bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐856: Investigation of Fluence Parameterization Methods for PARETO Multi‐Objective Radiation Therapy Treatment Planning Software
Authors: Champion H , Fiege J , Potrebko P , Cull A , McCurdy B
Published: November 2011

Purpose: To determine the best parameterization of fluence modulation for PARETO (Pareto‐Aware Radiotherapy Evolutionary Treatment Optimization) multi‐objective treatment planning software, as judged by the complexity of each parameterization, the efficiency, and the quality of the plans produced. Methods: PARETO simultaneously optimizes the number of beams, beam orientations, and fluence modulation. For this investigation, we have tested four fluence parameterizations on a paraspinal tumour phantom and a spine patient data set using a pre‐determined number of beams. The first method applies linear gradients over the projection of Planning Target Volume (PTV) in the beamˈs‐eye‐view plane. The second method applies the two‐dimensional inverse cosine transform of a few low‐frequency parameters. Another method interpolates between the intensities of a coarse grid of square beamlets. Also, an isodose‐based contour method defines regions on the fluence maps that are assigned different intensities. Methods which produce plans of the best quality (as judged by dose‐volume histograms) will have a similar distribution of non‐dominated solutions. The complexity of each parameterization is determined by the number of parameters, and the efficiency is determined by the run time. Results: For both geometries, we found that the set of non‐dominated solutions of each parameterization overlapped in the projection of the PTV conformity fitness function and the quadrature‐averaged Organs‐At‐Risk (OAR) fitness function. The beam group and cosine transform methods produced some plans which did slightly better in simultaneously achieving good PTV conformity and OAR dose sparing. The cosine transform and linear gradient methods proved to be the most efficient. The cosine transform method also has the least number of parameters per beam. Conclusions: We have found that several different parameterizations of fluence modulation produce non‐dominated solutions of similar quality. The cosine transform method is the best choice for efficiently producing solutions that do well in PTV conformity and OAR sparing.
SU‐E‐T‐861: Assessment of Collimator Jaw Optimization in Reducing Normal Tissue Irradiation with Intensity Modulated Radiation Therapy
Authors: Joy S , Balter P , Starkschall G , Kry S , Salehpour M
Published: November 2011

Purpose: To evaluate normal tissue dose reduction in step‐and‐shoot intensity‐modulated radiation therapy (IMRT) on the Varian 2100 platform by tracking the multileaf collimator (MLC) apertures with the accelerator jaws. Methods: Clinical radiation treatment plans for 10 thoracic, 3 pediatric and 3 head and neck patients were converted to plans with the jaws tracking each segmentˈs MLC apertures and compared to the original plans in a commercial radiation treatment planning system (TPS). Each segment was then renormalized to account for the change in collimator scatter to obtain target coverage within 1 % of that in the original plan. Reduction in normal tissue dose was evaluated in the new plan by using the parameters V5, V10, and V20 in the cumulative dose‐volume histogram for the following structures: total lung minus GTV (gross target volume), heart, esophagus, spinal cord, liver, parotids, and brainstem. In order to validate the accuracy of our beam model, MLC transmission measurements were made and compared to those predicted by the TPS. Results: The greatest change between the original plan and new plan occurred at lower dose levels. The reduction in V20 was never more than 6.3% and was typically less than 1% for all patients. The reduction in V5 was 16.7% maximum and was typically less than 3% for all patients. The variation in normal tissue dose reduction was not predictable, and we found no clear parameters that indicated which patients would benefit most from jaw tracking. Our TPS model of MLC transmission agreed with measurements with absolute transmission differences of less than 0.1 % and thus uncertainties in the model did not contribute significantly to the uncertainty in the dose determination. Conclusion: The amount of dose reduction achieved by collimating the jaws around each MLC aperture in step and shoot IMRT is probably not clinically significant.
SU‐E‐T‐870: Volumetric Modulated ARC Radiotherapy for O‐Shape and C‐Shape Tumor Volume
Authors: Kwak J , Cho B
Published: November 2011

Purpose: The VMAT(Volumetric Modulated ARC radiotherapy) technique have not shown enough dosimetric merits for O‐ or C‐shaped tumor volumes in which critical organs were located in central region without sufficient margins. We propose new VMAT planning technique for O‐ or C‐shaped tumor volume and have examined dosimetric benefits and utility in comparison with conventional IMRT and VMAT planning techniques. Methods: In the new split field method of VMAT planning, the isocenter is located in the central critical organ and the critical organs were shielded by collimators. Critical organs in central region and C‐shaped tumors in an artificial hexagonal phantom were contoured with Eclipse 8.9 planning system (Varian Medical System inc., Palo Alto, CA, USA) to determine margins and constraints in optimization process. For real cases, five Spine SBRT, one mesothelial and 2 H&N cases were involved to investigate the new techniques in comparison with 11 field IMRT and normal 2 arc VMAT plans. Results: The split field VMAT planning was shown the better dose distribution than normal VMAT planning, especially when the margin is not enough at the interface of tumor and critical organ. For the tumor coverage and uniformity, it was comparable with IMRT and for conformity index, the new method shown the best results. Since the MU value was increased almost up to the MU of IMRT cases, the upper limit of total MU was set in the optimization process of split field VMAT planning. Conclusions: The split field VMAT plan clearly has dosimetric benefits for O‐ and C‐shaped tumor volume with critical organs in the central region. That is attributable to the rotational symmetry of structures, which was used to minimize the dose in critical organ.
SU‐E‐T‐874: Investigation of the Interplay Effect Between MLC and Lung Tumor Motions Using 4DCT and RPM Profile Data
Authors: Li H , Zhong H , Kim J , Nurushev T , Chetty I
Published: November 2011

