A Comparative Study on the Shielding Calculation Methods for an Optimal Shielding Design of Isolation Rooms in a Nuclear Medicine Facility in the Philippines Providing 131I Thyroid Ablation Therapy

Iodine-131 ( 131 I) has been used widely in diagnosing and treating thyroid disorders, but its radioactive nature poses risks of gamma radiation exposure to those near the patient. To mitigate this, radiation protection measures are needed, among which is the provision of optimal structural shielding. In the Philippines, achieving this involves using minimum shielding thickness to meet safety limits from national regulations. Widely used conventional methods, like those based on the tenth-value layer (TVLs) measurements, may yield poor estimates, while computational simulations are precise but impractical to use due to their complexity. Archer's fitting method offers a simple and accurate alternative for designing optimal shielding in medical imaging and radiotherapy facilities based on multiple studies. However, little to no data is available regarding the use of Archer's fitting method in providing better accuracy in shielding calculations in isolation rooms of 131 I therapy facilities. A comparison of the transmission factors calculated using different calculation methods was done, and their effect on the minimum shielding thicknesses was investigated. Transmission curves generated with broad-beam TVLs reported from previous studies yielded the closest agreement with ANS/ANSI 6.4.3 buildup factors for lead barriers. On the other hand, results showed the closest agreement among the transmission curves and shielding thicknesses acquired with the American National Standard (ANSI/ANS) 6.4.3. buildup factors, Archer's fitting method, and Monte Carlo simulation through Particle Heavy Ion Transport System (PHITS) ver. 3.28 code for ordinary concrete barriers. Poor agreement was seen with the curves generated with the Narrow-Beam and Ideal Broad Beam TVL methods and the curve generated with ANSI/ANS 6.4.3. buildup factor data. Broad-Beam TVLs from previous studies, Monte Carlo Simulation, and Archer's fit can be alternative options for shielding design. An experimental study is proposed for verification.