Volume 2 Number 2 (2019)
*Click on the images to view articles
The Duties and Some Challenges Confronting Clinical Medical Physicists in Africa
Moses A. Aweda
Physics is a natural science subject dedicated to the search for facts about the natural laws and phenomena, ie the principles and laws that have evolved from observations and measurements of natural phenomena. As a part of natural science, Medicine is the quest for understanding one particular thing; the human body, its structures and functions under all conditions of health and sickness. This quest has led to the application of physical theories, concepts and models of human health and sickness that have been helpful in detecting and diagnosing sicknesses, and designing therapy techniques to alleviate pain and suffering and to restore the body to a state of good health. Hence there evolved a marriage between Physics and Medicine.
The Dosimetric Impact of Individual Setup Errors on Optimized Prostate IMRT Plans
Ehab M. Attalla, Mohamed Abdelmajeed, Nashaat A. Deiab, Wael M. Elshemey
Patient setup errors are well known to affect the accuracy of treatment plans. This work aims at quantifying their effects on the dosimetric outcomes of prostate treatment plans. SIB-IMRT treatment plans are carried out for 12 prostate cancer patients using Monaco TPS. Setup errors of the first three treatment fractions for each case are quantified using kV-CBCT. Accordingly, a plan isocenter is shifted and a recalculated plan is performed. For each of the target volume and the OARs, the dose distribution, the dose-volume metrics, the target homogeneity and the conformity are all quantified for the evaluation of their dosimetric impact. Mean 3D displacement of 3.4 ± 2.5 mm in AP direction, 2.8 ± 1.9 mm in SI direction and 4 ± 1.5 mm in LR direction are reported. A shift difference ≥ 3.0 mm in one or more dimensions occurred in 11 out of the 12 cases (91.66%) while 5 out of 12 cases (41.66%) have a shift difference ≥ 5 mm resulting in an average of 1-2 Gy reduction in the target dose and an average increase in the dose to OARs of 1Gy. There is a pronounced sensitivity of treatment plans to setup errors. The latter have detrimental dosimetric impact on prostate target coverage. KV-CBCT provides reliable IGRT means for defining setup errors in SIB-IMRT. Isocenter verification of setup errors is essential for achieving the approved treatment plan. A daily online correction protocol is suggested for successful elimination of setup errors.
Risk Evaluation of Blood Flow Resistance in Common Carotid Artery for an Apparently Healthy Nigerian Population
Sirisena Anil U. I., Ike Emeka E., Okeahialam Basil N., Chagok Nestor M. D., Pam Stephen D. and Ani Charles C.
Doppler ultrasound is used in evaluating the peak systolic (PSV) and end diastolic (EDV) velocities in blood vessels and to determine hemodynamic parameters, pulsatility (PI) and resistance (RI) indices. The objective of this study was to carry out the risk evaluation of blood flow resistance in common carotid artery to establish the normal and risk values of PSV, EDV and RI for an apparently healthy adult Nigerian population. This was required due to the fact that most apparently healthy individuals normally decline to undergo regular medical check-ups and suddenly rush to seek medical attention under emergency conditions in hospitals. GE Logiq 5 Expert Duplex scanner was used to carry out Doppler scans of right common carotid (RCC) artery of 221 apparently healthy adult volunteers. RCCPSV and RCCEDV were measured from the Doppler spectrums of each of the participants. RCCPI and RCCRI values were determined to ascertain the level of flow resistance in the common carotid artery. Using a standard protocol for risk evaluation using PI values, corresponding RI, PSV and EDV values were computed with non-linear regression curves. Data analysis was carried out with IBM SPSS Version 21 software. A strong positive correlation was found between RCCPI and RCCRI (R=0.628, p< 0.01). RCCRI was found to correlate better than RCCPI with both RCCPSV ( R=0.388, p < 0.01) and RCCED (R=- 0.481, p < 0.01). It was found that values of RCCRI between 0.47 and 0.63, RCCPSV between 47.8 cm/s and 85.0 cm/s and RCCEDV between 22.7 cm/s and 31.5 cm/s represent low resistance flow. RCCRI ≥ 0.78, RCCPSV ≥ 108.75 cm/s and RCCEDV ˂ 22.7 cm/s represent very high resistance flow. 32.1% of participants had very high blood flow resistance in common carotid artery based on RCCPSV classification. 29.9% and 21.7% had very high blood flow resistance according to RCCEDV and RCCRI classifications. The low resistance flow represents normal flow and very high resistance flow represents very high risk for cerebral cardiovascular diseases. About 1/3 of the apparently healthy adults in this cohort were found to have very high risk for cardiovascular diseases and needed urgent intervention.