Purpose: To evaluate the dosimetric impact of the interplay effect between the MLC motion and respiratory‐induced tumor motion in the context of 4D planning of small lung lesions treated with SBRT. Methods: IMRT plan was generated using the ITV from 10 respiratory‐correlated CT datasets on the reference (50% phase, CT50) image. The PTV included a 3 mm uniform expansion of ITV; the dose was calculated with Varian Eclipse AAA algorithm and 2.5 mm grid size. To account for the interplay effect, the time‐stamped signal from respiratory surrogate (RPM marker trace) was used to correlate the MLC control points to the individual CT phase. The dose to each phase was then computed using the actual MLC apertures and MU numbers for the specific phase. Doses from individual phases were mapped and accumulated to the CT50 dataset using a Demons‐based deformable registration algorithm. A “standard” 4D plan was also generated in which the entire treatment plan was applied to each phase with appropriate weighting of the time spent at each phase, but without accounting for the correlation of the MLC sequence with the respiratory phases. The method was applied to two lung SBRT cases with tumor motion 1.2 and 2.0 cm in amplitude sup/inf. Results: For mean PTV dose, the discrepancy induced by interplay effect was −5.7% to 33.4% (with mean −+ SD of 1.3 −+ 8.7%) for individual phases. For the accumulated dose it was 0.0% and 0.1% for the two cases respectively. The maximum point dose discrepancy within PTV was 0.4 out of 48 Gy. The interplay effect reduced the minimum PTV and ITV dose by about 0.5%. Conclusions: This initial study showed that the dosimetric impact of interplay effect dimmed out as 4D doses were accumulated. Further assessment for wide spectrum of plan and delivery scenarios should be performed.
SU‐E‐T‐875: The Potential for Respiratory‐Gated VMAT to Reduce the Normal Lung Dose When Treating Early‐Stage Lung Cancer with SBRT
Authors: Xhaferllari I , Hamelin N , Chen J , Gaede S
Published: November 2011

Purpose: To evaluate the dosimetric potential of respiratory‐gated volumetric‐modulated arc therapy (VMAT) to reduce the dose to normal lung when treating early stage non‐small cell lung cancer (NSCLC) with stereotactic body radiation therapy (SBRT). Methods: Seven early‐stage NSCLC patients were retrospectively planned with gated and un‐gated VMAT using Smart Arc (Pinnacle v9.0, Philips Medical Systems, Cleveland, USA). The average 4D‐CT of each patient was used as the planning CT for the un‐gated VMAT plans. A subset average CT that minimized the motion within a 30% gating window was used as the planning CT for the gated VMAT plans. Each VMAT plan consisted of one arc to minimize the delivery time. All plans were prescribed 54 Gy in 3 fractions and all dosimetric parameters satisfied the requirements of our in‐house lung SBRT protocol. In order to avoid dosimetry bias between the gated and un‐gated plans, a Pinnacle host script was generated and used to optimize all 14 plans. Dosimetric parameters such as D(2cm), V(20), and the total normal lung volume receiving 50% of the prescription dose were compared. Results: There was a significant decrease in all dosimetric parameters considered in this study. D(2cm) decreased from (53.960 +/− 2.680)% to (51.703 +/− 1.907)% (p<.05). V(20) decreased from (6.629 +/− 1.565)% to (5.213 +/−1.387)% (p<.005) and the total normal lung receiving 50% of the prescription dose decreased from (254.465 +/− 62.853) cm̂3 to (177.068 +/− 45.947) cm̂3 (p<0.004). Conclusions: Respiratory‐gated VMAT has the potential to reduce the dose to normal lung when treating early‐stage NSCLC with SBRT to moving targets with motion greater than 10 mm.
SU‐E‐T‐884: Dosimetric Evaluation of Arc Techniques in Stereotactic Radiosurgery
Authors: Zhang G , Ku L , Yu M , Sarangkasiri S , Li W , Feygelman V
Published: November 2011

Purpose: Conventionally, conformal arcs (called dynamic in BrainLab) are used in cranial stereotactic radiosurgery (SRS). This study dosimetrically evaluates the volumetric modulated arc therapy (VMAT) and VMAT‐conformal hybrid plans against conformal‐arc plans. In hybrid plans, various numbers of conformal arcs in a conformal plan are replaced with VMAT‐arcs.Methods: Ten brain‐cancer patients previously treated with SRS using conformal arcs were retrospectively studied with various numbers of VMAT‐arcs replacing conformal arcs. Pure VMAT plans of different numbers of arcs generated using the same angle and arc length of all or part of the conformal arcs were compared with the original and hybrid plans. SmartArc was used for VMAT planning for a Novalis accelerator. The conformity index (CI), defined as the ratio of the isodose volume to the isodose covered target volume, gradient index (GI), defined as the ratio of the 30%‐isodose volume (V30) to the 100%‐isodose volume, mean dose in target were studied.Results: With one of the conformal arcs replaced with a VMAT‐arc, the average CI improved from 1.28±0.11 of the conformal plans to 1.22±0.11 while GI degraded from 6.04±1.10 to 10.10±4.90. The CI and GI changed little with the number of arcs being replaced. Pure VMAT plans demonstrated better CI when the number of arcs was greater than 2. For plans of 3 VMAT arcs, the CI and GI were 1.22±0.16 and 9.54±2.95 respectively. GI improves with more arcs, but never gets better than conformal‐arc plans. The degraded GI in plans with VMAT‐arcs is because of the absence of beam‐margin limit in SmartArc planning. The target mean dose was about the same. Conclusions: VMAT and conformal‐VMAT hybrid plans usually offer better target conformity but compromise dose fall‐off in normal tissues. The number of arcs in VMAT plans is recommended to be greater than 2.
SU‐E‐T‐887: Cyberknife Treatment for Early Stage Oral Tongue Cancer — Feasibility Study
Authors: Fan J , Fourka E , Hayes S , Jin L , Wang L , Price R , Ma C
Published: November 2011

