Superposition Algorithm Research Articles

Research on Fuzzy Enhanced Learning Model of Multienhanced Signal Learning Automata

With the continuous iteration of information technology, information presents an explosive development trend, so how to effectively classify, retrieve, and summarize information is very important. Data classification and mining technology as the key technology to solve the aforementioned problems is of great significance. At present, in the fields of data processing, information classification and machine learning reinforcement learning, it is usually based on the learning automata, but the traditional learning automata algorithm cannot meet the development of information technology in terms of convergence and learning rate. In order to improve the convergence stability and learning efficiency of the learning automata algorithm in random environment and enhance its learning ability in dealing with large-scale space and action, this paper innovatively proposes an adaptive fuzzy reinforcement learning model of the learning automata, which makes full use of the randomness of gradient information to solve its stability problem, and abandons the original reinforcement learning method. For the linear function, an adaptive fuzzy numerical superposition algorithm is used to further enhance its learning rate and improve its stability. The experimental results show that the proposed learning automata fuzzy reinforcement learning model has practical application value, and can solve the problems of unstable convergence and poor learning efficiency of the current learning automata.

Effect of Bolus Frequency and Its Thickness in Postmastectomy Three-dimensional Conformal Radiotherapy on Skin Dose for Superposition Algorithm

Introduction: The postmastectomy radiotherapy uses bolus to improve the coverage close to the skin; however, it needs to be removed in case of severe skin toxicity. This study investigated the effect of bolus parameters (i.e., frequency and thickness) for the superposition algorithm on skin dose in postmastectomy three-dimensional conformal radiotherapy (3D-CRT). Material and Methods: The present study was carried out ona total of 22 patients. First, all the plans were calculated without using bolus. Then, the plans were recalculated using different bolus frequencies (5, 10, 15, 20, 25) and thicknesses (0.5 and 1 cm). To evaluate the dose delivered to the skin, a 2-mm thick skin was profiled, and statistical analysis was performed by studying the dosimetric parameters (i.e., minimum, mean, and maximum) of chest wall skin. Results: The superficial coverage of planning target volume (PTV) was better by using bolus. In the case of skin, the bolus thickness had a significant impact on the minimum and mean doses for all bolus frequencies , while there was no significant effect on the maximum before 20-bolus frequency. The bolus frequency increase demonstrated a significant difference on all dosimetric parameters of the skin , except the maximum showed no significant difference between 0 and 5-bolus frequencies . Conclusion: The obtained results indicated that the bolus use had generally a significant effect on the chest wall skin dosimetric parameters depending on bolus frequency and thickness. Therefore, the choice of bolus frequency and bolus thickness can affect the clinical decisions in certain cases.

Point Dose Measurement for Verification of Treatment Planning System using an Indigenous Heterogeneous Pelvis Phantom for Clarkson, Convolution, Superposition, and Fast Superposition Algorithms

Background: Nowadays, advanced radiotherapy equipment includes algorithms to calculate dose. The verification of the calculated doses is important to achieve accurate results. Mostly homogeneous dosimetric phantoms are available commercially which do not mimic the actual patient anatomy; therefore, an indigenous heterogeneous pelvic phantom mimicking actual human pelvic region has been used to verify the doses calculated by different algorithms. Objective: This study aims to compare the planed dose using different algorithms with measured dose using an indigenous heterogeneous pelvic phantom.Material and Methods: In this experimental study, various three dimensional conformal radiotherapy (3D-CRT) plans were made using different doses calculated by algorithms. The plans were delivered by medical linear accelerator and doses were measured by ion chamber placed in the indigenous pelvic phantom. Planned and measured doses were compared with together and analyzed. Results: The relative electron densities of different parts in the pelvic phantom were found to be in good agreement with that of actual pelvic parts, including bladder, rectum, fats and bones. The highest percentage deviations between planned and measured dose were calculated in the single field for Superposition algorithm (3.09%) and single field with 45˚wedge for Superposition (3.04%). The least percentage deviation was calculated in the opposite field for Convolution which was - 0.08%. The results were within the range of ±5% as recommended by International Commission on Radiation Units and Measurement. Conclusion: The cost-effective indigenous heterogeneous pelvic phantom has the density pattern similar to the actual pelvic region; thus, it can be used for routine patient-specific quality assurance.