Effects of Exposures of Mobile Phone Radiation on Cellular Architecture and Redox Status of Mammalian Brain Tissues
Faromika Oluwayomi Peace
Several reports have described the potential deleterious effect of radiofrequency electromagnetic radiation (RF-EMR) from mobile phone on cerebral redox status. However, the frequency and duration of exposure to such radiation in real life situation can vary widely thus suggesting that experimental simulation and evaluation of mammalian interaction with RF-EMR is seemingly endless and thus very open. In this study, Male Wistar albino rats were continuously exposed to RF-EMR with frequency 900 MHz for 0, 4, 8 and 12 h per day for 30 days. Thereafter, the enzymic and non-enzymic antioxidant defense statuses and histology of the brain were evaluated. The results showed that frequent exposure to RF-EMR diminished the antioxidant defense status and evoked distorted structural integrity of brain cells and this effect was exacerbated with increased daily duration of exposure. Within the limit of the present data, it appears that unwitting frequent occupational, intentional and inadvertent exposures to RF-EMR may evoke cerebral dysfunction in predisposed individuals. Hence, this study demonstrates the potential health risk associated with prolonged and frequent use of mobile phones.
Effect of pH of Water on Absolute Dosimetry Using TRS398 Protocol
Ige T. A., Adewole M., Opadele A., Ekpo M.
The IAEA published TRS 398 in 2000 to serve as a code of practice for the determination of absorbed dose to water in photon beams, electron beams, proton beams and heavy ion beams used for external radiation therapy. pH (potential of hydrogen) is a measure of the concentration of (H+) in a solution; it ranges from 6.5-8.5 for water. In this study, an experiment was conducted to evaluate the effect of pH variation of the water phantom on charge collection and aimed to establish water pH correction factor (KpH) as one of the correction factors for influence quantities of TRS 398. A water tank with the capacity of 27000cm3 was filled with water with an initial pH of 7.3. This was varied from 3.0 to 10.0 using diluted hydrochloric acid (HCl) and sodium hydroxide (NaOH) across acidity and alkalinity lines respectively. The water tank was positioned under the LINAC at 100cm SSD with 10cm x 10cm field size. The chamber (SNC Farmer with calibration factor of 5.18 x 107 Gy/C) was placed at a depth of 10cm along the central axis of the beam. Repeated electrometer measurements were obtained with 100MU for 6MV, 10MV and 15MV respectively. Results from the study indicated that the measurement was dependent on the pH of the water phantom as the plots showed similar sinusoidal wave structures for all the three photon energies. It also revealed that maximum ionization was obtained when the pH is between the ranges of 8.0 to 9.0 for all energies. The analysis of the variation in the charge collected suggests that there is no rationale for evaluating the KpH as the outputs were within the acceptable range
Comparative Assessment of Radioactive Source Strengths in Two High-Dose-Rate Brachytherapy Units Using Three Sets of Dosimetry Equipment
Oyekunle Emmanuel O., Akinlade Bidemi I., Uwadiae Iyobosa B., Ajeleti Olayemi G., Adedokun Adedotun G.
The uncertainty in ionization chamber calibration factors could contribute significantly to the total uncertainty in source strength measurement. It is therefore recommended that hospitals should verify the strength of each new brachytherapy source as part of the quality assurance programme. This study was aimed at calibrating new Cobalt-60 high-dose-rate (HDR) brachytherapy sources using three sets of dosimetry equipment to determine the accuracy and suitability of each method for routine calibrations. Two new units (Saginova) of HDR brachytherapy equipment (BEBIG, Germany) each using a Co-60 source (differing in activity), are available at the Department of Radiation Oncology, University College Hospital, Ibadan. While a well-type chamber (WC) and an electrometer from Physikalisch-TechnischeWerkstätten (PTW) were provided for one unit, the same type of dosimetry devices from a different provider, Standard Imaging (SI) were supplied for the second unit. Each of the HDR sources was calibrated in turn by the two new well chamber-electrometer systems and a 0.12 cc thimble ionization chamber used alongside its electrometer and a cylindrical phantom previously available for source calibration of the replaced HDR unit at the department. In each case, measurements were made using a dwell position that was fitting for maximum dose response from the detector. The measured source strengths for each equipment were compared with the manufacturer’s certified value corrected for decay till date of measurements at UCH.The percentage deviations of the measured source strengths relative to manufacturer quoted values observed with the PTW WC, SI WC and the cylindrical phantom were -2.80, -1.97 and 1.00 respectively for one HDR unit. Corresponding values for the other brachytherapy unit were -1.06, 0.65 and -2.40. In both HDR units, the source strength obtained with the SI well-type chamber were found to be in better agreement to certified values given the resulting smaller deviations compared to values determined with PTW dosimetry system. Overall, the source strengths measured with the three sets of dosimetry equipment were in good (<±3%) agreement with the manufacturer stated values for both HDR sources. A combination of ionization chamber and a solid phantom could therefore be used for verification of source strength at a center where well-chamber dosimetry system is not readily available.
