Optimization of dual slot antenna using floating metallic sleeve for microwave ablation.

Backward heating reduction is vital in power distribution optimization in microwave thermal ablation. In this study, we optimized dual slot antenna to yield reduction in backward heating pattern along the antenna shaft with the application of floating metallic sleeve. Finite element methods were used to generate the electromagnetic (EM) field and thermal distribution in liver tissue. The position of the sleeve from the tip of the probe (z = 0 mm) was varied within the range 14 ≤ z ≤ 22 mm while sleeve length was varied within 16 ≤ z ≤ 48 mm at 2 mm interval using operating frequency of 2.45 GHz. The best optimized design has reflection coefficient of -20.87 dB and axial ratio of 0.41 when the sleeve position was at 17 mm and sleeve length was 18 mm. Experimental validation shows that inclusion of a floating metallic sleeve on dual slot antenna for hepatic microwave ablation averagely increased ablation diameter and aspect ratio by 17.8% and 33.9% respectively and decreased ablation length by 11.2%. Reduction in backward heating and increase in power deposition into liver tissue could be achieved by using this antenna to provide greater efficiency and localization of specific absorption rate in delivering microwave energy for hepatic ablation.

Verification of Entrance Dose Measurements with Thermoluminescent Dosimeters in Conventional Radiotherapy Procedures Delivered with Co-60 Teletherapy Machine.

BACKGROUND: The use of in vivo dosimetry with thermolumiscent dosimeters (TLDs) as a veritable means of quality control in conventional radiotherapy procedures was determined in this work. AIM: The objective of this study was to determine the role of in vivo dosimetry with thermoluminescent dosimeters (TLDs) as part of quality control and audit in conventional radiotherapy procedures delivered with Co-60 teletherapy machine. SUBJECTS AND METHODS: Fifty-seven patients with cancers of the breast, pelvis, head and neck were admitted for this study. TLD system at the Radiation Monitoring and Protection Centre, Lagos State University, Ojo, Lagos-Nigeria was used for the in vivo entrance dose readings. All patients were treated with Co-60 (T780c) teletherapy machine at 80 cm source to surface distance located at Eko Hospitals, Lagos. Two TLDs were placed on the patient surface within 1 cm from the center of the field of treatment. Build-up material made of paraffin wax with a density of 0.939 g/cm(3) and a thickness 0.5 cm was placed on top of the TLDs. A RADOS RE 200 TLD reader was used to read out the TLDs over 12 s and at a temperature of 300°C. RESULTS: The results showed that there was no significant difference between the expected dose and measured dose of breast (P = 0.11), H and N (P = 0.52), and pelvis (P = 0.31) patients. Furthermore, percentage difference between expected dose and measured dose of the three treatment sites were not significantly different (P = 0.11). More so, 88.9% (16/18) treated breast, 91.3% (21/23) pelvis, and 86.7% (13/15) H and N patients had percentage deviation difference less than 5%. In general, 89.3% (50/56) patients admitted for this study had their percentage deviation difference below 5% recommended standard limit. CONCLUSION: The values obtained establish that there are no major differences from similar studies reported in literature. This study was also part of quality control and audit of the radiotherapy procedures in the center as expected by national and international regulatory bodies.

Assessment of radiofrequency power density distribution around GSM and broadcast antenna masts in Lagos City, Nigeria.

BACKGROUND: Global system of mobile communication (GSM) and other telecommunication technologies are now common place in Lagos state Nigeria. The introduction of GSM in 2002 considerably increased radiofrequency (RF) radiation exposure of the public from telecommunications transmitting and receiving antennae. The RF radiation emanating from these devices, if above international limits may pose health risk to the public. OBJECTIVE: There is need for database of RF distribution level in Nigeria for safety assessment. The purpose of this study is to determine power density around different telecommunications antenna base stations and compare the measured values with the international recommended exposure limits in order to assess the safety of the members of the public. METHODS: A radiofrequency meter, Electrosmog from LESSEMF USA was used for the measurement. It is a highly sensitive device capable of measuring frequency between 50 MHz and 3.5 GHz. Measurements were taken at distances of 25, 50, 100, 150 and 200 m from selected antenna base stations in Lagos state. The results were compared with the International Commission of NonIonizing Radiation and Protection (ICNIRP) and the Institute of Electrical and Electronics Engineering/American National Standard Institute (IEEE/ANSI). RESULTS: Power densities obtained varied between 0.219 and 302.40 mW.m(-2) from the studied base stations. Comparison of the results with the ICNIRP and IEEE/ANSI recommended safety standards of 12000 mW x m(-2) and 5700 mW x m(-2) showed that the exposure levels are very low. CONCLUSION: Power densities of the RF radiation from telecommunication transmitting/receiving antennae were far below international standard limits. The measured values are not likely capable of inducing significant hazardous health effects among the people that are at least 6 m away from the antennae.