Thermoluminescent responses of Li3B7O12:Cu to proton beam

A thermoluminescent (TL) phosphor Li3B7O12:Cu was irradiated by a proton beam at NIRS-HIMAC in Japan. Irradiation was performed at different water-equivalent depths using range shifters made of polymethyl methacrylate. The thermoluminescent responses of Li3B7O12:Cu were analysed, focusing on the TL efficiency and glow curve. The irradiated samples were heated from room temperature to 200°C at 0.16°C s(-1). The high-temperature area of the glow curve under proton irradiation changed in comparison with that under (60)Co gamma-ray irradiation. The relative TL efficiency of the main peak slightly varied between 0.8 and 1.1. The relationship between the relative TL efficiency of the main peak and the high-temperature area ratio (HTR) value, the relative TL ratio of the main peak to the high-temperature area, showed approximate linearity for proton dosimetry. Using correction based on the HTR method, the TL phosphor Li3B7O12:Cu can become a useful dosimetric tool for therapeutic proton beams.

Relative biological effectiveness of therapeutic proton beams for HSG cells at Japanese proton therapy facilities

We investigated the relative biological effectiveness (RBE) of therapeutic proton beams at six proton facilities in Japan with respect to cell lethality of HSG cells. The RBE of treatments could be determined from experimental data. For this purpose, we used a cell survival assay to compare the cell-killing efficiency of proton beams. Among the five linear accelerator (LINAC) X-ray machines at 4 or 6 MeV that were used as reference beams, there was only a small variation (coefficient of variation CV = 3.1% at D10) in biological effectiveness. The averaged value of D10 for the proton beams at the middle position of the spread-out Bragg peak (SOBP) was 4.98. These values showed good agreement, with a CV of 4.3% among the facilities. Thus, the average RBE10 (RBE at the D10 level) at the middle position of the SOBP beam for six facilities in Japan was 1.05 with a CV of 2.8%.

FT-NMR Detection of 45Sc, 49Ti and 93Nb in TiO2 Single Crystal

In order to determine the electric quadrupole moment of the short-lived β-emitter 41Sc from the quadrupole coupling constant in TiO2 , we measured the field gradient by detecting the Fourier-Transformed-NMR of stable isotope 45Sc doped in TiO2. Also, in order to study the electronic structure of impurities systematically, EFGs were measured for 45Sc, 49Ti and 93Nb in a TiO2 ingle single crystal.

Quadrupole Moments of the 40Ca Core Plus One Nucleon Nuclei 41Sc and 41Ca

The electric-field-gradient (EFG) and anisotropic chemical shift of 45Sc(Iπ = 7/2- , stable) in TiO2 crystal were determined by detecting the FT-NMR of 45Sc(0.5 atm% of Ti in TiO2) doped in TiO2 crystal at a high field of 7.0 T and 9.4 T. Using the EFG, an old β-NQR spectrum of 41Sc was reanalyzed to obtain (41Sc)/ which was combined with the renewed (45Sc) = -(23.6 0.2) fm2 to obtain (41Sc; Iπ= 7/2- , T1/2 = 0.596 s) = (15.6±0.3) fm2. Also the atomic EFG in Ca was recalculated, using a finite-element multi configuration Hartree-Fock method to renew Q(43Ca). Finally using the known hyperfine constants of 41Ca, the (41Ca) value has been renewed

Modeling the biological response of normal human cells, including repair processes, to fractionated carbon beam irradiation

To understand the biological response of normal cells to fractionated carbon beam irradiation, the effects of potentially lethal damage repair (PLDR) and sublethal damage repair (SLDR) were both taken into account in a linear-quadratic (LQ) model. The model was verified by the results of a fractionated cell survival experiment with normal human fibroblast cells. Cells were irradiated with 200-kV X-rays and monoenergetic carbon ion beams (290 MeV/u) at two irradiation depths, corresponding to linear energy transfers (LETs) of approximately 13 keV/μm and 75 keV/μm, respectively, at the Heavy Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences. When we only took into account the repair factor of PLDR, γ, which was derived from the delayed assay, the cell survival response to fractionated carbon ion irradiation was not fully explained in some cases. When both the effects of SLDR and PLDR were taken into account in the LQ model, the cell survival response was well reproduced. The model analysis suggested that PLDR occurs in any type of radiation. The γ factors ranged from 0.36-0.93. In addition, SLD was perfectly repaired during the fraction interval for the lower LET irradiations but remained at about 30% for the high-LET irradiation.

