Original Contour Research Articles

Place and role of titanium mesh in reconstruction of the frontal bone after trauma

The proper approach and surgical plan in solving impressive comminuted frontal bone trauma is reflected in adequate fixation of numerous fragments, which have to go through proper repositioning and osteosynthesis to achieve adequate stability of the fragments and to return the original contour of the frontal bone and/or frontal sinus walls. We carried out the restoration of the normal bone contour through a quick and easy way of treating frontal fractures using titanium 3D mesh - a technique that involves 'pulling the bone to the network' and fixing it with the mono cortical screws. We present our experience with this technique in solving the case of frontal impressive and comminuted fractures, on the material of 43 patients at the Centre for Medical Emergencies and Neurotrauma Emergency Centre of the Clinical Centre of Serbia through a retrospective cohort study accompanied with technical aspects and clinical results of this simple method application. The study was previously approved by the Ethics Committee of the Clinical Centre of Serbia. In the period of three years 43 patients had fractures in the area of the frontal bone and frontal sinus. The surveyed period was 1st January 2013 to 31st December 2016. The youngest patient was 17 and the oldest 78 years, the average age being 29 years. The main cause was traffic accidents in 29/43 (67.44%) patients, sport in 4/43 (9.30%), falling down from one's own height in 5/43 (11.63%), a fall from a height higher than 2m in 4/43 (9.30%) and machinery operation in 1/43 (2.33%). The ratio towards sex distribution was men/women 3:1. All patients were operated within the period of six days after the injury. The diagnostic evaluation of patients was made with multi slice computed tomography with 3D reconstruction (3D MDCT) pre- and postoperatively, all patients were controlled on the examinations within the follow-up period of the first 12 postoperative months. The stability of the fragments during the surgical procedure was achieved fully, the position of fragments in the reconstructive act was in satisfactory anatomic contours. The aesthetic results were satisfactory and there were no complications related to the procedure applied, such as uncontrolled bleeding from sinus infection, damage to the rear wall of the sinuses and brain. The effectiveness of the applied procedure indicated to us that we had no deformities of the forehead contour and that the full cosmetic result was achieved. The usage of the titanium 3D mesh in solving such complex impressive comminuted fractures showed as the procedure of choice because in a simple manner with good surgical approach it gives excellent results and the procedure is performed with minimal morbidity in addressing primarily comminuted fracture of the anterior wall of frontal sinus and the frontal bone.

Context Tree-Based Image Contour Coding Using a Geometric Prior.

Efficient encoding of object contours in images can facilitate advanced image/video compression techniques, such as shape-adaptive transform coding or motion prediction of arbitrarily shaped pixel blocks. We study the problem of lossless and lossy compression of detected contours in images. Specifically, we first convert a detected object contour into a sequence of directional symbols drawn from a small alphabet. To encode the symbol sequence using arithmetic coding, we compute an optimal variable-length context tree (VCT) T via a maximum a posterior (MAP) formulation to estimate symbols' conditional probabilities. MAP can avoid overfitting given a small training set X of past symbol sequences by identifying a VCT T with high likelihood P(X|T) of observing X given T , using a geometric prior P(T) stating that image contours are more often straight than curvy. For the lossy case, we design fast dynamic programming (DP) algorithms that optimally trade off coding rate of an approximate contour [Formula: see text] given a VCT T with two notions of distortion of [Formula: see text] with respect to the original contour x. To reduce the size of the DP tables, a total suffix tree is derived from a given VCT T for compact table entry indexing, reducing complexity. Experimental results show that for lossless contour coding, our proposed algorithm outperforms state-of-the-art context-based schemes consistently for both small and large training datasets. For lossy contour coding, our algorithms outperform comparable schemes in the literature in rate-distortion performance.

Customized Orbital Wall Reconstruction Using Three-Dimensionally Printed Rapid Prototype Model in Patients With Orbital Wall Fracture.

