COMPARATIVE EVALUATION OF MEASURING DEVICES OF RADIATION DOSES AND THEIR USE IN MEDICAL SURVEY

Abstract

The purpose of this study is to compare between different techniques of measuring devices of radioactive isotopes to the workers in the department of nuclear medicine. Thermoluminesience dosimeters, ion chamber survey meter, and propotional counter survey meter were used in this study. Also, study of the distribution of dose around whole body is very important and was done. In diagnostic nuclear medicine practice, the two most important isotopes are 99mTc and 13I L The majority of uses is 99mTc. Technetium has nearly ideal nuclear properties for diagnostic imaging. It has monoenergetic gamma emiSSIOn of I40 Kev which is well suited for use with the present gamma cameras. It has a short half life of 6.02 h and readily available to all hospitals via the 99Mo - 99mTc generator. The results obtained that, the dose per patient during the diagnosis ranges from I JJ.Sv to I5JJ.Sv, depending on the case of diagnosis and the distance between the patient and the worker. The values agree with the results shown in UNSCEAR I993 [40]. The typical world dose per patient ranges from 2001-1Sv to 201-1Sv in most industrialized countries and I 0-40 mSv in developing countries. The annual dose estimated by this work ranges between 5 mSv to 13 mSv during each diagnosis. This value is within the annual permissible dose 20 mSv UNSCEAR I993. The dose per patient and the annual dose were calculated in heart, bone, kidney and thyroid scan. The higher doses to workers were taken during the diagnosis of the heart scan. The dose per patient in case of heart scan is I41l Sv and the annual dose is I2.06 mSv. The dose per patient in bone scan is I 0 JJ.Sv and the annual dose is 14 mSv. In thyroid scan the dose per patient is 3.6 JJ.Sv and the annual dose is 13 mSv. In kidney scan the dose per patient is 1.5 JJ.Sv and the annual dose is 5 mSv. From this data we show that if the worker stay all time in this position he will record these annual doses but in fact the worker can do different diagnosis in the same day. The annual dose to the worker during the eight hours work ranged between 12 7JJ.Sv/h to l.6JJ.Sv/h which still within the range of permissible dose. The worker who had the largest value was : administrate the radioactive material and make a diagnostic scan to the patients. The worker who had the less value was : make a diagnostic scan for patients only. Also, it is observed that there is nonunifirmity of distribution of radiation during the whole body where the dose rate at the abdomen is 5 ll Sv/h and at the chest is 4 JJ.Sv/h. Then there is non-uniformity distribution of radiation in the whole body and the annual dose within the international levels. The dose to the hands also is below relevant limits. From this work we can summarized that, the radiation dose to the organ is a function of the amount administer, the physical half life, the residence time of the radioactive material in the body and in the vicinity of the irradiated organ. The results show that, due to the location of the liver and spleen, a TLD badge on the abdomen would be heavily irradiated more than any organ according to the biodistribution of activity.