bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐J‐145: Geometric Uncertainty in CBCT Extrapolation for Head and Neck Adaptive Radiotherapy
Authors: Liu C , Kumarasiri A , Chetvertkov M , Gordon J , Chetty I , Siddiqui F , Kim J 
Published: July 2014

Purpose:One primary limitation of using CBCT images for H' N adaptive radiotherapy (ART) is the limited field of view (FOV) range. We propose a method to extrapolate the CBCT by using a deformed planning CT for the dose of the day calculations. The aim was to estimate the geometric uncertainty of our extrapolation method.Methods:Ten H' N patients, each with a planning CT (CT1) and a subsequent CT (CT2) taken, were selected. Furthermore, a small FOV CBCT (CT2short) was synthetically created by cropping CT2 to the size of a CBCT image. Then, an extrapolated CBCT (CBCTextrp) was generated by deformably registering CT1 to CT2short and resampling with a wider FOV (42mm more from the CT2short borders), where CT1 is deformed through translation, rigid, affine, and b‐spline transformations in order. The geometric error is measured as the distance map ||DVF|| produced by a deformable registration between CBCTextrp and CT2. Mean errors were calculated as a function of the distance away from the CBCT borders. The quality of all the registrations was visually verified.Results:Results were collected based on the average numbers from 10 patients. The extrapolation error increased linearly as a function of the distance (at a rate of 0.7mm per 1 cm) away from the CBCT borders in the S/I direction. The errors (μ±σ) at the superior and inferior boarders were 0.8 ± 0.5mm and 3.0 ± 1.5mm respectively, and increased to 2.7 ± 2.2mm and 5.9 ± 1.9mm at 4.2cm away. The mean error within CBCT borders was 1.16 ± 0.54mm . The overall errors within 4.2cm error expansion were 2.0 ± 1.2mm (sup) and 4.5 ± 1.6mm (inf).Conclusion:The overall error in inf direction is larger due to more large unpredictable deformations in the chest. The error introduced by extrapolation is plan dependent. The mean error in the expanded region can be large, and must be considered during implementation.This work is supported in part by Varian Medical Systems, Palo Alto, CA.
SU‐E‐J‐147: Quantitative Analysis of 2.5 MV Portal Imaging Performance Compared to KV and 6MV Portal Imaging On the Novel Edge LINAC
Authors: Song K , Kim J , Wen N , Li H , Snyder K , Zhong H , Gordon J , Chetty I 
Published: July 2014

Purpose:To quantitatively evaluate the performance of 2.5 MV imaging compared to traditional kV and 6MV imaging on the new Edge LINAC (VarianMethods:The high and low contrast resolution and contrast‐tonoise ratios of kV, 2.5MV, and 6MV portal imaging were evaluated using Las Vegas, Leeds, CIRS torso, Rando torso, and BrainLab pelvis phantoms. Different thicknesses of solid water were added at both sides of phantom to simulate and assess the imaging characteristics associated with increased scatter in larger patients. The contrast‐to‐noise ratios of bone‐to‐soft tissue were obtained from aforementioned phantoms.Results:The 2.5 MV portal imaging resolved all objects in the Las Vegas phantom except the smallest object. 6 MV imaging couldn' t image three smallest objects. From the Leeds phantom, kV, 2.5 MV, and 6 MV imaging achieve 2.24, 1.4, and 1.25 LP/mm with no additional slabs, respectively. With 10 cm slabs added, resolutions deteriorate to 1.6, 1.25, and 0.7 LP/mm. In low contrast detectability, kV, 2.5 MV, and 6 MV imaging visualize 18, 18, and 15 different‐contrast objects in total. With 10cm slab added, they imaged 12, 15, and 8 objects. CIRS phantom CNRs of bone‐to‐soft tissue were 10, 27, and 17 for KV, 2.5 MV, and 6 MV, respectively with no slab added. Rando phantom CNRs were 11, 8, and 7 and similarly CNRs from the BrainLab pelvis phantom were 9, 13, and 11. With additional slab, KV imaging CNRs degraded much more than those of 2.5 MV and 6 MV imaging.Conclusion:In this study, we evaluated kV, 2.5 MV and 6 MV imaging using various phantoms. The 2.5 MV imaging shows better imaging performance at large phantom configurations in terms of high and low contrast resolutions and CNRs. We believe that the 2.5 MV portal imaging will be the next trend in portal imaging, especially for SRS/SBRT patient localization.
SU‐E‐J‐151: Dosimetric Evaluation of DIR Mapped Contours for Image Guided Adaptive Radiotherapy with 4D Cone‐Beam CT
Authors: Balik S , Weiss E , Jan N , Zhang L , Roman N , Christensen G , Williamson J , Hugo G 
Published: July 2014

