Measurement of the internal dose to families of outpatients treated with 131I for hyperthyroidism.

OBJECTIVE: The aim of this study was to measure the internal dose received by family members from ingestion of radioactive contamination after outpatient therapy. MATERIALS AND METHODS: Advice was given to minimise transfer of radioiodine. Home visits were made approximately 2, 7 and 21 days after treatment to measure radioactivity in the thyroids of family members. A decay correction was applied to radioactivity detected assuming ingestion had occurred at the earlier contact time, either the day of treatment or the previous home visit. An effective half-life of 6 or 7 days was used depending on age. Thyroid activity was summed if activity was found at more than one visit in excess of the amount attributable to radioactive decay. Effective dose (ED) was calculated using ICRP72. RESULTS AND DISCUSSION: Fifty-three adults and 92 children, median age 12 (range 4-17) years participated. Median administered activity was 576 (range 329-690) MBq (131)I. Thyroid activity ranged from 0 to 5.4 kBq in the adults with activity detected in 17. Maximum adult ED was 0.4 mSv. Thyroid activity ranged from 0 to 11.8 kBq in the children with activity detected in 26. The two highest values of 5.0 and 11.8 kBq occurred in children aged 5 and 14 years from different families. Eighty-five children had no activity or <1 kBq detected. ED was <0.2 mSv in 86 out of 92 children (93%). Previous published data showed 93% of children received an ED

Isolation of pluripotent embryonic stem cells from reprogrammed adult mouse somatic cell nuclei.

Pluripotent human stem cells isolated from early embryos represent a potentially unlimited source of many different cell types for cell-based gene and tissue therapies [1-3]. Nevertheless, if the full potential of cell lines derived from donor embryos is to be realised, the problem of donor-recipient tissue matching needs to be overcome. One approach, which avoids the problem of transplant rejection, would be to establish stem cell lines from the patient's own cells through therapeutic cloning [3,4]. Recent studies have shown that it is possible to transfer the nucleus from an adult somatic cell to an unfertilised oocyte that is devoid of maternal chromosomes, and achieve embryonic development under the control of the transferred nucleus [5-7]. Stem cells isolated from such a cloned embryo would be genetically identical to the patient and pose no risk of immune rejection. Here, we report the isolation of pluripotent murine stem cells from reprogrammed adult somatic cell nuclei. Embryos were generated by direct injection of mechanically isolated cumulus cell nuclei into mature oocytes. Embryonic stem (ES) cells isolated from cumulus-cell-derived blastocysts displayed the characteristic morphology and marker expression of conventional ES cells and underwent extensive differentiation into all three embryonic germ layers (endoderm, mesoderm and ectoderm) in tumours and in chimaeric foetuses and pups. The ES cells were also shown to differentiate readily into neurons and muscle in culture. This study shows that pluripotent stem cells can be derived from nuclei of terminally differentiated adult somatic cells and offers a model system for the development of therapies that rely on autologous, human pluripotent stem cells.

Internal ribosome entry sites and dicistronic RNAs in mammalian transgenesis.

Modification of the genetic content of cultured cells or of whole animals is now a key strategy in both basic biological research and applied biotechnology. Yet obtaining the desired level and specificity of expression of an introduced gene remains highly problematic. One solution could be to couple expression of a transgene to that of an appropriate intact genomic locus. The identification and functional characterization of RNA sequences known as internal ribosome entry sites now offer the possibility of achieving precise control of transgene expression through the generation of dicistronic fusion mRNAs.

Effect of electron contamination of a 6 MV x-ray beam on near surface diode dosimetry.

In critical organ in vivo x-ray dosimetry, the relative contaminating electron contribution to the total dose and total detector response outside the field will be different to the corresponding contributions at the central axis detector calibration position, mainly due to the effects of shielding in the linear accelerator head on the electron and x-ray energy spectrum. To investigate these contributions, the electron energy response of a Scanditronix PFD diode was measured using electrons with mean energies from 0.45 to 14.6 MeV, and the Monte Carlo code MCNP-4C was used to calculate the electron energy spectra on the central axis, and at 1 and 10 cm outside the edge of a 4 x 4, 10 x 10 and a 15 x 15 cm(2) 6 MV x-ray field. The electron contribution to the total dose varied from about 8% on the central axis of the smallest field to about 76% at 10 cm outside the edge of the largest field. The electron contribution to the total diode response varied from about 7-8% on the central axis of all three fields to about 58% at 10 cm outside the edge of the smallest field. The results indicated that a near surface x-ray dose measurement with a diode outside the treatment field has to be interpreted with caution and requires knowledge of the relative electron contribution specific to the measurement position and field size.

