bluuebunny/crossref_metadata_2025 huggingface dataset:
WE‐A‐BRB‐07: Critical Analysis of Strength‐Based Medical Event Definition in Prostate Seed Brachytherapy Based on a Comparative Retrospective Pre‐ and Post‐Implant Analysis
Authors: Todor D , Horn J , Karlin J , Hagan M
Published: June 2012

Purpose: To create a clinical basis and to describe a process that would lead to a better understanding of possible practical implementations of the treatment site concept in the strength‐base medical event definition. To explore various metrics and similarity measures defining the geometry of implants. Methods: Pre‐ and post‐implants were analyzed for 100 cases. Contour structures and seed data were extracted from Variseed (Varian Medical Systems, Inc., Palo Alto, CA). In house written Matlab software was developed to construct structures that would encompass 100% and 95% of seeds, identify seed distributions with greater than 20% of total number of seeds residing outside of ‘zones' at distances up‐to 5 mm beyond the prostate contour, determine inter‐distances between seeds, and calculate the center of mass for prostate contours as well as seed distributions. Similarity between pre‐ and post‐implant plans was evaluated by skewness and kurtosis of the inter‐seed distance distributions. All implants studied were considered ‘good ’ or better by current D90 criteria. Results: In our dataset there were no cases in which more than 20% of the seeds were implanted outside a zone expanded 4mm from prostate. A 3mm expansion would have produced 5 events, while a 2mm expansion would have produced 11 events. Skewness of inter‐seed distances was on average 0.06 for pre‐plans and 0.14 for post‐plans. This demonstrates a displacement of inter‐seed distances toward larger values. Post to pre‐plan ratios of minimum box volume encompassing 95% of seeds increased from 1.3 to 1.72 as zones were expanded from 0 to 4mm. Kurtosis analysis revealed a significant increase in post‐plans, but outlier‐prone distributions did not correlate with the cases having more than 20% of seeds in distant zones. Conclusions: We are proposing measures based on clinical data that can assist in defining ‘treatment site’ as well as help practitioners better understand the relation between pre‐ and post‐implants.
WE‐A‐BRB‐09: Dosimetric Effects of Needle Tip Localization Errors in Prostate Brachytherapy
Authors: Ruiz B , Leu S , Podder T
Published: June 2012

Purpose: In prostate seed implantation, beveled tip needles are used for convenience of steering. However, needle tip localization and seed deposition errors can occur due to the bevel tip orientation. Purpose of this study is to evaluate the dosimetric consequences of needle tip localization errors due to transrectal ultrasound (TRUS) elevation beamwidth artifacts and beveled needle tip orientation in prostate seed implantation cases. Methods: Using VariSeed brachytherapy seed planning software (Varian, version 8.0), 15 clinical cases were evaluated for dosimetry (145Gy prescription, I–125 seed each of 0.375mCi). Seed positions were adjusted to represent the localization errors of 0.8mm–6.5mm (combined errors due to elevation beamwidth artifacts (2.5mm) and needle tip orientation (4mm)) for an ultrasound setting of 50% gain, and 0.9mm‐8.5mm for 100% gain. Each plan had a corresponding reference plan for comparison purposes. Plan parameters were compared using the AAPM TG‐137 guidelines for the prostate, prostatic urethra, and rectum. Results: Compared to the reference plans, due to needle tip localization errors, prostate dosimetric parameters V100, V150, and V200 deviated by −2.8%, −2.4%, and −3.6%, respectively for TRUS setting of 50% gain. D90 was decreased by 7.3Gy. Observed rectal dose increased in V100, D2cc, and D0.1cc by 0.13%, 0.96Gy, and 2.78Gy, respectively. Urethral doses D30 and D10 changed by −0.85Gy and −0.44Gy respectively. For TRUS of 100% gain, prostate V100, V150, and V200 were decreased by 2.8%, 3.0%, and 3.8%, respectively. D90 was lowered by 6.7Gy. Rectal dose increased in V100, D2cc, and D0.1cc by 0.05%, 0.37Gy and 1.44Gy, respectively. Urethral doses D30 and D10 decreased by 1.03Gy and 1.37Gy, respectively. Conclusions: Seed deposition based on the erroneous needle tip localization can cause considerable dose deviation of the prostate, rectum, and urethra. These results may be prostate volume and shape dependent. Further investigation is warranted in this regard.
WE‐A‐BRB‐11: How Certain Can the Real‐Time Plan Predict the Post Dosimetry for Prostate Seed Implant?
Authors: Li JS , Buyyounouski M , Horwitz E , Ma C‐M
Published: June 2012

Purpose: To investigate the correlation between the post dosimetry and the real‐time plan for the transrectal ultrasound guided prostate seed implant. Methods: Prostate seed implants were performed with preloaded needles and transrectal ultrasound imaging guidance. Customized stranded seeds based on the real time treatment plan generated in the operation room were preloaded in the needles for the implant. Post dosimetry was performed at the same day and three week later based on patient's CT and MR images. Target DVH parameters of the real‐time plan and the post dosimetry at the week three were studied retrospectively for 100 patients. The correlation between them was analyzed and uncertainty of the prediction on the post dosimetry was calculated. Results: Though the post dosimetry meets clinic criteria for most of the patients, big uncertainty on the target dose is observed, 12.4% on D90 and 7.6% on V100. The correlation coefficient between the DVH parameters of the post dosimetry and the real time plan is poor. The mean ratio of the V100 (D90) between the post dosimetry and real time plan is 0.92 (0.88) with a standard deviation of 0.07 (0.1), which means on average that a 100% V100 is required in the real time plan for a 90% post dosimetry V100 and a 115% D90 for a 100% post dosimetry D90. The mean ratio between the post V100 (D90) and the real time V150 is 1.5 (1.76) with a standard deviation of 0.19 (0.25). The mean ratio of V200 between the post and the real time is 1.1 with a standard deviation of 0.4. Conclusions: In order to reduce the dosimetry uncertainty, the implant technique and the consistence need to be improved. The post dosimetry is necessary for patient dose evaluation because it cannot be predicted accurately based on the real time plan.
WE‐A‐BRA‐01: The Hybrid Linac‐MR System for Real‐Time Tumour Tracking and Radiation Treatment
Authors: Fallone BG
Published: June 2012

