment, a second pair of gated images was acquired to verify the shift. The uncertainties in the gating system were quantified by the residual error in fiducial location after the initial shift. In addition, cine megavoltage images were acquired of an AP field during the gated treatment (6–10/sec) and the fiducial positions were measured to quantify uncertainties in position between successive respiratory gates. Results: Gating uncertainties measured by the residual error of the patient shift were determined to be 1.4, 3.3, and 1.3 mm for the LR, SI, and AP directions, respectively. The variation each day in the fiducial position averaged over each respiratory gate was determined to be 1.0 and 2.2 mm in the LR and SI directions respectively. The variation in fiducial position in successive respiratory gates over the course of treatment was measured to be negligible in the LR direction and 1.8 mm in the SI direction. Conclusion: The uncertainties in respiratory gating were 3 mm over the course of treatment and 2 mm measured each day on successive gates used to deliver the treatment. Although respiratory gating may reduce tumor motion, the uncertainties in tumor position during respiratory gating must be considered when the internal margin is being designed.
SU‐FF‐J‐10: Optimization of Position Compensated Plans (PCPs) for Adaptive Radiotherapy
Authors: Haslam J , Aydogan B , Pelizzari C , Roeske JC
Published: July 2007

Purpose: Position compensated plans (PCPs) have been proposed as a method to adapt treatment delivery based on the daily patient position. In this approach, multiple plans are created in which the isocenter is displaced based on anticipated daily offsets. The plan that most closely matches the daily position is then selected for treatment. The goal of this study is to determine the optimal isocenter spacing of PCP for intensity‐modulated whole‐pelvic radiotherapy (IM‐WPRT). Method and Materials: The setup errors for 46 patients treated with IM‐WPRT were measured and the dosimetric effect of these errors on the volume of normal tissue and PTV irradiated was quantified. This analysis demonstrated that the anterior/posterior (AP) setup error had the greatest effect on the change in volume of normal tissue irradiated. Thus, PCPs were created with the isocenter shifted in the ±AP direction. In order to determine the optimal PCP spacing, random errors (σ) were varied from 0.1 to 1.0 cm in steps of 0.1 cm. For each random error, the daily setup deviation was sampled for 25 fractions for 100 hypothetical patients. The PCP correction scheme used the original plan plus two plans with isocenter displacements ranging from 0–2 cm in steps of 0.1 cm. The optimal PCP spacing was defined as the one which minimizes the RMS error in the AP direction. Results: A linear relationship was observed between the random setup error and the optimal PCP spacing. In particular, for the case of two additional PCPs, the required spacing is equal to ±1.22 σ. That is, for a random error of 4 mm, two PCP plans with spacings of ±4.9 mm will minimize the RMS variations in daily setup uncertainties. Conclusion: PCPs with AP isocenter displacements of ±1.22 σ represent an effective means of adapting treatment in IM‐WPRT based on the daily set‐up deviations.
SU‐FF‐P‐04: Evaluation of Treatment Planning Time Savings Using Direct Machine Parameter Optimization
Authors: Chase D , Ramsey C , Seibert R , Robison B , Harris C
Published: July 2007

