Radiation doses to patients during selected CT procedures at four hospitals in Tanzania.

The dose characteristics of CT scanners from local scanning protocols were investigated on the basis of questionnaire information provided by four hospitals conducting CT procedures in Tanzania. The information included scanner model, scanner manufacturer, number of most frequent CT examinations and the employed scanning parameters to previously diagnosed patients. For each scan technique, patient doses were estimated in terms of computerized tomography dose index, dose length product and effective dose using the software developed by the ImPACT scan group in conjunction with the NRPB conversion coefficients data. The results show that the mean CTDI_w,100, DLP and effective dose ranged from 8.5 +/- 2.8 to 79.3 +/- 23.7mGy, 145 +/- 5 to 1400 +/- 812.5 mGy cm and 3 +/- 2.3 to 15.7 +/- 10.4 mSv, respectively. On average, the observed CT doses are however roughly higher than the reported literature data such as 30 to 60 mGy, 570 to 1050 mGy cm and 2.4 to 11.7 mSv recommended by European Commission for similar CT examinations. The higher dose levels, which are possibly associated with significant risks, justify extensive similar studies at the national level in order to unify different approaches towards optimisation of CT examinations. In pursue of this noble objective, the need to train the radiology personnel, establish and using protocols and continuously monitor the performance of CT equipment to control patient CT doses is of utmost importance.

Comparison of four methods used in determination of secondary shielding requirements for a teletherapy facility: a case study of 137Cs room in Tanzania.

The performance of four methods often used to calculate the secondary barrier requirements is evaluated for a typical 137Cs-therapy room as a case study. The first two methods are provided by the NCRP49 and IAEA and both consider the influence of the primary, leakage and scattered radiation at a point as corrected for the workload, use and occupancy factors. A different shielding model encompasses the third method, which determines the doses as corrected for build-up effects assuming the narrow beam geometry. The fourth method is based on the calculation of the dose rates from the source activity with a relevant gamma constant. In all four methods, an appropriate transmission factor for the protective barrier in question is applied. The results show that for controlled area, the similarity in the calculated thicknesses using all four methods was nearly within 50%. For uncontrolled areas, a significant difference of magnitude up to a factor of 2.4 was found, which is mainly attributed to the non-consideration of occupancy factors in the latter two methods. Nevertheless, the non-agreement is useful to validate the specific assumptions taken for the employed shielding method. Despite being slightly high, it is concluded that the current shielding methods based on NCRP fundamentals are satisfactorily optimal in planning new therapy facilities. However for existing facilities, such as those undesigned according to the standard requirements, the combination of the four different methods with the dose rate measurements tend to offer a better cost effective shielding option. Retrospectively, additional 41-cm thick concrete is recommended for the unshielded southern barrier of the 137Cs room. Interestingly, the recommended thickness agrees to within +/-5% with that estimated by using the recently recommended method by IAEA.

Experiences with the European guidelines on quality criteria for radiographic images in Tanzania.

Objective assessment of the quality of radiographic images is practically a difficult task and protocols that address this problem are few. In 1996, the European union published nearly objective image quality criteria to unify the practices in Europe. However, experience with these criteria in countries of lower health care levels is little documented. As a case study in Tanzania, we present the general performance of European guidelines in some Tanzanian hospitals to a total of 200 radiographs obtained from some common x-ray examinations. The results show that more than 70% of chest (PA), lumbar spine (AP), and pelvis AP radiographs passed the quality criteria, while the performance of lumbar spine LAT x-ray examinations was about 50% and therefore less satisfactory. The corresponding mean entrance dose to the patient for specified x-ray techniques was of range 0.08-0.56 mGy, 3.1-7.7 mGy, 2.53-5.4 mGy, and 4.0-16.78 mGy for chest PA, lumbar spine AP, pelvis AP, and lumbar spine LAT x-ray examinations, respectively. Although a good number of observers were not well familiar to the guidelines, the quality criteria have been found useful and their adoption in the country recommended. The need to provide relevant education and training to staff in the radiology departments is of utmost importance.