Purpose: Oral tongue carcinoma is a highly curable cancer treated by radiation therapy and especially by interstitial brachytherapy. However, multiple hairpins, needles or hollow catheters are needed to be inserted into the tumor bed for both low‐dose‐rate (LDR) and high‐dose‐rate (HDR) interstitial radiotherapy. The whole insertion procedure is quite invasive and painful to the patient each time it is administered. Therefore, the main aim of this study is to investigate the potential use of Cyberknife in the treatment of oral tongue cancer, which would dramatically reduce unpleasant experiences associated with HDR/LDR treatments. Methods: Using CT images of the patient treated with the HDR interstitial implant, a structure (GTV) was created out of the applicator. A special device will be used to immobilize the tongue during treatment. In CyberKnife treatment planning, the Xsight Spine tracking method was used for patient localization. A 2 mm margin in all directions was added to account for potential localization uncertainties. Subsequent planning is based on prescribing 2000 cGy in 5 fractions to the PTV. Results: The isodose line of 66% (20 Gy in 5 fractions) covers the outer boundary of the PTV in the CyberKnife plan. The conformity index is 1.26 with 98.76% of the target volume covered by the prescription line. The maximum dose inside PTV is 30.3 Gy while the HDR treatment delivers more than 40 Gy to more than 20% of the PTV. Only 3.4 cc of the right mandible receives more than 10 Gy. The maximum dose to left mandible is only 4.4 Gy. The total treatment time is about 18 min/fraction. Conclusions: It is shown that Cyberknife treatment can be a viable alternative to interstitial HDR treatments, which may greatly improve the patient care with tongue cancer.
SU‐E‐T‐889: Target Definition in TomoTherapy Lung SBRT Treatment Plans
Authors: Wiant D , Terrell J , Sintay B
Published: November 2011

Purpose: An unresolved question in lung stereotactic body radiotherapy (SBRT) treatment planning is whether a free breathing computed tomography (CT) image set, an image set with the electron density of the internal target volume (ITV) set to water, or an averaged 4DCT scan provides the most realistic representation of the physical situation. Methods: TomoTherapy Hi Art treatment plans created on free breathing scans for three patients receiving lung SBRT at our institution were compared to plans created on 1) a scan with the ITV electron density set to water, 2) a scan with the planning target volume (PTV) electron density set to water, 3) a phase averaged 4DCT, and 4) a time averaged 4DCT. The comparison plans were made by creating TomoTherapy delivery quality assurance (DQA) phantoms from the additional image sets, then recalculating the free breathing plan on these phantoms. All doses were exported to MIMVista for analysis. Results: The maximum isodose line covering the entire PTV and ITV showed little change among the different plans for each patient. The maximum point dose to the ITV and the PTV was similar for the free breathing and average scans. The maximum point doses showed a slight increase for both the ITV and PTV override plans for all patients. The PTV override plan pushed the maximum point dose out of the ITV into the PTV. Conclusions: Plans calculated on the scans with density overridden target volumes show a marked change in dose distribution and target coverage from plans calculated on free breathing and average scans. The different treatment planning techniques are clearly not equivalent. The use of a poor model could lead to over or under‐dosing of the target. Further study is needed to determine which plan most accurately models the true physical situation.
MO‐D‐BRB‐11: Evaluation of the Accuracy of Eclipse AAA Modeling for Flatten Filter Free Beam Used for SBRT
Authors: Mok E , Kielar K , Wang L , Hsu A
Published: November 2011

Purpose: To evaluate the Eclipse analytical anisotropic algorithm (AAA) modeling of flattening filter free (FFF) megavoltage photon beams for a new Varian linear accelerator, TruebeamSTx, TM, used for Gated SBRT. Materials and Methods: With the new Varian TruebeamSTx, Eclipse AAA was configured by using the measured dosimetric data. The TruebeamSTx can operate 6 and 10 MV photon beams free of the flattening filter (FFF). FFF photon beams are especially suitable for use of SBRT since they can operate at high dose rate (1400MU/min for 6MVFFF, 2400MU/min for 10MVFFF). Gated IMRT, RapidArc and gated RapidArc have routinely been used for SBRT, using the FFF photon beams. The accuracy of treatment plans with field sizes as small as 1×1 sq. cm are evaluated by measurement performed using films, ion chamber, and also with a Delta4 measurement system (ScandiDos). For gated treatments, measurements were done on a Respiratory Gating Platform (Standard Imaging) with motion simulating the actual patient breathing pattern. Results: The dosimetric leaf gap of the HD120MLC was adjusted to 1.7 mm with leaf transmission set to 0.015 so the calculated isodose distribution has the best fit with the measurement. The comparison between Eclipse and measured isodose distribution show an agreement of better than 95% using a gamma index of (3%/3mm). For gated RapidArc, the difference of FWHM of the measured and calculated profiles is found to be less than 0.2 mm with target size larger than 3 cm in diameter, and less than 1 mm for 1 cm diameter target size. Conclusions: The Eclipse AAA (V8.9) is found to be within 1mm accuracy for target volume as small as 1 cm in diameter. No major difference of the isodose distribution produced between the WFF and the FFF beams.
MO‐D‐BRC‐04: Low CBCT Dose Measurement for Head Phantom Using XR‐QA Film and a Flatbed Scanner
Authors: Guan H , Feng W , Wen N , Xu Y
Published: November 2011