Purpose: The purpose of this study is to evaluate the capability for increasing treatment‐planning throughput by utilizing Direct Machine Parameter Optimization (DMPO). Traditional inverse treatment planning consists of an optimization phase followed by a separate leaf‐sequencing phase. With DMPO based optimization, there is no leaf‐sequencing step. As such, the treatment planning time for each IMRT case can potentially be decreased and treatment‐planning throughput could be increased. Method and Materials: Ten patients (5 prostate and 5 head & neck) were randomly selected for a comparative treatment planning study. IMRT treatment plans were created using the standard IMRT optimization algorithm with k‐mean clustering based leaf‐sequencing. A second treatment plan was created for each patient using the DMPO optimization algorithm. The only difference between the two plans for each patient was the optimization algorithm. For each case, the time required to optimize the plans, the number of segments required for step‐and‐shoot delivery, and total monitor units were recorded. Results: Both the DMPO and IMRT optimizations yielded similar dose distributions. The mean time to perform inverse planning and leaf sequencing for prostate patients was 8.00 minutes, verses 8.85 minutes for DMPO based optimization. In contrast, the efficiency of DMPO for Head & Neck cases is substantially different. The mean time to perform a DMPO optimization for Head & Neck cases was 12.05 minutes, as compared with 28.63 minutes for IMRT optimization. Conclusion: Over 16 minutes of treatment planning time can be saved per patient by utilizing the DMPO based optimization in Pinnacle for Head & Neck treatment planning. The time advantage can grow to hours saved per patient if multipe treatment plans are created, or if the planners agressively adjust the plan. Depending on the Head & Neck volumes treated, DMPO optimization can increase treatment planning effiency.
SU‐FF‐T‐23: A Monte Carlo Simulation and Deconvolution Study of Detector Response Function
Authors: Feng Y , Lamba M , Elson H , Kassing W , Spitz H
Published: July 2007

Purpose: The purpose of this study is to determine the detector response function using Monte Carlo simulations of small radiation fields and simulations of detector responses to those fields. The results may be used to deconvolve the effect of finite size detectors on beam broadening in small field measurements. Method and Materials: A Monte Carlo model of a linear accelerator was generated to simulate the characteristics of a clinically used photon beam. These simulations were used to create a true beam profile. Three clinically available radiation detectors and two theoretical detectors were modeled in the beam. Detector specific models of measured beam profiles were generated from simulated detector responses. Detector response functions were deconvolved from the models of simulated measured profiles and the true beam profile. The results were then analyzed using curve fitting method. Results: The penumbra of the beam profiles generated by different cylindrical detectors demonstrated a significant linear relationship with detector radius. Detector response functions of cylindrical detectors can be approximately represented as a Gaussian curve dependent upon the radius of the detector. Fourier transform methods can be used to deconvolve the detector response function for the penumbral areas, but can introduce noise in the non‐penumbral areas. Deconvolution methods can reduce, but cannot remove the effects of detector size. Conclusions: Monte Carlo simulation can be used to model small radiation fields and detector responses. Detector response functions can be determined from the simulated fields and simulated detector responses. A deconvolution method based on a detector specific Gaussian response function can be used to reduce detector size effect in the penumbral areas.
SU‐FF‐T‐30: A New Software Tool for Inter Treatment Planning System IMRT Comparison Study
Authors: Mu G , Xia P
Published: July 2007

Purpose: To develop a software tool to enable the direct comparison of the dose accuracy of different treatment planning systems (TPS) and the efficacy of different optimization methods while separating the effects of the dose engine and optimizer. Method and Materials: Based on TPS used at our institution, we have developed a software tool using the C programming language to convert RTP files exported from the Corvus system to the Pinnacle system. The planning CT along with the contoured structures can be transferred between these two TPS's. The developed software tool was used to convert the Corvus treatment delivery files to the Pinnacle system. The first application of this tool is to compare the dose calculations performed by these systems. The second application is to compare the efficacy of the optimization methods in these systems. We plan to test ten patients with head and neck tumors. Results: The new software tool successfully converts RTP files exported from any commercial TPS to the Pinnacle TPS, allowing us to separately study the optimization algorithm and dose calculation engine in the two systems. Preliminary results from one patient plan showed that Pinnacle and Corvus systems give different results, where Pinnacle system gave a 3.6% higher D95% value in the pGTV and 3.7% higher in the pCTV. The maximum dose to the brainstem and spinal cord in Pinnacle plan were 7.3% and 3.7%, higher respectively. Both TPS's have been commissioned for clinical use in our institution, and a patient specific phantom measurement is performed for each patient. Conclusion: A new software tool for inter‐TPS IMRT comparison study has been developed and tested. This tool allows us to directly compare TPS's using clinical data, revealing detailed dose differences in the coverage of the tumor volume as well as the doses to the sensitive structures.
SU‐FF‐T‐74: An Objective Function for TCP/NTCP Curve Fitting
Authors: Stavrev P , Stavreva N , Schinkel C , Fallone BG
Published: July 2007