Purpose:To estimate dosimetric errors resulting from using contours deformably mapped from planning CT to 4D cone beam CT (CBCT) images for image‐guided adaptive radiotherapy of locally advanced non‐small cell lung cancer (NSCLC).Methods:Ten locally advanced non‐small cell lung cancer (NSCLC) patients underwent one planning 4D fan‐beam CT (4DFBCT) and weekly 4DCBCT scans. Multiple physicians delineated the gross tumor volume (GTV) and normal structures in planning CT images and only GTV in CBCT images. Manual contours were mapped from planning CT to CBCTs using small deformation, inverse consistent linear elastic (SICLE) algorithm for two scans in each patient. Two physicians reviewed and rated the DIR‐mapped (auto) and manual GTV contours as clinically acceptable (CA), clinically acceptable after minor modification (CAMM) and unacceptable (CU). Mapped normal structures were visually inspected and corrected if necessary, and used to override tissue density for dose calculation. CTV (6mm expansion of GTV) and PTV (5mm expansion of CTV) were created. VMAT plans were generated using the DIR‐mapped contours to deliver 66 Gy in 33 fractions with 95% and 100% coverage (V66) to PTV and CTV, respectively. Plan evaluation for V66 was based on manual PTV and CTV contours.Results:Mean PTV V66 was 84% (range 75% – 95%) and mean CTV V66 was 97% (range 93% – 100%) for CAMM scored plans (12 plans); and was 90% (range 80% – 95%) and 99% (range 95% – 100%) for CA scored plans (7 plans). The difference in V66 between CAMM and CA was significant for PTV (p = 0.03) and approached significance for CTV (p = 0.07).Conclusion:The quality of DIR‐mapped contours directly impacted the plan quality for 4DCBCT‐based adaptation. Larger safety margins may be needed when planning with auto contours for IGART with 4DCBCT images.Reseach was supported by NIH P01CA116602.
SU‐E‐J‐161: Inverse Problems for Optical Parameters in Laser Induced Thermal Therapy
Authors: Fahrenholtz SJ , Stafford RJ , Fuentes DT 
Published: July 2014

Purpose:Magnetic resonance‐guided laser‐induced thermal therapy (MRgLITT) is investigated as a neurosurgical intervention for oncological applications throughout the body by active post market studies. Real‐time MR temperature imaging is used to monitor ablative thermal delivery in the clinic. Additionally, brain MRgLITT could improve through effective planning for laser fiber's placement. Mathematical bioheat models have been extensively investigated but require reliable patient specific physical parameter data, e.g. optical parameters. This abstract applies an inverse problem algorithm to characterize optical parameter data obtained from previous MRgLITT interventions.Methods:The implemented inverse problem has three primary components: a parameter‐space search algorithm, a physics model, and training data. First, the parameter‐space search algorithm uses a gradient‐based quasi‐Newton method to optimize the effective optical attenuation coefficient, μ_eff. A parameter reduction reduces the amount of optical parameter‐space the algorithm must search. Second, the physics model is a simplified bioheat model for homogeneous tissue where closed‐form Green's functions represent the exact solution. Third, the training data was temperature imaging data from 23 MRgLITT oncological brain ablations (980 nm wavelength) from seven different patients.Results:To three significant figures, the descriptive statistics for μ_eff were 1470 m−1 mean, 1360 m−1 median, 369 m−1 standard deviation, 933 m−1 minimum and 2260 m−1 maximum. The standard deviation normalized by the mean was 25.0%. The inverse problem took <30 minutes to optimize all 23 datasets.Conclusion:As expected, the inferred average is biased by underlying physics model. However, the standard deviation normalized by the mean is smaller than literature values and indicates an increased precision in the characterization of the optical parameters needed to plan MRgLITT procedures. This investigation demonstrates the potential for the optimization and validation of more sophisticated bioheat models that incorporate the uncertainty of the data into the predictions, e.g. stochastic finite element methods.
SU‐E‐J‐171: Surface Imaging Based Intrafraction Motion Assessments for Whole Brain Radiotherapy
Authors: Wiant D , Vanderstraeten C , Maurer J , Pursley J , Terrell J , Sintay B 
Published: July 2014