The development of a successful hybrid linac‐MR system is described that allows for both perpendicular and parallel radiation‐configurations to minimize perturbations in radiation dosimetry and to improve dosimetry due to magnetic‐field effects. Successful automatic contouring of tumours of MR images obtained during treatment at four frames a sec (as recommended for lung tracking) for various low magnetic‐field strengths is described, in addition to, our successful predictive tumour‐position algorithm based on patient‐specific (with and without initial weight (IW) for each patient and treatment fraction) feed‐forward 4 layered artificial neural networks (ANN) to compensate for delays in MLC leaf‐motions. The respective tracking and predictive performances of our algorithms are tested with a database of a large number of images for 29 patients obtained independently at very high frames, as well as, with in‐house motion MR phantoms that emulate the motion of any patient on the database. The automatic algorithm successfully contoured moving tumour from dynamic MR images obtained at 4 fps with Dice coefficients of >0.96 and >0.93, and tracked the tumour position with root‐mean‐squared‐errors (RMSE) of < 0.55 mm and <0.92 mm, for 0.5 and 0.2 T images, respectively. Mean RMSE values of 0.5 – 0.9 mm are achieved by our ANN predictor for MLC systems delays ranging from 120 – 520 ms for all the patients in the database. The advantage of using our patient‐specific ANN is shown by a 30 – 60 % decrease in mean RMSE values in motion prediction as compared to results achieved with a single ANN structure and randomly chosen IW. Our results successfully demonstrate the feasibility of using auto‐contouring in low field images and of using the intrafractional tumour‐motion auto‐tracking with our laboratory linac‐MR system

Learning Objectives:

1. Understand the solutions to the mutual interferences associated with a linac and an MRI

2. Understand the development of MR autocontouring algorithms for low‐field MR images obtained at 4 fps

3. Understand the development of algorithm that predict the tumour positions from MR images obtained at 4 fps and thus compensate for the delay in MLC leaf motions to the tumour.
WE‐A‐BRA‐04: Real‐Time Telerobotic 3D Ultrasound for Soft‐Tissue Guidance Concurrent with Beam Delivery
Authors: Hristov D , Schlosser J , Kirmizibayrak C , Shamdasani V , Salisbury K , Chang D , Metz S
Published: June 2012

Managing internal anatomy motion due to physiological random or quasi‐ periodical processes is a critical challenge in external beam radiation therapy especially in the context of single‐ or few‐fraction ablative regiments for abdominal targets. Existing and emerging technologies for localizing abdominal targets during beam delivery employ tracking of implanted fiducial markers, tracking of external surrogates, or guidance via magnetic resonance images. However, these technologies cannot meet the challenge of providing real‐time, volumetric, non‐invasive, markerless soft‐tissue image guidance to existing radiation delivery platforms. Diagnostic ultrasound is a safe, non‐ionizing, non‐invasive modality widely used in image‐guided cancer interventions that has significant potential to address this challenge. Modern matrix array transducers can generate real‐time soft‐ tissue single plane (2D), cross‐plane, and volumetric (3D) data thus allowing optimization of frame rate, field‐of‐view and image quality for the purposes of motion monitoring and tracking. Furthermore, digital navigation links that stream live data to other devices enable the development of real‐time image‐guidance applications on dedicated interventional workstations with no interference to the imaging process. Based on these capabilities we have been developing and evaluating a novel approach that combines robotics with diagnostic ultrasound imaging. It uses a customized add‐on human‐safe robotic manipulator to control the pressure and pitch of an abdominal probe while avoiding gantry collisions. The manipulator can maintain probe pressure and pose autonomously or interactively via a haptic device that is integrated to remotely control the robotic manipulator outside the therapy room. The transducer is optically tracked to localize the ultrasound images in the coordinate system of the delivery device. Image processing techniques are implemented to monitor anatomy displacements in real time. The approach is being evaluated with regard to imaging robustness, interference with delivery devices, impact on treatment plans, localization accuracy, and temporal lag.

Learning Objectives:

1. Understand how tele‐robotic 2D/3D ultrasound imaging and appropriately designed workflow can enable real‐time soft‐tissue image guidance concurrent with radiation delivery.

2. Recognize different imaging (2D/cross‐plane/3D) and image‐ processing approaches to real‐time anatomy motion monitoring and appreciate their performance for localization and tracking.

