Dynamic collimation for missing tissue compensation

Four-dimensional (4D) dose calculation algorithms, which explicitly incorporate respiratory motion in the calculation of doses, have the potential to improve the accuracy of dose calculations in thoracic treatment planning; however, they generally require greater computing power and resources than currently used for three-dimensional (3D) dose calculations. The purpose of this work was to quantify the increase in accuracy of 4D dose calculations versus 3D dose calculations. The accuracy of each dose calculation algorithm was assessed using measurements made with two phantoms. Specifically, the authors used a rigid moving anthropomorphic thoracic phantom and an anthropomorphic thoracic phantom with a deformable lung insert. To incorporate a clinically relevant range of scenarios, they programed the phantoms to move and deform with two motion patterns: A sinusoidal motion pattern and an irregular motion pattern that was extracted from an actual patient's breathing profile. For each combination of phantom and motion pattern, three plans were created: A single-beam plan, a multiple-beam plan, and an intensity-modulated radiation therapy plan. Doses were calculated using 4D dose calculation methods as well as conventional 3D dose calculation methods. The rigid moving and deforming phantoms were irradiated according to the three treatment plans and doses were measured using thermoluminescent dosimeters (TLDs) and radiochromic film. The accuracy of each dose calculation algorithm was assessed using measured-to-calculated TLD doses and a gamma analysis. No significant differences were observed between the measured-to-calculated TLD ratios among 4D and 3D dose calculations. The gamma results revealed that 4D dose calculations had significantly greater percentage of pixels passing the 5%/3 mm criteria than 3D dose calculations. These results indicate no significant differences in the accuracy between the 4D and the 3D dose calculation methods inside the gross tumor volume. On the other hand, the film results demonstrated that the 4D dose calculations provided greater accuracy than 3D dose calculations in heterogeneous dose regions. The increase in accuracy of the 4D dose calculations was evident throughout the planning target volume.

Monte Carlo (MC) algorithms are recognized as the most accurate methodology for patient dose assessment. For intensity-modulated radiation therapy (IMRT) delivered with dynamic multileaf collimators (DMLCs), accurate dose calculation, even with MC, is challenging. Accurate IMRT MC dose calculations require inclusion of the moving MLC in the MC simulation. Due to its complex geometry, full transport through the MLC can be time consuming. The aim of this work was to develop an MLC model for photon beam MC IMRT dose computations. The basis of the MC MLC model is that the complex MLC geometry can be separated into simple geometric regions, each of which readily lends itself to simplified radiation transport. For photons, only attenuation and first Compton scatter interactions are considered. The amount of attenuation material an individual particle encounters while traversing the entire MLC is determined by adding the individual amounts from each of the simplified geometric regions. Compton scatter is sampled based upon the total thickness traversed. Pair production and electron interactions (scattering and bremsstrahlung) within the MLC are ignored. The MLC model was tested for 6 MV and 18 MV photon beams by comparing it with measurements and MC simulations that incorporate the full physics and geometry for fields blocked by the MLC and with measurements for fields with the maximum possible tongue-and-groove and tongue-or-groove effects, for static test cases and for sliding windows of various widths. The MLC model predicts the field size dependence of the MLC leakage radiation within 0.1% of the open-field dose. The entrance dose and beam hardening behind a closed MLC are predicted within ±1% or 1 mm. Dose undulations due to differences in inter- and intra-leaf leakage are also correctly predicted. The MC MLC model predicts leaf-edge tongue-and-groove dose effect within ±1% or 1 mm for 95% of the points compared at 6 MV and 88% of the points compared at 18 MV. The dose through a static leaf tip is also predicted generally within ±1% or 1 mm. Tests with sliding windows of various widths confirm the accuracy of the MLC model for dynamic delivery and indicate that accounting for a slight leaf position error (0.008 cm for our MLC) will improve the accuracy of the model. The MLC model developed is applicable to both dynamic MLC and segmental MLC IMRT beam delivery and will be useful for patient IMRT dose calculations, pre-treatment verification of IMRT delivery and IMRT portal dose transmission dosimetry.

Background:Adjacent radiation fields are applied in some radiotherapeutic cases. When using these radiation fields, considerable dose errors across the junction of radiation fields are possible. Therefore, it is necessary to evaluate the accuracy of the dose calculated by treatment planning system (TPS) when using the adjacent radiation fields. The present study aimed to quantify the dose calculation accuracy of ISOgray TPS for the photon-photon adjacent fields.Materials and methods:To assess the accuracy of dose calculations, the dose profiles were first measured by a Semiflex ionization chamber at 1, 1·5, 5 and 10 cm depths for different field sizes (6 × 6, 10 × 10 and 20 × 20 cm2), source to surface distances (SSDs) (90, 100 and 110 cm) and beam angles (0º, 15º, 30º and 45º). In the second step, the data at corresponding depths were extracted from the ISOgray TPS. Finally, the dosimetric performance of TPS was evaluated using a gamma index analysis.Results:The overall dose calculation accuracy of ISOgray TPS was within the acceptable range for the build-up region (with acceptance criteria of dose difference (DD) = 15% and distance to agreement (DTA) = 3 mm) and the depths after the build-up region (with acceptance criteria of DD = 5% and DTA = 3 mm). Moreover, the overall accuracy of dose calculations was not affected by the field size and the SSD. It was also shown that the accuracy of dose calculations was similar for the adjacent radiation fields with beam angles of 0º, 15 º and 30 º, while a considerable decrease in the pass rate values is obtained for the adjacent radiation field with 45 º beam angle. A more detailed analysis of the findings revealed that the accuracy of dose calculations in the match line regions of the adjacent radiation fields for 1 cm beam profiles was within the acceptable range; however, it declined for other depths.Conclusions:The findings showed that the overall dose calculation accuracy of ISOgray TPS was acceptable for evaluated adjacent radiation fields. However, the accuracy of dose calculations in the match line regions of the adjacent radiation fields for the depth after build-up was not within the acceptable range.