Evaluation of Dose Calculation Algorithms Accuracy for Eclipse, PCRT3D, and Monaco Treatment Planning Systems Using IAEA TPS commissioning tests in a Heterogeneous Phantom

Introduction: The accuracy of dose calculation algorithm (DCA) is highly considered in the radiotherapy sequences. This study aims at assessing the accuracy of five dose calculation algorithms in tissue inhomogeneity corrections, based on the International Atomic Energy Agency TEC-DOC 1583. Material and Methods: A heterogeneous phantom was scanned using computed tomography and tests were planned on three-dimensional treatment planning systems (3D TPSs) based on IAEA TEC-DOC 1583.Doseswere measured for 6- and 18-MV photon beams with ion chambers and then the deviation between measured and calculated TPS doses were reported. The evaluated five DCAs include Monte Carlo (MC) algorithm employed by Monaco, pencil beam convolution (PBC) and anisotropic analytical algorithms (AAA) employed by Eclipse and Superposition (SP), and Clarkson algorithms employed by PCRT3D TPSs. Results: In Clarkson algorithm, low and high energy photons indicated 7.1% and 14.8% deviations out of agreement criteria, respectively. The SP, AAA, and PBC algorithms indicated 0.9%, 7.4%, and 13.8% for low energy photon and 9.5%, 21.3%, and 23.2% for high energy photon deviations out of agreement criteria, respectively. However, MC algorithm showed 1.8% and less than 1% deviations at high and low energy photons, respectively. Conclusion: The DCAs had different levels of accuracy in TPSs. Some simple DCAs, such as Clarkson, showed large deviations in some cases. Therefore, the transition to more advanced algorithms, such as MC would be desirable, particularly for the calculation in the presence of inhomogeneity or high energy beams.

Comparison of dose calculation algorithms model: Convolution, superposition, and fast superposition in 3-D Conformal Radiotherapy (3D-CRT) treatment plan

The important task of radiotherapy is to make sure that the radiation dose to the target tumour is accurate as prescribed and the dose to the organ at risk is minimized. Therefore, the aim of this study is to compare and evaluate the efficiency of the dose calculation algorithms: namely convolution, superposition, and fast superposition which installed in Treatment Planning System (TPS) (CMS XiO, USA). In this study, we modified protocols described in IAEATecdoc-1583, where four typical treatment techniques such as single field, multiple field, wedge field, and multi-leaf collimated (MLC) field were analysed from the system. The measurement data for calculated dose and measured dose were taken from thorax CIRS anthropomorphic phantom. The assessment of algorithms was done by comparing the point dose calculated with the measured dose. The study shows that the superposition algorithm produced relative error less than ± 3% which passed 100% of all reference points, whilst the convolution algorithm and fast superposition presented relative error more than ± 3% which passed 82% and 91% of reference points, respectively. In conclusion, the evaluation of radiotherapy treatment plan shall take into account the type of dose calculation algorithm model in order to optimize radiotherapy treatment and ensure the radiation safety to the patient.

Discrete dislocation dynamics algorithms and their application in modeling of plastic behaviors of crystalline materials

