Rachel Obed | University of Ibadan (original) (raw)

Papers by Rachel Obed

Environmental Health Insights

The distribution of natural radioactivity levels of 238U, 232Th, and 40K in soils overlying the 3... more The distribution of natural radioactivity levels of 238U, 232Th, and 40K in soils overlying the 3 lithologic units within Obafemi Awolowo University, Ile-Ife, Nigeria was investigated to characterize the gamma radiation dose distribution over the lithologies and to assess the radiation hazard due to the natural radionuclides. A thallium-doped cesium iodide detector was employed to determine the activity concentrations of 238U, 232Th, and 40K in 21 soil samples. The respective average concentrations of the 3 radionuclides are 37.7, 3.2, and 245.6 Bq kg−1 for granite gneiss, 31.9, 2.8, and 241.1 Bq kg−1 for banded gneiss, and 21.1, 1.7, and 196.7 Bq kg−1 for mica schist. The average concentration of 238U in granite gneiss lithology exceeds the world average value. The evaluated values of radiation hazard parameters including average absorbed dose rate, outdoor annual effective dose and external hazard index are below the recommended limits. The spatial distribution of the radiation ha...

Nigerian Postgraduate Medical Journal, 2021

Objective: The objective of this study was to evaluate the thyroid glands' radiation dose and... more Objective: The objective of this study was to evaluate the thyroid glands' radiation dose and the risk of thyroid cancer induction from head or neck computed tomography (CT) examinations. Methods: In a prospective study, we evaluated all participants of all ages and sex referred for Head or Neck CT Scan at the University College Hospital, Ibadan and Me Cure Healthcare Limited, Ibadan, Oyo State, Nigeria. Thyroid radiation dose was estimated with impact scan calculator, and real-time dose measurement with thermoluminescent badge dosimeters (TLDs). Data were analysed and P < 0.05 was considered statistically significant. Results: One hundred and sixty-three participants (128 adults and 35 children) participated in the study. In most participants (74%), the tube voltage was 120 kVp. The estimated median thyroid gland dose by the imPACT scan calculator was 4.95 mGy (range = 1.20–30.0 mGy) and 4.40 mGy (range = 3.0–5.10 mGy), while the real-time dose measured by the TLD was 4.79 m...

Introduction Radiation exposures from diagnostic medical examinations are generally low and are a... more Introduction Radiation exposures from diagnostic medical examinations are generally low and are almost always justified by the benefits of accurate diagnosis of possible disease conditions. Therefore, entrance skin dose (ESD), body organ dose (BOD), and effective dose (ED) from adult patients undergoing routine thorax posterior-anterior (PA) and thorax right lateral (RLAT) were estimated in University Hospital, Port Harcourt, Southern Nigeria. Materials and Methods Totally, 102 patients were considered in this work. Using software packages to carry out ESD, BOD, and ED is a recent resource in dosimetry and is being widely used in hospitals. The software used in this work was CALDose_X 5.0. The software makes use of the technical exposure parameters and the tube output of the X-ray machine. Results The estimated ESD median values were 0.96 and 1.85 mGy for thorax posterior anterior (PA) and right lateral (RLAT), respectively. The highest BOD was in the adrenals (270 µGy) for thorax P...

Purpose: In high-dose-rate (HDR) brachytherapy (BT), the source dwell times and dwell positions a... more Purpose: In high-dose-rate (HDR) brachytherapy (BT), the source dwell times and dwell positions are essential treatment planning parameters. An optimal choice of these factors is fundamental to obtain the desired target coverage with the lowest achievable dose to the organs at risk (OARs). This study evaluates relevant dose parameters in cervix brachytherapy in order to assess existing tandem-ring dwell time ratio used at the first HDR BT center in Nigeria, and compare it with an alternative source loading pattern. Material and methods: At the Radiotherapy Department, University College Hospital (UCH), Ibadan, Nigeria, a total of 370 standard treatment plans in two alternative sets were generated with HDR basic 2.6 software for one hundred and eighty five cervical cancer patients. The initial 185 individual plans were created for clinical treatment using the tandem-ring dwell time ratio of 1 : 1. Modifying the initial applicator loading ratio, the second set of plans with related do...