The Naval Research Laboratory (NRL) has developed a multi-channel, multi-mode, multi-band modular communications terminal called the Joint Combat Information Terminal (JCIT). The JCIT is the heart of the communications system for the Army Airborne Command and Control System (A2C2S). The production-ready JCIT has been field tested by the US Marine Corps (USMC) in command and control variants of the Light Armored Vehicle (LAV) and Amphibious Assault Vehicle (AAV). The functionality, expandability, and modularity of JCIT provide state-of-the-art communications for military and civil agencies. Interoperability with SINCGARS, HAVE QUICK, HF, National Satellite Intelligence Broadcasts, military precision GPS, IEEE-802.11, direct broadcast by satellite (DBS/GBS), air traffic control, police, fire, and civil maritime has been demonstrated in the field and in the laboratory. The JCIT architecture was designed to meet current and future military command, control, communications, computers, and intelligence (C41) requirements. It provides a total communications system solution from the antenna to the user the modules developed for the JCIT are not proprietary. The architecture is built from a common set of hardware and software modules. Software allows the hardware to interoperate with other legacy or future radio systems on operator command hardware and software insertion to meet future requirements is supported by the architecture. The architecture is readily adaptable to new platforms, utilizing unchanged hardware and software modules. Although the architecture is not considered "open" by the industry standards, full Government owned interface control documents exist that allow any third party to build hardware or software components for the system. Eight-channel vehicular/airborne units and two-channel vehicular/manpack units have been built. These units share hardware modules and software applications without modification.

The goal of this work is to develop a methodology for fast prototyping of highly modular and flexible electronic systems including both, software and hardware. The main contribution of this work is the ability to handle a wide range of architectures. We assume that hardware/software partitioning is already made. This stage of the codesign process starts with a virtual prototype, an heterogeneous architecture composed of a set of distributed modules, represented in VHDL for hardware elements and in C for software elements, communicating through communication modules. This work concentrates on a modelling strategy that allow virtual prototype to be used for both cosynthesis (mapping hardware and software modules onto an architectural platform) and cosimulation (that is the joint simulation of hardware and software components) into an unified environment. The main contribution is the use of a multi-view library concept in order to hide specific hardware/software implementation details and communication schemes. In particular this approach addresses the problem of communication between the hardware and software modules.

On the dose to a moving target while employing different IMRT delivery mechanisms

The safety and clinical efficacy of 125 I seed-loaded stent for the treatment of portal vein tumor thrombosis (PVTT) have been shown. Accurate and fast dose calculation of the 125 I seeds with the presence of the stent is necessary for the plan optimization and evaluation. However, the dosimetric characteristics of the seed-loaded stents remain unclear and there is no fast dose calculation technique available. This paper aims to explore a fast and accurate analytical dose calculation method based on Monte Carlo (MC) dose calculation, which takes into account the effect of stent and tissue inhomogeneity. A detailed model of the seed-loaded stent was developed using 3D modeling software and subsequently used in MC simulations to calculate the dose distribution around the stent. The dose perturbation caused by the presence of the stent was analyzed, and dose perturbation kernels (DPKs) were derived and stored for future use. Then, the dose calculation method from AAPM TG-43 was adapted by integrating the DPK and appropriate inhomogeneity correction factors (ICF) to calculate dose distributions analytically. To validate the proposed method, several comparisons were performed with other methods in water phantom and voxelized CT phantoms for three patients. The stent has a considerable dosimetric effect reducing the dose up to 47.2% for single-seed stent and 11.9%-16.1% for 16-seed stent. In a water phantom, dose distributions from MC simulations and TG-43-DP-ICF showed a good agreement with the relative error less than 3.3%. In voxelized CT phantoms, taking MC results as the reference, the relative errors of TG-43 method can be up to 33%, while those of TG-43-DP-ICF method were less than 5%. For a dose matrix with 256 × 256 × 46 grid (corresponding to a phantom of 17.2 × 17.2 × 11.5cm3 ) for 16-seed-loaded stent, it only takes 17s for TG-43-DP-ICF to compute, compared to 25h for the full MC calculation. The combination of DPK and inhomogeneity corrections is an effective approach to handle both the presence of stent and tissue heterogeneity. Exhibiting good agreement with MC calculation and computational efficiency, the proposed TG-43-DP-ICF method is adequate for dose evaluation and optimization in seed-loaded stent implantation treatment planning.