Purpose: To measure the 2D dose distribution inside a Rando head phantom in OBI CBCTˈs head scan mode using XR‐QA film and Monte Carlo calculation because CTDI can hardly be employed to characterize the highly uneven dose distribution. Methods: Two pieces of films were cut from a single XR‐QA film: the first has the same shape as one Rando head slab and the second is a 5 cm × 15 cm piece for air‐kerma calibration. Before CBCT scan, the two pieces were taped on a single piece of paper and traced on the paper, and scanned using a flatbed scanner to get the background color image. Then the first film was set inside the Rando head and a CBCT scan was acquired in the high quality head mode using a half‐bowtie filter. Right after that, the calibration film was cut into 12 pieces, each was 2.5 cm × 2.5 cm and delivered different exposure of x‐rays. Then the 12 pieces were taped together, placed back to the paper along with the phantom film, and scanned using the same scanner to get the irradiated color image. After the red components of this image and the background image were extracted, the difference between them was converted to a 2D dose image by using the air‐kerma calibration and the air‐kerma to dose conversion factor calculated by Monte Carlo. Results: CBCT scan delivered a maximum of 2.6cGy at the posterior area, 0.2cGy at the anterior area. The left and right areas received about 1.5cGy and 2.5cGy, respectively. The measurement accuracy was about ∼10%. Conclusions: It is crucial to eliminate the non‐uniformities of both the XR‐QA film and the document scanner and also not to align the film plane to beamˈs central‐axis plane for accurate low CBCT dose (<1 cGy) measurement.
MO‐D‐BRC‐06: A Multi‐Exposure Approach to Improve Image Quality for Linac‐Based Cone Beam Computed Tomography (CBCT)
Authors: Jin J , Ren L , Kim J , Kim S , Movsas B , Chetty I
Published: November 2011

Purpose: Recently we demonstrated the use of a 1‐D grid placed between the source and patient to directly reduce scatter, and correct the remaining scatter in cone‐beam computed tomography (CBCT). However, that technique required two 360° gantry rotations to acquire an entire image dataset. The purpose of this study was to investigate the feasibility and potential improvements of a multi‐exposure approach, which takes two or more partial projections at each gantry position with a rapidly oscillating grid to acquire the full dataset in one rotation. Methods: A Trilogy CBCT system was used for the experiment. Grids with various septa‐to‐interspace‐ratios (SIR) were tested. A grid with higher SIR may reduce scatter more effectively, but requires a larger number of exposures at each gantry position for full projection data. The multi‐exposure technique was simulated using multiple rotations, with the grid manually shifted after each rotation with a distance equal to the grid interspace, instead of multiple exposures at each gantry position, with the grid shifted after each exposure. Scatter‐to‐primary‐ratio (SPR) was measured and compared for various object thicknesses and grids with various SIRs. CBCT images were reconstructed after scatter correction for two grids with SIR of 1 and 3, corresponding to 2 and 4 exposures at each gantry position, and compared with conventional CBCT. Results: SPR was reduced linearly with increasing SIR. The scatter artifacts were removed after scatter correction for both grids. The contrast‐to‐noise‐ratios (CNRs) of three phantom inserts with different densities were 20.5, 13.2, and 6.9 for conventional CBCT. The corresponding CNRs were improved to 23.5, 15.8, and 7.9 with the grid of SIR=1, and to 27.2, 18.3, and 8.7 with the grid of SIR=3. Conclusion: Initial results suggest that the multi‐exposure approach may improve CBCT image quality by removing scatter artifacts, increasing CNR without increasing scanning time.
MO‐D‐BRC‐10: A Low Dose CBCT Stochastic Model and Applications
Authors: Yao W , Lu W , Corsten M
Published: November 2011

Purpose: Patient dose from daily CBCT positioning has been much concerned. Decreasing the dose, however, results in lower image quality because of the increased relative noise. In this study, we build a simple model for the stochastic, and apply the result to improving the image quality. Methods: Assume the photon fluence from the source is governed by truncated Gaussian. We derived the expression of CBCT numbers as summation of a noiseless part and a stochastic part. The standard deviation(SD) of the later term was derived. On the other hand, we measured the SDs of CBCT numbers in the water equivalent region of a CatPhan phantom scanned by our Varian OBI system with various mAs values. Fitting the SD in our expression by using the measured, we then applied it to simulating low dose CBCT patient images from the normal dose CBCT image, and to improving low dose image quality. Results: The SD from our model changes with mAs in a very similar way to those measured. This may indicate the usefulness of our model. The magnitude of the truncated Gaussian is thus the only parameter that needs to be fitted in our model by comparing the value of SD with that from measured at a certain mAs. Our model produced low dose CBCT images stochastically equivalent to those from real scans. This would be useful for the study of low dose CBCT of patient. Finally, the image quality of low dose CBCT is significantly improved by applying our model. Thus, patient dose would be decreased without loss of image quality. Conclusions: A stochastic model for low dose CBCT image is proposed. The model is used to simulate low patient dose CBCT image and to improve the image quality. It is possible to acquire equivalent CBCT with significantly lower patient dose.
MO‐D‐BRC‐11: Performance Study of Filtered Back‐Projection (FBP) and Prior Image Constrained Compressed Sensing (PICCS) Based 4D Cone Beam CT: The Effects of Gantry Rotation Time and the Number of Phase Bins on Tumor Motion Delineation
Authors: Chen G , Qi Z
Published: November 2011

