Ambient and personal dose assessment of a container inspection site using a mobile X-ray system.

Ambient monitor and phantom studies of absorbed and effective doses by TLDs were carried out in a non-intrusive inspection station for containers, Terminal I, of Taichung harbor, Taiwan. The doses from the X-ray scan in the control room and driver waiting room, located outside of the radiation control area, were quite small and could not be distinguished from the natural background radiation. The doses in the driver cab and the inspector cab of the X-ray scan car were also within background radiation levels. The protection wall, a 40-cm thick concrete barrier, can effectively attenuate the intensity of the primary X-ray scan. The possible effective dose of a person in the container or trailer is about 3.15 ± 0.23 µSv/scan and 2.31 ± 0.38 µSv/scan. This dose is below the annual background dose. If someone was to be scanned by the X-ray, the effective dose would be at an acceptable level.

Cellular dosimetry and microdosimetry for internal electron emitters.

Radiobiological descriptions of cellular dosimetry and microdosimetry require both radiation dose and radiation quality. The lineal energy, defined as a ratio of the energy deposition by a particle in the biological target and the mean chord length of this target, is generally adopted to characterise the radiation quality. Most microdosimetry applications assume that the cell nucleus is the target region. Therefore, the lineal energy is obtained for the source (S) to target (T) geometry, T ← S, where S = cell surface, cytoplasm, cell nucleus and T = cell nucleus. The definition of lineal energy is based on the approximation that the particle mean pathlength is equal to target mean chord length. This approximation is valid for crossers of external irradiations. In the case of starters, insiders and stoppers of internal sources, particle pathlengths are always shorter than target chord lengths. Thus, the lineal energy does not reflect the specific energy deposition along particle path. In the present work, the specific energy deposition in a target is calculated using three distance parameters, i.e. target mean chord length, particle mean pathlength in the target and particle individual pathlength in the target. Monte Carlo calculations are performed for electrons of various energies and cells of different sizes. Results are analysed and discussed.

Microdosimetry study of THOR BNCT beam using tissue equivalent proportional counter.

Boron neutron capture therapy (BNCT) is a cancer treatment modality using a nuclear reactor and a boron compound drug. In Taiwan, Tsing Hua open-pool reactor (THOR) has been modulated for the basic research of BNCT for years. A new BNCT beam port was built in 2004 and used to prepare the first clinical trial in the near future. This work reports the microdosimetry study of the THOR BNCT beam by means of the tissue equivalent proportional counter (TEPC). Two self-fabricated TEPCs (the boron-doped versus the boron-free counter wall) were introduced. These dual TEPCs were applied to measure the lineal energy distributions in air and water phantom irradiated by the THOR BNCT mixed radiation field. Dose contributions from component radiations of different linear energy transfers (LETs) were analyzed. Applying a lineal energy dependent biological weighting function, r(y), to the total and individual lineal energy distributions, the effective relative biological effectiveness (RBE), neutron RBE, photon RBE, and boron capture RBE (BNC RBE) were all determined at various depths of the water phantom. Minimum and maximum values of the effective RBE were 1.68 and 2.93, respectively. The maximum effective RBE occurred at 2cm depth in the phantom. The average neutron RBE, photon RBE, and BNC RBE values were 3.160+/-0.020, 1.018+/-0.001, and 1.570+/-0.270, respectively, for the THOR BNCT beam.

Verification of the accuracy of BNCT treatment planning system THORplan.

THORplan is a treatment planning system developed at Tsing Hua University, Taiwan, for boron neutron capture therapy (BNCT) purpose. It is recently developed with user-friendly interface using Interactive Data Language. In this article the accuracy of THORplan is verified by comparing results of Snyder phantom calculation with the analytical model results of MCNP. Neutron source from THOR epithermal neutron beam is used as the source for the calculation. The thermal neutron flux calculated by THORplan is very close to the reference results. SERA overestimates thermal neutron flux by 2-5%. NCTPlan underestimates thermal neutron flux by 4-9% in most locations. The total weighted dose calculated by THORplan is accurate to within 3% except at the tissue interface. SERA overestimates the total weighted dose at depth >1.5 cm by 2-5%. NCTPlan underestimates the total weighted dose by approximately 10% at depth >1cm.

Assessment of dose rate scaling factors used in NCTPlan treatment planning code for the BNCT beam of THOR.

