Kazumichi Suzuki

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.

Laser breakdown acoustic effect of ultrafine particle in liquids and its application to particle counting

The mechanism of acoustic signal generation from an ultrafine particle in liquids by laser irradiation was found to shift from the photoacoustic effect to optical breakdown of the particle as the power density of the excitation beam increased. The acoustic signal generated from a 0.085 µm polystyrene ultrafine particle in water increased discontinuously at the beam power density of 7.0 ×1010 W/cm2, corresponding to its dielectric breakdown threshold. Then, a novel method in which ultrafine particles were counted individually by counting the breakdown acoustic pulses was proposed, and its counting principle was verified using the polystyrene ultrafine particles.

Noncontact Measurement of Film Thickness by the Photothermal Deflection Method

A noncontact film-thickness measurement method using photothermal deflection was studied from theoretical and experimental results of the film-thickness dependency of the deflection amplitude. The calculated results showed that thicknesses in a range from the skin depth to the thermal-diffusion length of an opaque film could be determined from the deflection amplitude, which increased monotonously in that range. It was shown that the thicknesses of a transparent film could be determined from the vibrational structure of the deflection amplitude due to an interference effect of the excitation beam or from its decrease by an adiabatic effect of the film. Experimental results for NiO films (3–38 µm) and SiO2 films (20–110 nm) revealed the possibility of noncontact film-thickness measurements in air and water.

Measurement of vaporized atom flux and velocity in a vacuum using a microbalance

The flux and velocity of Cu and Ti vaporized by an electron beam were measured by a microbalance. A small disk was hung horizontally above the crucible and its weight change was measured by the microbalance. The flux was determined from the weight change due to vaporized atom deposition under the disk base. The total momentum of deposited atoms per unit time was determined from the weight change before and after the vapor was turned off by a shutter. The velocity could then be calculated from these two values. The velocity obtained for Cu depended slightly on the vaporization temperature and had reasonable agreement with the theoretical estimation obtained using an ideal gas treatment. The velocity of Ti was slightly higher than the theoretical result. Since Ti was excited to several metastable energy levels by electron beam heating, such an internal energy should be converted to kinetic energy following adiabatic expansion and would account for the velocity increase. The internal energy by excitation to the metastable energy levels must be taken into consideration in the case of high temperature heating, as with an electron beam evaporative source.

Ion Transport from Laser Induced Metal Plasma to Ion Extraction Electrodes

Ion transport from a laser-induced metal plasma in a vapor to a cathode surface has been investigated experimentally using conventional parallel plate electrodes and a new conceptual electrode system, which consists of an anode and two cathodes, designated as “M-type electrodes”. Rapid ion transport is possible using the M-type electrodes compared with the parallel plate electrodes and there are two modes of ion transport. One is a mode similar to that seen for parallel plate electrodes, in which the bulk plasma upstreams with a velocity of 1,160 m/s during the ion extraction. The other is a special mode for the M-type electrodes, in which the plasma upstream stops at its origin and ions are transported to the parallel cathodes from both sides of the plasma.

Simultaneous Determination of Uranium and HNO3 Concentrations in Solution by Laser-Induced Fluorescence Spectroscopy

A simultaneous determination method of U and HNO3 concentrations by fluorescence spectroscopy was proposed. In the method, the former was determined from UO2 2+ fluorescence intensity which is proportional to UO2 2+ ion concentration and the latter from UO2 2+ fluorescence spectrum profile which depends on the NO3 − ion configuration around the UO2 2+ ion. The UO2 2+ fluorescence spectra were measured by a laser-induced fluorescence spectrometer which was capable of remote measurement by utilizing fiber optics. The fluorescence spectrum profiles were evaluated by normalized integrated fluorescence intensities in the wavelength region of 510∼650 nm. The U and HNO3 concentrations were determined in the ranges of 1∼200 mg/dm3 with an accuracy of 0.5 mg/dm3, and 0.75∼6.0 mol/dm3 with an accuracy of 0.1 mol/dm3, respectively.