Purpose: To propose an objective function for TCP/NTCP curve fitting. Method and Materials: One of the widely used objective functions by physicists, when fitting theoretical models to experimental data, is the χ2 one, where:
urn:x-wiley:00942405:media:mp0725:mp0725-math-0001 which is the maximum likelihood function in case of Gaussian random variables. In the case of a binary outcome, as is the nature of clinical or experimental animal radiation outcome data, the random variable has a binomial distribution and the maximum likelihood function for ungrouped data becomes:
urn:x-wiley:00942405:media:mp0725:mp0725-math-0002 where Ptheor stands for TCPtheor or NTCPtheor. The maximization of L is often used by different authors for the estimation of the TCP/NTCP model parameters. Results: However, sometimes χ2 is used to fit TCP/NTCP functions for different purposes like theoretical comparison between different models. In this case the application of χ2 becomes inaccurate and inadequate especially when the function values are close to the ends of the interval in which they are defined, namely 0 or 1. This is why we propose t he application of the double logarithmic transformation, presuming that the random variable is not normally but log‐log‐normally distributed.

Conclusion: Thus the objective function in case of model comparison would become:
urn:x-wiley:00942405:media:mp0725:mp0725-math-0003 where . Here stands for the values of P predicted by one of the models that are being compared and stands for the values of P predicted by the other model.
SU‐FF‐T‐98: Characterization of Buildup Effects in OneDosePlus MOSFET‐Based Dosimeters
Authors: Pursley J , Beyer GP , Craciunescu O , Fraisse C , Carroll J , Oldham M
Published: July 2007

Purpose: Evaluate the buildup cap used on OneDosePlus™ MOSFET dosimeters and study the field size, angular, and SSD dependency. Method and Materials: OneDosePlus (ODP) dosimeters are single use, pre‐calibrated MOSFETs used to measure entrance patient dose. ODP has an integrated 1.2 mm thick tin cap. Custom dosimeters were created with buildup caps of varied thicknesses to determine the approximate tin dmax thickness for 6, 15, and 18 MV. Non‐calibrated ODP dosimeters were evaluated to assess the effect on response of the dosimeter as a function of field size, SSD, and anisotropy for different energies. Results: PDD curves for 6, 15 and 18MV show broad maximum responses centered near cap thicknesses of 1.2, 2.6 and 2.8 mm for 6, 15, and 18 MV, respectively. Evaluation of the field size response showed that higher energies have an over‐ and under‐response for larger/smaller field sizes as compared to 6 MV response, suggesting an increase in electron contamination dose contribution. Results of extended SSDs studies, typical of TBI treatments, show enhanced measurement precision, supporting these findings.

For patient use, the dosimeter response is pre‐calibrated and adjusted such that the reading corresponds to Dmax in‐tissue for each specific energy. In addition, the dosimeters are corrected for the 6 MV field size and SSD dependency. Therefore, for higher energies, a slight over‐ or under‐response can be observed for larger/smaller field sizes but not in excess of the reported dosimeter accuracy (± 5%,2σ). Conclusion: The buildup cap for ODP provides a partial buildup effect with results within the expected accuracy for different dosimetric parameters. The dosimeter factory calibration corrects the response from the partial buildup effect seen from the buildup cap. Extended SSD data suggests that ODP could be used to measure dose for TBI treatments.

