Author: Stephen Balter, Haegin Han, Cari M Kitahara, Taeeun Kwon, Choonsik Lee, Martha S Linet, Donald L. Miller 👨🔬
Affiliation: Columbia University Medical Center, National Cancer Institute, Food and Drug Administration 🌍
Purpose: Staff in fluoroscopically guided interventional (FGI) procedures are exposed to radiation. Inhomogeneous radiation fields and variability in procedural conditions make it challenging to derive organ and effective doses from Hp(10) estimates provided by personal dosimeters. We aimed to calculate and analyze conversion coefficients from Hp(10) to organ/effective doses by incorporating realistic exposure factors.
Methods: Conversion coefficients were calculated by simulating realistic FGI exposure scenarios using the Geant4 toolkit. The patient was modeled with UF/NCI phantoms for the computational efficiency, while the medical staff were represented by ICRP mesh-type phantoms, allowing for easy modification. Hp(10) values were determined at five different badge positions on the phantom by evaluating energy fluence and incident angles. Organ doses were calculated directly by scoring deposited energy within organs. A thin lead layer was explicitly modeled over the lead apron-covered areas to account for shielding. Conversion coefficients were calculated for approximately 300 cases varying by sex, position, and posture of the medical staff, thyroid shielding, lead equivalent thicknesses, energy spectra, and patient exposure area.
Results: The calculated conversion coefficients showed significant discrepancies compared to those derived from simple anterior-posterior (AP) irradiation geometry, particularly for staff positions within 3 feet of the patient, where values were generally 2-7 times higher. These differences were primarily due to the substantial decrease in Hp(10) with larger radiation incident angles, among other factors. It was also found that radiation exposure was not homogeneous by anatomic site, with region-specific variations observed in skin doses.
Conclusion: This study demonstrates that the inhomogeneity of irradiation geometry in FGI procedures can significantly bias the relationship between Hp(10) and organ/effective doses, highlighting that previous studies may have relied on oversimplified assumptions. The resulting dataset provides a valuable tool for dose reconstruction and optimizing radiation exposure for medical radiation workers.