It is difficult to restore original orbital contours because of their complex 3-dimensional structure. Moreover, slight implant malpositioning can result in enophthalmos or other complications. The authors describe our experience of using individualized prebent titanium-Medpor mesh implants and stereolithographic modeling in a series of patients who underwent orbital wall reconstruction. A consecutive series of 104 patients with orbital fractures received computer simulation-designed prebent titanium-Medpor mesh implants insertion. Preoperative computed tomography (CT) data were processed for each patient, and a rapid prototyping (RP) model was produced. The uninjured side was concurrently mirrored and superimposed onto the traumatized side to create a mirror image of the RP model. The authors fabricated the titanium-Medpor implants to intraoperatively reconstruct the 3-dimensional orbital structure. The prefabricated titanium-Medpor implants were inserted into the defective orbital wall and fixed. Postoperative CT images were immediately taken to evaluate the reconstructed contours and compare the preoperative and postoperative intraorbital volumes. All reconstructions were successful without postoperative complications. The implants were correctly positioned in the sagittal, axial, and coronal planes relative to the original orbital contours. The mean preoperative intraorbital volumes of the uninjured and traumatized sides were 21.39 ± 1.93 and 23.17 ± 2.00 cm, respectively, and the postoperative mean intraorbital volume was 20.74 ± 2.07 cm. Orbital reconstruction can be optimized using individually manufactured rapid prototype skull model and premolded synthetic scaffold by computer-aid of mirroring-reconstruction of 3-dimensional images and 3-dimensional printing techniques.

Implementation of an adaptive radiotherapy method using EPID and gamma analysis for head and neck and lung cases

Introduction The challenge of adaptive radiotherapy is to recognize the morphological changes that induce a sufficient dosimetric impact to affect the treatment delivery and require complete replanning. Purpose The objective was to analyze daily EPID images to identify and quantify changes in the anatomy and to detect patients at risk of deviation from their planned treatment. Materials and methods EPID images were acquired at every fraction for 50 patients of each of these 2 anatomical sites, head and neck and lung cases. A gamma analysis was performed relative to the first fraction and multiple parameters were extracted from the daily gamma map. The evolution of these parameters were characterized to identify categories of risk of deviation using a k-means clustering. A quarter of these patients had a complete dose evaluation at the end of the treatment by deforming the CT and original contours onto the last CBCT, and by re-computing the dose on the deformed dataset. Results Categories of risk were identified for each of the anatomical sites. These categories indicated the degree of errors of the daily treatment relative to the first fraction. The combination of gamma parameters and dosimetric analysis established a threshold for which patients were at risk of deviation. From the re-computing plan data, it been confirmed that patients with a strong dosimetric impact were above this threshold. Conclusion Analysis of daily EPID images provides a method to identify patients at risk of deviation from their planned treatment and help for the replanning decision.

Poster ‐ 37: Pre‐clinical geometric, dosimetric and timing assessment of head and neck OARs using an in‐house atlas‐based auto‐segmentation (ABAS) tool

Purpose:This study aims to validate the geometric and dosimetric performance of our in‐house ABAS tool using manual inter‐observer variation as benchmark data.Materials and methods:An in‐house ABAS constructed, using MIM MaestroTM version 6.5, from 36 previously treated head and neck cases. 15 OARs of eight nasopharynx patients were segmented via three observers from the same institution and using the in‐house ABAS. Percentage of volume differences (ΔV%,), degree of overlap (DICE), distance‐to‐agreement and the standard deviation of absolute dose difference ΔD SD(Gy) among the eight cases [ΔDmax SD(Gy) for serial organs and ΔDmean SD(Gy) for parallel organs] were compared between the manual segmentation and original ABAS contours for each OAR.Results:The geometric results indicated that ABAS ΔV% was within 1SD from the manual segmentation. DICE showed that manual segmentation marginally outperformed ABAS in the delineation of parotid glands, submandibular glands, and laryngopharynx, but ABSA performed as well as the manual segmentation or better for all other structures. The distance‐to‐agreement was <1.5 cm for 87% of ABAS structures. From a dosimetric perspective, only ABAS salivary glands demonstrated higher ΔD SD(Gy) compared to manual segmentation. For all other structures ABAS results were similar or better than the manual segmentation. The average time to segment a complete H&N OAR set was <3minutes versus 30minutes for manual segmentation.Conclusion:ABAS is a practical time‐saving tool. This study indicated up 90% time‐saving of the operator time per case. ABAS geometric and dosimetric results were within ±1SD inter‐observer variation for most of the structures.

