Aperture Weight Research Articles

Adaptive complementary neighboring sub-aperture beamforming for thermoacoustic imaging.

When applied to thermoacoustic imaging (TAI), the delay-and-sum (DAS) algorithm produces strong sidelobes due to its disadvantages of uniform aperture weighting. As a result, the quality of TAI images recovered by DAS is often severely degraded by strong non-coherent clutter, which restricts the development and application of TAI. To address this issue, we propose an adaptive complementary neighboring sub-aperture (NSA) beamforming algorithm for TAI. In NSA, we introduce a coordinate system transformation when calculating the normalized cross-correlation (NCC) matrix. This approach enables the computation of the NCC coefficient within the specified kernel without complex coordinate calculations. We first conducted the numerical simulation experiment to validate NSA using a tree branch phantom. In addition, we also conducted phantom (five sauce tubes), ex vivo (ablation needle in ex vivo porcine liver), and in vivo (human arm) TAI experiments using our TAI system with a center frequency of 3GHz. In the numerical simulation experiment, the structural similarity index (SSIM) value for NSA is increased from 0.37828 for DAS to 0.75492. In the point target phantom TAI experiment, the generalized contrast-to-noise ratio (gCNR) value for NSA is increased from 0.936 for DAS to 0.962. The experimental results show that NSA can recover clearer thermoacoustic images compared to DAS. In the ex vivo TAI experiment, the full width at half maxima (FWHM) of an ablation needle (diameter=1.5mm) for coherence factor (CF) weighted DAS and NSA are 0.9 and 1.3mm, respectively. Furthermore, in the in vivo TAI experiment, CF reduces the signals within the arm compared to NSA. Therefore, compared with CF, NSA can maintain the integrity of target information in TAI while effectively suppressing non-coherent background clutter. NSA can effectively reduce non-coherent background noise while ensuring the completeness of the target information. So, NSA offers the potential to provide high-quality thermoacoustic images and further advance their clinical application.

Form-finding and shape adjustment of cable-membrane reflectors

Cable-membrane reflector is a highly nonlinear flexible structure, which can represent a specific surface shape under the proper combination of cable tension and membrane stress. AstroMesh reflector is a representative of cable membrane reflector, which has advantages of large aperture, easy folding, and light weight, and is increasingly utilized in space antenna reflectors. In this paper, a finite element model of the cable-membrane structure is established together with the corresponding incremental equilibrium equation which provides the sensitivity of the nodal position with respect to the geometric parameter of the cables and triangular membranes. A form-finding strategy is detailed, which aims at a configuration with the reflector nodes locating on a specified paraboloid while all cables and membranes are tensioned uniformly as possible. In addition, the surface precision of the reflector is reduced due to the inevitable errors in the manufacturing process. Therefore, the tension ties in the cable network is designed to be adjustable to solve this problem. Carefully changing the length of these cables can increase the reflector surface precision, which is referred as shape adjustment. An adjustment strategy with model updating is proposed. The model updating using the measured positions of the reflector nodes can dramatically reduce the discrepancy of the finite element model with respect to the actual reflector, thus remarkably improving the efficiency of shape adjustment. Numerical example and physical experiment demonstrate the effectiveness of the proposed method.

High-frame-rate limited-diffraction beam imaging

Limited-diffraction beams such as Bessel beam, X wave, and array beam are a class of beams that in theory do not spread as they propagate to infinite distance. When realized with a finite aperture, these beams have a large depth of field. In this paper, limited-diffraction beams and their applications to high-frame rate imaging are reviewed and further studied. Using a limited-diffraction beams (in either transmission or reception, or both, or with spatial Fourier transform of received signals), images can be reconstructed in Fourier domain. This significantly reduces the amount of computation in 3D imaging since FFT can be used. As the bandwidth of the transducer is increased, the image reconstructed can cover a larger field of view since a frequency in limited-diffraction beam corresponds to one angular direction of the beam (similar to the “frequency encoding” in the magnetic resonance imaging or MRI). Using the angular dependence with frequency, focused limited-diffraction beams can be used for high-frame-rate and high-resolution tissue property imaging. When limited-diffraction beams are used in transmissions, no time delay (only amplitude weighting) is needed, which simplifies imaging system hardware. Also, flow vector imaging can be obtained with limited-diffraction beams using sine and cosine (quadrature) aperture weighting.