The plastic behaviors of crystalline materials are induced by the evolution of a series of dislocations. Discrete dislocation dynamics (DDD) can be used to model plastic deformation by taking into account the nucleation, annihilation, motion of dislocations, and formation of jogs, junctions, networks, and other dislocation structures directly. As a result, it can be used to investigate the physical correlation between material microstructures, dislocation structures, and plastic responses. It can also model the intrinsic size effect of plastic behaviors at the micron/submicron scales. Since its modeling scale is much larger than that of the microscopic molecular dynamics but is smaller than that of the macroscopic finite element method (FEM), DDD plays a connecting link role in multiscale modeling. In the present manuscript, three categories of DDD schemes, i.e., the DDD-FEM superposition algorithm, the DDD-FEM direct coupling algorithm, and DDD-extended FEM (XFEM) coupling algorithm, are further developed and optimized. In the DDD-FEM superposition algorithm, the consideration of dislocation climb is specifically included to take into account the high-temperature effect. In the DDD-FEM direct coupling algorithm, the so-called virtual dislocations are introduced to distribute the Eigen plastic strain by dislocation evolution to the FEM module more appropriately, and a special scheme is developed to calculate the Peach-Koehler force on the dislocation efficiently. To model the problems with strong or weak interfaces (such as cracks, voids, particles, and grain boundaries), the scheme coupling the DDD and XFEM, which is not sensitive to the finite element mesh, is further developed carefully. Each of these three DDD schemes has its own special characteristics, and so they are suitable for solving different plastic problems. Based on these three kinds of DDD algorithms, the plastic deformation mechanisms of nickel-based superalloy, the damage and fracture behaviors of crystalline materials, and the size effect and microstructure dependency of heterogeneous crystalline materials have been investigated systematically. For the nickel-based superalloy, the dislocation mechanisms for the hardening responses, the abnormal yielding behavior with increasing temperature, the loading rate effect, the lattice misfit effect, and the crystalline orientation effect and the dislocation climb effect have been studied in detail. Based on these dislocation mechanisms and the special two-phase material microstructures, a crystal plasticity constitutive law informed by dislocation and microstructure mechanisms suitable for single crystal nickel-based superalloy was here developed. Further, the microvoid growth mechanism, the crack tip-microvoid interaction, the crack tip ratchetting responses, the crack shielding effect by dislocation, and the effect of crack-tip dislocation emission on crack growth have also been investigated systematically through DDD simulations. In addition, the plastic behavior, its size effect, and intrinsic dislocation mechanisms for materials with heterogeneous structures, such as particle-enhanced metal matrix composites, multilayered metallic films, and polycrystalline materials, have also been studied carefully using DDD models, especially at elevated temperature. This type of DDD research has facilitated better understanding of the intrinsic mechanisms of hardening response, cyclic plasticity, fracture, damage evolution, size effect, and microstructure dependency. DDD can be further used to study the plastic behaviors of crystals under the extreme environmental conditions, such as high temperature, high pressure, high loading rate (shocking), chemical erosion environment, and high neutron irradiation. DDD has recently become a powerful model of the behavior of metallic materials at microscale in a more physical manner than existing plasticity models.

A multiscale reconstructing method for shale based on SEM image and experiment data

Owing to the presence of multiscale pore structures, characterization of laminated shales is both extremely difficult and substantially different from that of conventional reservoirs, and defies conventional methodologies. In this paper, a multiscale reconstructing method for shale is proposed to generate 3D layer representative elementary volume (lREV)-scale digital-experimental models to characterize the multiscale pore structure of the shale by means of the combination of a large area SEM image, nitrogen adsorption and pressure pulse decay experiment result. In this method an improved multiscale superposition algorithm is introduced to integrate the reconstructed complex models from nanoscale to mesoscale together, and it can preserve the details and main features enormously of each typical component (nanoscale organic pores in organic matter and pyrites, micro-nano inorganic pores and micro slits) in the shale. Especially, to accurately reproduce the realistic morphology for shale, the proposed method uses the experimental pore size distribution and permeability as constrain conditions to adjust and optimize the lREV-scale digital-experimental model. Our proposed method was tested on Longmaxi and Wufeng shale samples, and the reconstructed lREV-scale digital-experimental model are proved to accurately describe the representative structure of the complex multiscale pore space of the typical layer of the shale. The success of this method provides a promising way for reconstructing more realistic model to continuously and systematically characterize the pore (slits) structure from the nanopore-scale to the lREV-scale. It can advance the understanding of the various gas transport mechanisms at different scales and will be helpful for understanding the quality of the shale reservoir.

A Monte Carlo evaluation of dose distribution of commercial treatment planning systems in heterogeneous media.

Calculations from a treatment planning system (TPS) in heterogeneous regions may present significant inaccuracies due to loss of electronic equilibrium. The purpose of this study is to evaluate and quantify the differences of dose distributions computed by some of the newest dose calculation algorithms, including collapsed cone convolution (CCC), fast Fourier transform (FFT) convolution, and superposition convolution, in heterogeneity of the lung. A 6-MV Siemens Primus linear accelerator was simulated by MCNPX Monte Carlo (MC) code, and the results of percentage depth dose (PDD) and dose profile values were compared with measured data. The ISOgray TPS was used and PDDs of CCC, FFT, and superposition convolution algorithms were compared with the results obtained by MCNPX code. CT2MCNP software was used to convert the computed tomography images of the lung tissue to MC input files, and dose distributions from the three algorithms were compared to MC method. For PDD curves in buildup region, the maximum underdosage of ISOgray TPS was at the surface (19%) and comes in closer agreement when depth increases (average 7.08%). Dose differences (DD) between different algorithms and MC were typically 4.81% (range: 1.95% to 7.30%), -1.55% (range: -5.14% to 5.26%) and 4.96% (range: 2.00% to 7.4%) in the lung for the CCC, FFT, and superposition algorithms, respectively. The difference between monitor units and maximum dose calculated using the three algorithms were 0.5% and 1.61%, respectively. The maximum DD of 7% was observed between MC and TPS results. Significant differences were found when the calculation algorithms were compared with MC method in lung tissue, and this difference is not negligible. It is recommended to use of MC-based TPS for the treatment fields including lung tissue.