The low energy X-ray response of the LiF:Mg:Cu:P thermoluminescent dosemeter: a comparison with LiF:Mg:Ti.

LiF:Mg:Cu:P thermoluminescent dosemeters (TLD) can be used for the same X-ray dosimetry applications as LiF:Mg:Ti, with each type having the disadvantage of a response dependent on energy, particularly at low energies. Measurements were made of the response per unit air kerma of LiF:Mg:Cu:P and LiF:Mg:Ti to nine quasi-monoenergetic X-ray beams with mean energies from 12 keV to 208 keV. Each measurement was normalized to the value produced by 6 MV X-rays. LiF:Mg:Cu:P was found to under-respond to a majority of these radiations whereas LiF:Mg:Ti over-responded to a majority. Their smallest relative measured response was produced by the lowest energy beam, and the maximum measured relative response of 1.15+/-0.07 and 1.21+/-0.07 for LiF:Mg:Cu:P and LiF:Mg:Ti, respectively, occurred at 33 keV. Energy response coefficients were derived from these measurements to estimate the error introduced by using either type of TLD to measure the dose from an X-ray spectrum different to that used for its absolute response calibration. It was calculated that if the response of either type of TLD was calibrated at 100 kVp, then an error of no more than +/-2% would be introduced into measurements of tube output at potentials of 50-130 kVp. LiF:Mg:Cu:P was found to introduce a larger error (up to 30%) into the measurement of body exit dose than LiF:Mg:Ti at tube potentials of 40-150 kVp, if its absolute response was calibrated using the corresponding body entrance beam. The method should allow this type of error to be estimated in other dosimetry applications for either type of TLD.

Improved EBV-based shuttle vector system: dicistronic mRNA couples the synthesis of the Epstein-Barr nuclear antigen-1 protein to neomycin resistance.

Use of EBV-based vector systems has been limited by the requirement to generate EBNA+ cells which are 'permissive' for replication of an oriP-vector. In current constructs, selectable marker and EBNA-1 are not always co-expressed. This is a significant problem since the EBNA-1 gene product can be toxic in some cell types and may be selected against. In this paper, we describe a gene construct that overcomes this limitation. We have exploited the piconaviral internal ribosome entry site to allow the genes for Epstein-Barr nuclear antigen-1 and G-418 resistance to be transcribed as a dicistronic fusion mRNA under the control of the phosphoglucokinase promoter. This construct can be routinely integrated into human cell lines. The presence of EBNA-1 protein was reflected by a large increase in transfection frequencies (1000-fold) using an oriP-based vector which was shown to replicate stably in these cells with no apparent gross rearrangements detected after 8 weeks in culture. Using this system, G-418 resistance should directly reflect integration, as well as expression of the EBNA-1 gene, which, in turn, increases transfection frequencies and stability of EBV-based vector systems and should result in its increased use.

Expression and characterization of biologically active ovine FSH from mammalian cell lines.

Stably transfected cell lines expressing the alpha subunit, beta subunit and alpha/beta heterodimer of ovine (o)FSH have been established following the transfection of Chinese hamster ovary cells with alpha and beta subunit cDNA expression vectors. In the absence of the alpha subunit, FSH beta subunit polypeptides were inefficiently secreted and displayed a short intracellular half-life, while free alpha subunits were readily secreted in the absence of the beta subunit. Cotransfection of oFSH alpha and beta subunit cDNAs led to heterodimer assembly and secretion. While alteration of the nucleotide sequence flanking the beta subunit AUG initiation codon did not appreciably enhance heterodimer biosynthesis and secretion, the replacement of the 5' untranslated and signal peptide-coding regions of the beta subunit cDNA with the corresponding sequences from an oGH cDNA clone was associated with a twofold increase in oFSH heterodimer secretion. The recombinant oFSH had a higher molecular weight than pituitary-derived oFSH, and was more acidic than the native hormone when analysed using isoelectric focusing, suggesting a greater degree of sialylation of the recombinant hormone. A comparison of the activities of the recombinant and native hormones in the porcine testis radioreceptor assay and in the in vitro Sertoli cell bioassay revealed that the recombinant oFSH displayed enhanced biological activity in the Sertoli cell assay when compared with the native hormone.

Comparison of technetium-99m-HM-PAO leukocytes with indium-111-oxine leukocytes for localizing intraabdominal sepsis.