Purpose:To quantify and characterize intrafraction motion for whole brain radiotherapy treatments in open face masks using 3D surface imaging.Methods:Fifteen whole brain patients were monitored with 3D surface imaging over a total of 202 monitoring sessions. Mean translations and rotations were calculated over each minute, each session, and over all sessions combined. The percentage of each session that the root mean square (RMS) of the linear translations were outside of 2 mm, 3 mm, 4 mm, and 5 mm were determined for each patient. Correlations between mean translations per minute and time and between standard deviation per minute and time were evaluated using Pearson's r value.Results:The mean RMS translation averaged over all patients was 1.45 mm +/− 1.52 mm. The patients spent an average of 18%, 10%, 6%, and 3% of the monitoring time outside of 2 mm, 3 mm, 4 mm, and 5 mm RMS tolerances, respectively. The RMS values averaged over all patients were 1.31 mm +/− 0.98 mm, 1.52 +/‐ 1.04, and 1.30 mm +/− 0.71 mm over the 1th, 5th, and 10th minutes of monitoring, respectively. Neither, the RMS values (p = 0.15) or the standard deviations of the RMS values (p = 0.16) showed significant correlations with time.Conclusion:The patients were positioned within 2 mm of isocenter, which was the initial set‐up tolerance, for the majority of their treatments. The average position changed by < 0.3 mm over 10 minutes of monitoring. Short term movements, reflected by the standard deviations, where on the order of 1 mm. This immobilization system provides adequate immobilization over a course of treatment for whole brain radiotherapy. This system may also be suitable for head and neck or stereotactic radiosurgery treatments as well.
SU‐E‐J‐174: Adaptive PET‐Based Dose Painting with Tomotherapy
Authors: Darwish N , Mackie T , Thomadsen B 
Published: July 2014

Purpose:PET imaging can be converted into dose prescription directly. Due to the variability of the intensity of PET the image, PET prescription maybe superior over uniform dose prescription. Furthermore, unlike the case in image reconstruction of not knowing the image solution in advance, the prescribed dose is known from a PET image a priori. Therefore, optimum beam orientations are derivable.Methods:We can assume the PET image to be the prescribed dose and invert it to determine the energy fluence. The same method used to reconstruct tissue images from projections could be used to solve the inverse problem of determining beam orientations and modulation patterns from a dose prescription [10]. Unlike standard tomographic reconstruction of images from measured projection profiles, the inversion of the prescribed dose results in photon fluence which may be negative and therefore unphysical. Two‐dimensional modulated beams can be modelled in terms of the attenuated or exponential radon transform of the prescribed dose function (assumed to be the PET image in this case), an application of a Ram‐Lak filter, and inversion by backprojection. Unlike the case in PET processing, however, the filtered beam obtained from the inversion represents a physical photon fluence. Therefore, a positivity constraint for the fluence (setting negative fluence to zero) must be applied (Brahme et al 1982, Bortfeld et al 1990)Results:Truncating the negative profiles from the PET data results in an approximation of the derivable energy fluence. Backprojection of the deliverable fluence is an approximation of the dose delivered. The deliverable dose is comparable to the original PET image and is similar to the PET image.Conclusion:It is possible to use the PET data or image as a direct indicator of deliverable fluence for cylindrical radiotherapy systems such as TomoTherapy.
SU‐E‐J‐186: Acquiring and Assessing Upright CBCT Images for Future Treatment Planning
Authors: Fave X , Yang J , Balter P , Court L 
Published: July 2014