3. Recognize interferences between the radiation delivery system and the tele‐robotic imaging system and appreciate their magnitude and mutual impact.
WE‐A‐217A‐01: The Effects of Radiation Therapy on White Matter Fiber Tracts of the Limbic Circuit
Authors: Nazem‐Zadeh M , Chapman C , Lawrence T , Tsien C , Cao Y
Published: June 2012

Purpose: To assess radio‐sensitivity of white matter fiber tracts interconnected to hippocampus. Methods: Twelve patients who had brain metastases and received fractionated whole brain radiation therapy (WBRT) (30 or 37.5G) were included in the study. Diffusion weighted images were acquired pre RT, end of RT, and 1 ‐month post‐RT. The fornix, cingulum and corpus callosum were extracted from diffusion weighted images by combining fiber tracking and segmentation methods based upon characteristics of the fiber bundles. The ingulum was segmented by a seed‐ based tractography, the fornix by an ROI‐based tractography, and the corpus callosum by a level‐set segmentation algorithm. The radiation‐induced longitudinal changes in diffusion indices of the structures were evaluated. Results: Significant percentage decreases were observed in fractional anisotropy in the cingulum posterior part, fornix, and corpus callosum from pre RT to end of RT by −14.0%, −12.5%, and −5.2%, respectively (p<0.001), and from pre RT to 1‐month post‐RT by −11.9%, −12.8%, and −6.4%, respectively (p<0.001). Moreover, significant percentage increases were observed in mean diffusivity in the corpus callosum and cingulum posterior part from pre RT to end of RT by 6.8% and 6.5%, respectively, and from pre RT to 1‐month post‐RT by 8.5% and 6.3%, respectively. Furthermore, significant percentage increases were observed in radial diffusivity anisotropy in the cingulum posterior part, fornix, and corpus callosum from pre RT to end of RT by 11.4%, 7.1%, and 17.0%, respectively, and from pre RT to 1‐month post‐RT by 10.5%, 4.9%, and 21.8%, respectively (p<0.001). The increase in radial diffusivity primarily contributed to the significant decrease in fractional anisotropy, indicating demyelination is the predominant radiation effect on the white matter structures. Conclusions: Our findings indicate the fornix and cingulum posterior part are susceptible to radiation damage, particularly to demyelination. Further investigation of the relationship between the structural damage and cognitive dysfunction is on‐going. Supported in part by National Institutes of Health grants RO1 NS064973
WE‐A‐217A‐03: In Vivo Imaging to Monitor the Effects of Anti‐Angiogenesis and Re‐ Oxygenation on Pancreatic Tumor Radiosensitivity
Authors: Cao N , Song S , Cao M , Shaffer M , Maleki T , Ziaie B , Ko S , Stantz K
Published: June 2012

Purpose: The objectives are to: 1) longitudinally monitor and evaluate the physiology and oxygenation status of pancreatic tumor after treatment by anti‐angiogenic drug (DC101, anti‐VEGFR2 monoclonal antibody); and 2) to generate oxygen within tumor using a novel device, Implantable Micro‐ Oxygen Generator, IMOG. Functional and molecular imaging modalities, Dynamic Contrast‐Enhanced CT (DCE‐CT) and Photoacoustic Computed Tomography Spectroscopy (PCT‐S) will be used to longitudinally monitor tumor responses to DC101 or IMOG, develop a suitable time window for further combined radiotherapy, and identify prognostic factors to help develop individualized treatment plan in pancreatic cancer. Methods: A cohort of athymic mice bearing human BxPC‐3 pancreatic tumors was divided into six groups: control (n=9), DC101 therapeutic group (n=9), radio‐therapeutic group (RT, a single fraction of 5 Gy x‐ray, n=9), DC101 plus RT (n=9), IMOG control group (n=14), and IMOG plus RT (n=19). For the control and DC101 groups, DCE‐CT and PCT‐S scans were acquired at baseline, 2 days, 1 week, and 2 weeks post treatment. Based on the imaging results, radiotherapy was applied at 1 week post DC101. IMOG produced oxygen was in vivo measured by NeoFox Oxygen Measurement System and 3‐D monitored by PCT‐S. Radiotherapy will be applied immediately after IMOG stimulation. Results: The preliminary DCE‐CT and PCT‐S results showed that at one week post DC101 treatment, the tumor vasculature was temporarily normalized with better oxygenation. The combination of DC101 and radiotherapy significantly reduced tumor growth compared to single treatment. IMOG significantly produced oxygen within tumor upon ultrasonic stimulation, and IMOG generated oxygen sensitized the tumors to combined radiotherapy. Conclusions: DCE‐CT and PCT‐S provide uniquely monitoring over tumor physiology and oxygenation changes in response to DC101 or IMOG. We believe that applying radiotherapy in the ‘normalization window’ after DC101 or immediately after IMOG initiation period will greatly augment treatment outcomes for pancreatic tumor.
WE‐A‐217A‐04: Hepatic Function Estimated from HIDA SPECT for Assessment of Liver Response to Radiation Therapy
Authors: Wang H , Feng M , Frey K , Balter J , Haken R Ten , Lawrence T , Cao Y
Published: June 2012

