Kazuo Hiramoto

The M. D. Anderson proton therapy system

PURPOSE The purpose of this study is to describe the University of Texas M. D. Anderson proton therapy system (PTC-H) including the accelerator, beam transport, and treatment delivery systems, the functionality and clinical parameters for passive scattering and pencil beam scanning treatment modes, and the results of acceptance tests. METHODS The PTC-H has a synchrotron (70-250 MeV) and four treatment rooms. An overall control system manages the treatment, physics, and service modes of operation. An independent safety system ensures the safety of patients, staff, and equipment. Three treatment rooms have isocentric gantries and one room has two fixed horizontal beamlines, which include a large-field treatment nozzle, used primarily for prostate treatments, and a small-field treatment nozzle for ocular treatments. Two gantry treatment rooms and the fixed-beam treatment room have passive scattering nozzles. The third gantry has a pencil beam scanning nozzle for the delivery of intensity modulated proton treatments (IMPT) and single field uniform dose (SFUD) treatments. The PTC-H also has an experimental room with a fixed horizontal beamline and a passive scattering nozzle. The equipment described above was provided by Hitachi, Ltd. Treatment planning is performed using the Eclipse system from Varian Medical Systems and data management is handled by the MOSAIQ system from IMPAC Medical Systems, Inc. The large-field passive scattering nozzles use double scattering systems in which the first scatterers are physically integrated with the range modulation wheels. The proton beam is gated on the rotating range modulation wheels at gating angles designed to produce spread-out-Bragg peaks ranging in size from 2 to 16 g/cm2. Field sizes of up to 25 x 25 cm2 can be achieved with the double scattering system. The IMPT delivery technique is discrete spot scanning, which has a maximum field size of 30 x 30 cm2. Depth scanning is achieved by changing the energy extracted from the synchrotron (energy can be changed pulse to pulse). The PTC-H is fully integrated with DICOM-RT ION interfaces for imaging, treatment planning, data management, and treatment control functions. RESULTS The proton therapy system passed all acceptance tests for both passive scattering and pencil beam scanning. Treatments with passive scattering began in May 2006 and treatments with the scanning system began in May 2008. The PTC-H was the first commercial system to demonstrate capabilities for IMPT treatments and the first in the United States to treat using SFUD techniques. The facility has been in clinical operation since May 2006 with up-time of approximately 98%. CONCLUSIONS As with most projects for which a considerable amount of new technology is developed and which have duration spanning several years, at project completion it was determined that several upgrades would improve the overall system performance. Some possible upgrades are discussed. Overall, the system has been very robust, accurate, reproducible, and reliable. The authors found the pencil beam scanning system to be particularly satisfactory; prostate treatments can be delivered on the scanning nozzle in less time than is required on the passive scattering nozzle.

Resonant beam extraction scheme with constant separatrix

Abstract A new scheme for resonant extraction with a constant separatrix is presented to realize small emittance, constant position and size of the extracted beam. In this scheme, the amplitude of the betatron oscillations inside the constant separatrix is increased by electromagnetic transverse or longitudinal perturbations, or scattering by other particles. Particles outside the separatrix are extracted through nonlinear resonance. The scheme is applied to the second order resonant extraction in the computer simulations. As a measure of transverse perturbation, the filtered noise and monochromatic signal are studied. The position of the extracted beam in the phase space is found to be nearly constant, meaning that the emittance of the extracted beam almost vanishes.

Degradation of Gate Oxide Integrity by Metal Impurities

The degradation of gate oxide integrity (GOI) by metal impurities on Si wafers was studied. Ni and Cu tended to precipitate at the Si surface after high-temperature annealing. When these precipitates existed before gate oxidation, they penetrated into the gate oxide film and degraded GOI. Fe tended to remain in the oxide film after oxidation and degraded GOI. The degradation was observed for annealed samples when the surface metal concentration exceeded 1.0×1012 atoms/cm2 of Ni or 5.0×1012 atoms/cm2 of Cu. It was also observed with contamination of 1.0×1013 atoms/cm2 of Fe without annealing.

A proton beam therapy system dedicated to spot-scanning increases accuracy with moving tumors by real-time imaging and gating and reduces equipment size.

Purpose A proton beam therapy (PBT) system has been designed which dedicates to spot-scanning and has a gating function employing the fluoroscopy-based real-time-imaging of internal fiducial markers near tumors. The dose distribution and treatment time of the newly designed real-time-image gated, spot-scanning proton beam therapy (RGPT) were compared with free-breathing spot-scanning proton beam therapy (FBPT) in a simulation. Materials and Methods In-house simulation tools and treatment planning system VQA (Hitachi, Ltd., Japan) were used for estimating the dose distribution and treatment time. Simulations were performed for 48 motion parameters (including 8 respiratory patterns and 6 initial breathing timings) on CT data from two patients, A and B, with hepatocellular carcinoma and with clinical target volumes 14.6 cc and 63.1 cc. The respiratory patterns were derived from the actual trajectory of internal fiducial markers taken in X-ray real-time tumor-tracking radiotherapy (RTRT). Results With FBPT, 9/48 motion parameters achieved the criteria of successful delivery for patient A and 0/48 for B. With RGPT 48/48 and 42/48 achieved the criteria. Compared with FBPT, the mean liver dose was smaller with RGPT with statistical significance (p<0.001); it decreased from 27% to 13% and 28% to 23% of the prescribed doses for patients A and B, respectively. The relative lengthening of treatment time to administer 3 Gy (RBE) was estimated to be 1.22 (RGPT/FBPT: 138 s/113 s) and 1.72 (207 s/120 s) for patients A and B, respectively. Conclusions This simulation study demonstrated that the RGPT was able to improve the dose distribution markedly for moving tumors without very large treatment time extension. The proton beam therapy system dedicated to spot-scanning with a gating function for real-time imaging increases accuracy with moving tumors and reduces the physical size, and subsequently the cost of the equipment as well as of the building housing the equipment.