Evaluation of dose calculation algorithms using different density materials for in-field and out-of-field conditions

The accuracy of the dose calculation is vital in the stereotactic ablative body radiotherapy (SABR) technique to achieve clinically effective dose distribution for better tumor control. Multiple commercial radiotherapy treatment planning systems (TPS) were implemented with different algorithms, such as Acuros XB in Eclipse and Superposition in XiO. The aim of this study is to investigate five different dose calculation algorithms, namely, pencil beam convolution (PBC), Acuros XB, AAA implemented in an Eclipse system, collapsed cone convolution (CCC) algorithm implemented in Mobius3D and superposition algorithms implemented in the XiO system, and then validate the results against measurements using an Institute of Physical Sciences in Medicine (IPSM) phantom with different density materials for in-field and out-of- field conditions. The IPSM phantom was used to investigate the dose calculation algorithm performances in four different densities (water, lung, ribs, and dense bone) using different beam configurations, including small beam fields utilised in lung SABR. Five commercial algorithms implemented in two TPS (Eclipse and XiO) and one plan check(M3D) system were used for in-field and out-of-field measurement. In the in-field condition, the Acuros XB algorithm had lower mean differences than the measured dose by the IC ranging from -0.46 to 0.24for all the densities. In the out-of-field condition, the results of eclipse system: AAA, PBC and Acuros XB algorithms demonstrated underdose point's measurements by -40% for all densities except for AAA calculations in lung density (overdosed by 40%). The measured points of the superposition algorithms were overestimated to the actual dose less than 30% in water, lung and dense bone. At the same densities, the CCC algorithms showed relatively the lowest differences in percentage compared to the superposition algorithms. Our results showed that the Acuros XB and superposition algorithms are closer to the actual measured dose than AAA, PBC and CCC for majority of the field conditions for water-equivalent, lung, rib and dense bone densities. The CCC algorithm resulted in a better agreement with the measurement of the out-of-field points compared with the other algorithms.

The comparison of two calculation algorithms to evaluate the dosimetric effects of thermoplastic masks used in radiotherapy

Abstract In radiation therapy, the accuracy of dose calculation is extremely important for planning quality and treatment implementation. This is achieved through Treatment Planning Systems (TPS) that use different algorithms to calculate the specific dose. Radiation therapy for brain and head & neck (H&N) tumors requires the same high positioning precision of the patient throughout the treatment course. Thus, during fractionated radiotherapy, to immobilize the patient’s head and neck, and to avoid patient movement errors, an immobilization device is used, that is, a thermoplastic mask. However, many studies have shown that TPS overestimate the delivered dose to the skin during the treatment. The aim of this study is to quantify the dosimetric thermoplastic mask effects using two different algorithms that are the superposition and the fast superposition algorithms.

Fast Calculation of Computer Generated Holograms for 3D Photostimulation through Compressive-Sensing Gerchberg-Saxton Algorithm.

The use of spatial light modulators to project computer generated holograms is a common strategy for optogenetic stimulation of multiple structures of interest within a three-dimensional volume. A common requirement when addressing multiple targets sparsely distributed in three dimensions is the generation of a points cloud, focusing excitation light in multiple diffraction-limited locations throughout the sample. Calculation of this type of holograms is most commonly performed with either the high-speed, low-performance random superposition algorithm, or the low-speed, high performance Gerchberg–Saxton algorithm. This paper presents a variation of the Gerchberg–Saxton algorithm that, by only performing iterations on a subset of the data, according to compressive sensing principles, is rendered significantly faster while maintaining high quality outputs. The algorithm is presented in high-efficiency and high-uniformity variants. All source code for the method implementation is available as Supplementary Materials and as open-source software. The method was tested computationally against existing algorithms, and the results were confirmed experimentally on a custom setup for in-vivo multiphoton optogenetics. The results clearly show that the proposed method can achieve computational speed performances close to the random superposition algorithm, while retaining the high performance of the Gerchberg–Saxton algorithm, with a minimal hologram quality loss.