Purpose:To acquire upright CBCT images using the onboard imager of a Varian TrueBeam. An easy to implement upright imaging protocol could allow for widespread upright radiation therapy which would greatly benefit certain patients. These include thoracic cancer patients (because lung volume increases in a seated position) and patients who experience substantial discomfort during supine treatment.Methods:To acquire upright CBCT images, the gantry head remained stationary at 0 degrees with the KV imager arms extended to their lateral positions. Phantoms were placed upright at the end of the treatment couch. During a scan, the couch rotated from 270 to 90 degrees while continuous fluoroscopic projections were taken by the onboard imager. To extend the field‐of‐view, this sequence was performed twice: once with the KV detector longitudinally offset +14.5cm and once with it longitudinally offset −14.5cm. The resulting two image sets were stitched together before reconstruction. The imaging beam parameters were chosen to deliver a dose similar to that given during a simulation CT. Image quality was evaluated for spatial linearity, high and low contrast resolution, and HU linearity using CatPhan and anthropomorphic phantoms. A deformable registration technique was used to evaluate HU mapping from a simulation CT.Results:Spatial linearity and high contrast resolution were maintained in upright CBCT when compared to simulation CT. However, low contrast resolution and HU linearity degraded. Streak artifacts were caused by the limited 180 degree arc of the couch, and the stitching process created a sharp artifact at the center of the reconstruction. The deformable registration was robust in the HU mapping even with these artifacts and the loss of HU linearity.Conclusions:The image quality obtained from upright CBCT was sufficient for treatment planning. The success of this novel technique is an important step towards a future clinical protocol.This project was funded in part by Varian Medical Systems, Inc.
SU‐E‐J‐188: Impact of Unexpected Dose Warping with Deformable Image Registration in Lung Cancer
Authors: Moriya S , Tachibana H , Sugawara Y , Sato M , Sawant A 
Published: July 2014

Purpose:In our previous study of dose warping validation, four cases in twenty lung SBRT patients shows unexpected result. We clarify the impact of dose warping with a free‐downloadable deformable image registration (DIR) program and a commercially‐available DIR software program.Methods:Our in‐house software was implemented with the blockmatching algorithm for rigid registration and the free‐form deformation algorithm for non‐rigid registration from the NiftyReg. The deformation algorithm implemented in the MIM software was also based on the freeform deformation algorithm. In order to assess the accuracy of dose warping from the two software programs, generalized equivalent uniformed dose (gEUD) of the deformed dose distribution for peak inhale phase was compared with the gEUD of the dose distribution for peak inhale phase base on a assumption that a radiobiological equivalent dose would be stable before and after the deformation. The peak‐inhale deformed dose distribution was superimposed on peak‐exhale phase CT and structure datasets.Results:The in‐house software shows that the difference of gEUD for the tumor was less than 1% in the previous study. The difference was 21.4% on average in the four cases (Max: 51.2%). In the four cases in the MIM, the result was improved, however was still more than 1% (Average: 7.3%, Max: 24.3%). In the visual evaluation of the case with large gEUD difference, the shape of dose distribution from dose warping was not in nature from the motion of the tumor. The CT images of a case, which have large difference of gEUD, shows that the tumor was surrounded by the structure with the similar CT values, which were the chest wall or the diaphragm.Conclusion:A commissioning test of not only a freedownloadable DIR program but also a commercial software is essential and we should understand pitfalls of dose warping from the DIR.
SU‐E‐J‐198: Evaluation of a Free‐Form Intensity‐Based Deformable Registration Method Using the POPI Model
Authors: Nelson AS , Duchateau M , Piper JW , Verellen D , Ridder M De 
Published: July 2014

Purpose:Our goal is to evaluate the accuracy of a free‐form intensity‐based deformable registration method using the POPI model.Methods:Five subjects with 4DCT datasets from the POPI model (Vandemeulebrouke Med Phys 2011) were used to assess deformable registration accuracy. Each subject contained 100 or more identified landmark points that corresponded between the end‐inspiratory and end‐expiratory phases. The 0% phase was registered to the 50% phase first using a rigid alignment followed by a freeform intensity‐based deformable registration. Landmark displacement was measured after the rigid registration (initial displacement) and the deformable registration (residual error). A single subject (POPI2) with significant initial displacement was also registered using an interactive tool to influence the deformation by locking local alignments to help guide the deformation. Error was measured with and without using the tool for this subject.Results:The average initial displacement prior to deformable registration ranged from 5.7 mm to 14.0 mm. The mean (SD) residual error after deformation ranged from 1.0 mm (0.9) to 1.7 mm (3.3) for four of the five subjects. For POPI2 the initial residual deformable error was 4.6 mm (6.8). Using seven local alignments to guide the deformation the error for POPI2 decreased to 1.2 mm (1.0). The average error across all 5 subjects was 1.3 mm (2.0).Conclusion:A free‐form intensity‐based deformable registration method was found to provide good accuracy with an average error of 1.3 mm. A method for locally guided deformation allowed for the accurate registration of a challenging case with significant respiratory motion. References1. Vandemeulebrouke et al. Med Phys 2011.2. http://www.creatis.insa‐lyon.fr/rio/popi‐model/AS Nelson is an employee with ownership at MIM Software, Inc. JW Piper is an employee with ownership at MIM Software, Inc.
SU‐E‐J‐200: A Dosimetric Analysis of 3D Versus 4D Image‐Based Dose Calculation for Stereotactic Body Radiation Therapy in Lung Tumors
Authors: Ma M , Rouabhi O , Bayouth J , Flynn R , Xia J 
Published: July 2014