This research was sponsored by Sicel Technologies, Inc.
SU‐FF‐T‐232: Feasibility Study of a Carbon Nanotube Field Emission Microbeam System for Cellular Irradiation
Authors: Chang S , Zhang J , Bordelon D , Graboski S , Schreiber E , Cox A , Zhou O
Published: July 2007

Purpose: Tissue‐level radiobiological effects that influence tumor control or normal tissue complications stem from processes initiated at the cellular and sub‐cellular levels immediately following radiation energy deposition. The exact mechanisms of these processes at the critical moments are still poorly understood. We proposed to develop a nanotechnology based microbeam pixel array cellular irradiation system that promises to enable researchers to study the micro‐processes at the spatial and temporal scale of the events. This presentation reports the feasibility study results. Method and Materials: A multi‐pixel microbeam cellular irradiation system is proposed to selectively irradiate chosen target cells in a Petri dish under microscope observation. The microbeam system uses carbon nanotube (CNT) field emission technology. Each of the CNT pixels emits an electron beam and a silicon nitride window collimates the electron beam to a specific microbeam size. The electron microbeam has a tunable energy of 20–60 keV. Each of the pixel beams in the multi‐pixel microbeam can be controlled individually. The initial phase of the research is design and development of a prototype single pixel microbeam device and cell irradiation demonstration. Results: We have designed and fabricated a prototype single pixel CNT field emission microbeam system and performed dose calibration. GAFCHROMIC film is used to measure absolute dose and dose distribution. Microbeam radiation dose is calibrated as dose per radiation pulse. We performed cell irradiation using the prototype microbeam device on Rat‐1 cells. H2AX is phosphorylated at DNA damage sites and the microbeam irradiation pattern is confirmed by the pattern of DNA damage. Conclusion: We have demonstrated the feasibility of a single pixel CNT field emission microbeam for cellular irradiation. The next research step is study the feasibility of the multi‐pixel microbeam array.

This work is funded by NCI (R21 CA118351) and North Carolina Biotechnology Center (2005 MRG‐111).
SU‐FF‐T‐247: Implementation of MRI‐Based Monte Carlo Simulation for Gamma Knife SRS
Authors: Xiong W , Huang Y , Qin L , Lee L , Feng J , Morris K , Calugaru E , Li J , Burman C
Published: July 2007

Purpose: To verify the dosimetry accuracy for MRI‐based planning of Gamma Knife Stereotactic Radiosurgery. Method and Materials: In Monte Carlo simulation, Gamma Knife unit geometry was reconstructed exactly as the original unit. Materials were selected as close to the actual one as possible. Patients were scanned on both a CT unit and a 1.5 T MRI scanner. Simulations were performed for these patients using homogeneous geometry based on CT and MRI, and heterogeneous geometry built based on CT numbers or different densities for MR contoured skull structures. The homogenous density was chosen as 1.0g/cc and the density of skull was chosen in the range 1.5 – 2.0 g/cc. Isodose distributions and DVHs were used in comparison. Results: The dose in the homogeneous geometries based on CT was about 3.2% higher than the dose in heterogeneous geometry based on CT. The difference in the DVH between homogeneous MRI and heterogeneous CT geometry was also around 3.3%. After applying heterogeneity correction to the skull for MRI, the difference was reduced to less than 2%. The 90%, 50% and 10% isodose lines matched each other very well between homogeneous CT and MRI geometries and heterogeneous CT and MRI geometries. Conclusion: A useful CT and MRI based Monte Carlo simulation has been developed for Gamma Knife dose verification. For many Gamma Knife centers, MRI is the only choice for Gamma Knife planning. Our results show that MRI‐based Monte Carlo planning for Gamma Knife is feasible after applying proper skull heterogeneity correction.
SU‐FF‐T‐411: The Place of Helical Tomotherapy in Breast Cancer : A Planning and Positioning Comparison Between Tomotherapy and Conventional Techniques
Authors: Heymann S , Reynders T , Vinh‐Hung V , Tournel K , Verellen D , Linthout N , Storme G
Published: July 2007