Assessment of two different dose distribution algorithms (Clarkson and Superposition) in PCRT3D treatment planning system for Esophagus Cancer by using 3DCRT technique

Introduction: The functionality and quality of any treatment planning system (TPS) strongly depends on the type of Algorithm which is used by it. Obviously, the role of dose distribution algorithms in calculation of prescribed dose inside the tumor in modern radiotherapy techniques has more important than past to achieve the best clinical outcomes, especially in tumors which are placed in lung or near it like Esophagus cancer. The aim of this study is to evaluate and comparison of efficiency and accuracy of two dose distribution algorithms, Clarkson and Superposition which are using in PCRT 3D treatment planning system to calculate the dose distribution in Three- Dimensional Conformal Radiotherapy (3D-CRT) for Esophagus cancer cases. Materials and Methods: In this study ten patients with esophageal cancer were planned by Clarkson and Superposition algorithms. Treatment plan of the patients were created with a photon beam of 6 MV. Commercially available PCRT3D version6 (made in Spain) Planning system was used to calculate dose in ten planed patients. For this goal and to compare two dose distribution algorithms, the statistical analysis was performed by comparing Conformity Index and Homogeneity Index for target. Results: The maximum value of variation between algorithms for PTV in Dmin, Dmax, and Dmean were 11.7%, 8.3% and 0.73%, respectively. The maximum deviation of variation observed between algorithms in OAR's consist of Dmean is 8.9% for Left lung 7.14% for Right Lung and 2.65% for Spinal cord. Significant variation between algorithms for Homogeneity Index values is 9.06% and highest Percentage oscillation between algorithms for Conformity Index values are 6.33%. Conclusion: According to this study and because of the different results which was driven from treatment planning, significant care should be taken account when calculating treatment plans, due to different dose calculation algorithm may influence treatment planning as well as clinical results.

121. Automated planning for Hodgkin lymphoma radiotherapy

PurposePurpose of the present study was to report on the evaluation of Pinnacle3Auto-Planning (AP) algorithm for Hodgkin lymphoma (HL) radiation therapy (RT). MethodsPlanning CT-scans of 10 female patients with supradiaphragmatic HL were considered. Involved site clinical target volume (CTV) included the upper mediastinal and supraclavear nodes. Planning Target Volume (PTV) was obtained by CTV uniform 10-mm expansion. A total dose of 30 Gy was prescribed in 20 fractions.A “butterfly” (BF) volumetric modulated arc therapy was planned with Pinnacle3 v. 9.10 using SmartArc module and Collapsed Cone Convolution Superposition algorithm dose calculation. Human-driven (Manual-BF) and AP-BF optimization plans were generated using published priority and constraints on the OARs. In addition to BF technique, the AP engine was applied to a 2 coplanar disjointed arches (AP-ARC) technique. A single AP optimization list of PTV/OAR clinical goals was created for each patient. For plan comparison, DVHs of PTVs and OARs were extracted; homogeneity and conformity indices (HI and CI) computed and OARs dose-volume constraints and NTCP models for RP, HT, and CD evaluated. Non-parametric Friedman and Dunn tests were used to identify significant differences between groups. ResultsAP (AP-BF or AP-ARC) offers comparable coverage of the PTV as the manual plan and a consistently better sparing of OARs. In particular, the heart and thyroid mean doses and lung V20 were significantly reduced using AP engine. Accordingly, AP provides similar, if not lower, complication risks. The median number of monitor units was slightly reduced by AP (3.5%). Hands-on planning time decreased on average by a factor of 3 by AP. ConclusionsThe AP module was able to limit heart and thyroid complication risks, producing clinically acceptable HL plans with stable quality without additional user input. Overall AP-ARC provided better results in terms of OAR sparing when compared with AP-BF.

Evaluation of Three-dimensional Treatment Planning System (TPS) performance in dose calculation of virtual wedged fields using film dosimetry