Hybrid Methodology for Image Segmentation Based on Active Contour Module and Alpha-Shape Theory

The concept of the active contour model has been extensively utilized in the segmentation and analysis of images. This technology has been effectively employed in identifying the contours in object recognition, computer graphics and vision, biomedical processing of images that is normal images or medical images such as Magnetic Resonance Images (MRI), X-rays, plus Ultrasound imaging. Three colleagues, Kass, Witkin and Terzopoulos developed this energy, lessening “Active Contour Models” (equally identified as Snake) back in 1987. Being curved in nature, snakes are characterized in an image field and are capable of being set in motion by external and internal forces within image data and the curve itself in that order. The present study proposes the use of a hybrid image segmentation technique to acquire precise segmentation outcomes, while engaging “Alpha Shape (α-Shape)” in supposition to derive the original contour, followed by a refining process through engaging a conventional active contour model. Empirical results show high potential in the suggested computational method. Trials indicate that the primary contour is capable of being precisely set next to the objective contour and effectively have these objective contours extracted, devoid of any contour instigation. Some of the benefits associated with the novel hybrid contour include minimized cost of computation, enhanced anti-jamming capability, as well as enlarged utilization array of snake model.

MO-DE-207B-10: Impact of Morphologic Characteristics On Radiomics Features From Contast-Enhanced CT for Primary Lung Tumors

Purpose: Determine the impact of morphologic characteristics (e.g. necrosis, vascular enhancement, and cavitation) on radiomic features from contrast enhanced CT (CE-CT) in primary lung tumors. Methods: We developed an auto-segmentation algorithm to separate lung tumors on contrast-enhanced CT into cavitation (air), necrosis, tissue, and enhancing vessels using a combination of thresholding and region-growing. An auto-segmentation algorithm was also designed to identify necrosis on FDG-PET scans. Wilcoxon rank-sum tests were used to determine if significant differences existed in radiomics features (histogram-uniformity and Laplacian-of-Gaussian average) from 249 patients, found to prognostic in previous work, based on the presence/absence of morphologic features. Feature values were also compared between the original tumor contours and contours excluding a specific morphologic feature. Comparison of necrosis segmentation on CE-CT versus FDG-PET was performed in 78 patients to assess for agreement using the concordance correlation coefficient (CCC). Results: Tumors with cavitation and enhancing vasculature had lower uniformity values (p = 0.001 and p = 0.03, respectively). Tumors with enhancing vasculature and necrosis had higher Laplacian-of-Gaussian average values (measure of “edges” within the tumor) (p 0.8). This suggests there may be interactions between morphologic characteristics and the radiomic feature value of tumor tissue. Comparison of necrosis volume and percent necrosis volume of tumor were found to have CCC values of 0.85 and 0.76, respectively between CE-CT and FDG-PET segmentation methods. Conclusions: Tumors with enhancing vasculature, necrosis, and cavitation have higher radiomic feature values that are associated with poor prognosis than tumors without these features. Removing these tissue types from quantitative assessment did not drastically impact radiomic feature values. High reproducibility of CE-CT segmented necrosis compared to FDG-PET segmented necrosis provides a reasonable validation of segmentation accuracy on CE-CT.