Purpose: To study how the performance of 4D Cone Beam CT varies with gantry rotation time and the number of phase bins when two different reconstruction methods, Filtered Back‐Projection (FBP) and Prior Image Constrained Compressed Sensing (PICCS) are used. Methods: Numerical simulation studies were performed using a hybrid phantom. The phantom consists of in vivo human subject data and simulated lung cancer tumors with motion. The data acquisitions were simulated at 1, 2, 3, and 4 minutes. After data were sorted into different number of phase bins (5, 10, and 20), 4D CBCT images were reconstructed using FBP and PICCS methods. Motion trajectory of the tumor was then extracted using a free‐form deformable registration method. The root mean square error (RMSE) was used to characterize the deviation of motion trajectory from the ground truth. Results: (1) When gantry rotation time becomes longer, FBP‐4DCBCT images show reduced streak artifacts and improved accuracy in extraction of tumor motion profile (RMSE=5.4 mm, 2.5 mm, 1.5 mm, and 0.5 mm for 1, 2, 3, and 4 minutes gantry time respectively, for in‐plane motion); (2) PICCS‐4DCBCT enables streak‐free images starting at 1‐minute gantry rotation while FBP‐4DCBCT requires more than 4 minutes to achieve the comparable accuracy in motion trajectory (RMSE=0.2 mm for PICCS‐ 4DCBCT at 1‐minute gantry rotation and RMSE=0.5 mm for FBP‐4DCBCT at 4‐minute gantry rotation); (3) For in‐plane motion, when the number of phase bins increases, the RMSEs increase for FBP‐4DCBCT, while they are much more stable for PICCS‐4DCBCT. Conclusions: (1) To accurately extract tumor motion profiles, the number of phase bins should be more than 10. (2) PICCS‐4DCBCT enables accurate extraction of tumor motion profile using 1‐minute gantry rotation. In contrast, more than 4 minutes are required for FBP‐4DCBCT to achieve acceptable accuracy for extraction of tumor motion profiles.
MO‐D‐110‐02: Calculating Patient‐Specific Skin Dose
Authors: Pavlicek W
Published: November 2011

Records of radiation exposure with fluoroscopic guided interventional (FGI) exposures commonly include fluoroscopy duration, KAP, cumulative AK at the RP but may or may not include fluoroscopic exposure location information. Newer equipment use DICOM Radiation Dose SR (RDSR) which if coupled with simulation tools can re‐create an entire exposure history to calculate patient skin dose distributions and locate the regions of peak skin dose (PSD). A software tool will be described that automatically captures RDSR data to a database. A separate physicist screen (web enabled or laptop) provides prompts to set up a new or upgraded FGI lab. This task would be similair to acceptance testing a complex imaging device. This activity permits corrections for vendor specified AK at the RP, inclusion of backscatter factors, table and pad attenuation, specifying distance from the x‐ray tube, field size corrections, patient positioning (supine or prone, left or right sided, head or feet first), table movement, patient location on the table and field shape. Other fields that address QA are set by the physicist and include the list of authorized users, email alerts and action levels. A separate technologist web screen is used for each patient to choose a correct simulated patient size, positioning on the table and the individuals performing the procedure. At the end of the procedure the technologist receives a record of skin dose mapping, including an Alert if the reference values are exceeded. As the data are stored in the DICOM Tracker database, a number of QA tools can be applied including the ability monitor individual types of procedures and fluoroscopists comparative values. For legacy FGI equipment (having some, but not all of the required DICOM fields) it is possible to estimate PSD by making assumptions about the proportion of fluoroscopic exposure relative to acquistions (digital spots and cine).
MO‐D‐220‐07: Semi‐Automated Segmentation Method to Quantify Carotid Atherosclerosis from 3D Ultrasound Images
Authors: Ukwatta E , Awad J , Ward A , Buchanan D , Samarabandu J , Parraga G , Fenster A
Published: November 2011

Purpose: 3D ultrasound (3DUS) vessel wall volume (VWV) is a 3D measurement of vessel wall thickness plus plaque within the carotid artery for monitoring carotid plaque progression and regression. In this paper, we describe a segmentation algorithm to delineate the media‐adventitia (MAB) and lumen‐intima (LIB) boundaries of the carotid arteries to quantify VWV measurements. Methods: An operator places four anchor points on each boundary of every transverse carotid image slice to initialize the algorithm. The MAB and LIB boundaries are segmented using two level set segmentations that are coupled. The two segmentations evolve independently based on their objective functions, when they are separated by more than a minimum allowable separation distance. When two curves are closer than the minimal allowable distance, they repel each other to maintain the separation. The algorithm was evaluated with respect to manual segmentations using volume‐, region‐, and boundary distance‐based metrics. Our data set consisted of manual and algorithm repeatedly (5) segmented boundaries of 231 transverse 2D slices extracted from 21 3DUS carotid images. Results: The algorithm provided a mean VWV error of 5.2%±3.9%. For the MAB and LIB respectively, our method yielded Dice coefficients of 95.6%±1.5% and 92.8%±3.2%, and mean absolute distances of 0.2±0.1 mm and 0.3±0.1 mm. The algorithm yielded a minimum detectable difference (MDD) of 63.1 mm3, which is smaller than the previously reported annual VWV change of 120 mm3/year. The average time saved using the algorithm was 4.6 min (8.3 min − 3.7 min). Conclusions: The algorithm provided small volume‐based errors, high Dice coefficients, and sub‐millimeter boundary distance‐based errors. The MDD suggests that a follow‐up period of seven months or more would be appropriate using our method for monitoring carotid atherosclerosis. The realization of a semi‐automated method would assist the translation of carotid 3DUS for clinical research and clinical care.
MO‐D‐220‐10: Automatic Quality Control Processing for Detection of Elements Dropout in Ultrasound Transducers
Authors: Padilla F , Carson P , Hooi F , Goodsitt M , van der Spek S , Larson S , Hanes C
Published: November 2011