BEAMnrc/DOSXYZnrc Monte Carlo code is widely used for accurate dose calculation. This study simul... more BEAMnrc/DOSXYZnrc Monte Carlo code is widely used for accurate dose calculation. This study simulated and tested two incident electron-source parameters on dosimetric characteristics of photon beam for an Elekta Precise linear accelerator (linac) model. The linac model of a 6 MV photon beam for 10 × 10 cm2 field was used to investigate the sensitivity of the two-incident electron sources. Optimal source parameter was achieved by varying the parallel and mean angular spread (2D Gaussian distribution) circular beam sources. In a parallel incident electron source, the beam radius (r) parameter was varied while the sigma (σ) parameter in the mean angular spread beam source was varied. The accuracy of this source model was evaluated by calculating the dose distribution in a homogeneous water phantom. The simulated data were benchmarked with measurements for percentage depth doses (PDDs) and lateral dose profiles using 2%/2mm and 3%/3mm gamma (γ) criteria. This study showed that variation...

Introduction: A reject rate is the percentage of diagnostic images repeated due to errors during ... more Introduction: A reject rate is the percentage of diagnostic images repeated due to errors during radiological examinations. The present study aimed to evaluate the patient radiation doses and analyze the film reject rate as part of quality assurance program in three diagnostic centers in Nigeria. Materials and Methods: This study was conducted in three hospitals, namely Federal Medical Center (FMC), General Hospital (GH), and Sacred Heart Hospital (SHH), located in Abeokuta, Ogun State, Southwestern Nigeria. For the purpose of the study, the accepted and rejected radiographs during different X-ray examinations were recorded. A total of 376 rejected and accepted radiographs were evaluated in the three hospitals, and the economic losses due to rejected films were determined. The quality control (QC) tests, which involve kilo voltage (kV), milliampere seconds (mAs), etc, were carried out on the facilities of two out of three hospitals using Victoreen 6000m QC kits. The results of the Q...

Public Health in Practice

Abstract Objectives The seriousness and long-term health effects of radon exposure are often unde... more Abstract Objectives The seriousness and long-term health effects of radon exposure are often underestimated due to inaccurate perceptions of radon risk. The aim of this study was to assess radon risk perception and barriers for residential radon levels testing among Obafemi Awolowo University faculty. Study design A quantitative cross-sectional design was used for this study. Methods Lecturers’ residents of the Obafemi Awolowo University participated in the study. A semi-structured questionnaire was administered to 296 residents to assess their knowledge about radon and determine their perceived susceptibility to radon health risks. Data were analysed and summarised using descriptive and inferential statistics. Results The respondents’ mean age was 43 ± 8.5 years and 71% were male. The study revealed that awareness of radon was low (46%), while 61% of respondents had poor knowledge. Only a fifth (19.5%) of the respondents had a high perceived risk of radon, and 70% were not aware of measures to detect radon in their respective homes. A majority (74%) of the respondents reported not knowing where to get a radon testing kit as a barrier to radon testing. Professional background (p Conclusion Despite having a high level of education, knowledge/awareness about radon health risks is low in the Obafemi Awolowo University faculty members; furthermore, lack of knowledge about house testing supplies are a significant barrier to residential testing.

