Yasushi Iseki

Washout measurement of radioisotope implanted by radioactive beams in the rabbit.

Washout of 10C and 11C implanted by radioactive beams in brain and thigh muscle of rabbits was studied. The biological washout effect in a living body is important in the range verification system or three-dimensional volume imaging in heavy ion therapy. Positron emitter beams were implanted in the rabbit and the annihilation gamma-rays were measured by an in situ positron camera which consisted of a pair of scintillation cameras set on either side of the target. The ROI (region of interest) was set as a two-dimensional position distribution and the time-activity curve of the ROI was measured. Experiments were done under two conditions: live and dead. By comparing the two sets of measurement data, it was deduced that there are at least three components in the washout process. Time-activity curves of both brain and thigh muscle were clearly explained by the three-component model analysis. The three components ratios (and washout half-lives) were 35% (2.0 s), 30% (140 s) and 35% (10 191 s) for brain and 30% (10 s), 19% (195 s) and 52% (3175 s) for thigh muscle. The washout effect must be taken into account for the verification of treatment plans by means of positron camera measurements.

Spot Scanning Using Radioactive 11C Beams for Heavy-Ion Radiotherapy

A scheme for spot scanning using 11C beams has been developed in order to form and verify a three-dimensionally conformal irradiation field for cancer radiotherapy. By selecting the momentum spread of a 11C beam, we could considerably decrease the distal falloff of the irradiation field, thus conserving the beam quality. To estimate and optimize the dose distribution in the irradiation field, it is essential to evaluate the precise dose distribution of spot beams. The coupling of the lateral dose and depth-dose distributions originating from a wide momentum spread should be taken into account to calculate the dose distribution of 11C beams. The reconstructed dose distribution of the irradiation field was in good agreement with the experimental results, i.e., within ±0.2%. An irradiation field of 35×35×43 mm3 was optimized and spot scanning using 11C beams was carried out. The flatness was within ±2.3% with an error of 1% in the detector resolution.

Application of an RI-beam for cancer therapy: In-vivo verification of the ion-beam range by means of positron imaging

Abstract In cancer treatment with heavy ions, verification of the ion range in the patients body is important. For this purpose, a positron emitter beam provides the possibility of range verification. To use the positron emitter beam, we have constructed a secondary beam course and its irradiation system. In this paper the constructed system is presented together with some results of beam experiments.

Range verification system using positron emitting beams for heavy-ion radiotherapy

It is desirable to reduce range ambiguities in treatment planning for making full use of the major advantage of heavy-ion radiotherapy, that is, good dose localization. A range verification system using positron emitting beams has been developed to verify the ranges in patients directly. The performance of the system was evaluated in beam experiments to confirm the designed properties. It was shown that a 10C beam could be used as a probing beam for range verification when measuring beam properties. Parametric measurements indicated the beam size and the momentum acceptance and the target volume did not influence range verification significantly. It was found that the range could be measured within an analysis uncertainty of +/-0.3 mm under the condition of 2.7 x 10(5) particle irradiation, corresponding to a peak dose of 96 mGyE (gray-equivalent dose), in a 150 mm diameter spherical polymethyl methacrylate phantom which simulated a human head.

Focusing and spectral enhancement of a repetition-rated, laser-driven, divergent multi-MeV proton beam using permanent quadrupole magnets

A pair of conventional permanent magnet quadrupoles is used to focus a 2.4 MeV laser-driven proton beam at a 1 Hz repetition rate. The magnetic field strengths are 55 and 60 T/m for the first and second quadrupoles, respectively. The proton beam is focused to a spot with a size of less than ∼3×8 mm2 at a distance of 650 mm from the source. This result is in good agreement with the Monte Carlo particle trajectory simulation.

Improvement in the Output Characteristics of a Large-Bore Copper Vapor Laser by Hydrogen

It has been experimentally confirmed that addition of about 1% hydrogen gas to the copper vapor laser (CVL) discharge improves the output characteristics of a large-bore CVL with 80 mm beam diameter and 1500 mm discharge length. The annular distribution of the beam intensity became uniform and the output power increased. The increase in the green laser power was larger than that in the yellow one. The hydrogen gas addition was effectual when the input power to the discharge was large and the copper temperature was high. A 120 W output power was obtained continuously for 26 hours.

Medical application of radioactive nuclear beams at HIMAC

By using the radioactive nuclear beam with relativistic high energy of short-lived positron emitting nuclei, such as C10 and C11, a verification system for the precise radiotherapy has been developed. It is possible to determine the precise particle range and the three-dimensional irradiated area in the human body by a positron camera detector and a positron emission tomography system, respectively. The biological and chemical process of the metabolism is an important parameter for the precise measurement. The biological lifetimes of the C10 and C11 injected into the rabbit’s organs have been observed for the study of metabolism. The microscopic process around the cell is also of interest in the study of biological effectiveness. The observation of the difference between radiological effectiveness of C9 and that of C12 is in progress.By using the radioactive nuclear beam with relativistic high energy of short-lived positron emitting nuclei, such as C10 and C11, a verification system for the precise radiotherapy has been developed. It is possible to determine the precise particle range and the three-dimensional irradiated area in the human body by a positron camera detector and a positron emission tomography system, respectively. The biological and chemical process of the metabolism is an important parameter for the precise measurement. The biological lifetimes of the C10 and C11 injected into the rabbit’s organs have been observed for the study of metabolism. The microscopic process around the cell is also of interest in the study of biological effectiveness. The observation of the difference between radiological effectiveness of C9 and that of C12 is in progress.

Characteristics of a large-bore copper vapor laser with gas-cooling plates

It has been experimentally found that the insertion of plates into the plasma tube has improved the output characteristics of an 80-mm copper vapor laser. It has been revealed that the buffer gas temperature decreases and the metastable-state (the lower laser level) density of copper atoms decreases near the center axis of the plasma tube. Moreover, electric power is transferred into plasma more efficiently because of the increase in plasma impedance. As a result, the average output power is increased by 57 % and the beam intensity profile has become uniform.

Prompt In-Line Diagnosis of Single Bunch Transverse Profiles and Energy Spectra for Laser-Accelerated Ions

Many applications of laser-accelerated ions will require beamlines with diagnostic capability for validating simulations and machine performance at the single bunch level as well as for the development of controls to optimize machine performance. We demonstrated prompt, in-line, single bunch transverse profile and energy spectrum detection using a thin luminescent diagnostic and scintillator-based time-of-flight spectrometer simultaneously. The Monte Carlo code, particle and heavy ion transport code systems (PHITS) simulation is shown to be reasonably predictive at low proton energy for the observed transverse profiles measured by the thin luminescent monitor and also for single bunch energy spectra measured by time-of-flight spectrometry.

Characteristics of a 100-mm-Bore Copper Vapor Laser and Their Prediction by a Gas Cooling Model

A high-power copper vapor laser (CVL) scaled up to a 100 mm bore has been developed. In a large-bore CVL, there is a problem that the radial beam profile becomes nonuniform, which is caused by the high temperature of the buffer gas. Two methods have been applied to gas cooling: hydrogen addition to the buffer gas and insertion of gas cooling plates. Modeling of the increased thermal conductivity by hydrogen addition and of the radiation effect by plate insertion predicted that the buffer gas temperature would drop from 4160 K to 2650 K under typical operating conditions. Experimental results showed that the beam profile was improved especially at high repetition frequencies and high input powers. The CVL with a plasma tube length of 2.3 m was able to generate an output power of 329 W as an oscillator.