Purpose: The feasibility to use helical tomotherapy on breast cancer patients was investigated using conventional treatment (tangential beams) as golden standard. A diversification was made between prone and supine positioning techniques. Method and materials: Five clinical breast cancer patients were enrolled in this study. To study the influence of treatment position, 2 planning‐CTs in prone and supine were acquired and planning target voume (PTV), ipsi‐ and contralateral lung, heart and contralateral breast were delineated. Both conventional (tangential beams) and tomotherapy (rotational) plans were generated leading to 4 plans per patient. Dose prescription was 42Gy in 15 fractions with at least 95% on the full PTV volume and a maximum of dose of 110%. The V17 and mean dose for the lung, and maximum, mean and V17‐dose for the heart and contralateral breast were used for reporting. Results: For ipsilateral lung the tomotherapy prone plan was superior in 3/5 cases with a V17 ranging from 0.73 to 7.45% and mean dose from 1.55 to 3.99Gy. However, for the heart, conventional supine was superior . The conventional supine plans show to give less dose to the contralateral breast in 4/5 cases. The differences between the 2 modalities for heart dose were negligible. In a case by case overview the optimal plans were tomotherapy supine (2/5), tomotherapy prone (1/5) and ‘equivalent’ (tomotherapy and conventional) supine (2/5). : Tomotherapy in prone position provided dosimetric improvements mainly for ipsilateral lung, but with an increase of dose on the contralateral breast. Conclusion: It is feasible to use the helical tomotherapy technique for breast cancer and, in some cases, improve target coverage. However, this could result in a higher dose on the contralateral breast, but this is mainly due to anatomical issues and not technique dependant.
SU‐FF‐T‐412: The Reliability of Surrogates in Predicting Tumour Motion: A Comparison of Surrogate Based and Non‐Surrogate Based Approach
Authors: Ghasroddashti E , Pantarotto J , MacRae R , Gerig L
Published: July 2007

Purpose: To assess the interfraction reproducibility of external surrogates in predicting lung tumor motion and to compare that with the reliability of the non‐surrogate approach Methods: 10 patients with fluoroscopically visible non‐operable lung tumors were studied. Data were acquired twice for each patient, pretreatment and post 20 fractions. Chest and abdominal wall surface motion was measured with 3D photogrammetry of retro‐reflective skin markers. Simultaneous time‐stamped A/P fluoroscopic images were used to determine tumor motion in two dimensions. A linear model was formulated to describe the relationship between the surface markers and tumor motion and then applied to predict tumor motion during both the first and second visit. Quantification of the difference between the predicted and actual tumor position demonstrated the surrogate's ability to predict tumor motion. This difference defines the Internal Margins (IM) that must be applied when the surrogate is employed for tracking or gating. Comparison of IM's thus obtained over a four week course of radiotherapy would give a measure of the reliability of the surrogate. Results: Comparison of surrogate based margins on day1 and day20 indicated that prediction ability of the surrogate deteriorated during this time and the required IM' increased by an average of 1.27mm. Furthermore, analysis of non‐surrogate‐based case showed that tumor motion amplitude had increased significantly form day1 to day20 requiring an average increase of 1.16 mm in the IM's. Statistical analysis showed that for both cases assuming a 6mm additional margin would provide the desired tumor coverage with a 99% C.L. Conclusions: Predictive models of motion can reduce the IM component of the PTV by a significant volume, however interfraction reproducibility is poor and the chance of geometric miss is high. Our observations of tumor motion variability suggest that static field margins should also be reassessed over a standard treatment course.
SU‐FF‐T‐424: Treatment Errors in Radiation Therapy Performed Using Modern Technology
Authors: Saw C , Surgent R , Rakfal S , Huq M , Heron D
Published: July 2007