Scientific Reports

Radiation dose from natural sources is mainly from exposure to radon in the environment. Radon ha... more Radiation dose from natural sources is mainly from exposure to radon in the environment. Radon has its origin from uranium-bearing bedrocks and overburden. In the present study, assessment of the level of radon over the three lithological units upon which the residential areas of ObafemiAwolowo University Campus, Ile-Ife (OAU) was situated was carried out. Soil gas radon concentration measurement was carried out at a constant depth of 0.80 m across the three lithologies (granite gneiss, grey gneiss and mica schist) using a RAD7 electronic radon detector. A total of 138 in-situ soil gas radon measurements were carried out. Obtained experimental data were analysed and summarised using descriptive and inferential statistics with statistical significance set at p

Journal of Radiation and Cancer Research

Background: Estimating organ dose from computed tomography (CT) procedures is still ongoing. The ... more Background: Estimating organ dose from computed tomography (CT) procedures is still ongoing. The aim is to reduce induced cancer risk associated with over dose. Aim and Objectives: The aim of this study was to estimate organ dose using CT-Expo software, to compare obtained values with thermoluminescent dosimeter (TLD) measurements from validated in-house phantoms, and to compare the CT-Expo results with other related studies. Materials and Methods: Four CT diagnostic centers denoted as A, B, C, and D were randomly selected for this study. A CT-Expo software (version 2.5 Germany) was used. A preliminary study was carried out to determine organ dose from the in-house phantoms using bovine tissues. The CT dose parameters used with the in-house phantoms were retrieved from the CT monitor and were used with CT-Expo worksheet to estimate organ dose as well. Results: The CT-Expo mean organ dose to the brain, eye lens, esophagus, and thyroid were 29.05 ± 10.78, 35.65 ± 15.1, 12.45 ± 10.13, and 4.25 ± 2.78 mGy, respectively; to the heart and lungs were 13.08 ± 9.84 and 11.5 ± 7.26 mGy, respectively; and to the liver, stomach, and kidney were 14.42 ± 9.07, 12.78 ± 7.97, and 11.73 ± 7.92 mGy, respectively. There was no statistically significant difference between the TLD measurements and CT-Expo (P = 0.361). The relative difference between CT-Expo and TLD measurements for brain, eye lens, heart, lungs, kidney, liver, and stomach were ≤21%. Investigated organ doses from the software were between 4.25 and 35.65 mGy. There was no difference in mean organ dose when compared to the studies in Thailand, Tanzania, Japan, USA (cadavers 1 and 2), and Nigeria. Conclusion: Large percentage differences were noticed in the thyroid and esophagus which was as a result of the software not recognizing them as organs in the head/neck but rather as organs in the chest; however, there was no difference in organ dose between the CT-Expo and TLD measurement from the in-house-validated phantom.

Journal of Radiation Research and Applied Sciences

In the industrialized area of Lagos, vegetables are mostly cultivated through surface water irrig... more In the industrialized area of Lagos, vegetables are mostly cultivated through surface water irrigation. Untreated surface water has the potential of being contaminated with radionuclides from industrial effluents. This study evaluated the concentration of radionuclides in the leafy vegetables cultivated through surface water irrigation in Lagos metropolis and the potential health risks associated with their consumption. The specific activities of 226 Ra, 232 Th and 40 K in some commonly consumed leafy vegetables were determined using High Purity Germanium (HPGe) detector. To assess the radiation hazards associated with the consumption of these vegetables, annual effective dose (AED) and excess lifetime cancer risk (ELCR) were also determined. The specific activities of 226 Ra, 232 Th and 40 K in the investigated samples ranged from 0.49±044 to 6.00±1.19 Bq/kg, with an average value of 2.08±0.59 Bq/ for 226 Ra, from 0.10±0.07 to 0.61±0.12 Bq/kg with an average value of 0.85 ±0.08 Bq/kg for 232 Th and from 28.69±3.09 to 126.71±5.86 Bq/kg with an average value of 72.56±5.36 Bq/kg for 40 K. The mean activities of 226 Ra and 232 Th were 40 and 56 times higher than the World Health Organization (WHO) reference values for 226 Ra and 232 Th in leafy vegetables respectively. The AED estimated from the consumption of vegetables was 0.048 mSv/y, which is about 16 % of the reference AED value for radionuclides of natural origin in the total diet while leafy vegetable represents about 8 % of the total diet of an adult in Lagos. The ELCR obtained from this study was this is lower than the world's average value. This study has found elevated concentrations of 226 Ra and 232 Th in leafy vegetables, and noticeable increase in AED associated with 226 Ra exposure in the consumption of leafy vegetables cultivated in Lagos. There are therefore potential radiological health risks to the health of the public from long-term consumption of leafy vegetables cultivated through surface water irrigation in Lagos, Nigeria.