Spot-Scanning Proton Therapy Patient- Specific Quality Assurance: Results from 309 Treatment Plans

Abstract Purpose: We report the outcomes of patient-specific quality assurance (PSQA) for spot-scanning proton therapy (SSPT) treatment plans by disease site. Patients and Methods: We analyzed quality assurance outcomes for 309 SSPT plans. The PSQA measurements consisted of 2 parts: (1) an end-to-end test in which the beam was delivered at the prescribed gantry angle and (2) dose plane measurements made from gantry angle 270°. The HPlusQ software was used for gamma analysis of the dose planes using dose-tolerance and distance-to-agreement levels of 2%, 2 mm and 3%, 3 mm, respectively. Passing was defined as a gamma score <1 in at least 90% of the pixels. Results: The overall quality assurance measurement passing rate was 96.2% for the gamma index criteria of 3%, 3 mm but fell to 85.3% when the criteria were tightened to 2%, 2 mm. The passing rate was dependent on the treatment site. With the 3%, 3 mm criteria, the passing rate was 95% for head-and-neck treatment plans and 100% for prostate plans. No signi...

Quantitative analysis of beam delivery parameters and treatment process time for proton beam therapy

PURPOSE To evaluate patient census, equipment clinical availability, maximum daily treatment capacity, use factor for major beam delivery parameters, and treatment process time for actual treatments delivered by proton therapy systems. METHODS The authors have been recording all beam delivery parameters, including delivered dose, energy, range, spread-out Bragg peak widths, gantry angles, and couch angles for every treatment field in an electronic medical record system. We analyzed delivery system downtimes that had been recorded for every equipment failure and associated incidents. These data were used to evaluate the use factor of beam delivery parameters, the size of the patient census, and the equipment clinical availability of the facility. The duration of each treatment session from patient walk-in and to patient walk-out of the treatment room was measured for 82 patients with cancers at various sites. RESULTS The yearly average equipment clinical availability in the last 3 yrs (June 2007-August 2010) was 97%, which exceeded the target of 95%. Approximately 2200 patients had been treated as of August 2010. The major disease sites were genitourinary (49%), thoracic (25%), central nervous system (22%), and gastrointestinal (2%). Beams have been delivered in approximately 8300 treatment fields. The use factor for six beam delivery parameters was also evaluated. Analysis of the treatment process times indicated that approximately 80% of this time was spent for patient and equipment setup. The other 20% was spent waiting for beam delivery and beam on. The total treatment process time can be expressed by a quadratic polynomial of the number of fields per session. The maximum daily treatment capacity of our facility using the current treatment processes was estimated to be 133 +/- 35 patients. CONCLUSIONS This analysis shows that the facility has operated at a high performance level and has treated a large number of patients with a variety of diseases. The use factor of beam delivery parameters varies by disease site. Further improvements in efficiency may be realized in the equipment- and patient-related processes of treatment.

Ion extraction from plasma by using a radio frequency resonant electric field

In order to raise an ion extraction efficiency from a plasma, a new method using an rf field has been proposed and demonstrated. The resonant frequencies of the rf field were theoretically evaluated to excite the eigenwave of the plasma. The lower frequency of the two plasma‐sheath resonances under the magnetic field was selected because it has hardly any dependence on the plasma density when the density is over a critical value. Verification of this method was carried out using Xe discharge plasma (electron density, 1×1016 m−3; electron temperature, 8 eV) between the parallel plate electrodes (length, 0.5 m). The resonance was found at about 10 MHz, which agreed with the theoretical result. The ion current at the resonance was anisotropic and was twice as large as the ion saturated current, which is the limiting value of the conventional electrostatic method.

Fluorometry of UO2+2 ion in nitric acid solutions

The UO2 2+ fluorescence spectra were measured for solutions whose conditions, except for coexisting species, corresponded to high level waste (HLW) solutions in the nuclear fuel reprocessing plants. From these spectra it was ascertained that the U concentration can be determined in the range of 2–200g/m3 with an accuracy of 1g/m3 at 30–40°C. The UO2 2+ fluorescence was influenced significantly by the temperature. The apparant activation energy of the temperature effect was 35.7 kJ/mol. The fluorescence intensities increased with nitric acid concentration in the range of 0.75–4.5mol/dm3. The temperature effect was considered to be caused by a chemical process concerned with water molecules.