Three-dimensional Beam Scanning Research Articles

Design of Wideband Concentric-Ring Arrays with Three-Dimensional Beam Scanning Based on the Optimization of Array Geometry

Absract Optimization design of wideband concentric-ring arrays for three-dimensional beam scanning with a minimum peak side-lobe level is addressed in this article. To obtain three-dimensional beam scanning with the lowest peak side-lobe level over a wide bandwidth, concentric-ring array geometries, i.e., radius and inter-element spacing of each ring, are optimized. Optimal array geometries are solved via the differential evolution algorithm, and the results are presented for wideband concentric-ring arrays with different scan angles. The peak side-lobe level of the optimal wideband concentric-ring arrays dropped significantly compared to the periodic arrays after geometry optimization was performed. In addition, the comparison with the periodic wideband array shows that not only does the optimal wideband concentric-ring array have a comparable directivity, but the number of elements is also saved.

The future of heavy ion radiotherapy

Currently, there is an increasing interest in heavy ion radiotherapy (RT) and a number of new facilities are being installed in Europe and Japan. This development is accompanied by intensive technical, physical, and clinical research. The authors identify six research fields where progress is likely and propose a thesis on the expected achievements for each of the fields: (1) Synchrotrons with active energy variation and three-dimensional beam scanning will be the standard in ion beam RT. (2) Common standards for precise measurement, prescription, and reporting of dose will be available. (3) Intensity-modulated particle therapy will be state-of-the-art. (4) Time-adaptive treatments of moving targets will be feasible. (5) Therapeutic effectiveness of heavy ions will be known for the most important indications while cost effectiveness will remain to be shown. (6) The potential of high-linear energy transfer radiation will be known. The rationale for each of these theses is described.

Three-dimensional beam scanning for proton therapy

An important goal of radiation therapy is to localize the dose in the target volume. The favorable properties of proton beams, such as a well-determined range and straight penetration through tissues, have been used to develop a three-dimensional beam scanning method. This system consists of a two-dimensional beam scanning system and an energy degrader of variable thickness which are both controlled by a beam monitor that is connected to a minicomputer. A typically conformed dose distribution with the three-dimensional beam scanning system was measured by a specially designed multiwire ionization chamber. The results have shown that the system works satisfactorily and considerably reduces the radiation dose outside the target volume.

Present and future sources of protons and heavy ions

A brief outline of existing medical heavy-ion facilities is given. The beam specifications for future dedicated medical ion accelerators are discussed. Machines capable of delivering dose rates of approximately 1 krad/min in volumes of a few liters are shown to represent existing technology. A cost and performance analysis shows the synchrotrons to be the most economical source for the heavier ions while conventional cyclotrons seem optimal for an exclusive proton facility. It is seen that the incorporation of additional capabilities such as neutron generation or radioisotope production can be achieved at modest incremental costs. In addition to the accelerators, feasible layouts of hypothetical facilities are discussed, and three-dimensional beam scanning is shown to allow the irradiation of large volumes without sacrificing the precise dose localization capabilities of heavy-ion beams. Concepts of quality-controlled engineering and modern computer technology are introduced as a means to obtain the desired high degree of reliability and ease of operation and maintenance.