Dosimetric Effect of Metal Implant on Absorbed Dose
Michael Onoriode Akpochafor1, Samuel Olaolu Adeneye1, Muhammad Yaqub Habeebu1, Akintayo Daniel Omojola2, Moses Adebayo Aweda1, Temitope Aminat Orotoye1, Abayomi Emmanuel Opadele1, Mary-ann Etim Ekpo3, Oluyemi Bright Aboyewa41Department of Radiation Biology, Radiotherapy, Radiodiagnosis and Radiography, College of Medicine,University of Lagos, Idi-Araba, Lagos, Nigeria, 2Department of Radiology, Medical Physics Unit, Federal Medical Centre Asaba, Delta State, Nigeria, 3Department of Physics, University of Ibadan, Faculty of Science, Ibadan, Oyo State, Nigeria, 4Department of Physics, Federal University of Technology, Akure, Ondo State, Nigeria
Objectives: The aim of this study was to evaluate the effect of a metal implant on the absorbed dose in a homogeneous phantom. Methods: Thin sheets of stainless steel 1.0 mm, 1.5 mm, and 2.0 mm in thickness were used in this study. They were reduced to 3 samples of a width of 1.0 mm and 9.0 mm in height for each thickness to serve as the metal implant. A Farmer chamber (FC65-G) was used to measure the absorbed dose of radiation in a solid water phantom 30x30x1 cm and 30x30x2 cm in size. The entrance window to the phantom was 1 mm from the center of the chamber with a 0.7-cm radius. The set-up was irradiated for 30 seconds using a Cobalt-60 unit at a Source to Surface Distance (SSD) of 80 cm. An electrometer produced by Wellhofer calibrated with the chamber was used to record the absorbed dose (mGy) in samples with the implant and without, in position at field sizes of 5x5 cm2 and 10x10 cm2. Depths of 1.7 cm, 2.7 cm, 3.7 cm, and 4.7 cm were used for each measurement. Results: There was a greater variation in dose measured at higher depth (greater than 5 cm) with the 1-mm implant in the 10x10 cm2 field. The absorbed dose measured decreased as the depth of the implant increased. Also, the dose measured for the 1-mm implant was within the recommended ±5% accuracy, except at a depth greater than 5 cm. However, for the 1.5-mm and 2-mm implants, deviations were higher at almost all depths. There was an increase in dose at large field sizes. Furthermore, a decrease in dose was observed as the thickness and depth of the implant increases. Conclusion: The higher attenuation of a metal implant causes variations in dose.
Cite This Article
Akpochafor M, Adeneye S, Habeebu M, Omojola A, Aweda M, Orotoye T, Opadele A, Ekpo M, Aboyewa O. Dosimetric Effect of Metal Implant on Absorbed Dose. EJMI. 2018; 2(2): 90-94
Corresponding Author: Michael Onoriode Akpochafor