Thermal-Structural Analysis of the Support Structure for a Modular Space Deployable Antenna

A modular space deployable antenna has the advantages of extensibility, adaptability, and versatility, which is an ideal structure to meet the development trend of large aperture, high precision, and light weight for the deployable antenna in the future. To date, there are few reports on the temperature response of a modular deployable antenna in the thermal alternating environment in orbit. The aim of this study is at investigating the influence of a modular deployable antenna support structure on the surface accuracy and stability under the space thermal alternating environment. For this purpose, the thermal-structure analysis of the deployable antenna support structure was carried out by ANSYS APDL finite-element software. Using the transient temperature field obtained by thermal analysis as the boundary condition, the coupling law of stress development and thermal deformation of the support chord and cable caused by the antenna structure constraint position and other parameters is analyzed. In a uniform thermal field, the thermal stress of cables in the central module of the structure is the highest and that of the chord components in the same-circle modules is essentially the same. The thermally stress of the upper chords increases progressively toward the outer module, whereas that of cables decreases in the same direction. The thermal deformation at the upper-layer centroid of the structure can reach about 15 mm, so the influence on the accuracy of the antenna cannot be ignored. When the splicing vertical rod of adjacent modules in the outermost of the support structure is taken as the constraint connecting with the extension arm, the thermal deformation of the structure is minimum. The heat-insulating composite coating should be adopted on the surface of the antenna structure to reduce the thermal deformation and improve the adaptability. The thermal-structural analysis model proposed in this study could accurately estimate the behaviour of thermal deformation for the modular space deployable antenna, but the further coupling condition of the nonuniform temperature field could still be conducted. The results can provide a reference for the basic theory and engineering application of thermal-structural analysis for extralarge-aperture modular deployable antennas in the future.

A sparse orthogonal collimator for small animal intensity-modulated radiation therapy part I: Planning system development and commissioning.

To achieve more translatable preclinical research results, small animal irradiation needs to more closely simulate human radiotherapy. Although the clinical gold standard is intensity-modulated radiation therapy (IMRT), the direct translation of this method for small animals is impractical. In this study we describe the treatment planning system for a novel dose modulation device to address this challenge. Using delineated target and avoidance structures, a rectangular aperture optimization (RAO) problem was formulated to penalize deviations from a desired dose distribution and limit the number of selected rectangular apertures. RAO was used to create IMRT plans with highly concave targets in the mouse brain, and the plan quality was compared to that using a hypothetical miniaturized multileaf collimator (MLC). RAO plans were also created for a realistic application of mouse whole liver irradiation and for a highly complex two-dimensional (2D) dose distribution as a proof-of-principle. Beam commissioning data, including output and off-axis factors and percent depth dose (PDD) curves, were acquired for our small animal irradiation system and incorporated into the treatment planning system. A plan post-processing step was implemented for aperture size-specific dose recalculation and aperture weighting reoptimization. The first RAO test case achieved highly conformal doses to concave targets in the brain, with substantially better dose gradient, conformity, and target dose homogeneity than the hypothetical miniaturized MLC plans. In the second test case, a highly conformal dose to the liver was achieved with significant sparing of the kidneys. RAO also successfully replicated a complex 2D dose distribution with three prescription dose levels. Energy spectra for field sizes 1 to 20mm were calculated to match the measured PDD curves, with maximum and mean dose deviations of 4.47±0.30% and 1.71±0.18%. The final reoptimization of aperture weightings for the complex RAO test plan was able to reduce the maximum and mean dose deviations between the optimized and recalculated dose distributions from 10.3% to 6.6% and 4.0% to 2.8%, respectively. Using the advanced optimization techniques, complex IMRT plans were achieved using a simple dose modulation device. Beam commissioning data were incorporated into the treatment planning process to more accurately predict the resulting dose distribution. This platform substantially reduces the gap in treatment plan quality between clinical and preclinical radiotherapy, potentially increasing the value and flexibility of small animal studies.