Evaluation of a Model-based Dose Calculation Algorithm (Acuros) for Intraosseous High Dose Rate Brachytherapy (HDR) With Intramedullary Nailing for Bone Metastases

Improved dose calculation accuracy for low energy brachytherapy by optimizing dual energy CT imaging protocols for noise reduction using sinogram affirmed iterative reconstruction

Accuracy of dose calculation based on artefact corrected Cone Beam CT images of lung cancer patients

Modern intensity-modulated radiotherapy, aiming to deliver an accurate dose to the planning target volume while protecting the surrounding organs at risk, is regarded as the indispensable treatment for cancer in the clinic. An accurate and efficient dose calculation algorithm is essential to support and accelerate the treatment plan optimization process. To improve the effectiveness of the dose calculation, deep learning methods are widely adopted to compute dose distributions from several variables mimicking the physical features required for dose calculation. However, these methods employed similar concepts and neural network inputs, and had only limited improvements to traditional dose calculation methods. In this work, we propose a new computing process, named DeepBEVdose, which is essentially distinct to the previous deep learning-based dose calculation methods. We present a novel image-domain dose calculation algorithm to automatically compute dose distributions from the computer tomography images and radiation field fluence maps. Specifically, a novel beam's eye view calculation scheme is introduced to substitute the traditional trivial ray-tracing procedure that cannot be removed in the previously published dose calculation system. Under this new calculation scheme, a generic two-dimensional convolutional neural network with minimal input requirements is sufficient to perform accurate dose calculation. We demonstrate the feasibility of this approach with datasets acquired from multi-institutions with two different tumor sites (nasopharynx and lung). The average pixel-wise difference between the ground truth and the predicted results across all testing cases (both internal and external) is within 2%. The average 3D gamma passing rate is above 95% for all testing cases. We have developed a novel deep learning framework that effectively maps radiation fluences to dose distributions. The high accuracy and efficiency of the proposed approach indicate its potential for use in online adaptive plan optimization.

ID: 160 Advanced personalised 3D dosimetry based on Monte Carlo simulation for Peptide Receptor Radionuclide Therapy

The working principle and system design of the laser tracker measurement system are introduced, as well as the key technologies and solutions in the implementation of the system. The design and implementation of the hardware and configuration of the software are mainly researched. The components of the hardware include distance measuring unit, angle measuring unit, tracking and servo control unit and electronic control unit. The distance measuring devices include the relative distance measuring device (IFM) and the absolute distance measuring device (ADM). The main component of the angle measuring device, the precision rotating stage, is mainly comprised of the precision axis and the encoders which are both set in the tracking head. The data processing unit, tracking and control unit and power supply unit are all set in the control box. The software module is comprised of the communication module, calibration and error compensation module, data analysis module, database management module, 3D display module and the man-machine interface module. The prototype of the laser tracker system has been accomplished and experiments have been carried out to verify the proposed strategies of the hardware and software modules. The experiments showed that the IFM distance measuring error is within 0.15mm, the ADM distance measuring error is within 3.5mm and the angle measuring error is within 3〞which demonstrates that the preliminary prototype can realize fundamental measurement tasks.

<div class="htmlview paragraph">In modern automotive systems, the complexity is growing by incorporating highly sophisticated microcontrollers running with more than 100MHz and consisting of more than 2500 registers. Software complexity is also growing in a similar, if not higher, rate.</div> <div class="htmlview paragraph">As semiconductor suppliers are also expected by their customers to include a hardware-dependent software layer in their products, testing must now include not only the hardware product but the delivery bundle of hardware and software modules.</div> <div class="htmlview paragraph">Testing this hardware-dependent software is complicated by the big amount of possible hardware-dependent configurations for this software layer which also extensively change the hardware test bench used in verification. The challenge of configuration complexity is solved by extensive use of test automation for both software generation, test bench configuration and test case runs. Additionally, in order to test the full delivery, all software modules have to be configured and tested together in a system-like test.</div> <div class="htmlview paragraph">This paper will discuss the Infineon approach in testing the microcontroller abstraction layer (MCAL) of the AUTOSAR implementation on 32-bit platforms.</div>

A wedge filter is one of the most commonly used beam modifying devices. The introduction of a wedge filter alters both the distribution of the primary photon fluence and the first and second scatter patterns. The effect of the wedge filter is normally expressed in terms of an exponential attenuation function that is used to modify the primary photon fluence. This paper describes a new three-dimensional (3-D) wedged field dose calculation algorithm. This algorithm automatically takes into account (1) the scatter distribution pattern correction due to the effect of wedge filters and (2) the fixed primary photon fluence correction, by utilizing a tissue maximum ratio table calculated from the measured percent depth dose of the wedge, a measured in-plane scan and a measured cross-plane scan of the largest rectangular wedge field size. As a result, the calculation accuracy achieved by this algorithm is better than the calculation accuracy achieved by other algorithms. The results show better than 1% accuracy of the wedge central axis percent depth dose calculation and better than 3% accuracy of the off-axis dose calculation when compared with measurements.