Purpose: To investigate the dose response of the hepatic extraction fraction derived from HIDA SPECT for assessment of hepatic function in response to radiation therapy (RT). Methods: Eleven patients with intrahepatic cancers were treated by fractionated conformai RT (30–65 Gy), and underwent HIDA SPECT/CT scans before, during and 1 month after the therapy. Voxel‐by‐voxel hepatic extraction fraction (HEF) was estimated from HIDA SPECT by the deconvolution method. The dose distributions were mapped on the HEF images via co‐registration with the treatment planning CT. The liver voxels, excluding gross tumor volumes and vessels, were segregated into subvolumes based upon the accumulated biologically‐ corrected doses at the end of RT for analysis of response of hepatic function to radition. Results: The HEF 1 month after RT decreased compared to pre RT. The averaged regional decreases in the HEF from the 11 patients were correlated linearly with the doses accumulated to the end of RT (R2=0.87). Substantial individual responses of the HEF to doses were observed 1 month after RT. Conclusions: Our study shows dose‐dependent hepatic function changes in local liver regions. There is substantial individual variability in the sensitivity of hepatic function to irradiation. The quantitative HEF images as a measure of spatial hepatic function may be a valuable tool for preserving liver function and avoiding injury after irradiation. The work is supported in part by RO1CA132834.
WE‐A‐217A‐06: Can Pre‐Chemoradiotherapy FDG PET/CT Identify Residual Metabolically Active Areas Within Individual Esophageal Tumors?
Authors: Lu W , Tan S , Kligerman S , Chen W , Feigenberg S , Zhang H , Suntharalingam M , D'Souza W
Published: June 2012

Purpose: To study whether residual metabolically active areas within esophageal tumors can be identified by areas of high FDG uptake on the pre‐chemoradiotherapy (CRT) PET/CT scans. This will allow dose escalation to these areas at the highest risk for residual tumor in order to improve outcomes. Methods: Twenty patient s were included from a prospectively collected database. A rigid registration was used to align the post‐CRT PET/CT with the pre‐CRT PET/CT images. The primary tumor and the residual metabolically active areas were delineated using a region‐ growing algorithm with a threshold of standard uptake value (SUV) = 2.5 on the pre‐CRT and post‐CRT images, respectively. Seven areas of high FDG uptake pre‐CRT were delineated using thresholds of SUV 2.5, 5.0, 34%, 40%, 50%, 60%, and 70% of the maximal SUV, respectively. Overlap fraction and centroid distance were computed to quantify the similarity and proximity between these areas and the residual areas. Results: Six of the 20 patients had residual metabolically active areas within the primary tumor on the post‐CRT PET/CT. Representative images were shown to illustrate four different relationships between the primary tumors and the residual areas. The average overlap fractions between areas of high FDG uptake pre‐CRT and the residual areas were all less than 60%. The average centroid distances were all greater than 8.6 mm, and increased as the threshold increased. Areas of higher FDG uptake pre‐CRT had lower overlap and larger distance to the residual areas post‐CRT. Conclusions: The results suggested that pre‐CRT PET/CT cannot reliably identify the residual metabolically active areas in esophageal cancer. Selective dose escalation to areas of high FDG uptake may not be benefit for many patients. This work was supported in part by the National Cancer Institute Grant R21 CA131979. This work was supported in part by the National Cancer Institute Grant R21 CA131979.
WE‐A‐217A‐08: Modeling of Thermal Effects in Antivascular Ultrasound Therapy from Contrast Enhanced Ultrasound Images
Authors: Smithline S , Avery S , Sehgal C
Published: June 2012

Purpose: To study the role of intravascular microbubble‐induced heating resulting from in‐vivo low‐intensity sonication of solid tumors using contrast‐enhanced ultrasound images. Methods: Solid tumors are modeled as a compressible inhomogeneous medium that consists of a network of micro‐blood vessels in a microenvironment of cells and interstitial fluids through which microbubbles flow. A mathematical model based on the Penne Bioheat equation was used to calculate the microbubble‐enhanced temperature increase during sonication of solid tumors. This mathematical framework was applied to contrast‐enhanced ultrasound images to simulate the in‐vivo conditions of antivascular ultrasound therapy. Results: The results show that the presence of microbubbles causes local heating in the tumor at the locations of the microbubbles in the image. The temperature initially increases rapidly initially as a function of time and then levels off. The temperature elevation calculated as a function of sonication frequency, show that, the maximum temperature change occurs near the resonance frequency of the microbubbles. The mathematical simulations also show that as the flow rate increases, the temperature elevation decreases. Conclusions: Our results show that microbubbles circulating in the blood provide a mechanism for delivering acoustic energy at the location of the microbubbles. Since previous experimental studies show that sonication of intravascular microbubbles disrupt tumor microvessels, antivascular ultrasound treatment has the potential for treating patients with cancer.
WE‐A‐217A‐10: Feasibility of Dose Painting Using PET‐Based Treatment Response
Authors: Simoncic U , Jeraj R
Published: June 2012

Purpose: The main prerequisite for biologically‐conformal radiotherapy, or dose painting, is an accurate definition of the treatment targets, which is still an unresolved problem. The purpose of this study was to assess the feasibility of using early PET‐based response for spatial modulation of tumor dose. Methods: Ten patients with solid tumors were imaged with FLT PET/CT before the start of radiotherapy and during the treatment. PET‐ based responses were evaluated in two ways: the differences of mid‐ treatment and pre‐treatment FLT PET/CT images, and the ratios of the images. Tumor dose was modulated using PET‐based response, while integral tumor dose was kept unchanged. Non‐uniformity of dose prescriptions was quantified with the relative mean difference (RMD), that quantifies the relative amplitude of modulation. The RMD is defined as the mean difference in a population, normalized to the population mean. The helical tomotherapy plans conformity was quantified with the Q95‐105 factors, that represents the fraction of voxels with planned dose within 5% of the prescription. Results: Both PET‐based responses have similar spatial distributions. Their correlation coefficients is between 0.7 and 0.9. The difference‐based dose prescriptions have RMD between 3.0% and 11.8%. The ratio‐based dose prescriptions are considerably more non‐uniform, with RMD in range 14.0% to 32%. The conformity of the difference‐based dose painting is close to the uniform dose delivery (Q95‐105 in range 0.62 to 0.96), while the conformity of the ratio‐based dose painting is significantly lower (Q95‐105 in range 0.37 to 0.67). Conclusions: These results demonstrate that dose redistribution based on the difference of two sequential PET images is feasible and could potentially be considered for implementation in a clinical setting. Dose redistribution based on ratio of two sequential PET images results dose plans with highly compromised conformity. It is also more sensitive to uncertainties in the dose prescription.
WE‐A‐217A‐11: Fast and Low‐Dose 4DCBCT for Small Animal Lung Ventilation Study
Authors: Qi Z , Chen Q , Ding K , Benedict S , Lernen L , Chen G
Published: June 2012