Introduction: Nowadays radiotherapy plays an important role in cancer treatment. Different radiotherapy techniques improvement emphasizes on using of the precise ، appropriate and useful algorithms. one of these techniques are wedged which is used in radiotherapy to compensate missing tissues and create a uniform dose distribution in tissues. The Siemens Artiste linear accelerator supports a virtual wedge ، that this wedge creates a dose distribution similar to a physical wedge without the use of any extra accessory and wedged profiles are produced moving collimator jaw during irradiation with a constant speed but varying the dose rate. In this study ، TPS performance is evaluated in virtual wedged fields by comparing the calculated and measured results. Materials and Methods: The calculations were performed by the collapsed cone superposition algorithm based TPS for two tangent fields in anthropomorphic slab phantom using 15، 30، 45، 60 virtual wedges for field size of 20 × 20 cm2 for 6 and 15 MV photon beams. Measurements were produced by Gafchromic EBT films and reading exposed films with scanner. Results: Good agreement between the measured dose with film dosimetry and calculated dose with collapsed cone superposition algorithm based TPS with using virtual wedge in heterogeneous environment and different energies were found ، with the maximum difference not exceed 3 -5%. The increase in wedge angle due to increase in the difference between calculated and measured data. Conclusion: : The results from this study showed that the accuracy of collapsed cone superposition algorithm based TPS used with the virtual wedges for two tangent fields is enough for the clinical usage under the studied experimental conditions.

225. Low modulated 6 MV Flattening Filter Free Intensity Modulated Radiation Therapy (FFF-IMRT) for left breast treatments with Active Breath Coordinator™ (ABC): A feasibility study

Purpose The Flattening Filter Free (FFF) modality of the LINAC generates an unflattened X-ray beam with a dose rate up to 5 times (1200 MU/min) the maximum dose rate of a standard flattened beam. Aim of this study is to take advantage of high dose rate to spare treatment time for left breast breath-holding patients and to deliver an equal or better treatment in dose distribution. Here a 6 MV three-fields FFF-IMRT technique is proposed and compared to the standard two tangential 3D-CR conformal radiotherapy (3D-CR). Methods Our 6 MV three-fields IMRT technique adds a slightly tilted beam to the usual two tangential beams. The low modulation allows the maximum dose rate. For a group of 22 patients undergoing left breast treatment with ABC, a comparison was made between 3D-CR standard treatments and FFF-IMRT. 3D-CR plans were calculated by CMS XIO® (v.5.11 convolution superposition algorithm) and Monaco® (v.5.11.02 collapsed cone algorithm), FFF-IMRT plans by Monaco® (v.5.11.02 Monte Carlo algorithm). For plan comparison, 14 indicators were examined by a paired Student T-test to assess statistical significance of differences (p • Left lung: V 20 Gy , V 10 Gy • Heart: Mean Dose, V 25 Gy • Right breast: V 2 Gy • Patient: Maximum Dose ( D 1 % ) • PTV: V 95 % , Maximum Dose ( D 1 % ) , V 105 % (cm3), V 105 % (%), Conformity Index (as defined in Monaco® v.5.11.02) • CTV: V 98 % • Apnoeas number • Treatment time Overall treatment times were evaluated for 3D-CR and FFF-IMRT plans by simulating a patient with a 25 s breath hold phase and a breath recover phase of 30 s. Times for patient set-up, portal imaging and treatment room leaving were also taken into account (total 600 s). Results Significant differences were found for the indicators listed in Table 1 . FFF-IMRT plans showed better CTV coverage, high doses (hot spots) control and conformity. All the FFF-IMRT plans were faster and achieved a mean time gain of 15.1% (2%–18%) for 50 Gy, 2 Gy/fraction prescriptions and 14.9% (4%–18%) for 42.40 Gy, 2.65 Gy/fraction prescriptions, and a mean reduction of apnoeas number by two. Conclusions The FFF-IMRT technique delivers an equal or better dose distribution with a significant reduction of treatment time and number of apnoeas, substantially improving patient comfort.

Treatment planning dose accuracy improvement in the presence of dental implants

Streaking artifacts in computed tomography (CT) scans caused by metallic dental implants (MDIs) can lead to inaccuracies in dose calculations. This study quantifies and compares the effect of MDIs on dose distributions using the collapsed cone convolution superposition (CCCS) and Monte Carlo (MC) algorithms, with and without correcting for the density of the MDIs. Ion chamber measurements were taken to test the ability of the algorithms in Pinnacle3 and Monaco to calculate dose near high-Z materials. Nine previously treated patients with head and neck cancer were included in this study. The MDI and the streaking artifacts on the CT images were carefully contoured. For each patient, a plan was optimized and calculated using the Pinnacle3 treatment planning system (TPS). Two dose calculations were performed for each patient: one with overridden densities of the MDI and CT artifacts and one without overridden densities of the MDI and CT artifacts. The plans were then exported to the Monaco TPS and recalculated for the same number of monitor units (MUs) using its MC dose calculation algorithm. The changes in dose to the planning target volume (PTV) and surrounding healthy tissues were examined between all the plans using VelocityAI. For the ion chamber measurements, when correct density information was used, Monaco was within 3% of the measured values, whereas the doses calculated in Pinnacle3 varied up to 7%. The CCCS algorithm in Pinnacle3 calculated only a significant decrease in PTV coverage for 1 patient when the densities were overridden. The MC algorithm in Monaco was able to calculate a significant change in PTV coverage for five of the patients when the density was overridden. Additionally, when healthy tissues affected by streaking artifacts were assigned the correct density, cumulative (from all the fractions) point doses increased up to 46.2 Gy. Not properly accounting for MDIs can impact both the high-dose regions (PTVs) and surrounding healthy tissues. This study demonstrates that if MDIs and the artifacts are not appropriately accounted for by contouring and assigning to them the correct density, there is a potential risk of compromising the quality of the plan regarding PTV coverage and dose to healthy tissues.