Journal of Radiation Research and Applied Sciences

A radon survey was carried out in some nursery and primary schools located in Ibadan-North Local ... more A radon survey was carried out in some nursery and primary schools located in Ibadan-North Local Government of Oyo State, Nigeria. Radon concentration was measured using passive diffusion cup technique fitted with CR-39 detectors. The detectors were exposed for a period of 90 days in different locations inside the school buildings: classrooms and offices. After this period, the detectors were etched with 6.25M NaOH at 90°C for 3 h. The tracks were counted and captured using a digital camera connected to a microscope and a laptop with the aid of VIMCRO USB software. The arithmetic mean of radon concentration in the studied area was 176.15 Bq/m 3 and the mean annual effective dose to the lung was found to be 1.14 mSvy −1. These mean values of radon levels are considered safe while comparing with the upper reference level of 1000 Bq/m 3 , the action level recommended for workplaces by The International Commission on Radiological Protection (ICRP, 2014).

International Journal of Low Radiation, 2016

Indoor radon concentration measurements in 116 rooms and gamma activity measurements in the soil ... more Indoor radon concentration measurements in 116 rooms and gamma activity measurements in the soil samples around the rooms were carried out in Oke-Ogun area (Southwestern, Nigeria). The mean activity concentrations of 40K, 232Th, and 238U in the soil were 3±5, 25±7 and 212±99 Bqkg−1, respectively. The mean absorbed dose rate (D) and the effective dose estimated were 44±8 nGy h−1 and 45±8 μSv y−1, respectively. Radon concentrations in the rooms varied from 148 Bqm−3 to 627 Bqm−3 with mean of 282±99 Bqm−3. The estimated mean annual effective dose is 7±2 mSv y−1. It is therefore advisable for the inhabitants of the study area to ventilate their houses regularly, to reduce the possible risk of contracting lung cancer. Radon concentration in the rooms surveyed show a good correlation (R² = 0.702) with 238U/226Ra activity in soil samples.

Developing an accurate Monte Carlo dose calculation engine is of clinical importance.Since it is ... more Developing an accurate Monte Carlo dose calculation engine is of clinical importance.Since it is not convenient to perform such dose calculation after every clinical treatment, MC dose calculation engine is helpful in facilitating radiotherapeutic treatment plan. It is well understandable that to every radiotherapeutic treatment, there will be an absorbed dose.This research work focused on the calculation of dose deposited at each depth with respect to specified energy using the EGSnrc Monte Carlo simulation, which has been considered to be fast and accurate. Incident pencil beam of 1

Journal of contemporary brachytherapy, 2015

In-vivo measurements to determine doses to organs-at-risk can be an essential part of brachythera... more In-vivo measurements to determine doses to organs-at-risk can be an essential part of brachytherapy quality assurance (QA). This study compares calculated doses to the rectum with measured dose values as a means of QA in vaginal vault brachytherapy using cylinder applicators. At the Department of Radiotherapy, University College Hospital (UCH), Ibadan, Nigeria, intracavitary brachytherapy (ICBT) was delivered by a GyneSource high-dose-rate (HDR) unit with (60)Co. Standard 2D treatment plans were created with HDR basic 2.6 software for prescription doses 5-7 Gy at points 5 mm away from the posterior surface of vaginal cylinder applicators (20, 25, and 30 mm diameters). The LiF:Mg, Ti thermoluminescent dosimeter rods (1 x 6 mm) were irradiated to a dose of 7 Gy on Theratron (60)Co machine for calibration purpose prior to clinical use. Measurements in each of 34 insertions involving fourteen patients were performed with 5 TLD-100 rods placed along a re-usable rectal marker positioned i...