Technetium-99m-HM-PAO [( 99mTc]HM-PAO) leukocyte and indium-111-oxine (111In-oxine) leukocyte scanning were carried out simultaneously in 41 patients at 4 hr and 24 hr after reinjection to determine whether the 4-hr 99mTc scan could replace the 24-hr 111In scan for detecting intraabdominal sepsis. Abdominal infection was confirmed in 12 cases. The 4-hr 99Tc-leukocyte scan, the 4-hr 111In-leukocyte scan, and the 24-hr 111In-leukocyte scan yielded a sensitivity of 100%, 67%, and 100%, respectively, and a specificity of 62%, 90%, and 86%, respectively. The 24-hr 99mTc-leukocyte scan also produced a sensitivity of 100%, but it was falsely positive in all 29 cases without infection due to physiologic bowel uptake. False-positive 4-hr 99mTc-leukocyte scans were also produced by physiologic bowel uptake in seven cases all of whom had true-negative 4-hr and 24-hr 111In-leukocyte scans. Because of the high incidence of false-positive 4-hr [99mTc]HM-PAO leukocyte scans, it was concluded that they could not replace 24-hr 111In-leukocyte scans for detecting intraabdominal sepsis, and that serial 99mTc leukocyte scans starting earlier than 4 hr after reinjection must be evaluated.

Suppression by perchlorate of technetium-99m and iodine-123 secretion in milk of lactating goats.

Lactating goats were infused with either technetium-99m (99mTc) or iodine-123 (123I) together with chlorine-36 (36Cl) through an indwelling catheter previously placed in an external pudic mammary artery. The radioisotope infusions were repeated together with 100 mg of sodium perchlorate. There was a rapid transfer of 99mTc and 123I into milk, reaching a peak concentration 30 min after a 15-min infusion. The fractional secretion of 99mTc and 123I in milk was reduced by 70%-80% and 60%-66%, respectively, by perchlorate. The fractional secretion of 36Cl was not affected by perchlorate, and the shape of the 36Cl secretion curve differed from those of 99mTc and 123I, which were similar. It is probable, therefore, that the latter nuclides were secreted by a transport route different from that of chloride. Available data describing the secretion of 99mTc in human milk after pertechnetate administration was reviewed, and it was concluded that perchlorate pretreatment significantly reduced the secretion of 99mTc in human breast milk.

Breast-milk radioactivity after a Tc-99m DTPA aerosol/Tc-99m MAA lung study.

Measurements were made of the concentration of Tc-99m activity in samples of breast milk following an administration of Tc-99m DTPA aerosol for a lung ventilation image and one of Tc-99m MAA for lung perfusion. The activity was 222 nCi/ml of milk (8.2 kBq/ml) at 2 hr after the MAA injection, and it was found to be excreted exponentially with an effective half-life of 4.6 hr. There was a small incorporation of Tc-99m into breast-milk protein. We conclude that the combined use of these two Tc-99m agents did not indicate the interruption of breast feeding beyond 24 hr after administration of the MAA, and that for an aerosol ventilation study alone, breast feeding need not be interrupted for more than 4 hr after the test.

Techniques for radioactive decontamination in nuclear medicine.

Working with unsealed radioactive sources in nuclear medicine carries the potential risk of contamination. Careful design of a department and its operational procedures will minimize but never completely eliminate the possibility of such incidents occurring. Contingency planning forms as important a part of handling such incidents as the procedures to reduce the hazard once an incident has occurred. It should include anticipating where such incidents are likely to occur, training and exercising staff in the appropriate procedures to deal with these incidents, providing a comprehensive decontamination kit, and implementing a routine contamination monitoring survey. Assessing the magnitude of the radiation hazard and the effect of decontamination efforts, containing the spread of contamination, minimizing the radiation dose to individuals, and continuing to decontaminate to the lowest level possible are principles to follow in managing any incident. Nuclear medicine staff should be familiar with techniques for decontaminating different anatomical sites on the body; for eliminating or reducing the uptake of radioactivity absorbed into the body; and for decontaminating dry and wet surfaces, equipment, clothing, and bedding. Radiopharmaceutical dispensing procedures, ventilation scanning, and decontaminating 131I treatment areas are identified as the most likely causes of body surface and internal contamination of nuclear medicine staff.

Removal of 3'untranslated sequences dramatically enhances transient expression of ovine follicle-stimulating hormone Beta gene messenger ribonucleic Acid.