Purpose: To develop a simple and reliable method of detection of lost or reduced sensitivity elements in diagnostic ultrasound arrays through analysis of the systematic features evident in appropriately acquired cineloops Methods: An algorithm was developed to detect the systematic features produced by element/channel signal loss evident in a cineloop acquired with a random background signal: A temporal median of the cineloop is produced followed by construction of a profile defined as the mean over depth [column‐wise mean] within a horizontal strip of the median image. A modified anisotropic diffusion filter is applied to the profile to isolate outlying features from characteristic noise, and simple statistical methods are then used to identify regions of the profile which exhibit characteristics of reduced sensitivity elements such as well‐defined, symmetric troughs. With an element occluded by fishing line to simulate dropout, cineloops were acquired with a GE‐Logiq 9 scanner either by rapidly scanning a transducer over a tissue mimicking phantom or by placing the transducer in a liquid phantom composed of an agitated cornstarch and water suspension. Results: Analysis with the algorithm clearly revealed the occluded section of the array as well as previously unnoticed reduced‐sensitivity elements. The efficacy of a simple and inexpensive method of detecting lost or reduced sensitivity elements of diagnostic ultrasound arrays was demonstrated in a confined dataset. The algorithm has been developed into an ImageJ plugin which presently handles uncompressed DICOM data containing rectangular scan regions; this should soon be made available for use by the medical ultrasound community after testing by Ultrasound Subcommittee members.

Supported in part by the Ultrasound Subcommittee of the AAPM Science Council andNIH Grant CA91713
MO‐E‐211‐01: Breast MRI: Pulse Sequences, Acquisition Protocols, and Analysis
Authors: Price R
Published: November 2011

Breast MRI is becoming an increasingly important diagnostic tool for evaluating breast cancer disease extent, monitoring therapy response and for screening women that are at high risk. The most common imaging protocol includes initial T2‐weighted bright‐fluid and pre‐contrast T1‐weighted 3D gradient‐echo (GE) sequences, followed by the injection of a gadolinium (Gd) contrast agent and a series of 3D‐GE images: dynamic contrast enhanced MRI (DCE‐MRI).

Because of the high background signal in T1‐weighted images due to fatty tissues, it is preferred that all sequences be acquired with fat‐suppression. For images acquired without fat‐suppression, it is essential that image subtraction (post‐injection minus pre‐injection) be used to assure adequate contrast‐enhancement sensitivity.

The sensitivity of DCE‐MRI for detecting cancerous lesions is determined by the degree of contrast enhancement that can be achieved relative to the surrounding normal tissues. The specificity of DCE‐MRI, for distinguishing malignant from benign lesions, relies upon the DCE‐MRI kinetic data. Malignant lesions generally exhibit rapid uptake and washout while benign lesions typically have a slower uptake that gradually increases with time. In an effort to achieve both the high sensitivity and specifically, breast MRI pulse sequences should be optimized to achieve high gadolinium contrast enhancement, high three‐dimensional spatial resolution (< 1 mm in‐plane) as well as adequate temporal resolution. The evolution of breast MR imaging has lead to the general use of fat‐suppressed, 3D T1‐weighted GE pulse sequences that can be acquired with a temporal resolution of approximately 60–90 seconds.

Learning Objectives

1. Review protocols and pulse sequences used for breast MR imaging.

2. Review the MRI timing diagram used for T1‐weighted, fat‐suppressed, 3D gradient echo‐pulse sequences.

3. Understand how k‐space sampling and parallel imaging affect temporal resolution.

4. Review how parallel imaging can be used to help achieve the temporal resolution needed for breast DCE‐MRI.

5. Discuss issues related to data acquisition and post‐acquisition image processing.
MO‐E‐211‐02: Breast MRI: Image Quality, Artifacts & Quality Control
Authors: Reeve D
Published: November 2011

The quality of clinical breast MR images is influenced by the design and performance of the MR system, the breast coil, the breast MRI protocol, proper patient positioning, as well as patient‐specific factors. MR system and coil quality control, protocol optimization, and technologist training are important to ensure high quality breast MR images.

Common image quality issues encountered in clinical breast MR image include signal non‐uniformity and inadequate breast tissue coverage, both of which can be influenced by the coil design. Inadequate fat or silicone saturation, wrap‐around artifacts, and parallel imaging artifacts can often be minimized through technologist training. Breast MR protocol modification may be necessary to achieve improvements in signal‐to‐noise ratio (SNR), high contrast spatial resolution, or artifact reduction. Low SNR or non‐ uniform breast MR images may be coil performance related. Therefore it is important that breast coils be tested annually and whenever coil performance issues are suspected, as part of a comprehensive MR system quality control program.

