High-energy beams of charged nuclear particles (protons and heavier ions) offer significant advantages for the treatment of deep-seated local tumors in comparison to conventional megavolt photon therapy. Their physical depth-dose distribution in tissue is characterized by a small entrance dose and a distinct maximum (Bragg peak) near the end of range with a sharp fall-off at the distal edge. Taking full advantage of the well-defined range and the small lateral beam spread, modern scanning beam systems allow delivery of the dose with millimeter precision. In addition, projectiles heavier than protons such as carbon ions exhibit an enhanced biological effectiveness in the Bragg peak region caused by the dense ionization of individual particle tracks resulting in reduced cellular repair. This makes them particularly attractive for the treatment of radio-resistant tumors localized near organs at risk. While tumor therapy with protons is a well-established treatment modality with more than 60 000 patients treated worldwide, the application of heavy ions is so far restricted to a few facilities only. Nevertheless, results of clinical phase I-II trials provide evidence that carbon-ion radiotherapy might be beneficial in several tumor entities. This article reviews the progress in heavy-ion therapy, including physical and technical developments, radiobiological studiesmore » and models, as well as radiooncological studies. As a result of the promising clinical results obtained with carbon-ion beams in the past ten years at the Heavy Ion Medical Accelerator facility (Japan) and in a pilot project at GSI Darmstadt (Germany), the plans for new clinical centers for heavy-ion or combined proton and heavy-ion therapy have recently received a substantial boost.« less

Heavy-ion tumor therapy: Physical and radiobiological benefits

https://dr.ntu.edu.sg/bitstream/10356/101824/1/A%20comprehensive%20review%20on%20the%20progress%20of%20lead%20zirconate-based%20antiferroelectric%20materials.pdf

A comprehensive review on the progress of lead zirconate-based antiferroelectric materials

Electron emission from ferroelectrics (FEE) is an unconventional electron emission effect. Methods of FEE excitation are quite different compared to classic electron emission from solids. Two kinds of FEE have been observed, “weak” and “strong.” “Weak” electron emission (current density 10−12–10−7 A/cm2) occurs from polar surfaces of ferroelectric materials in the ferroelectric phase only. A source of the electric field for “weak” FEE excitation is an uncompensated charge, generated by a deviation of macroscopic spontaneous polarization from its equilibrium state under a pyroelectric effect, piezoelectric effect, or polarization switching. The FEE is a tunneling emission current which screens uncompensated polarization charges. It is shown that the FEE is an effective tool for direct domain imaging and studies of electronic properties of ferroelectrics. “Strong” FEE, which is 10–12 orders of magnitude higher than “weak” FEE, achieves 100 A/cm2 and is plasma-assisted electron emission. Two modes of the sur...

Electron emission from ferroelectrics

A plasma processing apparatus wherein a layer structure consisting of plural layers formed in stack one upon another on a semiconductor wafer placed on the sample holder located in the process chamber, is etched with plasma generated in the process chamber by supplying high frequency power to the electrode disposed in the sample holder, the apparatus comprising a ring-shaped electrode disposed above the electrode and around the periphery of the top portion of the sample holder, an outer circumferential ring of dielectric material disposed above the ring-shaped electrode and opposite to the plasma, and a power source for supplying power at different values to the ring-shaped electrode depending on the sorts of layers of the layer structure.

Plasma Processing Apparatus

A patient positioning system for use with a radiation therapy system that monitors the location of fixed and movable components and pre-plans movement of the movable components so as to inhibit movement if a collision would be indicated. The positioning system can also coordinate movement of multiple movable components for reduced overall latency in registering a patient. The positioning system includes external measurement devices which measure the location and orientation of objects, including components of the radiation therapy system, in space and can also monitor for intrusion into the active area of the therapy system by personnel or foreign objects to improve operational safety of the radiation therapy system.

Path planning and collision avoidance for movement of instruments in a radiation therapy environment

A dielectric-wall linear accelerator is improved by a high-voltage, fast rise-time switch that includes a pair of electrodes between which are laminated alternating layers of isolated conductors and insulators. A high voltage is placed between the electrodes sufficient to stress the voltage breakdown of the insulator on command. A light trigger, such as a laser, is focused along at least one line along the edge surface of the laminated alternating layers of isolated conductors and insulators extending between the electrodes. The laser is energized to initiate a surface breakdown by a fluence of photons, thus causing the electrical switch to close very promptly. Such insulators and lasers are incorporated in a dielectric wall linear accelerator with Blumlein modules, and phasing is controlled by adjusting the length of fiber optic cables that carry the laser light to the insulator surface.

Vacuum-surface flashover switch with cantilever conductors

A compact accelerator system having an integrated particle generator-linear accelerator with a compact, small-scale construction capable of producing an energetic (˜70-250 MeV) proton beam or other nuclei and transporting the beam direction to a medical therapy patient without the need for bending magnets or other hardware often required for remote beam transport. The integrated particle generator-accelerator is actuable as a unitary body on a support structure to enable scanning of a particle beam by direction actuation of the particle generator-accelerator.

Compact accelerator for medical therapy

An improved photoconductive switch having a SiC or other wide band gap substrate material, such as GaAs and field-grading liners composed of preferably SiN formed on the substrate adjacent the electrode perimeters or adjacent the substrate perimeters for grading the electric fields.

Optically- initiated silicon carbide high voltage switch

Dielectric-wall linear accelerator with a high voltage fast rise time switch that includes a pair of electrodes between which are laminated alternating layers of isolated conductors and insulators

Dielectric wall accelerators, a class of induction accelerators, employ a novel insulating beam tube to impress a longitudinal electric field on a bunch of charged particles. The surface flashover characteristics of this tube may permit the attainment of accelerating gradients on the order of 100 MV/m for accelerating pulses on the order of a nanosecond in duration. A virtual traveling wave of excitation along the tube is produced at any desired speed by controlling the timing of pulse-generating modules that supply a tangential electric field to the tube wall. Because of the ability to control the speed of this virtual wave, the accelerator is capable of handling any charge-to-mass-ratio particle; hence it can be used for electrons, protons and any ion. The accelerator architectures, key technologies and development challenges will be described.

Stephen Sampayan

Papers

Vacuum-surface flashover switch with cantilever conductors

Compact accelerator for medical therapy

Optically- initiated silicon carbide high voltage switch

Dielectric-wall linear accelerator with a high voltage fast rise time switch that includes a pair of electrodes between which are laminated alternating layers of isolated conductors and insulators

The Dielectric Wall Accelerator