SU‐F‐T‐55: Reproducibility of Interstitial HDR Brachytherapy Plans

Purpose:Treating gynecological cancers with interstitial high‐dose‐rate (HDR) brachytherapy requires precise reconstruction of catheter positions to obtain accurate dosimetric plans. In this study, we investigated the degree of reproducibility of dosimetric plans for Syed HDR brachytherapy.Methods:We randomly selected five patients having cervix‐vaginal cancer who were recently treated in our clinic with interstitial HDR brachytherapy with a prescription dose of 25–30 Gy in five fractions. Interstitial needles/catheters were placed under fluoroscopic guidance and intra‐operative 3T MRI scan was performed to confirm the desired catheter placement for adequate target volume coverage. A CT scan was performed and fused with the MRI for delineating high‐risk CTV (HR‐CTV), intermediate‐risk CTV (IR‐CTV) and OARs. HDR treatment plans were generated using Oncentra planning software. A single plan was used for all five fractions of treatment for each patient. For this study, we took the original clinical plan and removed all the reconstructed catheters from the plan keeping the original contours unchanged. Then, we manually reconstructed all the catheters and entered the same dwell time from the first original clinical plan. The dosimetric parameters studied were: D90 for HR‐CTV and IR‐CV, and D2cc for bladder, rectum, sigmoid and bowel.Results:The mean of absolute differences in dosimetric coverage (D90) were (range): 1.3% (1.0–2.0%) and 2.0% (0.9–3.6%) for HR‐CTV and IR‐CTV, respectively. In case of OARs, the mean of absolute variations in D2cc were (range): 4.7% (0.7–8.9%) for bladder, 1.60% (0.3–3.2%) for rectum, 1.6% (0–3.9%) for sigmoid, and 1.8% (0–5.1%) for bowel.Conclusion:Overall, the reproducibility of interstitial HDR plans was within clinically acceptable limit. Observed maximum variation in D2cc for bladder. If number of catchers and dwell points were relatively low or any one catheter was heavily loaded, then reproducibility of the plan was more sensitive to the accuracy of catheter reconstruction.

SU‐F‐J‐97: A Joint Registration and Segmentation Approach for Large Bladder Deformations in Adaptive Radiotherapy

Purpose:To improve results of deformable image registration (DIR) in adaptive radiotherapy for large bladder deformations in CT/CBCT pelvis imaging.Methods:A variational multi‐modal DIR algorithm is incorporated in a joint iterative scheme, alternating between segmentation based bladder matching and registration. Using an initial DIR to propagate the bladder contour to the CBCT, in a segmentation step the contour is improved by discrete image gradient sampling along all surface normals and adapting the delineation to match the location of each maximum (with a search range of +−5/2mm at the superior/inferior bladder side and step size of 0.5mm). An additional graph‐cut based constraint limits the maximum difference between neighboring points. This improved contour is utilized in a subsequent DIR with a surface matching constraint. By calculating an euclidean distance map of the improved contour surface, the new constraint enforces the DIR to map each point of the original contour onto the improved contour. The resulting deformation is then used as a starting guess to compute a deformation update, which can again be used for the next segmentation step. The result is a dense deformation, able to capture much larger bladder deformations. The new method is evaluated on ten CT/CBCT male pelvis datasets, calculating Dice similarity coefficients (DSC) between the final propagated bladder contour and a manually delineated gold standard on the CBCT image.Results:Over all ten cases, an average DSC of 0.93±0.03 is achieved on the bladder. Compared with the initial DIR (0.88±0.05), the DSC is equal (2 cases) or improved (8 cases). Additionally, DSC accuracy of femoral bones (0.94±0.02) was not affected.Conclusion:The new approach shows that using the presented alternating segmentation/registration approach, the results of bladder DIR in the pelvis region can be greatly improved, especially for cases with large variations in bladder volume.Fraunhofer MEVIS received funding from a research grant by Varian Medical Systems.

SU-F-P-60: Optimization of Cyberknife Treatment Planning Using a Dose-Limiting Auto-Shells Method for Brain Metastases

Purpose: In pursuit of high precision in target localization and steeper dose fall-off in stereotactic radiosurgery, we investigated the impact of optimizing dose-limiting auto-shell function on the quality of Cyberknife (CK) plans in treating brain metastases (BMs). Methods: Nineteen BMs previously treated using CK were selected for this study. The original CK plans (CK_original) had been produced using one to three dose-limiting auto-shells at prescription dose (PD) level and low dose levels of 10 to 30% of PD. In each case, a modified CK plan (CK_modified) was generated using five dose-limiting shells at PD level, intermediate dose level of 50% of PD, and low dose levels with an optimal shell-dilation size based on our experience. In addition, a Gamma Knife plan (GK) was also produced using the original contour set. Thus, a triplet data set of dosimetric parameters was generated and analyzed. Results: While no differences in conformity index (mean±SD 1.22 ± 0.1, 1.18 ± 0.1, and 1.24 ± 0.1 in CK_original, CK_modified, and GK, respectively; over all P > 0.05) and tumor coverage (mean±SD 99.5 ± 0.4%, 99.5 ± 0.3%, and 99.4 ± 0.2% in CK_original, CK_modified, and GK, respectively; over all P > 0.05) were observed among the plans, the normal tissue volume receiving 50% of PD was significantly decreased in CK_modified and GK compared with CKoriginal by 1.28 and 1.27-fold, respectively (P < 0.001, each). No significant differences in dose fall-off were observed between CK_modified and GK (P = 0.345). Conclusion: By optimizing auto-shell function, a significantly steeper dose fall-off can be achieved in CK system, while maintaining high precision in target localization.