The influence of the 3'untranslated (3'-UT) region of the ovine follicle-stimulating hormone (FSH) ß mRNA on the level of transcript expression was studied. Only very low levels of FSH ß mRNA were detected following transient transfection of COS cells with a eukaryotic expression vector containing a full-length ovine FSH ß cDNA that includes 1.1 kilobases (kb) of 3'-UT. In contrast, deletion of all but 135 basepairs (bp) of the 3'-UT resulted in a striking increase in FSH ß mRNA expression following transfection of the truncated cDNA construct. These observations suggest that sequences within the 3'-UT of the ovine FSH ß mRNA may play a significant role in the post-transcriptional regulation of FSH ß expression.

Effect of collimator and depth in a phantom on the neutron spectrum from a 238Pu,Be neutron source.

A study has been made of some factors influencing the fast neutron spectrum emerging from the aperture of a collimated 238Pu,Be source, and influencing the spectrum at a depth in a water phantom, using a miniature liquid scintillator fast neutron spectrometer. The greatest changes in the spectrum emerging from the aperture were produced by changes in the length of the collimator and the field size of the collimator. No difference between the source spectrum above 1.5 MeV of 370 GBq (10 Ci) and 740 GBq (20 Ci) 238Pu,Be sources and a 37 GBq (1 Ci) 241Am,Be source was observed. Graphite was found to be a slightly more efficient reflector than steel or lead, and much better than wax. The mean energy and the proportion of the total neutron fluence with an energy between 1.5 MeV and 3.5 MeV reached a minimum and a maximum value respectively with increase in depth in the phantom. With further increase in depth, the two parameters increased and decreased respectively. The depth at which these minimum and maximum values occurred increased with field size. The overall changes through 15 cm depth in the mean energy and in the low energy fluence proportion were small (less than or equal to +/- 5%). No significant changes were detected in the spectral shape after the neutron beam traversed an air cavity or a bovine tibia in the phantom.

Near surface photon energy spectra outside a 6 MV field edge.

The purpose of this study was to investigate the difference between a 6 MV linear accelerator x-ray energy spectrum outside the field edge near a phantom surface, and the corresponding spectrum on the central axis. The Monte Carlo code MCNP-4A was used to calculate the spectra on the central axis and at 1, 2, 5 and 10 cm from the edge of a 4 x 4 cm2, 10 x 10 cm2 and 15 x 15 cm2 field. Compared to the spectrum on the central axis, the spectra outside the field edge showed two distinct regions: a broad peak below about 0.5 MeV, and a lower amplitude, less rapidly changing region at higher energies from 0.5 to 6 MeV. The lower energy peak was due to scattered photons, and the higher energy component was due mainly to primary photons transmitted through the jaws of the secondary collimator. The potential impact of these spectral differences on critical organ photon dosimetry was determined by calculating the ratio of the sensitivity of a Scanditronix EDD-5 diode and of a LiF:Mg:Ti thermoluminescent dosimeter (TLD) outside the field edge to their respective sensitivity at the calibration position on the central axis. The lower energy peak combined with the non-uniform energy sensitivity of each detector produced up to a two-thirds overestimate of x-ray dose outside the field by the diode, whereas the response ratio of the TLD was about unity. These results indicated that a similar evaluation was required for profile measurements of a dynamic wedged field and measurements in an intensity modulated beam with either type of detector.

A meter for ultraviolet dose and irradiance.

A compact, portable, battery-powered meter has been developed to monitor and to integrate ultraviolet irradiance. The meter has been designed to accept signals from either a thermopile or a solid-state (GaAsP) diode detector. A variable scale factor is provided to accommodate a range of different detector sensitivities. The measurable irradiance range is 100 microW cm-2 to 100 mW cm-2 and that of dose is 200 mJ cm-2 to 200 J cm-2. The meter can be operated manually or for a range of preset times. The irradiance, dose and elapsed times are displayed. Outputs from the preamplifier and from the scaling amplifier are available for interfacing the instrument with a computer or chart recorder. The meter has been designed to have an overall measurement uncertainty of the order of 1% in order to ensure that the major error contribution lies with the detecting devices.

An on-line ultraviolet radiation monitoring system for control of photosensitivity test dose.

A system has been developed to monitor and integrate on-line a small fraction of the monochromatic ultraviolet radiation directed at the skin from a phototest source, thus correcting for fluctuations in the irradiance. On completion of the required test dose, the exposure is terminated automatically. Radiation is reflected from a silica plate, housed in a skin applicator, onto a photodiode connected to an integrator. The variation of the reflectivity of the silica plate with wavelength and with incident angle was calculated. The reflectivity of the applicator with and without the silica plate in situ was studied experimentally. Measurements were made of the spatial distribution of irradiance from and across the face of the applicator. To calibrate the photodiode current, the absolute irradiance at the face of the applicator had to be measured with a wide angle detector. No significant deviation from a linear variation was observed between changes in the skin irradiance and changes in the photodiode current.