Purpose: To demonstrate that a fast and low‐dose 4DCBCT can be used to the lung ventilation of small animals for treatment assessment. As 4DCBCT scan goes faster, fewer projections are acquired and under‐sampling‐induced streaking artifacts will be rampant if the conventional reconstruction algorithm is used. The enabling method to be proposed is the PICCS algorithm, which is capable of reconstructing streak free images from vastly under‐sampled projections by using a high SNR prior image. Methods: A 20‐minute 4DCBCT scan of a mouse was performed and 7200 projections were acquired. By under‐sampling these projections, faster 4DCBCT scans with acquisition times equivalent of 4, 2, 1.4, and 1 minute are simulated. Both FBP and PICCS were used for image reconstructing these faster scans and these images were compared with the original slow scan for performance evaluation. A non‐linear deformable registration algorithm was applied to the reconstructed dynamic images to generate lung ventilation maps. The fidelity of the generated lung ventilation maps was used as a metric for quantitative evaluation to determine the optimal scan time. Results: The qualitative evaluation shows unnoticeable differences between PICCS images from faster scans and FBP images from the original scan. The quantitative evaluation is ongoing to demonstrate the equivalence of PICCS images from faster scans and FBP images from the original slow scan, in terms of the accuracy of the extracted lung ventilation maps. Conclusion: The proposed method shows promises to accelerate small animal 4DCBCT scans by an order of magnitude (data acquisition time down to about 2 minutes) without impacting the faithfulness of the lung ventilation map. Significant radiation dose reduction (∼10) is also expected.
WE‐A‐218‐03: Translating X‐Ray Tube Modulation Parameters between Different CT Scanner Models Using Dose Metrics
Authors: McKenney SE , Burkett G , Lamba R , Seibert JA , Boone JM
Published: June 2012

Purpose: While auto tube current modulation is an effective dose reduction technique, manufacturer‐specific implementation of the technique leads to inconsistencies between scans obtained on different scanners. This research describes efforts to translate comprehensive scan protocols from a reference CT scanner to progeny scanners by matching x‐ray output using a variable diameter phantom. Methods: The phantom consisted of six cylinders of PMMA with increasingly large diameters, much like a wedding cake. The diameters of the cylinders were 10, 13, 16, 20, 25, and 32 cm. The reference CT scanner was a GE LightSpeed 16; the progeny scanners were a GE LightSpeed VCT and Siemens Definition AS+. The phantom was scanned while varying the tube modulation metric (either noise index or reference mAs). Using custom software, the mAs was determined on a slice‐by‐slice basis and then averaged along the length of each phantom. Two conversion metrics were examined as a way to translate x‐ray output between scanners: (1) CTDIw or (2) air exposure. The modulation metric of the progeny CT scanner that produced the output closest to that of the reference CT scanner was then selected as the optimal metric for each phantom size. The metric was then compared to the ad hoc scan protocols currently used for the progeny scanners. Results: The range of appropriate tube modulation metrics is highly dependent on patient diameter. When applied to patients of varying sizes, tube current modulation may be hitting the maximum or minimum limits. Conclusions: Both CTDIw and air exposure are reasonable conversion metrics to match x‐ray output between CT scanners. While matching x‐ray output is the first step towards standardizing scan protocols across different types of scanners, thorough image quality analysis must be done to ensure that clinical tasks can be performed sufficiently
WE‐A‐218‐08: Comparison of Automated Methods to Measure Patient Size for Dose‐ Monitoring in Computed Tomography
Authors: Christianson O , Frush D , Samei E
Published: June 2012

Purpose: There has been a growing movement to monitor the size‐specific dose estimate (SSDE) for patients undergoing computed tomography (CT) examinations. Information on the patient size, however, is not easily accessible in the DICOM headers. Here, we compare three different automated methods to extract the patient size in terms of their accuracy and precision. Methods: Patient size was determined using three automated algorithms. Method A used a thresholded scout image to determine the patient size. A correction factor of 0.85 was applied to the thickness for the chest region to account for the reduced attenuation of the lungs. Method B converted the central slice of the data set into a water equivalent thickness. Method C converted all slices to a water equivalent thickness and computed an average patient thickness. Testing on a clinical data set of 77 chest and 177 abdomen‐pelvis CT exams, the patient size and SSDE were calculated using all three algorithms. Additionally, the local SSDE was calculated using the local CTDI and the patient thickness for each slice. The SSDEs calculated using the three methods were compared with the average of the local SSDE to evaluate the accuracy of each method. Results: The average absolute error in patient size was 4.2%, 3.1% and 0.0% for methods A, B, and C, respectively. The average absolute error in SSDE was 4.3%, 3.2%, and 0.5% for method A, B, and C respectively. Conclusions: All three methods accurately calculated SSDE to within 5%. Method A, which uses a thresholded scout image, offers the simplest and most computationally efficient approach to measure patient size for dose monitoring purposes.
WE‐B‐213CD‐03: Fluoroscopy Training and Compliance ‐ Experience of a Large Academic Institution
Authors: Mahesh M
Published: June 2012