Purpose:To evaluate the dosimetric difference between 3D and 4Dweighted dose calculation using patient specific respiratory trace and deformable image registration for stereotactic body radiation therapy in lung tumors.Methods:Two dose calculation techniques, 3D and 4D‐weighed dose calculation, were used for dosimetric comparison for 9 lung cancer patients. The magnitude of the tumor motion varied from 3 mm to 23 mm. Breath‐hold exhale CT was used for 3D dose calculation with ITV generated from the motion observed from 4D‐CT. For 4D‐weighted calculation, dose of each binned CT image from the ten breathing amplitudes was first recomputed using the same planning parameters as those used in the 3D calculation. The dose distribution of each binned CT was mapped to the breath‐hold CT using deformable image registration. The 4D‐weighted dose was computed by summing the deformed doses with the temporal probabilities calculated from their corresponding respiratory traces. Dosimetric evaluation criteria includes lung V20, mean lung dose, and mean tumor dose.Results:Comparing with 3D calculation, lung V20, mean lung dose, and mean tumor dose using 4D‐weighted dose calculation were changed by −0.67% ± 2.13%, −4.11% ± 6.94% (−0.36 Gy ± 0.87 Gy), −1.16% ± 1.36%(−0.73 Gy ± 0.85 Gy) accordingly.Conclusion:This work demonstrates that conventional 3D dose calculation method may overestimate the lung V20, MLD, and MTD. The absolute difference between 3D and 4D‐weighted dose calculation in lung tumor may not be clinically significant.This research is supported by Siemens Medical Solutions USA, Inc and Iowa Center for Research By Undergraduates
SU‐E‐J‐205: Monte Carlo Modeling of Ultrasound Probes for Real‐Time Ultrasound Image‐Guided Radiotherapy
Authors: Hristov D , Schlosser J , Chen J , Bazalova M 
Published: July 2014

Purpose:To quantify the effect of ultrasound (US) probe beam attenuation for radiation therapy delivered under real‐time US image guidance by means of Monte Carlo (MC) simulations.Methods:MC models of two Philips US probes, an X6‐1 matrix‐array transducer and a C5‐2 curved‐array transducer, were built based on their CT images in the EGSnrc BEAMnrc and DOSXYZnrc codes. Due to the metal parts, the probes were scanned in a Tomotherapy machine with a 3.5 MV beam. Mass densities in the probes were assigned based on an electron density calibration phantom consisting of cylinders with mass densities between 0.2–8.0 g/cm3. Beam attenuation due to the probes was measured in a solid water phantom for a 6 MV and 15 MV 15×15 cm2 beam delivered on a Varian Trilogy linear accelerator. The dose was measured with the PTW‐729 ionization chamber array at two depths and compared to MC simulations. The extreme case beam attenuation expected in robotic US image guided radiotherapy for probes in upright position was quantified by means of MC simulations.Results:The 3.5 MV CT number to mass density calibration curve was found to be linear with R2 > 0.99. The maximum mass densities were 4.6 and 4.2 g/cm3 in the C5‐2 and X6‐1 probe, respectively. Gamma analysis of the simulated and measured doses revealed that over 98% of measurement points passed the 3%/3mm criteria for both probes and measurement depths. The extreme attenuation for probes in upright position was found to be 25% and 31% for the C5‐2 and X6‐1 probe, respectively, for both 6 and 15 MV beams at 10 cm depth.Conclusion:MC models of two US probes used for real‐time image guidance during radiotherapy have been built. As a Result, radiotherapy treatment planning with the imaging probes in place can now be performed.J Schlosser is an employee of SoniTrack Systems, Inc. D Hristov has financial interest in SoniTrack Systems, Inc.