Near-field phase modulation using a semicircular radially gradient metasurface for beam steering of an RF antenna

A semicircular radially gradient metasurface (SCRGM) structure is proposed to modulate the phase of the electric field of a radiofrequency (RF) antenna in the near field. The metasurface partially covers the antenna aperture, thus facilitating tilting of the beam in the elevation plane (E-plane). In the proposed configuration, the phase modulation capability of the radially gradient metasurface is utilized in combination with a semicircular superstrate made of low-dielectric-constant material, placed at a height of $$0.17 \lambda _0$$ above and parallel to the antenna aperture. Firstly, the broadside beam of the patch antenna is tilted away from the normal direction by the phase modulation of the electric field over the aperture of the antenna. Beam steering in the E-plane is achieved by in-plane translation of the SCRGM in front of a stationary primary feed antenna, further modulating the phase. The aperture area and weight of the proposed SCRGM are $$3.77\lambda _0^2$$ and 22.0 g, respectively. The compact antenna structure with integrated SCRGM offers $$-45^{\circ }$$ to $$+45^{\circ }$$ beam steering in the E-plane with reasonably constant gain in the range of 10–11 dBi (with scan loss better than 1 dB). The strategy of partially covering the antenna aperture and further translating the radially gradient metasurface enables a considerably wide beam scanning range using a compact configuration.

AESA 레이더 능동위상배열 안테나의 배열오차 분석 및 보정

본 논문에서는 항공기 레이더에 적용 가능한 능동배열 안테나의 배열오차 분석 및 보정에 대한 시험 결과를 기술하였다. 복사소자, TR 모듈, 급전기 등으로 구성되는 배열소자 간의 크기 및 위상오차는 안테나 부엽 준위에 영향을 미치며, 이는 안테나 개구면 weighting에 따른 이상적인 부엽레벨, 배열소자 개수, 안테나 효율 등에 의해 그 민감도가 달라진다. 시스템에서 요구되는 부엽준위를 만족시키기 위해서는 배열소자의 오차 보정이 반드시 이루어져야 한다. 그 방법은 오차요소에 따라 다르게 적용되어야 하며, 안테나 형태, 목표 부엽 준위에 따라 고려되는 수준의 차이가 달리 적용되어야 한다. 본 논문에서는 배열오차 요소와 그 영향에 대해 분석하였으며, 오차 보정 방안을 제시하였다. 또한, 근접 전계 시험을 통해 그 결과를 확인하였다. Array error analysis and correction of active array antenna are described in this paper. Array elements composed of radiator and TR(Transmit & Recive) module have error(magnitude and phase difference among array elements) which affects SLL(Side Lobe Level). Error affectedness level depends on ideal SLL according to antenna aperture weighting, number of array elements and antenna effective aperture. To satisfy required SLL, correction of array elements is necessary; adopted differently per errors, and weighted differently per shapes of antenna and required SLL. Errors of every individual element had been defined, performance of the antenna with or without error correction had been estimated and proved through near field test.

Simultaneous beam sampling and aperture shape optimization for SPORT.

Station parameter optimized radiation therapy (SPORT) was recently proposed to fully utilize the technical capability of emerging digital linear accelerators, in which the station parameters of a delivery system, such as aperture shape and weight, couch position/angle, gantry/collimator angle, can be optimized simultaneously. SPORT promises to deliver remarkable radiation dose distributions in an efficient manner, yet there exists no optimization algorithm for its implementation. The purpose of this work is to develop an algorithm to simultaneously optimize the beam sampling and aperture shapes. The authors build a mathematical model with the fundamental station point parameters as the decision variables. To solve the resulting large-scale optimization problem, the authors devise an effective algorithm by integrating three advanced optimization techniques: column generation, subgradient method, and pattern search. Column generation adds the most beneficial stations sequentially until the plan quality improvement saturates and provides a good starting point for the subsequent optimization. It also adds the new stations during the algorithm if beneficial. For each update resulted from column generation, the subgradient method improves the selected stations locally by reshaping the apertures and updating the beam angles toward a descent subgradient direction. The algorithm continues to improve the selected stations locally and globally by a pattern search algorithm to explore the part of search space not reachable by the subgradient method. By combining these three techniques together, all plausible combinations of station parameters are searched efficiently to yield the optimal solution. A SPORT optimization framework with seamlessly integration of three complementary algorithms, column generation, subgradient method, and pattern search, was established. The proposed technique was applied to two previously treated clinical cases: a head and neck and a prostate case. It significantly improved the target conformality and at the same time critical structure sparing compared with conventional intensity modulated radiation therapy (IMRT). In the head and neck case, for example, the average PTV coverage D99% for two PTVs, cord and brainstem max doses, and right parotid gland mean dose were improved, respectively, by about 7%, 37%, 12%, and 16%. The proposed method automatically determines the number of the stations required to generate a satisfactory plan and optimizes simultaneously the involved station parameters, leading to improved quality of the resultant treatment plans as compared with the conventional IMRT plans.

