Correction of coincidence summing effects for add-back mode measurements with a 4π clover detector using experimental total efficiency.

We demonstrated coincidence summing corrections for the measured spectra of multi γ-ray emitters with the add-back mode of a 4π clover detector with an almost 98% solid angle condition using a Monte Carlo calculation based on nuclear decay data. The total and peak efficiencies were determined by Monte Carlo simulation code GEANT4 so that the experimental efficiencies measured mono/quasi-mono energetic γ-ray sources of 109Cd, 139Ce, 137Cs, 54Mn, 57, 60Co and 88Y may be reproduced well. Under a large solid angle condition, (i.e., a large coincidence summing condition), the corrected peak efficiencies, deduced from 134Cs and 152,154Eu measured, were in agreement within 5% with peak efficiencies in the absence of coincidence summing. The coincidence summing effects were corrected properly according to the decay scheme information, using experimental and simulated values of the total efficiency. We thus demonstrated the effectiveness of measurement with the add-back mode of the detector for γ-ray spectroscopy.

On the iteration of coincidence summing correction for determination of gamma-ray intensities.

In order to determine the γ-ray emission intensities of nuclei far from the ß-stability line with HPGe detectors under large solid-angle geometry, coincidence summing corrections should be performed, even if full energy peak efficiencies of detectors are accurately measured with standard sources. Because the summing effects depend on decay schemes and emission intensities, the correction needs to be iterated several times starting from the initial values of intensities obtained directly from the measured peak counts of γ-rays. Considering (134)Cs, (154)Eu and (56)Co as typical examples, we discuss the number of iterations of summing correction required for self-consistency with respect to the total efficiencies of the detectors.

Determination of full-energy peak efficiency at the center position of a through-hole-type clover detector between 0.05 MeV and 3.2 MeV by source measurements and Monte Carlo simulations.

Full-energy peak efficiency at the center position of a through-hole-type clover detector was determined by the measurement of standard sources and by Monte Carlo simulation. The coincidence summing under the large-solid-angle condition was corrected using Monte Carlo calculation based on the specific decay scheme for (133)Ba, (152,154)Eu, and (56)Co. This allowed the peak efficiency to be extended from 0.05 MeV to 3.2 MeV with an approximate uncertainty of 3%.

Relative intensities of prompt γ-rays from the 35Cl(n,γ)36Cl reaction with thermal neutrons as secondary γ-ray intensity standards.

The relative intensities of 16 prompt γ-rays from the (35)Cl(n,γ)(36)Cl reaction with a thermal neutron were precisely determined as secondary γ-ray intensity standards with HPGe detectors. The detection efficiencies were calibrated from 0.2 to 10.8 MeV using the standard sources (152)Eu and (56)Co and the (14)N(n,γ)(15)N reaction. We performed appropriate analyses for the evaluation of doublet peaks, subtraction of mixing with escape γ-rays and other corrections; consequently, the values were determined within 1% accuracy. Relative intensities in the range of 0.7 to 8.6 MeV are proposed as reliable secondary standards for 16 γ-rays.

Measurement of microdosimetric spectra produced from a 290 MeV/n Spread Out Bragg Peak carbon beam.

This study describes measurements on secondary particles produced by a 290 MeV/n Spread Out Bragg Peak (SOBP) carbon beam. Microdosimetric distributions of secondary fragments from the SOBP carbon beam have been measured by using a new tissue equivalent proportional counter (TEPC) system at the Heavy Ion Medical Accelerator in Chiba of the National Institute of Radiological Sciences. The new TEPC system consists of a TEPC, two solid-state detectors (SSD) and a scintillation counter (FSC: forward scintillation counter). The SSDs and FSC can separately identify charged fragments and secondary neutrons produced by the incident carbon ions. Microdosimetric distributions were measured for secondary particles including neutrons produced by a body-simulated phantom consisting of various PMMA plates (thickness: 0, 34.81, 55.2, 60.95, 64.83, 95.03, 114.79, 124.69, 135.2 and 144.98 mm, respectively) to cover the SOBP (at 60-125 mm depth). The new system can separately determine produced fragments from the incident SOBP carbon beam in a body-simulated phantom.