Purpose: Conformal and intensity‐modulated radiation therapy techniques use clinical data transferred electronically from one radiation therapy equipment to another. Before treatment, patient treatment parameters are downloaded into the linear accelerator for dose delivery. This study evaluates recordable events to identify the types of treatment errors associated with these sophisticated treatment techniques. Methods and Materials:Our institution consists of 20 community and academic facilities with 30 medical linear accelerators, and about 650 external beam patients per day are treated. All records of events are reviewed within our quality assurance program. By definition, any unintended deviation from the prescription constitutes a “recordable event.” The records of events that occurred at our institution for the years 2005 and 2006 were evaluated. Although the number of recordable events is small, it gives a trend of possible occurrence of the types of treatment errors. Results: Traditional types of treatment errors such as transcription and dosimetric errors have been minimized. New types of treatment errors classified as (a) treatment of incorrectly identified patients, (b) downloading different patient files, (c) incomplete treatment of prescribed fields, (d) failure to implement patient shift according to treatment plan, and (e) failure to invoke gating system are observed in the record of events. These constitute over half of the events. Conclusion: A failure mode and effect analysis (FMEA) can help in identifying areas where quality assurance should be emphasized. Such analysis is recommended for all new technologies implemented in busy clinics.
SU‐FF‐T‐428: Treatment Planning for Large Patients with Anatomy Outside of Imager FOV
Authors: Kumaraswamy L , Liu J , Podgorsak M
Published: July 2007

Purpose: A 3D dose distribution for a large patient is usually obtained by projecting the treatment fields on to digitized wire contours, resulting in the loss of all anatomical information. This study evaluates a more accurate approach of obtaining a full volumetric image set for patients that cannot be completely imaged within the available field of view. Method and Materials: Two laterally shifted CT scans of an anthropomorphic pelvic phantom with fiducial markers were acquired, each simulating the CT scan of a large patient with missing anatomy resulting from the limited FOV. A complete scan of the phantom was also performed for comparison purposes. In the TPS, an empty phantom image set was created with very large FOV. Both shifted scans were fused with this image set by aligning the point intersected by the fiducial markers on the CT image to the Dicom origin of the empty set. All the contours can be copied from the CT scans into the empty image set, to provide a complete fused contour set. This method was evaluated by comparing a 3 field plan created on the fused contour set with a similar plan on the complete scan. Results: The contour set was successfully fused into the empty image set. Partial scan of the phantom can be overlaid inside the contour set to permit visualization of the anatomy. The differences between the two plans in the SSDs for the AP, RtLat, and LtLat fields were 4.0, 1.0, and 1.0 mm, respectively, and the differences in isocentric doses for these fields were 0%, 0.7%, and 0.2% respectively. Conclusion: Entire patient contours for large patients can be accurately contoured by fusing multiple CT scans, each acquired with different patient positioning. This will allow obtaining accurate 3D dose distribution and DVH for target volumes and critical structures.
SU‐FF‐T‐431: Uncertainties in Superficial Dose From Helical Tomotherapy Delivery Due to Target Localization Errors
Authors: Goddu S , Yaddanapudi S , Chaudhari S , Mutic S , Rangaraj D , Garcia Ramirez J , Esthappan J , Santanam L , Powell S , Low D
Published: July 2007

Purpose: To quantitate shallow‐depth dose calculation accuracy for IMRT breast treatment plans created with Tomotherapy system and to estimate the dose errors caused by setup errors. Methods: A cylindrical solid water phantom with radiochromic film was used for this purpose. The split phantom can hold a film in coronal or sagittal planes. A 5cm thick PTV was contoured by extending it to the surface of the phantom. A plan was optimized to treat the superficial PTV while limiting the dose to the surrounding critical structures. To evaluate the setup uncertainties multiple phantom plans were generated by shifting the phantom 5, 10 and 20 mm to right and up (7, 14, and 28mm distance) and simulated doses were compared against the measured doses. The 3D dose matrices from TPS for no‐shift and shifted phantom plans were exported in DICOM and were analyzed in MatLab. Doses from eleven transverse slices were analyzed to estimate the dose differences in the shifted phantom plans. Shifted phantom plan dose distributions were transposed back onto the patient PTV and computed dose difference histograms (DDHs) in the PTV volume. Results: The planning system overestimated the shallow‐depth dose by as much as 14%, but was smaller than 3% at depths greater than 5mm. PTV DDHs for no and 7 mm shifts showed <5% dose differences, while for 14 mm, the dose differences were ⩽10% and were very large for the 28 mm shift. Conclusion: Tomotherapy planning system computes the shallow‐depth dose within 14% accuracy at 1.0 mm and better than 3% for depths greater than 5mm. Setup errors ⩽7mm showed negligible dose errors, consistent with the use of image‐guided therapy. Large shifts were required to induce large dose errors in the PTV. Conflict of Interest: This work supported in part by Tomotherapy, Inc.
SU‐FF‐T‐448: Verification of Infra‐Red Camera Localization System for Stereotactic External Beam Treatment
Authors: Wang J , Rice R
Published: July 2007