West African Journal of Radiology, 2016

Background: Computed tomography (CT) has remained an important tool in medical diagnosis. However... more Background: Computed tomography (CT) has remained an important tool in medical diagnosis. However the radiation dose imparted to patients, especially to radiosensitive organs during a CT scan, continues to raise concern. Our aim was to determine the radiation dose to the ovary and the uterus during routine abdomen/pelvis CT examinations at the University College Hospital, Ibadan, Nigeria using appropriate dose computational methods. Materials and Methods: Technical factors and parameters were obtained for three groups of 60 randomly selected patients who had abdominal CT examinations using three machines, namely; the CT/e, BrightSpeed S and Toshiba Aquilion 64. The scanning parameters were used to estimate the patient organ doses using measurements of CT dose indexes and organ doses obtained with the aid of the ImPACT CT Dosimetry Calculator SpreadSheet based on National Radiological Protection Board conversion factors. Results: The mean total organ dose from the CT/e machine to the ovary was 11.15 ±2.48 (mGy) and to the uterus was 12.10 ±2.57 (mGy), and the mean total organ dose from the BrightSpeed S machine to the ovary was 39.2 ± 22.66 (mGy) and to the uterus was 43.05 ±24.88 (mGy), while the mean total organ dose from the Toshiba Aquilion 64 to the ovary was 33.07 ±16.86 (mGy) and to the uterus was 33.85 ±18.58 (mGy). These values were mostly comparable to but slightly higher than values of similar organ doses reported in the literature for Tanzania, the United Kingdom, Germany, and Japan. The doses to the ovary and uterus obtained varied from other international surveys by 3.8–12.9 mGy and 3.17–15.07 mGy, respectively, representing a 25–50% dose increase. Conclusion: The organ doses to the ovary and the uterus at our facility are higher than those obtainable in other countries; however, this could be substantially minimized through optimization of CT scanning protocols.

West African Journal of Radiology, 2014

Background: Establishment and use of "diagnostic reference levels" (DRLs) is essential ... more Background: Establishment and use of "diagnostic reference levels" (DRLs) is essential for proper use and audit of ionizing radiation in medicine and other radiation applications. Nigeria does not yet have a guideline for DRL. The European Commission reference dose levels were applied to routine computed tomography (CT) examinations in Nigeria′s major hospitals. Aim: To determine the dose of CT examinations at the University College Hospital, Ibadan, Nigeria and provide a template for dose optimization. Materials and Methods: Data were obtained from a GE Brightspeed multidetector CT scanner. The dose characteristics and estimates were derived from computed tomography dose index (CTDI vol ), and dose length product (DLP) with the effective dose (E) calculated using software developed by ImPACTscan group with the National Radiological Protection Board-S250 conversion coefficients data for a random sampling of 1 per 10 typical CT patients. Results: The mean values of CTDI vol in mGy were 73.5 ± 4.2 (head), 22.7 ± 6.7 (chest), 37.9 ± 5.6 (abdomen), 28.2 ± 8.3 (abdomen-pelvis), 41.4 ± 13.2 (cervical spine), and 40.1 ± 4.2 (lumbar spine) examinations. The corresponding mean values of DLP in mGy.cm were 1898, 1189, 1902, 2548, 1372, and 1563, respectively. The calculated E values in mSv for the above examinations were 2.8, 11.8, 22.5, 39.6, 4.6, and 29.0, respectively. All values consistently exceeded recommended ECRDLs except the CTDI vol for chest, cervical, and abdomen-pelvis examinations. Conclusion: CT doses were higher than EC recommended guidelines necessitating a need for optimization of CT practice and the requirement for a CT dose survey in Nigeria.

Environmental Health Insights

Nigerian Postgraduate Medical Journal, 2021

Public Health in Practice

Scientific Reports

Journal of Radiation and Cancer Research

Journal of Radiation Research and Applied Sciences

International Journal of Low Radiation, 2016

Journal of contemporary brachytherapy, 2015

West African Journal of Radiology, 2016

West African Journal of Radiology, 2014