Unique Beam Scanning Device for Active Beam Delivery System in Proton Therapy

A new Beam Delivery System (BDS) has been proposed for a proton therapy project, partially funded, called AMIDERHA. That BDS is characterized by an active scanning system which irradiates target with a pencil beam. The feature of this project was the using of an accelerator Linac with variable final energies and the Robotized Patient Positioning System instead of the traditional gantry. The active BDS of AMIDERHA then does not include a gantry and a pencil beam scanning system with a relatively long Source to Axis Distance (SAD) could be used. In this condition, the using of a unique device capable of scanning the beam for both horizontal and vertical plane in the active BDS of the project is possible. In this contribution this new beam scanning device will be presented. Furthermore, a preliminary design of the device and the trajectory simulations for beam parameter optimization will also be discussed.

Study of an Online Plan Verification Method and the Sensitivity of Plan Delivery Accuracy to Different Beam Parameter Errors in Proton and Carbon Ion Radiotherapy

For scanning beam particle therapy, the plan delivery accuracy is affected by spot size deviation, position deviation and particle number deviation. Until now, all plan verification systems available for particle therapy have been designed for pretreatment verification. The purpose of this study is to introduce a method for online plan delivery accuracy checks and to evaluate the sensitivity of plan delivery accuracy to different beam parameter errors. A program was developed using MATLAB to reconstruct doses from beam parameters recorded in log files and to compare them with the doses calculated by treatment planning system (TPS). Both carbon ion plans and proton plans were evaluated in this study. The dose reconstruction algorithm is verified by comparing the dose from the TPS with the reconstructed dose under the same beam parameters. The sensitivity of plan delivery accuracy to different beam parameter errors was analyzed by comparing the dose reconstructed from the pseudo plans that manually added errors with the original plan dose. For the validation of dose reconstruction algorithm, mean dose difference between the reconstructed dose and the plan dose were 0.70% ± 0.24% and 0.51% ± 0.25% for carbon ion beam and proton beam, respectively. According to our simulation, the delivery accuracy of the carbon ion plan is more sensitive to spot position deviation and particle number deviation, and the delivery accuracy of the proton plan is more sensitive to spot size deviation. To achieve a 90% gamma pass rate with 3 mm/3% criteria, the average spot size deviation, position deviation, particle number deviation should be within 23%, 1.9 mm, and 1.5% and 20%, 2.1 mm, and 1.6% for carbon ion beam and proton beam, respectively. In conclusion, the method that we introduced for online plan delivery verification is feasible and reliable. The sensitivity of plan delivery accuracy to different errors was clarified for our system. The methods used in this study can be easily repeated in other particle therapy centers.

High-Order Fiber Mode Beam Parameter Optimization for Transport and Rotation of Single Cells

Optical tweezers are becoming increasingly important in biomedical applications for the trapping, propelling, binding, and controlled rotation of biological particles. These capabilities enable applications such as cell surgery, microinjections, organelle extraction and modification, and preimplantation genetic diagnosis. In particular, optical fiber-based tweezers are compact, highly flexible, and can be readily integrated into lab-on-a-chip devices. Taking advantage of the beam structure inherent in high-order modes of propagation in optical fiber, LP11, LP21, and LP31 fiber modes can generate structured radial light fields with two or more concentrations in the cross-section of a beam, forming multiple traps for bioparticles with a single optical fiber. In this paper, we report the dynamic modeling and optimization of single cell manipulation with two to six optical traps formed by a single fiber, generated by either spatial light modulation (SLM) or slanted incidence in laser-fiber coupling. In particular, we focus on beam size optimization for arbitrary target cell sizes to enable trapped transport and controlled rotation of a single cell, using a point matching method (PMM) of the T-matrix to compute trapping forces and rotation torque. Finally, we validated these optimized beam sizes experimentally for the LP21 mode. This work provides a new understanding of optimal optical manipulation using high-order fiber modes at the single-cell level.

Analytical account for off-axis effects in X-ray radiation of free electron lasers

We give analytical description of generation of harmonics of the undulator radiation (UR) with account for the finite electron beam size, emittance, off-axis beam deviation and electron energy spread, as well as for the constant magnetic components and field harmonics effects. We give exact analytical expressions for the generalized Bessel and Airy functions, which describe the spectrum line shape and intensities in the two-frequency bi-harmonic undulator with account for the above factors. The obtained analytical formulae distinguish contributions of each field component and every undulator and beam parameter on the harmonic radiation in free electron lasers (FEL). The effect of the field on the harmonic radiation is analyzed with account for the beam finite size and its off-axis deviation. The phenomenological model is employed for the FEL modeling; with its help we study the harmonic generation, including even ones, in the experiments LCLS and LEUTL. We demonstrate analytically that strong second FEL harmonic in X-ray FEL at the wavelengths λ = 0.75nm in the LCLS experiment is caused by the deviation of the electron trajectories off the axis in 15 μm on the gain length 1.6 m, which is comparable with the beam size; the strong second FEL harmonic in the LEUTL experiment at the wavelength λ = 192nm can be attributed to interaction of the electrons in wide, ~ 0.2 mm, beam with the photon radiation at the gain length 0.87 m. The modeling results fully agree with the measurements. The developed formalism allows the analysis of projected and built FELs and their radiation, helps minimizing losses and correcting magnetic fields; it also shows physical background and reasons for each harmonic radiated power in the FEL.

Study of Tissue Inhomogeneity Effects on Central Axis Radiation Beam Parameters using Monte Carlo Methods

Introduction: The central axis radiation beam parameters are used for the dose calculations inradiotherapy and usually measured in a homogeneous medium. Human body is not homogeneous innature and the incident beam has to travel through different medium such as bone tissue air etc toreach the tumor. Objective: The objective of the present work is to study the effects of tissueInhomogeneity on central axis beam parameter such as percentage Depth Dose using Monte CarloMethods Materials and Methods: The Monte Carlo simulation is a virtual experiment and can beconducted with the Monte Carlo software tool installed in a PC. Input files are written as per thespecification of the Monte Carlo code. Two radiation beams beans commonly used for radiationtreatment such as Cobalt 60 and 6MV X ray were used for the simulation. Results: Depth Dosecharacteristics in homogeneous tissue medium for Cobalt60 and 6MV X rays beams were studied andis consistent with the published experimental values.In the second case, at the interface betweentissue and bone the PDD pattern changed as reported by the previous works. And the absorbed doseat bone layer is higher than the dose value predicated in a homogeneous condition. In the nextsimulation we conducted the simulation for a tissue air tissue medium. Conclusion: The presentstudy clearly demonstrate that Monte Carlo methods simulation can be used as a tool for estimationof dose in tissue Inhomogeneity where measurements are seldom possible.