Recovering a Function from Circular Means or Wave Data on the Boundary of Parabolic Domains

Determining a function from its circular means with restricted centers is crucial for many modern medical imaging and remote sensing applications. Examples include photo- and thermoacoustic tomography, ultrasound imaging, and synthetic aperture radar. In this paper we derive an explicit inversion formula for the case where the centers of the circles of integration are restricted to the boundary of parabolic domains. A similar result is obtained for recovering the initial data of the wave equation from data on the boundary of a parabolic domain. These results show that the universal back-projection formulas, previously known to be exact for half-spaces, discs, and ellipsoids, are also exact for parabolic domains. We further present numerical simulations supporting our theoretical results. There, we also include two previously proposed strategies (dynamic aperture length correction and weight factor correction) accounting for the truncation of the parabola in practical applications.

SU‐E‐T‐295: Simultaneous Beam Sampling and Aperture Shape Optimization for Station Parameter Optimized Radiation Therapy (SPORT)

Purpose:Station Parameter Optimized Radiation Therapy (SPORT) was recently proposed to fully utilize the technical capability of emerging digital LINACs, in which the station parameters of a delivery system, (such as aperture shape and weight, couch position/angle, gantry/collimator angle) are optimized altogether. SPORT promises to deliver unprecedented radiation dose distributions efficiently, yet there does not exist any optimization algorithm to implement it. The purpose of this work is to propose an optimization algorithm to simultaneously optimize the beam sampling and aperture shapes.Methods:We build a mathematical model whose variables are beam angles (including non‐coplanar and/or even nonisocentric beams) and aperture shapes. To solve the resulting large scale optimization problem, we devise an exact, convergent and fast optimization algorithm by integrating three advanced optimization techniques named column generation, gradient method, and pattern search. Column generation is used to find a good set of aperture shapes as an initial solution by adding apertures sequentially. Then we apply the gradient method to iteratively improve the current solution by reshaping the aperture shapes and updating the beam angles toward the gradient. Algorithm continues by pattern search method to explore the part of the search space that cannot be reached by the gradient method.Results:The proposed technique is applied to a series of patient cases and significantly improves the plan quality. In a head‐and‐neck case, for example, the left parotid gland mean‐dose, brainstem max‐dose, spinal cord max‐dose, and mandible mean‐dose are reduced by 10%, 7%, 24% and 12% respectively, compared to the conventional VMAT plan while maintaining the same PTV coverage.Conclusion:Combined use of column generation, gradient search and pattern search algorithms provide an effective way to optimize simultaneously the large collection of station parameters and significantly improves quality of resultant treatment plans as compared with conventional VMAT or IMRT treatments.

Beam controlled arc therapy–a delivery concept for stationary targets

Volumetric modulated arc therapy (VMAT) presupposes that it is beneficial to deliver radiation from all beam angles as the gantry rotates, requiring the multi-leaf collimator to maintain continuity in shape from one angle to another. In turn, radiation from undesirable beam angles could compromise the dose distribution. In this work, we challenge the notion that the radiation beam must be held on as the gantry rotates around the patient. We propose a new approach for delivering intensity-modulated arc therapy, beam-controlled arc therapy (BCAT), during which the radiation beam is controlled on or off and the dose rate is modulated while the gantry rotates around the patient. We employ linear-programming-based dose optimization to each aperture weight, resulting in some zero weight apertures. During delivery, the radiation beam is held off at control points with zero weights as the MLC shape transits to the next non-zero weight shape. This was tested on ten head and neck cases. Plan quality and delivery efficiency were compared with VMAT. Improvements of up to 17% (p-value 0.001) and 57% (p-value 0.018) in organ-at-risk sparing and target dose uniformity, respectively, were achieved. Compared to the fixed number of apertures used in single-arc and double-arc VMAT, the BCAT used 109 and 175 apertures on average, respectively. The difference in total MUs for VMAT and BCAT plans was less than 4%. Plan quality improvement was confirmed after delivery with γ analysis resulting in over 99% agreement, or 4 in 1099 points that failed.