Educational objectives:

1. Describe common artifacts and image quality issues encountered in clinical breast MR images.

2. Discuss methods for addressing breast MR image quality problems.

3. Describe quality control procedures and accreditation programs specific to breast MRI.
MO‐F‐BRA‐01: Polymer Composite‐Based Shielding of Diagnostic X‐Rays
Authors: Nambiar S , Osei E , Yeow J
Published: November 2011

Purpose: To develop lead‐free polymer composites for shielding diagnostic x‐rays employed in interventional radiological (IVR) procedures. Methods: Polydimethylsiloxane (PDMS) composites of different weight percentages (wt%) were developed from the following high atomic‐number (Z) materials: (i) bismuth tungsten oxide (BTO), (ii) bismuth oxide (BO). X‐ray attenuation tests were performed using the diagnostic x‐ray machine (Ysio, Siemens) for energies from 40 kV to 150 kV. Each sample was placed at a distance of about 20 cm from the ion chamber (x‐ray detector) connected to an electrometer (Capintec). For each experiment, the distance between the ion chamber and the floor was at least 50 cm in order to avoid backscattered radiation. All measurements were normalized with reference to the readings obtained with no sample between the source and the detector. Results: Analysis of percentage attenuation versus x‐ray energy indicates that the attenuation capability of all the composites decreases with increasing energy. PDMS composite with 36.36 wt% of BTO shows an overall increase of 18.3% and 50% attenuation relative (absolute differential between the % attenuation) to that achieved by 18.18 wt% of BTO and pure PDMS (no BTO) respectively. For both BTO and BO composites, doubling of the sample thickness showed a relative increase of 16.4% and 12.3% attenuation respectively at 60 kV, the energy typically employed in IVR. Conclusions: Protective aprons made of high Z metals such as lead or composites of lead are heavy and also toxic due to the presence of lead. In this study, we have shown that light‐weight, conformable, cost effective, and non‐toxic polymer composites of high Z materials can be designed to effectively attenuate diagnostic x‐rays. A composite sample with 60.6 wt% of BO (thickness of 2.67 mm) has shown the best result, by far, with 92.5% attenuation of the beam at 60 kV.
MO‐F‐BRA‐04: Neutron Dose Equivalent at the Maze Entrance of GRID Therapy
Authors: Wang X , Charlton M , Esquivel C , Stathakis S , Papanikolaou N
Published: November 2011

Purpose: To evaluate the neutron and photon dose equivalent (Hn,D and HG) at the outer maze entrance with a grid block on a Varian Clinac 23EX accelerator; and to evaluate the neutron activation on the surface of the grid. Method and Materials:A Varian Clinac 23EX accelerator was used to produce 18 MV photons with a 7.62 cm brass grid. The neutron dose equivalent Hn,D was measured using an Andersson‐Braun neutron Rem meter, and the photon dose equivalent HG was measured using a Geiger Müller gamma‐ray survey meter at the outer maze entrance. The neutron activation dose on the surface of the grid was measured by the Geiger Müller survey meter after the irradiation. Results: With the gantry head tilted close to the inner maze entrance and with the jaws closed, the neutron dose equivalent reached its maximum, which is the same as the non‐grid beam. The difference between the grid and non‐grid measurement results was within the measurement uncertainty for different gantry angles. The measurement taken at 5 min after the irradiation shows the exposure rate at the surface of the grid can reach up to 360 mR/hr. The neutron activation activities have an average half life about 10 min. Conclusions: This work indicates that the neutron production in GRID therapy does not change from a conventional external beam therapy. However, the users of a grid should be aware of the possible high dose to the radiation worker from the neutron activation on the surface of the grid.
MO‐F‐BRA‐06: Neutron Dose Equivalent at the Maze Entrance of a Flattening Filter Free Accelerator
Authors: Wang X , Esquivel C , Charlton M , Stathakis S , Nes E
Published: November 2011

Purpose: To evaluate the neutron and photon dose equivalent (Hn,D and HG) at the outer maze entrance after the removal of the flattening filter of a Varian Clinac 23EX accelerator; and to evaluate the effectiveness of semiempirical calculations for a flattening filter free (FFF) accelerator. Methods: A Varian Clinac 23EX accelerator was used to produce 18 MV photons without the flattening filter. The Hn,D was measured using an Andersson‐Braun neutron Rem meter, and the HG was measured using a Geiger Müller gamma‐ray survey meter at the outer maze entrance. The measurements were compared with semiempirical calculations such as the Kersey method, the modified Kersey method and a newly proposed method by Falcão et al. Results: With the gantry head tilted close to the inner maze entrance and with the jaws closed, the neutron dose equivalent reached its maximum. The FFF dose equivalent per monitor unit (MU) is 14 –41% lower than that of a flattened beam under different field size and gantry angle settings. The calculation to measurement ratio of the Hn,D was 4.6 for the Kersey method and 16.7 for the Falcão method. The modified Kersey method has a calculation to measurement ratio about 0.8. The total photon dose equivalent calculation using formulae in NCRP report No. 151 is about 1.5 times of the measurement. Conclusions: This work indicates that the neutron production per MU from a flattening filter free accelerator is reduced at the maze entrance. The Kersey method and the Falcão method overestimate the neutron dose equivalent. The modified Kersey method gives the closest estimation of a Varian Clinac 23EX accelerator operated at 18 MV photon mode without flattening filter in a maze with a similar design as in our study. However, its tendency to underestimate the Hn,D need to be considered during shielding calculation.
MO‐F‐BRB‐01: Convolution Based Dose Calculation in Microbeam Radiation Therapy
Authors: Bartzsch S , Oelfke U
Published: November 2011

