Comparison of effective dose in phantom from computed tomography using monte carlo simulation and thermoluminescent dosimetry methods

Abstract

Computed tomography (CT) is the examination procedure in diagnostic radiology and the dose given to the patient is higher than general radiographic procedures. This research work is to study the organ doses and effective doses from calculation by ImPACT spreadsheet of Monte Carlo simulation and measurement by thermoluminescent dosimeter (TLD) in the Rando phantom. The organ doses and effective doses for chest and abdominal examinations were estimated from Siemens Sensation 16 computed tomography equipment used at King Chulalongkorn Memorial Hospital. The computed tomography dose index (CTDI) was measured in air and in body phantom with Scanditronix/Wellhofer DCT 10-RS ionization chamber then the CTDIs and exposed parameters were entered in ImPACT spreadsheet for calculation of the organ and effective doses. The TLD-100 chips were calibrated with [superscript 60]Co beams. The sensitivity, linearity and energy response of TLD-100 chips were determined. The TLD-100 chips were inserted in the Rando phantom and were irradiated. The organ doses and effective doses were calculated. Finally, the results from two methods were compared in term of percentage difference. From our study, most of the organ doses for chest and abdominal examinations from thermoluminescent dosimetry were higher than those calculated by Monte Carlo simulation except breast, esophagus, and bone surfaces for chest examination and gonads, lung, and esophagus for abdominal examination. The differences between the organ doses from two methods were within the 11.74 % uncertainty of TLD measurement for the organ located in the radiation field except the organs that were difficult to search for the exact location. The effective doses of chest examination were 4.37 mSv from Monte Carlo simulation and 5.42 mSv for thermoluminescent dosimetry, resulted in 19.37% difference. The effective doses of abdominal examination were 7.31 mSv from Monte Carlo simulation and 8.52 mSv for thermoluminescent dosimetry, resulted in 14.20% difference. The results showed the higher measured dose than calculated which agreed with the other published studies. The underestimation of the calculated dose was mainly due to the difference of the design between the Rando phantom and Medical Internal Radiation Dosimetry (MIRD) mathematical phantom in Monte Carlo simulation. For the clinical patient, the organ and effective doses could be estimated by Monte Carlo simulation with the awareness of the under estimation within 20%.