GPU-Based Real-Time Volumetric Ultrasound Image Reconstruction for a Ring Array

Synthetic phased array (SPA) beamforming with Hadamard coding and aperture weighting is an optimal option for real-time volumetric imaging with a ring array, a particularly attractive geometry in intracardiac and intravascular applications. However, the imaging frame rate of this method is limited by the immense computational load required in synthetic beamforming. For fast imaging with a ring array, we developed graphics processing unit (GPU)-based, real-time image reconstruction software that exploits massive data-level parallelism in beamforming operations. The GPU-based software reconstructs and displays three cross-sectional images at 45 frames per second (fps). This frame rate is 4.5 times higher than that for our previously-developed multi-core CPU-based software. In an alternative imaging mode, it shows one B-mode image rotating about the axis and its maximum intensity projection, processed at a rate of 104 fps . This paper describes the image reconstruction procedure on the GPU platform and presents the experimental images obtained using this software.

Volumetric real-time imaging using a CMUT ring array

A ring array provides a very suitable geometry for forward-looking volumetric intracardiac and intravascular ultrasound imaging. We fabricated an annular 64-element capacitive micromachined ultrasonic transducer (CMUT) array featuring a 10-MHz operating frequency and a 1.27-mm outer radius. A custom software suite was developed to run on a PC-based imaging system for real-time imaging using this device. This paper presents simulated and experimental imaging results for the described CMUT ring array. Three different imaging methods--flash, classic phased array (CPA), and synthetic phased array (SPA)--were used in the study. For SPA imaging, two techniques to improve the image quality--Hadamard coding and aperture weighting--were also applied. The results show that SPA with Hadamard coding and aperture weighting is a good option for ring-array imaging. Compared with CPA, it achieves better image resolution and comparable signal-to-noise ratio at a much faster image acquisition rate. Using this method, a fast frame rate of up to 463 volumes per second is achievable if limited only by the ultrasound time of flight; with the described system we reconstructed three cross-sectional images in real-time at 10 frames per second, which was limited by the computation time in synthetic beamforming.

Total-Variation Regularization Based Inverse Planning for Intensity Modulated Arc Therapy

Intensity modulated arc therapy (IMAT) delivers conformal dose distributions through continuous gantry rotation with constant or variable speed while modulating the field aperture shape and weight. The enlarged angular space and machine delivery constraints make inverse planning of IMAT more intractable as compared to its counterpart of fixed gantry IMRT. Currently, IMAT inverse planning is being done using two extreme methods: the first one computes in beamlet domain with a subsequent arc leaf sequencing, and the second proceeds in machine parameter domain with entire emphasis placed on a pre-determined delivery method without exploring potentially better alternative delivery schemes. Towards truly optimizing the IMAT treatment on a patient specific basis, in this work we propose a total-variation based inverse planning framework for IMAT, which takes advantage of the useful features of the above two existing approaches while avoiding their shortcomings. A quadratic optimization algorithm has been implemented to demonstrate the performance and advantage of the proposed approach. Applications of the technique to a prostate case and a head and neck case indicate that the algorithm is capable of generating IMAT plans with patient specific numbers of arcs efficiently. Superior dose distributions and delivery time are achieved with a maximum number of apertures of three for each field. As compared to conventional beamlet-based algorithms, our method regularizes the field modulation complexity during optimization, and permits us to obtain the best possible plan with a pre-set modulation complexity of fluences. As illustrated in both prostate and head-and-neck case studies, the proposed method produces more favorable dose distributions than the segment-based algorithms, by optimally accommodating the clinical need of intensity modulation levels for each individual field. On a more fundamental level, our formulation preserves the convexity of optimization and makes the search of the global optimal solution possible with a deterministic method.

