Standard calibration of ionization chambers used in radiation therapy dosimetry and evaluation of uncertainties

Absolute dosimetry of external beam radiotherapy is carried out by the use of ionization chambers. These chambers must be calibrated at a standard dosimetry laboratory before any use in clinical dosimetry. The secondary standard dosimetry laboratory of Iran [SSDL] has the duty of calibrating the ionization chambers used in radiotherapy centers in Iran. The present work has described traceability of SSDL radiation measurement standards to relevant international standards, and calibration of therapy level ionization chambers in terms of air kerma and absorbed dose to water against [60]Co gamma radiation, as well as uncertainty evaluation of calibration coefficients. The expanded uncertainties in the determination of air kerma and absorbed dose to water are estimated to be 2% and 2.3% at approximately 95% confidence level, respectively. In order to maintain the requirement of +/- 5% accuracy in the dose delivery, the combined standard uncertainty of the other factors in the dose delivery; i.e., dose measurement set-up, dose calculations, treatment planning, patient set-up, etc, should be less than 2.3%

Evaluation of 4,4-methylene diphenyl diisocyanate effects on foam producing workers of car manufacture

4, 4 - Methylendiphenyl diisocyanate[MDI], is the most widely used chemical in the manufacturing of polyurethanes [a field of plastic industries], and it is one of the major causes of the occupational asthmas. Assessing the MDI concentration in air and also evaluating the effect of this chemical on eyes, skin, respiratory and gastrointestinal systems in workers of a foam producing section in a car manufacturing company. The effects of MDI on skin, eyes, respiratory and gastrointestinal systems were evaluated in two 40-person groups of exposed and unexposed workers and the MDI concentration in air was determined. The data were analyzed using t-Student test, pair-t-test, lamda[2] test, Regression Analyze, and correlation test. MDI concentration was lower than the threshold limit value while the local ventilation and air conditioning systems were both on, however, it was higher than the expected value when both systems were switched off. Our results showed that the presence of symptoms such as coughing, smart pain and dryness of skin, and the smart pain and itching of eyes in exposed group were significantly different from those in unexposed group[P<0.05]. Some of respiratory volumes were indicative of a significant difference between exposed and unexposed groups [P<0.05]. Exposure to MDI can result in reduction of respiratory volumes while increasing the occurrence of eye, skin and respiratory symptoms