Calculation method using Clarkson integration for the physical dose at the center of the spread-out Bragg peak in carbon-ion radiotherapy

PURPOSE

In broad-beam carbon-ion radiotherapy performed using the heavy-ion medical accelerator in Chiba, the number of monitor units is determined by measuring the physical dose at the center of the spread-out Bragg peak (SOBP) for the treatment beam. The total measurement time increases as the number of treatment beams increases, which hinders the treatment of an increased number of patients. Hence, Kusano et al. [Jpn. J. Med. Phys. 23(Suppl. 2), 65-68 (2003)] proposed a method to calculate the physical dose at the center of the SOBP for a treatment beam. Based on a recent study, the authors here propose a more accurate calculation method.

METHODS

The authors measured the physical dose at the center of the SOBP while varying the circular field size and range-shifter thickness. The authors obtained the physical dose at the center of the SOBP for an irregularly shaped beam using Clarkson integration based on these measurements.

RESULTS

The difference between the calculated and measured physical doses at the center of the SOBP varied with a change in the central angle of the sector segment. The differences between the calculated and measured physical doses at the center of the SOBP were within ± 1% for all irregularly shaped beams that were used to validate the calculation method.

CONCLUSIONS

The accuracy of the proposed method depends on both the number of angular intervals used for Clarkson integration and the fineness of the basic data used for calculations: sampling numbers for the field size and thickness of the range shifter. If those parameters are properly chosen, the authors can obtain a calculated monitor unit number with high accuracy sufficient for clinical applications.

NIRS external dose estimation system for Fukushima residents after the Fukushima Dai-ichi NPP accident

The great east Japan earthquake and subsequent tsunamis caused Fukushima Dai-ichi Nuclear Power Plant (NPP) accident. National Institute of Radiological Sciences (NIRS) developed the external dose estimation system for Fukushima residents. The system is being used in the Fukushima health management survey. The doses can be obtained by superimposing the behavior data of the residents on the dose rate maps. For grasping the doses, 18 evacuation patterns of the residents were assumed by considering the actual evacuation information before using the survey data. The doses of the residents from the deliberate evacuation area were relatively higher than those from the area within 20 km radius. The estimated doses varied from around 1 to 6 mSv for the residents evacuated from the representative places in the deliberate evacuation area. The maximum dose in 18 evacuation patterns was estimated to be 19 mSv.

Lifestyle, stress and cortisol response: Review I : Mental stress

The incidences of diseases related to mental stress are increasing in Japan. Mental stress, unacknowledged for long periods, has been shown to lead to the development of a number of diseases. Thus, an index for mental stress is important to induce awareness of its presence. We focused on the relationship between cortisol and mental stress in this review. We will discuss both the usefulness and problems of cortisol as a mental stress index by summarizing the relationship between cortisol and mental stress. The present findings suggested that cortisol appears to be an adequate index for mental stress. However, there are several problems; the present group clarifies these problems and builds the comprehensive mental stress assessment systems by using saliva samples.

Development of a therapeutically important radiation induced promoter

Radio-genetic therapy is a combination of radiation therapy and gene therapy that may solve some of the problems associated with conventional radiotherapy. A promoter responsive to radiation was obtained from a promoter library composed of DNA fragments created by linking the TATA box signal to randomly combined binding sequences of transcription factors that are reactive to radiation. Each promoter connected to the luciferase gene, was evaluated by luciferase expression enhancement in transfected cells after X-ray irradiation. The reactivity of the best promoter was improved by the random introduction of point mutations and the resultant promoter showed more than a 20-fold enhancement of the luciferase expression after X-ray irradiation at 10 Gy. The expression of downstream genes was also enhanced in stably transfected cells not only by X-rays but also by proton beam irradiation; and either enhancement was attenuated when an anti-oxidant was added, thus suggesting the involvement of oxidative stress in the promoter activation. Constructed promoters were also activated in tumors grown in mice. In addition, cell killing with the fcy::fur gene (a suicide gene converting 5-fluorocytosin to highly toxic 5-fluorouracil) increased dose-dependently with 5-fluorocytosin only after X-ray irradiation in vitro. These results suggest that promoters obtained through this method could be used for possible clinical applications.