TU-A-BRB-05: Beam Controlled Arc Therapy: A Novel Delivery Concept for Stationary Targets

Purpose: To challenge the notion that the radiation beam must be held on as the gantry rotates around the patient and to describe a new approach for delivering intensity modulated arc therapy, beam‐controlled arc therapy (BCAT), during which the radiation beam is controlled on or off and the dose rate is modulated.Methods: Conventional IMAT presupposes that it is beneficial to deliveryradiation from all beam angles as the gantry rotates, requiring the MLC to maintain continuity in shape from one angle to another. In turn, radiation from undesirable beam angles compromises the dose distribution. We propose a new approach to IMAT, BCAT, in which the radiation beam is held on or off and the dose rate is modulated while the gantry rotates around the patient. We employ linear‐programming‐based dose optimization to each aperture weight, resulting in some zero weight apertures. During delivery, the radiation beam is held off at control points with zero weights as the MLC shape transits to the next non‐zero weight shape. This was tested on 10 head and neck cases. Plan quality and delivery efficiency were compared with conventional IMAT.Results: Improvements in OAR sparing and target dose uniformity at dose/volume constraint levels were up to 18% (p‐value 0.002) and 67% (p‐value 0.04) respectively. Comparing to 180 and 360 apertures used in single‐arc and double‐arc IMAT plans, BCAT used 98 and 170 apertures on average respectively. The difference of total MUs used for IMAT and BCAT plans was less than 4%. Although BCAT resulted in a significant number of control points having zero MUs associated with them, the delivery times were comparable. Conclusions: Our results demonstrate that the BCAT approach, which allows the radiation beam to be controlled on and off, yields superior dosimetric results relative to the conventional IMAT while maintaining the delivery efficiency. NIH grant CA130814

Inverse planning for four‐dimensional (4D) volumetric modulated arc therapya)

To develop a 4D volumetric modulated arc therapy (VMAT) inverse planning framework. 4D VMAT inverse planning aims to derive an aperture and weight modulated arc therapy treatment plan that optimizes the accumulated dose distribution from all gantry angles and breathing phases. Under an assumption that the gantry rotation and patient breathing are synchronized (i.e., there is a functional relationship between the phase of the patient breathing cycle and the beam angle), the authors compute the contribution from different respiration phases through the registration of the phased CT images. The accumulative dose distribution is optimized by iteratively adjusting the aperture shape and weight of each beam through the minimization of the planning objective function. For comparison, traditional 3D VMAT plans are also performed for the two cases and the performance of the proposed technique is demonstrated. A framework for 4D VMAT inverse planning has been proposed. With the consideration of the extra dimension of time in VMAT, a tighter target margin can be achieved with a full duty cycle, which is otherwise not achievable simultaneously by either 3D VMAT optimization or gated VMAT. The 4D VMAT planning formulism proposed here provides useful insight on how the "time" dimension can be exploited in rotational arc therapy to maximally compensate for the intrafraction organ motion.

Relative Growth and Reproduction in Tunisian Populations ofHexaplex trunculuswith Contrasting Imposex Levels

The banded murex Hexaplex trunculus was sampled at Menzel Jemil and Bizerta Channel (Bizerta Lagoon, northern Tunisia) to study imposex, growth, and reproduction. Butyltin concentrations were analyzed in females from the 2 sampling sites using the gas chromatographic flame photometric detection technique. Results showed that the Bizerta Channel population was severely affected by imposex, which was confirmed by the high level of butyltins recorded in females from this site. Growth in shell width and shell weight was higher in Bizerta Channel, whereas growth in shell aperture and flesh weight was favored in Menzel Jemil. The assessment of reproductive activity, made by calculating fecundity and using 2 condition indices, showed that the Menzel Jemil population was reproductively more active.

SU‐FF‐T‐79: Dosimetric QA Tests of An Online Replanning Technique for Prostate Adaptive Radiotherapy