Training of physicians performing fluoroscopy is key to patient and staff safety. In the absence of uniform regulations regarding credentialing of physicians performing fluoroscopy, various states have adopted/implemented regulations. State of Maryland requires a 4‐hour initial training in fluoroscopy operations and safety and a one‐hour refresher course on the same subject once every 2 years. This applies to all physicians performing fluoroscopy with exception to board certified radiologists. The implementation of a program to comply with such regulatory requirements in a large academic center (Johns Hopkins) and the challenges to ensure compliance of all physicians performing fluoroscopy is the focus of this presentation. Along with that, the process on how to prepare and comply for the Joint Commission's sentinel event policy pertaining to prolonged fluoroscopy will be discussed. In addition, the presentation will also discuss process set in place to comply with regulatory requirements of monitoring personal radiation monitors, other training issues and radiation dose reduction strategies in fluoroscopy.

Learning Objectives:

1. To understand the credentialing and other requirements for physicians performing fluoroscopy.

2. To become familiar with the process set to comply with regulations at a large academic medical center.

3. To be able to utilize the information to implement similar process at other institutions.
WE‐C‐211‐02: The Legal Framework for the Control of Radiation Protection and Nuclear Safety in Senegal
Authors: Faye A Boye
Published: June 2012

The Senegalese Authority for Radiation protection and Nuclear Safety (ARSN), placed under the supervision of the Prime Minister, was setting up by the Law 2009‐14 relating to nuclear security and to radiation protection which repeals and replaces the opposite measures of the Law 2004‐17 relating to protection against ionizing radiations. The implementation of the ARSN enters within the scope of the international commitments of the Senegalese Government. Indeed, the member states of the International Atomic Energy Agency, the IAEA, participate collectively, through the structures of the Agency or in bilateral cooperation, in the implementation of the programs of radioprotection. Furthermore, from the moment a state makes a commitment in the implementation of nuclear programs, it has to set up the adequate legal framework. So, the global aim of ARSN is to regulate activities involving nuclear materials or radioactive sources and to control the traffic of such materials within the country. To that effect, all activities involving radiation exposure are subjected to regulatory control by a system of notification, authorization by registration or licensing and inspection. ARSN has the mandate to advise the Government on matters relating to radiation protection and disposal of radioactive waste; and to provide an effective national framework for the safety and security of radioactive sources and radiological installations, including physical protection. While the ARSN is specific to Senegal, other countries within Africa may have similar laws pertaining to local regulations that will also most likely be different. We will provide a brief overview of ARSN and how it applies to some of the activities within Senegal, including industrial and medical. When possible, notifications and/or comparison with other similar authorities within the African continent will be made.
WE‐C‐213AB‐01: How to Prepare for the ABR Therapy Oral Exam
Authors: Becker SJ
Published: June 2012

Preparing for Part III (Oral Exam) of the ABR Therapy Physics boards is more than just studying as much material as possible. There will always be material that is missed and gaps in one's knowledge. Therefore, in order to fill those gaps, it is crucial to understand how the parts of the material relate to each other and to the clinical experience. Part III presents its own challenges compared to the written exams. It requires not only knowledge of and experience with clinical procedures, but also the ability to explain orally how they are performed and what they mean. One must be able to easily and confidently respond to oral questions about all aspects of working in the clinic and clearly explain why those clinical methods and procedures are performed that way. This talk is not a comprehensive review of all required study material. Instead, it focuses on the required experiences, skill sets, and study methods that are needed to pass Part III of the board exam.

Learning Objectives:

1. Generate a list of clinical experiences needed for the exam

2. Understand how the study material and clinical experiences relate to each other

3. Learn how to effectively prepare for an oral style exam
WE‐C‐BRB‐02: A Monte Carlo Feasibility Study for Calculating Dose Perturbations in Patient Geometries Due to Homogenous Magnetic Fields from MRIgRT
Authors: Yang Y , Bednarz B
Published: June 2012

Purpose: Magnetic resonance image‐guided radiotherapy (MRIgRT) has emerged as a promising new technology to reduce tumor position uncertainty during photon radiotherapy. The use of MRI during beam delivery complicates treatment planning since the magnetic field will perturb the radiation dose distribution especially in fields prescribed in heterogeneous regions of the body. The purpose of this study was to investigate the magnetic field effect on dose distributions in patient geometry using Monte Carlo methods. Methods: The Monte Carlo code Geant4 was used for all simulations performed in this study. We investigated dose distributions from a 6‐MV photon beam energy spectra in patient geometries subjected to homogeneous transverse magnetic fields with varying field strengths. For this study perturbations in the dose distribution from a single rectangular field were simulated in a prostate patient scan. Results: Preliminary results show perturbations in the overall dose profile due to the magnetic field can be seen when a transverse magnetic field was applied to the patient geometry. Regions of under‐ and over‐dosing occur throughout the beam path near the penumbra of the photon beam. Conclusions: This study demonstrated that patient‐specific dose calculations for MRIgRT treatments are feasible using Geant4. Work is currently ongoing to include treatment specific field parameters and 4D time‐resolved geometries.
WE‐C‐BRB‐05: Monte Carlo Simulations and Experimental Validation of Rapid Dose Delivery with Very High‐Energy Electron Beams
Authors: Bazalova M , Maxim P , Tantawi S , Colby E , Koong A , Loo BW
Published: June 2012