Dosimetric Consequences of Using Wedge Angles as Major Determinants of Tumor Dose Homogeneity in Breast Cancer Teletherapy
Rilwanu Idris and Hassan Ibrahim
Advanced radiotherapy techniques such as intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT) and proton beam therapy replaced the use of wedge angles in achieving tumor dose homogeneity in developed nations. The availability of such machines is limited in our environment, therefore, wedge angles remains the major alternative beam modifiers to produce dose uniformity to target volumes. This study aimed at evaluating the dosimetric consequences of using wedge angles in achieving tumor dose homogeneity. Twenty Computed Tomography (CT) images of female patients with breast cancer (ten each for left and right side) were reviewed, their mean age was 42 years, Bi-tangential beams were used and dose of 50 Gy in 25 fractions was prescribed to each patient. Three commonly used wedge angles (15o, 30o and 45o) were sequentially inserted across the beams for each plan and tumor dose homogeneity was evaluated using 95% isodose coverage. Hot spot, mean dose, dose rate and monitor units generated were recorded for each wedge angle used. Statistical package for social sciences (SPSS) version 23.0 was used to find overall mean of each parameter. A two ways Analysis of Variance (ANOVA) was conducted to find variation in using different degrees of wedge angles on above stated parameters at 5% α level of significance. Results were presented in tables and bar-chart. After plan evaluation, the overall percentage mean doses were 97.8% for 15o, 97.4% for 30o and 96.4% for 45o. For the hot spot it was 111.7% for 15o, 109.7% for 30o and 108.7% for 45o. Dose rates for medial and lateral fields were (0.5385, 0.6921 cGy/MU) for 15o, (0.3918, 0.5012 cGy/MU) for 30o and (0.2801, 0.3544 cGy/MU) for 45o respectively. Similarly, the corresponding monitor units generated for medial and lateral fields were (78.02, 66.18MU), (170.81, 147.12MU) and (311.86, 269.03MU) according to increasing order of wedge angles. No significant differences seen between the use of different wedge angles and percentage mean doses or hot spots (p ˃ 0.05).The use of wedge angles (EDWs) ˃ 15o showed no benefit in improving tumor bed percentage mean dose, but rather it increase number of MUs which prolong treatment time and likelihood of patient movement during treatment.
Effect of Local Temperature and Pressure on the Photon Beam Outputs from Linear Accelerator
Birchi H. S., Saidu A., Muhammad S. B., Ibrahim H., Idris R., Abubakar A., Aliyu U. M., Bello G.
Daily quality control (QC) is mandatory in radiotherapy so that tumor dose delivery should be within ±3% of the prescribed dose. However, daily variation of Local temperature and pressure are reported to affect machine outputs, hence the need for daily quality audit. Three years (January 2011 – December 2013) daily records of 6 and 15 MV photon output from Elekta precise machine using standard set up procedure with quality control tools were extracted. Corresponding bunker temperature and pressure were also retrieved and reviewed. SPSS Software package was used to determine ranges, means and standard deviations of all the factors. The photon outputs for the two energies were also plotted against temperature and pressure. The most frequently observed photon outputs over the study period were 0.975 cGy ∕ MU for 6 MV and 0.800 cGy/MU for 15 MV with ±2.5% and ±3.1% deviation from the reference values of 1.00 and 0.826 cGy/MU respectively. Temperature and pressure showed inverse correlation with p-value < 0.01. The magnitude of photon outputs for 6 and 15 MV attained peak values of 1.000 and 0.900 cGy ∕ MU respectively at the lowest bunker temperature of 24.05oC, but dropped to 0.870 and 0.800 cGy ∕ MU as bunker temperature raised to 30.02oC. The bunker pressure showed a linear relationship with photon output, as bunker pressure raises from 972.3 to 981.7 hpa their corresponding outputs also rises from 0.870 to 1.000 cGy ∕ MU for 6 MV and 0.8000 to 0.8900 cGy/MU for 15 MV respectively. Daily variation of bunker temperature and pressure influenced photon outputs from LINAC, despite the use of dose checker with sealed ionization chamber. However, daily quality control should be maintained to ensure safety in dosimetry.
Dosimetric Testing of Two Incident Electron Parameters for Photon Beam Monte Carlo Model of an Elekta Precise Linac
Oluwaseyi M. Oderinde, Michael O. Akpochafor, Rachel I. Obed and Ramotallah D. Jubril
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 variations of the two incident beam sources parameter have an influence on dose distribution characteristic apart from the depth-dose curves which are unaffected. The most accurate source models(r = 0.01 mm and σ = 0.05 mm) discrepancies fell within 2%/2mm and 3%/3mm γ criteria for the symmetry field considered. Parallel source beam radii of 0.01 – 4 mm generated the pass rates of 97.46 – 96.61% and 98.31 – 96.61% for 2%/2mm and 3%/3mm, respectively, while σ variations (0.05-2 mm) in mean angular spread beam source resulted into pass rates of 97.46 – 96.61% and 98.31- 97.46%, respectively. The two incident electron sources are suitable for dose calculation if tuned precisely. However, lateral dose profiles are insensitive to minimal variation of incident electron source parameters. When it comes to the choice of source parameter, preference can be given to the mean angular spread beam source based on clinical consideration.
AJMP is the official journal of FAMPO
Published by the Global Health Catalyst