Robust representation of shape in a Grey parrot (Psittacus erithacus)

A Grey parrot, Griffin (Psittacus erithacus), previously taught English labels for various colors and shapes with respect to three-dimensional (3D) stimuli, was tested on his ability to transfer to very different two-dimensional (2D) images consisting of modal and amodal completion stimuli. For modal completion (aka subjective contours), Kanizsa figures were constructed using black ‘pac-men’ to form regular polygons on colored paper. For amodal completion, portions of variously colored regular 2D polygons were occluded by black circles or other black figures. For each task, Griffin provided a vocal English shape label for five possible shapes designated by their vertices (one, two, three, four, six). His accuracy was high for both amodal completed figures, including probe stimuli (28/38 correct) and modally completed figures (29/38 correct), with chance=0.20. The modally completed case (i.e., Kanizsa subjective figures) is of particular importance as there are no shared image parts between training and testing stimuli. We draw several conclusions from these results. First, a surface level completion process is fully operative insofar as Griffin was able to correctly identify shapes that differed considerably from training images. Second, because parrots can generalize from shapes of real objects to drawings where original image contours were clearly absent, the data provide a compelling example of shape invariance, indicating that visual shapes are processed far beyond that of their image description. Third, parrots with a repertoire of multiple vocal responses can be rigorously tested for visual competencies, an option as yet to be tried in other experimental animals.

The use of piezoelectric surgery to lateralize the inferior alveolar nerve with simultaneous implant placement and immediate buccal cortical bone repositioning: a prospective clinical study

A prospective study was conducted to assess a variation of inferior alveolar nerve (IAN) lateralization. This study included 13 patients. An osteotomy was made with a piezoelectric device, and the IAN bundle was moved buccally. Dental implants were then inserted medial to the nerve bundle, and the inner surface of the buccal cortical bone plate was shaped to reduce its thickness. Finally, the bone plate was repositioned to restore the original shape and contour of the mandible. Neurosensory examinations of the lower lip and chin were performed using three tests: light touch, pain, and two-point discrimination. Three months after surgery, the function of the IAN was judged to be completely restored at 11 of the 13 surgical sites. Differences in the tests comparing the operated and non-operated sides were not significant. No implants were lost, and all patients were satisfied with the result. Although IAN lateralization in conjunction with dental implant placement is rarely indicated, the use of a piezoelectric device to perform a buccal osteotomy with final repositioning of the buccal cortical plate over the bony defect contributes to the recovery of the contour and shape of the mandible, without impairment of IAN function.

Corpus-Based Hidden Markov Modelling of the Fundamental Frequency of Lithuanian

This paper presents the corpus-driven approach in building the computational model of fundamental frequency, or F0, for Lithuanian language. The model was obtained by training the HMM-based speech synthesis system HTS on six hours of speech coming from multiple speakers. Several gender specific models, using different parameters and different contextual factors, were investigated. The models were evaluated by synthesizing F0 contours and by comparing them to the original F0 contours using criteria of root mean square error (RMSE) and voicing classification error. The HMM-based models showed an improvement of the RMSE over the mean-based model that predicted F0 of the vowel on the basis of its average normalized pitch.

Parameter-sparse modification of Fourier methods to analyse the shape of closed contours with application to otolith outlines

Elliptical Fourier descriptors (EFDs) have been used extensively in shape analysis of closed contours and have a range of marine applications, such as automatic identification of fish species and discrimination between fish stocks based on EFDs of otolith contours. A recent method (the ‘MIRR’ method) transforms the two-dimensional contour to a one-dimensional function by mirroring (reflecting) the lower half of the contour around a vertical axis at the right end of the contour. MIRR then applies the fast Fourier transform (FFT) to the vertical contour points corresponding to equidistant coordinate values along the horizontal axis. MIRR has the advantage of reducing the number of Fourier coefficients to two coefficients per frequency component compared with four EFDs. However, both Fourier methods require several frequency components to reproduce a pure ellipse properly. This paper shows how the methods can be easily modified so that a virtually perfect reproduction of a pure ellipse is obtained with only one frequency component. In addition, real otolith examples for cod (Gadus morhua) and Greenland halibut (Reinhardtius hippoglossoides) are used to demonstrate that the modified methods give better approximations to the large-scale shape of the original contour with fewer coefficients than the traditional Fourier methods, with negligible additional computing time.