Purpose: We have previously developed an online replanning technique to be completed within 8 minutes. In preparation for its clinical implementation, a comprehensive QA test was performed to ensure its dosimetric accuracy and operational efficiency. Method and Materials: The newly developed online replanning technique based on fast aperture morphing and weight optimization has been integrated into a planning system (Prowess). Daily CTs acquired using a CT‐on‐Rails (Siemens) of 3 randomly selected fractions for each of 5 representative prostate cancer cases were used to generate 15 daily plans in total. An independent MU calculation tool (RadCalc) was used to verify the MU numbers. All daily plans were delivered and measured with a 2D diode array (MapCheck). Results: The time required for the entire replanning process starting from loading daily CT to getting the daily plan ready for delivery were less than 8 minutes, comparable to the time of the current IGRT repositioning procedure. The average time required for generating contours of prostate, rectum and bladder, aperture morphing and weight optimization, plan review, and transferring into the delivery system were 3, 2, 1, and 0.5 minutes, respectively. The agreement between MU numbers from RadCalc and from the online replanning tool remained the same as for the original plans and was acceptable (within 5%). The QA passing rates (the agreements between the measured and calculated dose distributions) for daily plans were equivalent to those for the original plans and were acceptable (within 95%). Conclusion: This new online replanning technique is dosiemtrically accurate and practically efficient. Since the daily adaptive plans are not drastically different from the original plan, a QA measurement may not be necessary. A clinical trial to test the feasibility and efficacy of this replanning technique for prostate cancer is being initiated.

SU-FF-T-167: A 3-Step Methodology-Cum-Algorithm for Fast Optimization of Beam Weights and Shapes in Aperture-Based IMRT

Purpose: We presented a 3‐step methodology‐cum‐algorithm that can perform a fast optimization of beam weights and shapes in aperture‐based IMRT.Method and Materials: In the presented work, we propose a “3‐step methodology‐cum‐algorithm” that can optimize beam weights & shapes at a fast pace in Aperture‐based IMRT. Step 1: the initial aperture angles & shapes are customized by the planner based on the patient anatomy. Step 2: the weights for these apertures are optimized by using Gaussian‐Elimination code along with few additional codes to avoid negative weights. Step 3: the optimum/final aperture shapes are derived by a feed back sub‐routine incorporated in the Gaussian‐Elimination code. The feed back sub‐routine fine‐tunes the MLC positions in each aperture to improve the dose distribution further. During fine‐tuning of the aperture shape, the aperture weight is automatically updated with respect to the current shape of the aperture. The objective for steps 2 & 3 is to minimize the cost function below a pre‐set value. Moreover, step 3 is kept as an optional to save time in many patient cases. The principal feature of this algorithm is that the time taken for the optimization is very less, approximately of the order of few seconds, regardless of the complexity of the given case. Results: We tested this algorithm on a variety of patient cases using CMS XiO (4.3.1) planning system for beam placement & dose calculation. Also few cases have been treated using the algorithm in our department. The results obtained using the algorithm show that the number of segments and MUs are significantly reduced (upto 60% and 50% respectively), while providing dose distribution that is comparable to that of beamlet‐based IMRT plan obtained using KonRad® (2.2.23) inverse planning system. Conclusion: The results demonstrate that the proposed 3‐step methodology‐cum‐algorithm can be effectively used for clinical applications.

TU-D-BRC-07: An Online Replanning Technique with Deformation-Based Aperture Morphing and Weight Optimization

Purpose: We have previously proposed a fast online replanning method using contour‐based segment aperture morphing (SAM) and segment weight optimization (SWO), that was shown to be effective in correcting interfractional variations. Here we propose to enhance the replanning method by developing new SAM algorithm using deformation field. Methods: A new software tool was developed to incorporate the full 3D deformation field between the planning and daily CTs to morph the planed apertures based on the daily CT. The previously reported deformable registration algorithm based on a fast symmetric Demons method with the use of masks was utilized to generate the deformation vector field. The vector field was used to generate daily contours and to morph aperture shapes. The SWO was applied to further improve the dosimetry for the morphed apertures. The resulting doses were compared with those obtained with the full‐scope reoptimization (the golden standard), rigid‐body‐registration based repositioning (the current IGRT practice), and the previous contour‐based SAM. The new deformation‐based SAM and SWO process was tested for selected prostate cases with large daily organ deformation. Results: The deformable image registration took 1 minute, and the entire deformation‐based SAM and SWO process was completed within 5 minutes. The plans generated by the new deformation‐based SAM were considerably better than those from the repositioning, and were comparable to the contour‐based SAM. SWO further improved the plan quality, resulting in the final plans that are comparable to the full‐blown reoptimization plan. Conclusion: An algorithm using deformation field for aperture morphing was successfully developed and tested. The replanning process including the new algorithm is effective and can be completed within a reasonable timeframe (5–10 minutes) for practical implementation. The new replanning process can be fully automated and can effectively correct for interfraction errors, even for complex cases with multiple targets and overlapping critical structures.