Dose rate estimation around a 60Co gamma-ray irradiation source by means of 115mIn photoactivation.

Photoactivation of nuclear isomer (115m)In with a halflife of 4.48 h occurs by (60)Co gamma-ray irradiation. This is because the resonance gamma-ray absorption occurs at 1078 keV level for stable (115)In, and that energy gamma-rays are produced by Compton scattering of (60)Co primary gamma-rays. In this work, photoactivation of (115m)In was applied to estimate the dose rate distribution around a (60)Co irradiation source utilizing a standard dose rate taken by alanine dosimeter. The (115m)In photoactivation was measured at 10 to 160 cm from the (60)Co source. The derived dose rate distribution shows a good agreement with both alanine dosimeter data and Monte Carlo simulation. It is found that angular distribution of the dose rate along a circumference at radius 2.8 cm from the central axis shows +/- 10% periodical variation reflecting the radioactive strength of the source rods, but less periodic distribution at radius 10 and 20 cm. The (115m)In photoactivation along the vertical direction in the central irradiation port strongly depends on the height and radius as indicated by Monte Carlo simulation. It is demonstrated that (115m)In photoactivation is a convenient method to estimate the dose rate distribution around a (60)Co source.

Microdosimetry on a mini-reactor UTR-KINKI for educational uses and biological researches.

Microdosimetry study has been carried out at the education and research mini-reactor of Kinki University (UTR-KINKI) using a tissue equivalent gas proportional counter (TEPC). The microdosimetric single event spectra for 0.5, 1, 2, 3 and 5 microm site sizes were obtained in the lineal energy range from 1 to 1000 keV/microm. Neutron and gamma-ray fractional doses were estimated from the single event spectra. The neutron dose fraction was varied from 35 to 55% for 0.5 to 5 microm site size. The averaged lineal energy, y(D), for each site size was likewise estimated and found to be dependent on the site size. The averaged lineal energy for neutron was slightly larger than that of the fission neutrons from (252)Cf, and the averaged lineal energy for gamma-ray had similar site-size-dependence of 25 keV gamma-rays and 250 kV X-rays. Relative biological effectiveness was found to be 4.1 +/- 0.13 for UTR-KINKI using Tilikidis's 2 Gy-response function. The estimated RBE for UTR-KINKI neutrons is quite close to the previous biological experimental value of 4.3 +/- 0.6 for micronucleated cells in gill cell of Medaka and 4.6 +/- 0.5 for induction of lymphocyte apoptosis in the thymus of ICR mice.

Randomized phase II study comparing mitomycin, cisplatin plus doxifluridine with cisplatin plus doxifluridine in advanced unresectable gastric cancer.

UNLABELLED: Various chemotherapies have been used to treat inoperable gastric cancer. Most combination therapies include cisplatin (CDDP) and fluoropyrimidine (5-FUs), which are thought of as key drugs. In the present study, we randomly compared mitomycin (MMC) and CDDP plus doxifluridine (5'-DFUR), which is an oral 5-FU and an intermediate metabolite of capecitabine (Xeloda), with CDDP plus 5'-DFUR in advanced unresectable gastric cancer. Regimen A was CDDP (70 mg/m2, by 2-hour intravenous drip infusion on day 1), MMC (7 mg/m2, injected intravenously on day 2), and oral 5'-DFUR (1200 mg/m2, on days 4 to 7, 11 to 14, 18 to 21 and 25 to 28; 3 days rest and 4 days administration). Regimen B was identical to regimen A without MMC. RESULTS: The response rate was 25.0% (8/32 patients) in Regimen A, 17.2% (5/29) in Regimen B (p=0.541). The median survival time was 241 days in Regimen A and 179 days in Regimen B (p=0.498). In Regimen A, although no significant difference was observed, end points such as response rate and suvival improved. Thus, we concluded that a randomized controlled phase III study with more subjects should be conducted.