Abstract
Monte Carlo (MC) simulation is a simpler radiation dose assessment method than the conventional method, thermoluminescent dosimetry (TLD). MC simulation and TLD were compared as tools to evaluate the effective dose from paediatric panoramic radiography. Various exposure conditions and machine geometries were simulated using the MC method to investigate factors resulting in effective dose reduction. The effective dose of paediatric panoramic radiography was obtained using an MC simulation and its reliability was verified by a comparison with the value obtained using TLD. Next, 7 factors determining the effective dose in the MC simulation were input with 6 equally-spaced values, and a total of 36 simulations were performed to obtain effective dose values. The correlations between each dose-determining factor and the resulting effective dose were evaluated using linear regression analysis. The TLD-measured dose was 3.850 µSv, while the MC simulation yielded a dose of 3.474 µSv. Beam height was the factor that most strongly influenced the effective dose, while rotation angle and focus-to-patient distance were the least influential factors. MC simulation is comparable to TLD for obtaining effective dose values in paediatric panoramic radiography. Obtaining panoramic radiography with a short beam height can effectively reduce the dose in paediatric patients.
Highlights
The human body is known to be more sensitive to radiation at younger ages, because the cells comprising the body organs have a high potential for differentiation and actively divide in children[1,2]
Monte Carlo (MC) simulation is a relatively uncommon method of obtaining the effective dose in dentistry, it is widely used in the medical field due to its simplicity and high accuracy
In panoramic radiography units, for which the principles of machine operation are much more complex than those of cone-beam computed tomography (CBCT), the MC method showed comparable results to thermoluminescent dosimetry (TLD) for effective dose acquisition when appropriate input values were used in the simulation[8]
Summary
Since TLD was read as gamma energy which presents 1.25 times higher sensitivity compared to the x-ray, a correction factor of 0.8 was multiplied to normalize the value. The TLD chips were left for 24 hours, and the energy level stored in the chips was read with a RADOS RE-1 reader (Rados Technology, Turku, Finland). The absorbed dose of each anatomic site was obtained by averaging the measured value of the 3 chips in micrograys (μGy). The values from each anatomic site were integrated into the organ dose considering the tissue-irradiated fraction of the head and neck (Table 2). The individual organ doses were integrated into the effective dose considering the tissue weighting factors suggested in 2007 by the International Commission of Radiological Protection (Table 2)[14]. The virtual phantom of a 5-year-old in the program was 19 kg in weight and 109.1 cm in height
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