Development of Signal Processing Methods for Imaging Buned Pipes

A new imaging technique for subsurface radars is described for reconstructing clear images of buried pipes in soil. The method developed has two signal processing stages; preprocessing and aperture synthesis. The preprocessing extracts signals scattered from the pipes by reducing clutter noise. The synthetic-aperture processing analyzes only the scattered signals derived by the first stage and reconstructs high-quality images in a short processing time. The imaging technique developed was successfully applied to the imaging of actual buried metallic pipes. It was experimentally confirmed that the new imaging method was capable of reconstructing clear images in a short time without losing image quality.

Advanced subsurface radar system for imaging buried pipes

A subsurface radar system for imaging buried pipes was developed. The system is capable of reconstructing clear pipe images under unfavorable conditions, such as large attenuation rate of the radio waves propagating in soil. The output power of a pulse generator, the amplifier gain, and average number are controlled by moving the observation depth to improve the detection capability. Fast image processing methods are also used. A 6.5-cm-diameter steel pipe, buried at a depth of 2.5 m, was clearly reconstructed as a color image averaged attenuation rate of 12.6 dB/m in the soil. A plastic pipe (6.5 cm in diameter), buried at a depth of 1 m, was also imaged by the system. >

Preliminary analysis for integration of spot-scanning proton beam therapy and real-time imaging and gating

PURPOSE Spot-scanning proton beam therapy (PBT) can create good dose distribution for static targets. However, there exists larger uncertainty for tumors that move due to respiration, bowel gas or other internal circumstances within the patients. We have developed a real-time tumor-tracking radiation therapy (RTRT) system that uses an X-ray linear accelerator gated to the motion of internal fiducial markers introduced in the late 1990s. Relying on more than 10 years of clinical experience and big log data, we established a real-time image gated proton beam therapy system dedicated to spot scanning. MATERIALS AND METHODS Using log data and clinical outcomes derived from the clinical usage of the RTRT system since 1999, we have established a library to be used for in-house simulation for tumor targeting and evaluation. Factors considered to be the dominant causes of the interplay effects related to the spot scanning dedicated proton therapy system are listed and discussed. RESULTS/CONCLUSIONS Total facility design, synchrotron operation cycle, and gating windows were listed as the important factors causing the interplay effects contributing to the irradiation time and motion-induced dose error. Fiducial markers that we have developed and used for the RTRT in X-ray therapy were suggested to have the capacity to improve dose distribution. Accumulated internal motion data in the RTRT system enable us to improve the operation and function of a Spot-scanning proton beam therapy (SSPT) system. A real-time-image gated SSPT system can increase accuracy for treating moving tumors. The system will start clinical service in early 2014.

Development of a high-current microwave ion source for proton linac application systems

A microwave hydrogen ion source was developed to improve reliability, and to increase operation time of proton linac application systems. The ion source needs no filament in the discharge chamber, which leads to better reliability and less maintenance time. The developed source produced a maximum hydrogen ion beam current of 70 mA (high current density of 360 mA/cm2, beam energy of 30 keV) with a 5 mm diam extraction aperture and 1.2 kW microwave power. The proton fraction was increased with an increase in rf power and reached around 90% at 1 kW. Measured 90% beam normalized emittance was 0.4 π mm mrad. Rise times of rf power and beam current to 90% of the final values were about 30 and 35 μs, respectively, at a pulse operation mode with 400 μs pulse width and 100 Hz repetition rate. The dynamic range of beam currents was enlarged (3–63 mA) in the pulse mode with a modified rf wave form to assist ignition of microwave discharge. These performance parameters will be desirable for pulse operation accelerato...

Reduction of the number of stacking layers in proton uniform scanning

Uniform scanning with a relatively large beam size can improve beam utilization efficiency more than conventional irradiation methods using scatterers and can achieve a large-field, long-range and large spread-out Bragg peak (SOBP). The SOBP is obtained by energy stacking in uniform scanning, but its disadvantage is that the number of stacking layers is large, especially in the low-energy region, because the Bragg peak of the pristine beam is very sharp. We applied a mini-ridge filter to broaden the pristine Bragg peak up to a stacked layer thickness of 1 or 2 cm in order to decrease the number of stacking layers. The number of stacking layers can be reduced to 20% or less than that in the case of pristine beam stacking. Although the distal falloff of the SOBP is deteriorated by applying the mini-ridge filter, we can improve the distal falloff to that of pristine beam stacking by introducing the distal filter to the irradiation of the most distal layer. Uniform scanning in combination with mini-ridge filter use can more than double the beam utilization efficiency over that of passive irradiation techniques.

A ferrite loaded untuned cavity for a compact proton synchrotron

A small untuned RF cavity using a doubly re-entrant resonator and Ni-Zn ferrite cores with highly complex permeability has been designed for a compact proton synchrotron. A new method for power feeding named as multiple power feeding (multi-feed coupling) as against to direct coupling was developed to increase the accelerating voltage. The RF power is fed into the cavity through a set of couplers with the same number as the ferrites. The coupler consists of one-turn loop which is wound on to each ferrite core. The effect of multi-feed coupling was verified by measurements of the VSWR and electric field in the accelerating gap using the low and the high power model cavities.