Purpose: To evaluate the feasibility to treat lung cancer with very high‐ energy electrons (VHEE) by Monte Carlo (MC) simulations and to estimate the beam‐on time based on experimental dose measurements on an existing VHEE beam line. Methods: Manually optimized VHEE treatment plans for a simulated lung tumor were calculated for beam energies ranging from 50 to 150 MeV in the EGSnrc/DOSXYZnrc MC code. A state‐of‐the‐art RapidArc plan with a 6 MV photon beam was calculated for the same scenario using the Eclipse treatment planning system. The minimal electron beam energy matching the 6MV photon RapidArc plan was identified. VHEE dose from 50 and 70 MeV electrons was measured with Gafchromic EBT2 films on the Next Linear Collider Test Accelerator (NLCTA) beam line adapted to our experiments at the SLAC National Accelerator Laboratory. The experimental setup was modeled in the MCNPX code and the proton and neutron contributions to the total dose were quantified. The total treatment time for the lung case was estimated based on the parameters of the NLCTA beam line and experimental data. Results: For the selected clinical scenario, 75–100 MeV electron beams produced plans of comparably high quality to the best photon plans. The simulated NLCTA percentage depth dose curves and beam profiles at 6 mm depth generally agreed with measurements within 5% for both energies and all beam sizes. The dose contribution from protons and neutrons was negligible, accounting for less than 1×10−2% of the maximum total dose. Based on the beam line parameters and the measurements, a dose of 10 Gy to 95% of the 8 cc PTV could be in principle delivered in 1.3 s. Conclusions: Our results combining MC simulations with experimental measurements suggest that treatments of lung cancer with VHEE are feasible and very fast. We anticipate superior results with plan optimization.
WE‐C‐BRB‐11: On the Biological Basis for Competing Macroscopic Dose Descriptors for Kilovoltage Dosimetry
Authors: Thomson R , Tedgren A Carlsson , Williamson J
Published: June 2012

Purpose: To determine which competing macroscopic dose descriptor best tracks absorbed dose to biologically relevant subcellular targets via Monte Carlo analysis of cellular models for a variety of normal and cancerous tissues, and evaluate relations between bulk dose‐specification media and absorbed doses to cellular targets for kilovoltage radiation. Methods: The relative proportions of water, proteins, inorganic elements, and lipids in cell cytoplasm and nuclei, extracellular fluid, and the corresponding average bulk media were determined for normal and cancerous tissues through a literature review. Mass‐energy absorption coefficients, attenuation coefficients, and stopping powers for these media were calculated. Representative models of cells and cell clusters for normal and cancerous tissues were developed; doses to cellular targets were computed with Monte Carlo (MC) simulation for photon sources (energies between 20 keV and 380 keV) and compared to bulk medium dose descriptors. Results: Cells contain significant and varying mass fractions of proteins, inorganic elements, and lipids (adipocytes only). Variations in mass energy absorption coefficients for cytoplasmic and nuclear media as large as 10% compared to water are observed for sub‐50 keV photon energies (I‐125 and Pd‐103). In adipose tissues, 10% differences persist to 90 keV. Doses to cellular targets differ by up to 10% compared to doses to the corresponding average bulk medium or to water. The relationships between cellular target doses and doses to the bulk medium are sensitive to source energy and cell morphology, particularly for low energy brachytherapy. Conclusions: There are significant variations in cellular morphology (composition, size) with cell type; cells are not generally radiologically water equivalent. Thus neither dose to bulk medium nor dose to water in inhomogeneous macroscopic media quantitatively tracks energy imparted to biologically relevant subcellular targets for the range of cellular geometries investigated and kilovoltage photon sources.
WE‐C‐BRA‐02: Best in Physics (Joint Imaging‐Therapy) ‐ Assessment of Radiation‐Induced White Matter Injury in Sub‐Structures of Normal‐Appearing Brainstem Using Diffusion Tensor Imaging
Authors: Uh J , Merchant T , Ogg R , Hua C
Published: June 2012

Purpose: To test the hypothesis that treatment‐induced white matter injury assessed by diffusion tensor imaging (DTI) is uniform across sub‐regions of the normal appearing brainstem. Methods: We analyzed serial DTI data, acquired before radiation/chemotherapy and over 4–6 years of follow‐up, from 11 pediatric patients (age 5‐16 years) with medulloblastoma. FSL4.1 software (FMRIB, Oxford, UK) was used to calculate fractional anisotropy (FA) and mean, axial, and radial diffusivities. For a consistent identification of regions of interest (ROIs), parametric maps of each patient were transformed to a standard brain space (ICBM), on which we identified motor (corticospinal tract, CST) and sensory (medial lemiscus, ML) tracts in the pons and transverse pontine fibers (TPF) involved in coordination. Temporal changes of DTI parameters in ROIs were evaluated using a linear mixed effect model. Results: Therapy‐induced white matter injury was marked by a decline in FA at 1–3 years after treatment. The decline was often accompanied by decreased axial diffusivity and/or increased radial diffusivity. This implied axonal damage and demyelination. We observed that the magnitude of the changes was not always uniform across sub‐regions of the brainstem. Specifically, the changes in DTI parameters for TPF were more pronounced than in other regions (p<0.001 for FA) despite similarities in the distribution of dose. The mean dose to CST, TPF, and ML was 52.3, 56.0, and 56.6 Gy, respectively. We did not find a significant difference between CST and ML in these patients (p>0.08 for all parameters). Conclusions: These results indicate that fiber tract sensitivity to radiation effect may be associated with the type and function of fiber tracts and support a role for tract‐based assessment in radiation treatment planning and evaluation of treatment response.
WE‐C‐BRA‐09: Towards Treatment Monitoring of Tumour Radiation Response with Raman Spectroscopy
Authors: Matthews Q , Jirasek A , Brolo AG , Lum JJ
Published: June 2012