Soil biochemical properties in brown and gray mine soils with and without hydroseeding

Abstract. Surface coal mining in the eastern USA disturbs hundreds of hectares of land every year and removes valuable and ecologically diverse eastern deciduous forests. Reclamation involves restoring the landscape to approximate original contour, replacing the topsoil, and revegetating the site with trees and herbaceous species to a designated post-mining land use. Re-establishing an ecosystem of ecological and economic value as well as restoring soil quality on disturbed sites are the goals of land reclamation, and microbial properties of mine soils can be indicators of restoration success. Reforestation plots were constructed in 2007 using weathered brown sandstone or unweathered gray sandstone as topsoil substitutes to evaluate tree growth and soil properties at Arch Coal's Birch River mine in West Virginia, USA. All plots were planted with 12 hardwood tree species and subplots were hydroseeded with a herbaceous seed mix and fertilizer. After 6 years, the average tree volume index was nearly 10 times greater for trees grown in brown (3853 cm3) compared to gray mine soils (407 cm3). Average pH of brown mine soils increased from 4.7 to 5.0, while gray mine soils declined from 7.9 to 7.0. Hydroseeding doubled tree volume index and ground cover on both mine soils. Hydroseeding doubled microbial biomass carbon (MBC) on brown mine soils (8.7 vs. 17.5 mg kg−1), but showed no effect on gray mine soils (13.3 vs. 12.8 mg kg−1). Hydroseeding also increased the ratio of MBC to soil organic C in both soils and more than tripled the ratio for potentially mineralizable nitrogen (PMN) to total N. Brown mine soils were a better growth medium than gray mine soils and hydroseeding was an important component of reclamation due to improved biochemical properties and microbial activity in mine soils.

Методика трехмерного моделирования земной поверхности

Abstract: At the present stage of development of cartography much attention is paid to the transition to three-dimensional mapping of the earth’s surface and the presentation of the territory and objects on it in the 3D-models. The process of three-dimensional maps has several ways of re-establishment of the survey data or data of terrestrial laser scanning or remote sensing, transmission and preparation of 2D-maps, materials. Proposed methods of creation of digital 3D-models of the Earth’s surface using a software package Engage 3D-Professional. This article also discussed different methods of interpolation of heights: – the method «triangulation»; method «spatial neighborhood»; method «minimum curvature» When compared with the original contours the best approximation to the original contours for the conditions of this experiment is achieved by applying the method «spatial neighborhood». The use of this technology allows you to create 3D-maps much faster than compiling them again on the basis of the collected information. Are technological sequence of action figures and tables illustrating the essence of the proposed solution.

Cultural Transformation in the Lingua-didactical Dimension

The concept of “culture” is viewed from a lingua-didactical position as transformation of cultural facts with original contours, specific content and distinctive features, such as: transformation of cultural facts relevant to the cultural approach to teaching foreign languages; transformation of cultural facts of the target language's country; transformation of students’ country cultural facts; transformation of the facts of two contacting cultures which are characteristic for the teaching of foreign social-bicultural competence. Relative-comparative analysis of cultural transformations is described as the teaching method for the formation of foreign language social-bicultural competence.