The response of a MOSFET, p-type semiconductor and LiF TLD to quasi-monoenergetic x-rays.

A metal oxide semiconductor field effect transistor (MOSFET), p-type semiconductor and a TLD can all be used for x-ray dosimetry, with each system having the common disadvantage of a response which is dependent upon the incident photon energy, particularly for energies < 1 MeV. A Pantak HF-320 quasi-monoenergetic x-ray unit was used to determine the response of two Thomson and Nielson TN-502RD MOSFETs, a Scanditronix EDP-10 semiconductor (build-up cap 10 mm: tissue equivalence), an EDD-5 semiconductor (build-up cap 4.5 mm: tissue equivalence) and an Lif:Mg:Ti TLD over the energy range 12-208 keV. The sensitivity of each detector was normalized to the value produced by exposure to 6 MV x-rays. The maximum relative sensitivities of the two MOSFET detectors were 4.19 +/- 0.25 and 4.44 +/- 0.26 respectively, occurring at an incident x-ray energy of 33 keV. The maximum relative sensitivity of the Scanditronix EDP-10 of 2.24 +/- 0.13 occurred at 65 keV, and for the EDD-5, it was 7.72 +/- 0.45 at 48 keV. The TLD produced a maximum relative sensitivity of 1.31 +/- 0.09 at 33 keV. Compared with available data based on heteroenergetic x-ray sources, these measurements have identified a more representative response for each detector to low-energy x-rays.

Tibial lead determination by 99Tcm radiopharmaceutical x-ray fluorescence.

The feasibility of measuring tibial lead concentration by x-ray fluorescence with an internal 99Tcm labelled bone-seeking radiopharmaceutical was investigated using phantoms containing known values of lead concentration and 99Tcm activity. The minimum detectable concentration (MDC) at two standard deviations based on the counts in the Kalpha1 peak of 10.9 microg Pb ml(-1) was estimated to correspond to an MDC for an individual within a range of approximately 8-15 microg Pb (g bone mineral)(-1) if the counts from all four K x-ray peaks were included. Due to its much greater dose compared to an external source, the MDC of this internal source technique would have to be reduced before it could be used for measurements of occupationally or environmentally exposed individuals other than as an adjunct for a patient undergoing a bone scan. Methods of achieving such a reduction include increasing the acquisition time and the number of HPGE detectors, and optimizing the design of their collimators.

An enhanced sensitivity K-shell x-ray fluorescence technique for tibial lead determination.

A novel irradiation-detection geometry capable of enhancing sensitivity for the measurement of tibial lead content by K-shell x-ray fluorescence (XRF) is described. The high-count-rate system comprised a small-area high-specific-activity (0.147 GBq mm-2) 109Cd source and a large-area (nominally 20 cm2) uncollimated detector, forming an axially symmetric back-scattering arrangement. Precisions in the range +/- 4.9 to +/- 14.2 micrograms Pb (g bone mineral)-1 have been obtained in a study of a cohort of 63 controls and 73 workers industrially exposed to lead. These precisions are comparable with those obtained in results using earlier systems, but at reduced source activities (less than 50% of the activity of other systems) and with significant reduction in measurement time (some 30% less than the measurement times of other systems). Subsequent investigation of detector collimation resulted in a marginal improvement in energy resolution, but the restriction in detected photon fluence meant that there was an insignificant change in detection sensitivity. For the resistive feedback preamplifier used in this study a maximum energy rate of the order of 7000 MeV s-1 was found to limit measurement precisions significantly. Higher-count-rate detector systems offer a basis for obtaining mean precisions down to +/- 3 micrograms Pb (g bone mineral)-1 at one standard deviation.

Maintenance of pluripotential embryonic stem cells by stem cell selection.

As gastrulation proceeds, pluripotential stem cells with the capacity to contribute to all primary germ layers disappear from the mammalian embryo. The extinction of pluripotency also occurs during the formation of embryoid bodies from embryonic stem (ES) cells. In this report we show that if the initial differentiated progeny are removed from ES cell aggregates, further differentiation does not proceed and the stem cell population persists and expands. Significantly, the presence of even minor populations of differentiated cells lead to the complete loss of stem cells from the cultures. This finding implies that the normal elimination of pluripotent cells is dictated by inductive signals provided by differentiated progeny. We have exploited this observation to develop a strategy for the isolation of pluripotential cells. This approach, termed stem cell selection, may have widespread applicability to the derivation and propagation of stem cells.