Purpose: In our clinic we utilize a frameless localization system for external beam radiosurgery. The system utilizes a biteblock with fiducials, and an infra‐red camera for setting up and monitoring patient position prior to treatment. The purpose of this work is to investigate and quantify the accuracy of the system. Method and Materials: A phantom with integrated targets and fiducials was utilized to test the positional accuracy of the system. After mounting the phantom to the treatment couch or a BRW floorstand, relative positions reported by the camera system were compared to digital couch position readouts and vernier readings from the floorstand. MV images recorded with an EPID were used to evaluate the absolute accuracy of isocenter positioning. After repeated localization of a spherical target, images were taken at different gantry and couch angles similar to the Winston‐Lutz test. The digital images were analyzed to determine the accuracy of the target placement in a circular field by measuring the distance between the field center and the target center. Results: The relative positional accuracy of the camera based system was determined to be less than 0.4 mm over a 50 mm range of travel in the three orthogonal directions of couch motion and less than 0.1 degrees in couch rotation. Data showing the correlation between camera reported position, floorstand position and digital couch position are presented. The EPID based measurements show absolute accuracy of positioning a target at the isocenter is < 1 mm. Conclusion: A frameless fiducial and infra‐red camera based patient positioning system is used for stereotactic treatments in our department. The positional accuracy of the camera based system was verified and found to be sufficiently accurate for stereotactic treatments.
SU‐GG‐AUD‐08: Real‐Time Three‐Dimensional Position and Orientation Data of a Brachytherapy Robot Using Magnetic Tracking
Authors: Meltsner M , Ferrier N , Thomadsen B
Published: July 2007

Purpose: To incorporate a magnetic tracking system with a brachytherapy robot to provide real‐time information on position and orientation of anatomical structures. Methods and Materials: A custom‐built six‐degree‐of‐ freedom robot was engineered for highly accurate prostate brachytherapy implantations. The robot was tested and optimized in phantom to provide sub‐millimeter error in seed placement. However, an implantation's accuracy may be limited by the ability to transfer 3‐D anatomical data and convert it to the robot's coordinate frame. This transformation is difficult if the imager is not fixed, because the transformation from anatomical coordinates to robot coordinates changes dynamically. We tested the characteristics of a Minibird II tracking system (Ascension Technology, Burlington, VT) which consists of a transmitter that emits a magnetic field and a sensor to provide feedback of position and orientation. Multiple sensors can be added to determine the relationship between the robot and an ultrasound probe, for example. An analysis of the Minibird's accuracy in relationship to the highly precise movements of the robot in three dimensions was performed. Results: The robot's movement compared to the magnetic tracker's positional information over 24 cm of travel was within 1.21%, 0.77% and 1.18% in the x, y, and z directions respectively. Conclusion: Using magnetic tracking, a robot designed for brachytherapy implantation may use nearly any imaging modality to acquire anatomical data. A sensor may attach to a free‐hand ultrasound probe or fluoroscopy machine, for example. This opens the possibility of using the robot for needle insertions other than prostate LDR procedures with a rectal probe. The robot can be modified easily for accurate needle targeting of many soft tissue structures. Lastly, the cost of magnetic tracking is small (in equipment and upkeep cost) when compared to 3‐D infrared tracking, while also eliminating the “line‐of‐sight” issues that may occur with those systems.
MO‐E‐L100J‐05: High Quantum Efficiency Portal Imaging Using a Structured Fiber‐Optic Scintillation Glass Array (FOSGA)
Authors: Gopal A , Samant S
Published: July 2007