Purpose: To use single‐cell Raman spectroscopy (RS) and principal component analysis (PCA) for early treatment monitoring of radiation response. Methods: Two human tumour cell lines, one known to be radioresistant (H460, SF2 = 0.64) and one radiosensitive (LNCaP, SF2 = 0.27), were treated with daily 2 Gy fractions of 6 MV photons, up to a maximum total dose of 10 Gy. Irradiated and unirradiated cultures were harvested and analyzed with RS each day after the previous daily fraction, and also at 2 and 3 days after the final fraction. Single‐cell Raman spectra were acquired from 20 cells per sample with a Raman microscope utilizing a 785 nm excitation laser. All spectra (280 per cell line) were post‐processed, and the total data set for each cell line was analyzed with PCA using standard algorithms. Results: One radiation‐induced PCA component was detected for each cell line by identification of statistically significant changes in the PCA score distributions for irradiated samples, as compared to unirradiated samples, at time points after the start of radiation treatment. The radioresistant cells (H460) exhibit a strong RS molecular radiation response signature, detectable as early as 2 days after the start of treatment, of which radiation‐induced glycogen synthesis is a significant contributor. The radiosensitive cells (LNCaP) exhibit a weak molecular radiation response signature that is not correlated with the radioresistant cell response, with no contributions from glycogen. The glycogen synthesis observed in the radioresistant cells is confirmed via Western blotting to be the result of radiation‐induced activation of the phosphatidylinositol‐3‐kinase/Akt (PI3K/Akt) signalling pathway, a molecular radiation response known to promote cell survival and confer radiation resistance. Conclusions: This work supports the feasibility of using RS for early treatment monitoring of tumour radiation response, leading to personalized therapy.
WE‐G‐211‐01: Cross‐Sectional Imaging ‐ Computed Tomography
Authors: Rothenberg L
Published: June 2012

The introduction of new cross‐sectional imaging techniques in the 1970's and 1980's led to great improvements in the diagnosis and treatment of medical conditions. In this symposium, we will chronicle the development of three of these Methods: computed tomography (CT), magnetic resonance imaging (MRI), and ultrasonic imaging (US). Computed Tomography Early attempts to obtain trans‐axial radiographs employed unconventional mechanical motions of the x‐ray tube and screen‐film image receptor that produced images of limited utility. The introduction of the EMI Mk I computerized axial tomography (CAT) unit revolutionized imaging by providing electronic trans‐axial images of the brain that allowed clear separation of various tissues with very similar attenuation coefficients. The great success of this imaging process led to the Nobel Prize for Hounsfield and Cormack in 1979. Examples from the evolution of the x‐ray computed tomography technique, introduced initially by a large number of manufacturers over several “generations” of CT scanners will be presented. The changes include improvements in x‐ray detectors and detector arrays, image reconstruction algorithms, and body bolus/filters, as well as the introduction of slip ring technology. These upgrades led to shorter scanning and reconstruction times, greater body coverage per rotation, and reduced artifacts, along with increased spatial resolution and improved low contrast performance. A very brief overview of additional cross sectional x‐ray imaging devices and techniques that have been developed in recent years will conclude this section of the symposium.
WE‐G‐BRCD‐01: A Procedure for Efficient Large‐Scale Retrospective Clinical Studies for Online Adaptive Radiotherapy
Authors: Lambrecht M , Graves Y , Gautier Q , Tian Z , Kim G , Uribe‐Sanchez A , Jia X , Jiang S
Published: June 2012

Purpose: Online adaptive radiotherapy (ART) is promising for handling inter‐fraction variations of patient's geometry. Before a clinical implementation of this advanced technology, it is necessary to study its potential clinical gains and optimal frequencies to be used for various tumor sites. The goal of this work is to establish and examine a procedure for efficient large‐scale retrospective clinical studies for online ART using a GPU‐based re‐planning platform. Methods: The proposed procedure utilizes an in‐house developed GPU‐based replanning software called SCORE. SCORE starts by applying deformable registration from CT to CBCT and correcting CBCT artifacts and intensities. However, the CBCT image may not cover the whole treatment region due to the limited field of view. In that case, we use deformed CT for replanning and dose calculation. The final optimized fractional dose is calculated using the optimized fluence maps and a finite size pencil beam model. We also use the deformed CT to calculate the delivered fractional dose using the fluence maps from the original plan. The delivered fractional dose is compared to the optimized fractional dose to estimate the daily gain of replanning. To compare accumulated optimized dose and delivered dose, the delivered and optimized doses are mapped back to the original CT geometry using the deformation vector fields. Results: We tested this procedure using prostate cancer IMRT cases and found that the re‐optimized and delivered DVHs and dose distributions can be generated in a couple of minutes. Conclusions: We have developed a procedure using a GPU‐based replanning software to retrospectively study the clinical gains of online ART in an efficient and large scale manner.