Reduced Multi-class Contour Preserving Classification

This research presents the augmentation of the original contour preserving classification technique to support multi-class data and to reduce the number of synthesized vectors, called multi-class outpost vectors (MCOVs). The technique has been proven to function on both synthetic-problem data sets and real-world data sets correctly. The technique also includes three methods to reduce the number of MCOVs by using minimum vector distance selection between fundamental multi-class outpost vectors and additional multi-class outpost vectors to select only MCOVs located at the decision boundary between consecutive classes of data. The three MCOV reduction methods include the FF-AA reduction method, the FA-AF reduction method, and the FAF-AFA reduction method. An evaluation has been conducted to show the reduction capability, the contour preservation capability, and the levels of classification accuracy of the three MCOV reduction methods on both non-overlapping and highly overlapping synthetic-problem data sets and highly overlapping real-world data sets. For non-overlapping problems, the experimental results present that the FA-AF reduction method can partially reduce the number of MCOVs while preserving the contour of the problem most accurately and obtaining similar levels of classification accuracy as when the whole set of MCOVs is used. For highly overlapping problems, the experimental results present that the FF-AA reduction method can partially reduce the number of MCOVs while preserving the contour of the problem most accurately and obtaining similar levels of classification accuracy as when the whole set of MCOVs is used.

MO‐F‐CAMPUS‐J‐05: Using 2D Relative Gamma Analysis From EPID Image as a Predictor of Plan Deterioration Due to Anatomical Changes

Purpose:One of the side effects of radiotherapy for head and neck (H&amp;N) cancer is the patient's anatomical changes. The changes can strongly affect the planned dose distribution. In this work, our goal is to demonstrate that relative analysis of EPID images is a fast and simple method to detect anatomical changes that can have a strong dosimetric impact on the treatment plan for H&amp;N patients.Methods:EPID images were recorded at every beam and all fractions for 50 H&amp;N patients. Of these, five patients that showed important anatomical changes were selected to evaluate dosimetric impacts of these changes and to correlate them with a 2D relative gamma analysis of EPID images. The planning CT and original contours were deformed onto CBCTs (one mid treatment and one at the end of treatment). By using deformable image registration, it was possible to map accurate CT numbers from the planning CT to the anatomy of the day obtained with CBCTs. Clinical treatment plan were then copied on the deformed dataset and dose was re‐computed. In parallel, EPID images were analysed using the gamma index (3%3mm) relative to the first image.Results:It was possible to divide patients in two distinct, statistically different (p&lt;0.001) categories using an average gamma index of 0.5 as a threshold. Below this threshold no significant dosimetric degradation of the plan are observed. Above this threshold two types of plan deterioration were seen: (1) target dose increases, but coverage remains adequate while dose to at least one OAR increases beyond tolerances; (2) the OAR doses remain low, but the target dose is reduced and coverage becomes inadequate.Conclusion:Relative analysis gamma of EPID images could indeed be a fast and simple method to detect anatomical changes that can potentially deteriorates treatment plan for H&amp;N patients.This work was supported in part by Varian Medical System

SU-E-J-108: Solving the Chinese Postman Problem for Effective Contour Deformation

Purpose: To develop a practical approach for accurate contour deformation when deformable image registration (DIR) is used for atlas-based segmentation or contour propagation in image-guided radiotherapy. Methods: A contour deformation approach was developed on the basis of 3D mesh operations. The 2D contours represented by a series of points in each slice were first converted to a 3D triangular mesh, which was deformed by the deformation vectors resulting from DIR. A set of parallel 2D planes then cut through the deformed 3D mesh, generating unordered points and line segments, which should be reorganized into a set of 2D contour points. It was realized that the reorganization problem was equivalent to solving the Chinese Postman Problem (CPP) by traversing a graph built from the unordered points with the least cost. Alternatively, deformation could be applied to a binary mask converted from the original contours. The deformed binary mask was then converted back into contours at the CT slice locations. We performed a qualitative comparison to validate the mesh-based approach against the image-based approach. Results: The DIR could considerably change the 3D mesh, making complicated 2D contour representations after deformation. CPP was able to effectively reorganize the points in 2D planes no matter how complicated the 2D contours were. The mesh-based approach did not require a post-processing of the contour, thus accurately showing the actual deformation in DIR. The mesh-based approach could keep some fine details and resulted in smoother contours than the image-based approach did, especially for the lung structure. Image-based approach appeared to over-process contours and suffered from image resolution limits. The mesh-based approach was integrated into in-house DIR software for use in routine clinic and research. Conclusion: We developed a practical approach for accurate contour deformation. The efficiency of this approach was demonstrated in both clinic and research applications. This work was partially supported by Cancer Prevention & Research Institute of Texas (CPRIT) RP110562.