Purpose: Preliminary studies of a high quantum efficiency (QE) portal imager based on a fiber‐optic scintillation glass array (FOSGA) within a focused polymer‐tungsten grid and coupled to a‐Si photodiodes are presented. These include characterization of intrinsic imaging performance using Monte Carlo simulations and validation of mechanical fabrication accuracy and automated glass fiber insertion. Method and Materials: The scintillator array comprises of high‐density Tb‐activated scintillation glass (proprietary material composition) fibers drawn into uniform fiber‐optic bundles. The polymer‐tungsten grid is constructed using tomo‐lithographic molding (TLM), a patent‐pending manufacturing technology that can create precisely focused grids using cast‐molding and stack‐lamination. Glass fibers are inserted using an automated loading jig based on electrostatic alignment and vaccum gradients for precise pixel loading. Monte Carlo simulations were used to model the effects of scintillator geometry (thickness and fill factor) on intrinsic detector performance indicated by the modulation transfer function (MTF), and detective quantum efficiency (DQE). Results: Results indicated that DQE(0) increased and MTF decreased with scintillator thickness and fill factor. However, upon calculating DQE(f) ≈ DQE(0)MTF(f)2, it was found that the effect of thickness and fill factor on DQE(0) was more significant than that on the MTF. Intrinsic QE = 0.43 and DQE(0) = 0.25 could be obtained for a 5 cm thick scintillator array with a fill factor ⩾ 70%. Conclusions: FOSGA provides high QE due to good x‐ray absorption, scintillation, and fiber‐optic coupling characteristics of Tb‐glass fibers, while the polymer‐tungsten grid improves spatial resolution by limiting the spread of secondary electrons leading to greater MTF and DQE. Based on high QE, high DQE megavoltage imaging in conjunction with cost‐effective methodologies for accurate (±3%) mass‐production of large‐field uniform detector arrays, FOSGA is well suited for 2D localization and verification imaging as well as megavoltage computed tomography (MVCT) for image guided radiation therapy (IGRT).
MO‐E‐L100J‐07: Multiplexing Radiography for Ultra‐Fast Computed Tomography: A Feasibility Study
Authors: Zhang J , Yang G , Lee Y , Chang S , Lu J , Zhou O
Published: July 2007

Purpose: Current CT scanners collect the projection images by a step‐and‐shoot process using a single x‐ray source. The inefficient serial data collection scheme severely limits the data collection speed. Multiplexing technique, which has been widely adopted in communication devices, holds the promise to significantly increase the data throughput. It however, has not been applied to x‐ray radiography, mainly due to limitations of the current x‐ray source technology. Method and Materials: We demonstrated the feasibility of multiplexing radiography technique based on the frequency division multiplexing (FDM) principle and the multi‐pixel x‐ray technology. The carbon nanotube based field emission multi‐pixel x‐ray source can generate spatially and temporally modulated x‐ray radiation. During the multiplexing imaging process, all the x‐ray pixels were turned on simultaneously with each beam modulated at a different frequency. The superimposed x‐ray signals were captured by an x‐ray detector and then demultiplexed to recover the original nine projection images from different view angles. Results: In general a factor of N/2 (N= total number of images) increase in the speed can be achieved using the multiplexing scheme. This becomes significant when N is large, for example for clinical CT scanners which use ∼1000 views per gantry rotation. On the other hand, if the total imaging time and x‐ray dose are kept the same as used in the sequential process, then the x‐ray power, i.e. the tube current, can be reduced by a factor of N/2 by multiplexing because the exposure time per image is now longer. Conclusion: In summary, we show the feasibility of multiplexing radiography that enables simultaneous collection of multiple projection images. Overall the experiment has sufficiently demonstrated the efficiency of multiplexing for data collection compared to the current serial approach. It has the potential to significantly increase the imaging speed for CT scanning without compromising the imaging quality.