New multi-resolution and multi-scale electromagnetic detection methods for urban underground spaces

The “transparent” detections of urban underground spaces pose difficult challenges in the field of geophysics. Due to the complexities of urban underground environments, the existing detection methods are hard to reach the high capabilities of radiation sources and distinguish small-scale abnormal bodies at the same time. The “transparent” detections of urban underground spaces must achieve multi-resolution and multi-scale detection abilities. The previously applied electromagnetic detection methods have displayed limitations in achieving high radiation capability and rich harmonic component detections. Therefore, this paper focused on three key scientific issues: the design of a high-performance excitation source; a multi-resolution detection theory; and a multi-scale information extraction technique. First, in order to increase the radiation intensity, improve the directional radiation capability, and realize powerful and directional radiation, a new type of high-performance transient electromagnetic source was designed. Then, complex waveforms would be transmitted in order to enrich the frequency component of the excitation signals. The complex excitations were carried out using pulse scanning technology for the purpose of obtaining increased abundant underground information. The multi-resolution detections of the underground targets were realized in combination with a superposition algorithm. Finally, based on a related superposition principle, multi-aperture synthetic aperture technology was examined. By setting the sizes of the apertures, the vertical and lateral resolutions were adjusted, and the multi-scale information extractions of the urban underground spaces were realized. In this study, a large number of numerical model tests and simulation calculations were carried out. The results confirmed that, from the point of view of a detection mechanism, a high performance radiant source combined with a multi-resolution method and multi-scale signal extraction technology could successfully obtain correct and effective clear detection results in both transverse and longitudinal directions. The research results of this study will significantly promote the development of urban underground space detection technology, which will potentially be of major importance in making the underground spaces up to 200 m ‘transparent’ in urban areas.

Auto- versus human-driven plan in mediastinal Hodgkin lymphoma radiation treatment

BackgroundTechnological advances in Hodgkin lymphoma (HL) radiation therapy (RT) by high conformal treatments potentially increase control over organs-at-risk (OARs) dose distribution. However, plan optimization remains a time-consuming task with great operator dependent variability. Purpose of the present study was to devise a fully automated pipeline based on the Pinnacle3 Auto-Planning (AP) algorithm for treating female supradiaphragmatic HL (SHL) patients.MethodsCT-scans of 10 female patients with SHL were considered. A “butterfly” (BF) volumetric modulated arc therapy was optimized using SmartArc module integrated in Pinnacle3 v. 9.10 using Collapsed Cone Convolution Superposition algorithm (30 Gy in 20 fractions). Human-driven (Manual-BF) and AP-BF optimization plans were generated. For AP, an optimization objective list of Planning Target Volume (PTV)/OAR clinical goals was first implemented, starting from a subset of 5 patients used for algorithm training. This list was then tested on the remaining 5 patients (validation set). In addition to the BF technique, the AP engine was applied to a 2 coplanar disjointed arc (AP-ARC) technique using the same objective list. For plan evaluation, dose-volume-histograms of PTVs and OARs were extracted; homogeneity and conformity indices (HI and CI), OARs dose-volume metrics and odds for different toxicity endpoints were computed. Non-parametric Friedman and Dunn tests were used to identify significant differences between groups.ResultsA single AP objective list for SHL was obtained. Compared to the manual plan, both AP-plans offer comparable CIs while AP-ARC also achieved comparable HIs. All plans fulfilled the clinical dose criteria set for OARs: both AP solutions performed at least as good as Manual-BF plan. In particular, AP-ARC outperformed AP-BF in terms of heart sparing involving a lower risk of coronary events and radiation-induced lung fibrosis. Hands-on planning time decreased by a factor of 10 using AP on average.ConclusionsDespite the high interpatient PTV (size and position) variability, it was possible to set a standard SHL AP optimization list with a high level of generalizability. Using the implemented list, the AP module was able to limit OAR doses, producing clinically acceptable plans with stable quality without additional user input. Overall, the AP engine associated to the arc technique represents the best option for SHL.