Purpose: Microbeam Radiation Therapy (MRT) uses synchrotron keV x‐ray sources. So far dose calculations in MRT are based on time consuming Monte Carlo (MC) simulations. We have developed convolution based methods to calculate dose in MRT employing theoretically motivated kernels. Methods: Whereas the Compton effect is the only dominant effect in the MeV x‐ray range, the photoelectric effect becomes more important at lower energy (E<150keV) rendering simple electron density scaling impossible. Furthermore photon scattering becomes more important, whereas electrons are absorbed locally. We have split energy absorption into scattering orders according to the number of preceding Compton events. With some reasonable approximations of the scattering cross sections, spatial energy distributions can be derived analytically in different scattering orders. From this we derive rules to scale kernels in different materials. The microbeam profile is produced by electrons created in primary photon interactions that have a range of less than 300μm. We also simplified electron scattering in order to predict beam penumbras. Results: Comparisons with MC simulations at different energies show good agreement. Differences for broad field irradiation of homogeneous material are less than 1% along the beam axis and less than 20% inside a 100mm radius. Simulations of bone in water show differences of up to 12% close to interfaces. Application of the methods to a real head CT also showed good agreement. Due to the integrating character of the method structures in the scattered dose cannot be resolved. The microbeam profile is well resolved and agreement in the valley region is better than 5%. Conclusions: The developed methods reduce dose calculation times in MRT down to a few minutes and make parameter optimisation and treatment planning possible. However, the accuracy cannot compete with MC simulations, but this seems not to be a big compromise considering biological uncertainties.
MO‐F‐BRB‐04: Multi‐Source Modeling of Flattening Filter Free (FFF) Beam and the Optimization of Model Parameters
Authors: Cho W , Kielar K , Mok E , Xing L , Park J , Jung W , Suh T
Published: November 2011

Purpose: To suggest a novel analytic beam source model for a flattening filter free(FFF) beam, a multi‐source model and its optimization method applicable to a treatment planning system were developed. Methods: Previous three source model was improved by introducing off axis ratio (OAR) of primary photon fluence to generate cone shape profiles. The parameters of the model and the OAR were determined from measured head scatter factors and a measured dose profile of a 40 × 40 cm2 field size using a line search optimization technique. A new method to acquire gradient terms for OARˈs was developed to enhance the speed of the optimization process. The improved model was validated with measured dose profiles from 3 × 3 cm2 to 40 × 40 cm2 field sizes at 6 and 10 MV from a TrueBeamTM STx linear accelerator. Furthermore, planar dose distributions for clinically used radiation fields were also calculated and compared with measurements using a 2D array detector using the gamma index method. Results: All dose values for the calculated profiles agreed with the measured dose profiles within 0.5% at 6 and 10 MV beams, except for some low dose regions for larger field sizes. A slight overestimation was seen in the lower penumbra region near the field edge for the large field sizes by 1 % ∼ 4%. The planar dose calculations showed comparable passing rates (> 98%) when the criterion of the gamma index method was selected to be 3%/3 mm. Conclusions: Developed source model showed good agreements between measured and calculated dose distributions. The model is easily applicable to any other linear accelerator using FFF beams as the data required include only the measured PDD, dose profiles and output factors for various field sizes, which are easily acquired during conventional beam commissioning process.
MO‐F‐BRB‐06: Experimental Characterization of the Dosimetric Properties of a Newly Designed I‐Seed Model AgX100 125I Interstitial Brachytherapy Source
Authors: Chen Z , Bongiorni P , Nath R
Published: November 2011

Purpose: To characterize and determine the dosimetric properties of a newly designed 125I source (Model AgX100 I‐Seed) for interstitial brachytherapy. Methods: High‐resolution photon spectrometry and thermoluminescent dosimetry (TLD) techniques were utilized for a comprehensive experimental characterization of the AgX100 source introduced recently by Theragenics Corporation® (Buford, GA). The photon characteristics emitted by the AgX100 source were determined by a high‐purity germanium spectrometer. The dose distributions around the source were measured using 1 mm  1 mm  1 mm TLD cubes placed in SolidWaterTM phantoms. The dosimetric parameters needed for dose calculation using the American Association of Physicists in Medicine (AAPM) Task Group (TG) No. 43 formalism were derived from the measured dose rate distributions with Monte Carlo calculated SolidWaterTM‐to‐water conversion factors. Results: It was found that 1) the photon energy spectrum emitted by the AgX100 source was nearly identical to that emitted by the well‐established model 6711 OncoSeedTM manufactured by GE Healthcare; 2) the dose‐rate constant determined by the photon spectrometry technique (0.957 ± 0.037 cGyh‐1U‐1) and by the TLD technique (0.995 ± 0.007 cGyh‐1U‐1) was within 1.5% of the corresponding values determined for the model 6711 source; 3) the radial dose function and the anisotropy function of the AgX100 source were also found to be similar to the TG‐43 consensus data for the model 6711 source. The anisotropy constant determined for the model AgX100 source (0.941) was virtually identical to the TG‐43 consensus value (0.942) for the model 6711 source. Conclusions: A comprehensive dosimetric characterization has been carried out for the new AgX100 source. The AAPM TG‐43 dosimetry parameters for the new source have been determined from the experiment data.

The work was supported in part by NIH grant R01‐CA134627 and Theragenics Corporation