Tsing Hua open-pool reactor (THOR) at Tsing Hua University in Taiwan has been used to investigate the feasibility and to enhance the technology of boron neutron capture therapy (BNCT) for years. A rebuilt epithermal beam port for BNCT at THOR was finished in the summer of 2004, and then researches and experiments were performed to hasten the first clinical treatment case of BNCT in Taiwan in the near future. NCTPlan, a Monte Carlo-based clinical treatment planning code, was used to calculate the dose-rate distributions of BNCT in this work. A self-made Snyder head phantom with a servo-motor control system was irradiated in front of the THOR BNCT beam exit. The phantom was made from a 3mm shell of quartz wool impregnated with acrylic casting resin mounted on an acrylic base, and was filled with water. Gold foils (bare and cadmium-covered) and paired ion chambers (one with graphite wall and filled with CO(2) gas, another with A-150 plastic tissue equivalent wall and filled with tissue equivalent gas) were placed inside the Snyder phantom to measure and estimate the depth-dose distributions in the central axis of the beam. Dose components include the contribution of thermal neutrons, fast neutrons, photons and emitted alpha particles from (10)B(n,alpha)(7)Li reaction. Comparison and analysis between computed and measured results of depth-dose distributions were made in this work. Dose rate scaling factors (DRSFs) were defined as normalization factors derived individually for each dose component in the BNCT in-phantom radiation field that provide the best agreement between measured and computed data. This paper reports the in-phantom calculated and experimental dosimetry and the determined DRSFs used in NCTPlan code for the BNCT beam of THOR.

Using medical accelerators and photon activation to determine Sr/Ca concentration ratios in teeth.

This paper describes a photon activation method, studied by using two medical accelerators (energies: 15 and 18 MeV) as photon sources, for determining Sr and Ca levels and Sr/Ca ratios in tooth samples. The radionuclides formed by various photonuclear reactions were measured and identified using a gamma-spectrometry with HPGe detection system. The yields of the corresponding photonuclear reactions and the detection sensitivities for the alkaline earth metals (e.g., Ca, Sr) were surveyed and estimated in relation to the radiation dose. The minimum detectable amount of Sr was estimated to be less than 1 microg g(-1), allowing the Sr/Ca ratios in teeth to be determined conveniently. The Sr/Ca ratios in deciduous and permanent tooth samples obtained from local dental clinics were 0.390 and 0.565 mg g(-1), respectively. This photon activation method of determining Sr/Ca ratio in bones and teeth using medical accelerators for cancer treatment is thought to be useful also in biological and archaeological studies.

Characteristics of the new THOR epithermal neutron beam for BNCT.

A characterization of the new Tsing Hua open-pool reactor (THOR) epithermal neutron beam designed for boron neutron capture therapy (BNCT) has been performed. The facility is currently under construction and expected in completion in March 2004. The designed epithermal neutron flux for 1 MW power is 1.7x10(9)n cm(-2)s(-1) in air at the beam exit, accompanied by photon and fast neutron absorbed dose rates of 0.21 and 0.47 mGys(-1), respectively. With (10)B concentrations in normal tissue and tumor of 11.4 and 40 ppm, the calculated advantage depth dose rate to the modified Snyder head phantom is 0.53RBE-Gymin(-1) at the advantage depth of 85 mm, giving an advantage ratio of 4.8. The dose patterns determined by the NCTPlan treatment planning system using the new THOR beam for a patient treated in the Harvard-MIT clinical trial were compared with results of the MITR-II M67 beam. The present study confirms the suitability of the new THOR beam for possible BNCT clinical trials.

Dose-rate scaling factor estimation of THOR BNCT test beam.

In 1998, an epithermal neutron test beam was designed and constructed at the Tsing Hua Open-Pool Reactor (THOR) for the purpose of preliminary dosimetric experiments in boron neutron capture therapy (BNCT). A new epithermal neutron beam was designed at this facility, and is currently under construction, with clinical trials targeted in late 2004. Depth dose-rate distributions for the THOR BNCT test beam have been measured by means of activation foil and dual ion chamber techniques. Neutron and structure-induced gamma spectra measured at the test beam exit were configured into a source function for the Monte Carlo-based treatment planning code NCTPlan. Dose-rate scaling factors (DRSFs) were determined to normalize computationally derived dose-rate distributions with experimental measurements in corresponding mathematical and physical phantoms, and to thus enable accurate treatment planning using the NCTPlan code. A similar approach will be implemented in characterizing the new THOR epithermal beam in preparation for clinical studies. This paper reports the in-phantom calculated and experimental dosimetry comparisons and derived DRSFs obtained with the THOR test beam.

MicroPET-based pharmacokinetic analysis of the radiolabeled boron compound [18F]FBPA-F in rats with F98 glioma.

Boron neutron capture therapy (BNCT) is one of the effective methods of radiation therapy for the treatment of tumors such as malignant glioma. Boronophenylalanine ((10)B-BPA) solution has been used as a potential boron carrier for such a treatment. The aim of this study is to investigate 4-borono-2-[(18)F]-fluoro-l-phenylalanine-fructose ([(18)F]FBPA-F) in rats injected in the brain with glioma using in vivo small animal positron emission tomography (PET) imaging (microPET). Male Fischer 344 rats with F98 glioma in the left brain were used for these studies. Dynamic PET imaging of [(18)F]FBPA-F was performed on the 13th day after tumor inoculation. Arterial blood sampling was performed to obtain an input function for tracer kinetic modeling. The accumulation ratios of [(18)F]FBPA-F for the glioma-to-normal brain approached 3. The uptake characteristics of BPA-F and [(18)F]FBPA-F were similar. The results indicate that 4h after BPA-F injection would be the optimal irradiation time for BNCT. Rate constants were estimated using a three-compartment model. This study provides useful information for the clinical application of BNCT in patients with brain tumors.