Metabolism, bioavailability, and toxicokinetics of benzo(alpha)pyrene in F-344 rats following oral administration.

The objective of this study was to evaluate the bioavailability of Benzo(a)pyrene [B(a)p], subsequent to oral exposure. Eight-week-old F-344 rats were dosed orally with 100 mg/kg body weight B(a)p and sacrificed at 0, 0.5, 1.0, 2.0, 4.0. 8.0, 24, 48 and 72 hours post exposure. Blood, liver, reproductive tissues, urine and fecal samples were collected at necropsy and were analyzed for parent B(a)p and metabolites by HPLC with fluorescence detection. Peak levels of B(a)p in plasma occurred 8 hours after exposure (67%) followed by a gradual decrease. Liver retained 10% of the administered B(a)p up to 24 hours following, which the levels dropped during the remaining time periods studied. Twenty-four hours after administration, 45% of the dose was excreted in feces and urine. Metabolite levels in plasma peaked at 24 hours (10%) and decreased to 1% at 72 hours. In the liver, metabolite levels were higher at 8 hours (10%) but were only 3% at 72 hours. Benzo(a)pyrene levels increased after 24 hours in the reproductive organs and constituted 10% of the administered dose at 72 hours. Blood showed high levels of 7,8-diol than 9,10 and 4,5-diols which were high in liver and reproductive organs. Compared to diols, the hydroxy metabolites were detected at high levels in urine and fecal samples. Among the aqueous phase metabolites, glucuronides were at higher levels compared to glutathiones and sulfates. The slow release of unmetabolized B(a)p from reproductive organs and the presence of reactive metabolites in these organs is a matter of concern as they could interfere with gonadal steroid synthesis and release and its regulatory role in gamete production, maturation and function of male animals in a continuous exposure paradigm.

The potential for reduction of radiation doses to patients undergoing some common X ray examinations in Tanzania.

The potential for patient dose reduction in diagnostic radiology was investigated in five major Tanzanian hospitals. The aim of this study was to follow up previously reported suggestions for improved practices to achieve dose reductions. The suggestions were implemented and entrance surface dose measurement repeated by using well-calibrated LiF thermoluminescence dosemeters. The results show that dose reductions in chest PA X ray examinations ranged from 15% to 50%. For abdomen AP and pelvis AP X ray examinations, the dose reductions ranged from 24% to 73% and from 25% to 72%, respectively. The respective dose reductions for lumbar spine AP and LAT projections ranged from 4% to 58% and from 16% to 77%. Interestingly, the majority of radiographs obtained after the implementation of dose reduction measures were useful for intended diagnosis according to the opinion of radiologists. It is concluded that significant dose reductions can be achieved in the country without loss of diagnostic information. Such dose reductions also predict reductions of radiation risk to patients.

A simple high-performance liquid chromatography method for the quantitation of tricyclic antidepressant drugs in human plasma or serum.

OBJECTIVE: A simple reversed-phase high performance liquid chromatography method with a variable wavelength detection has been developed for determining the commonly used tricyclic antidepressant drugs in plasma. METHODS: The assay procedure involves a liquid-liquid extraction with an initial extraction into hexane:ethyl acetate after basification of the homogenate. The column used was a Supelco Hypersil 5 microm, 150 x 3.2 mm. The mobile phase was acetonitrile, methanol, and phosphate buffer (0.01M, pH 7.4) at 12:3:5 ratio (v/v/v). RESULTS: The recoveries ranged from 89 to 108% and the day-to-day precision was 1.1 to 13% CV depending on the compound. The method is sensitive to 15 ng/mL and linear to 400 ng/mL with a 25 microL injection. CONCLUSION: This method is simple, sensitive, precise, inexpensive, and is currently used in our laboratory for therapeutic monitoring of tricyclics. The data generated by this method were within the range outlined by the College of American Pathologists.