P249] Influence of gamma index comparison on differences in dose calculation algorithm deposition method

Purpose Phantomless patient specific QA saves time and is able to detect errors by comparing the TPS dose distribution with a secondary independent dose calculation. TG 218 recommends that gamma analysis should be performed on metrics such as, mean gamma, γ > 1 and γ > 1.5, per structure. The aim of this study is to investigate how gamma index comparison is affected by differences on dose calculation algorithms when treating bone metastases. Methods 10 patients treated for bone metastases in different sites were chosen and 3D and VMAT plans were created using Elekta Monaco TPS in a Versa linac and 10 MV photons. Both 3D and VMAT dose distributions were calculated with Monaco XVMC Monte Carlo (MC) calculation algorithm using dose to medium in medium MC(Dm,m) and dose to water in medium MC(Dw,m) dose deposition modes. All plans were also calculated and evaluated using IBA Compass incorporating a Collapsed Cone convolution superposition algorithm calculating dose to water in medium CC(Dw,m). 3D dose distribution evaluation was performed in terms of gamma metrics such as mean gamma values and % PTV with γ > 1 and γ > 1.5 using 3%, 3 mm criteria for the following combinations: (a) MC(Dw,m) vs CC(Dw,m) and (b) MC(Dm,m) vs CC(Dw,m). Results For the 3D plans, average mean gamma values for MC(Dw,m) vs CC(Dw,m) and MC(Dm,m) vs CC(Dw,m) were found 0.37 ± 0.1 and 0.52 ± 0.12 respectively. The average % PTV points with γ > 1 were found 6.34 ± 5.7% and 12.6 ± 7.5% and the average % PTV points with γ > 1.5 1.45 ± 1.87% and 2.21 ± 2.28%, respectively. Corresponding values for the VMAT plans were 0.46 ± 0.12 and 0.68 ± 0.09 (mean gamma values), 9.48 ± 7.26% and 21.5 ± 7.3% (% PTV points with γ > 1) and 2.37 ± 2.8% and 7.95 ± 7.4% (% PTV points with γ > 1.5). Conclusions Gamma index comparison revealed that both MC and CC calculation algorithms are in fair agreement in dose calculation determination providing that the same dose deposition mode (i.e. Dw,m or Dm,m) is used. The use of different dose deposition mode, results in increased differences in dose calculation determination in structures/areas where materials different than water, such as bone, is included. The observed differences are also increased as the complexity of the plan increases (e.g. VMAT vs 3D).

Dosimetric end-to-end tests in a national audit of 3D conformal radiotherapy.

Independent dosimetry audits improve quality and safety of radiation therapy. This work reports on design and findings of a comprehensive 3D conformal radiotherapy (3D-CRT) Level III audit. The audit was conducted as onsite audit using an anthropomorphic thorax phantom in an end-to-end test by the Australian Clinical Dosimetry Service (ACDS). Absolute dose point measurements were performed with Farmer-type ionization chambers. The audited treatment plans included open and half blocked fields, wedges and lung inhomogeneities. Audit results were determined as Pass Optimal Level (deviations within 3.3%), Pass Action Level (greater than 3.3% but within 5%) and Out of Tolerance (beyond 5%), as well as Reported Not Scored (RNS). The audit has been performed between July 2012 and January 2018 on 94 occasions, covering approximately 90% of all Australian facilities. The audit pass rate was 87% (53% optimal). Fifty recommendations were given, mainly related to planning system commissioning. Dose overestimation behind low density inhomogeneities by the analytical anisotropic algorithm (AAA) was identified across facilities and found to extend to beam setups which resemble a typical breast cancer treatment beam placement. RNS measurements inside lung showed a variation in the opposite direction: AAA under-dosed a target beyond lung and over-dosed the lung upstream and downstream of the target. Results also highlighted shortcomings of some superposition and convolution algorithms in modelling large angle wedges. This audit showed that 3D-CRT dosimetry audits remain relevant and can identify fundamental global and local problems that also affect advanced treatments.