Microdosimetric spectra of the THOR neutron beam for boron neutron capture therapy.

A primary objective of the BNCT project in Taiwan, involving THOR (Tsing Hua Open Pool Reactor), was to examine the potential treatment of hepatoma. To characterise the epithermal neutron beam in THOR, the microdosimetry distributions in lineal energy were determined using paired tissue-equivalent proportional counters with and without boron microfoils. Microdosimetry results were obtained in free-air and at various depths in a PMMA phantom near the exit of the beam port. A biological weighting function, dependent on lineal energy, was used to estimate the relative biological effectiveness of the beam. An effective RBE of 2.7 was found at several depths in the phantom.

Dose reconstruction for residents living in buildings with moderate and minor 60Co contamination in rebar.

Previously, we have reconstructed cohort dependent individual doses for residents living in rebar buildings of high 60Co contamination. These reconstructions were carried out using intensively collected TLD data on exposure rates at locations of 1 m height and 1 m x 1 m intersections. The present work deals with dose reconstructions for residents living in rebar buildings of moderate and minor 60Co contamination. Since only limited data on exposure rates from survey meters were available, dose reconstructions were based on these data using interpolations. To utilize such data, we examined them with respect to all factors that influenced the dose uncertainties. The interpolated results were given in terms of contour plots (isodose curves) and compared with corresponding results derived from TLD data and Monte Carlo simulations. The comparison revealed that survey meter data could be used to provide reasonable and conservative estimates of residential doses. By applying the cohort-dependent room occupancy factor and the site-dependent area occupancy factor, we reconstructed cohort dependent individual doses and associated uncertainties. Results of dose reconstructions for all residents living in contaminated rebar buildings were provided to the Atomic Energy Council and health authorities for epidemiologic and medical uses.

The collagen-containing alginate/poly(L-lysine)/alginate microcapsules.

A method of preparing microcapsules containing collagen fibrous network is reported in this study. This method takes advantage of miscibility of collagen and alginate and the ability of this mixture to form spherical gel beads in the presence of CaCl2. Collagen was then reconstituted within the microcapsules at 37 after alginate was liquefied with citrate. GH3 rat pituitary tumor cell, which can be cultured in both suspended and attached forms, were entrapped within the microcapsules. The cell proliferated faster in the collagen-containing capsule as compared to those in the conventional microcapsules.

Microspheres of hydroxyapatite/reconstituted collagen as supports for osteoblast cell growth.

Microspheres comprised of particulate hydroxyapatites dispersed in fibrous collagen matrices were prepared. The procedure involved the droplet formation of hydroxyapatite/collagen mixture emulsified in olive oil, followed by the reconstitution of collagen in the presence of hydroxyapatite particles at 37 degrees C. Various sizes of microspheres could be obtained by controlling the stirring speed of the emulsified mixture. By increasing the stirring speed from 200 to 350 and 500 rpm, the average diameter of the microspheres decreased from 1038 to 513 and 226 microm, respectively. The sizes of the microspheres reduced substantially to a range of 141 microm when 2%. Span 85 was present in the emulsion mixture stirring at 200 rpm. The microspheres thus obtained can be used as carriers to support the growth of osteoblast cells. Osteoblast cells derived from calvaria proliferated from 1.5 x 10(5) to 4.5 x 10(5) cells/ml in 7 days. Correspondingly, the alkaline phosphatase activity increased 6 fold during this period. These results suggested that the hydroxyapatite/collagen microspheres could be used as the filling materials for bone defect.

Dose reconstruction for residents living in 60Co-contaminated rebar buildings.

The first 60Co-contaminated rebar building was discovered in Taipei city in 1992. As of 18 July 1997, 144 buildings with 1,327 housing units were confirmed to contain 60Co-contaminated rebars. All these reinforced concrete buildings were constructed between 1982 and 1984. Thousands of residents have been exposed to ionizing radiation of various degrees. Preliminary assessments by the Atomic Energy Council showed that the accumulated maximal doses ranged from a few mSv to several Sv. The purpose of this work was to reconstruct more reliable individual doses for epidemiologic and medical uses. This reconstruction provided the best estimated doses as well as conceivable upper and lower bounds. The variation of residential day-life activities by individual members in a family was considered according to their sex, age, profession, etc. Intensive data on exposure rates were collected using thermoluminescent dosimeters positioned at 1 m height and 1 m x 1 m intersections with additional measurements at special locations such as bed, sofa, dining table, etc. Thermoluminescent dosimeter measurements were performed in all 24 residences studied in this work. This showed that the Atomic Energy Council maximal doses were 2-6 times higher than the present best estimated doses. Among all family members, elders and housewives received the highest doses; children received the lowest doses. The difference in doses among all family members belonging to different cohort categories is within a factor of two.