Mechanism for antagonism of paraoxon by hemicholinium-3 analogues.

In a newly synthesized series of DMAE analogues (bis-diethyl analogue of hemicholinium-3), selected chemicals (TL-402 = NAM-242 greater than JGC-VII-110) showed significant protection of mouse lethality after acute toxic doses of paraoxon (in vivo). DMAE and NAM-250 (like hemicholinium-3) showed minimal or no antagonism against paraoxon-induced toxicity in mice. Studies with DMAE analogues demonstrate weak anticholinesterase activity. The pattern for the neuromuscular inhibition of TL-402, NAM-242 and JGC-VII-110 is different from that of hemicholinium-3. LD50 studies identified compounds with less inherent toxicity (TL-402, NAM-242 and JGC-VII-110) and showed significant antagonism in contrast to DMAE and NAM-250. These chemicals (DMAE and NAM-250) are as toxic as the parent compound hemicholinium-3. All compounds in this series showed potent antinicotinic activity in different nicotinic-receptor preparations. The antinicotinic activity correlates with their action on the acetylcholine receptor-ion channel complex at frog neuromuscular junctions (in vitro). Electrophysiological studies demonstrate that the antinicotinic agents significantly depressed both the end plate current (EPC) amplitude and the time constant of decay (tau EPC) at the end plate of frog. In presence of paraoxon, voltage- and concentration-dependent shortening of tau EPC is observed which is more prominent than the decrease of the amplitude of EPC. The antinicotinic agents which showed significant antagonism of paraoxon both in vivo and in vitro (TL-402, NAM-242 and JGC-VII-110) also produced profound tetanic rundown after neurally or ionophoretically evoked EPC. These effects are voltage-dependent. The marked shortening of tau EPC, linear relationship between 1/tau vs DMAE analogue concentrations and potential-dependent tetanic rundown suggest that these analogues produce antagonism of paraoxon primarily by reducing end plate permeability by blocking nicotinic ACh-R associated ion channels in their open form. The antinicotinic activity of these agents is related to acetal or corresponding ether substitution.

Structure-activity relationship studies of hemicholinium (HC-3) congeners.

In a continuing investigation of structural requirements for hemicholinium-like activity (inhibition of neuromuscular transmission due to inhibition of uptake of choline into nerve terminals), some additional molecular modifications of hemicholinium ("HC-3"; structure 1) were made. The target compounds were prepared by standard one- or two-step sequences. Noncyclic acetal moieties in general permitted retention of pharmacological activity, as did concomitant replacement of the central biphenyl "spacer" by other bulky cyclic groupings and replacement of the oxazinium rings by piperidine or 4-methylpiperidine. However, these modifications generally produced compounds of a lower potency. Replacement of the biphenyl moiety of HC-3 with polyakylene chains permitted retention of a considerable degree of activity. In these target compounds, the two quaternary nitrogens can exist the same distance apart (approximately 14 A) as in the hemicholinium molecule. The ditertiary amino congener of a pharmacologically active bis-quaternary oxazinium compound was almost completely inactive. To date, only one tertiary amine has been found which displays a significant degree of hemicholinium-like activity.

Structure-activity relationship studies in the hemicholinium ('HC-3') series.

A series of congeners of hemicholinium ('HC-3') has been synthesized, in which the central biphenyl portion of the molecule has been modified, in order to gain insight into possible structural requirements of the biphenyl moiety needed for inhibition of choline uptake into nerve terminals. All molecular modifications resulted in compounds with qualitatively and quantitatively similar pharmacological properties to hemicholinium. It is concluded that the biphenyl portion of the hemicholinium molecule serves as a spacer for maintaining the separation of either the quaternary nitrogens, or the oxazonium rings, at an optimal distance for appropriate interaction with receptor site(s).