Occupational exposure assessment in ROLL procedures with Tc-99m: A Monte Carlo simulation approach.

Abstract

The surgical removal of non-palpable breast tumors is frequently performed using radioguided occult lesion localization (ROLL) with ⁹⁹ᵐTc. Because the surgical team works close to the patient, photons emitted from the lesion may contribute to occupational exposure. Monte Carlo simulations were performed with the MCNPX 2.7.0 code the FASH3 voxel phantoms to estimate organ equivalent dose rates for the physician and source-normalized organ dose-rate estimates for the patient phantom. A⁹⁹ᵐTc activity of 74 MBq was assumed to be present in the breast at the time of the procedure. Three occupational configurations were simulated: (A) no personal protective equipment (PPE), (B) a 0.5 mm Pb-equivalent apron together with 0.5 mm Pb-equivalent protective glasses, and (C) a 0.5 mm Pb-equivalent mobile shielding screen without PPE. The dose-rate estimate for the physician phantom decreased from 3.4 μSv h-1 without PPE to 0.83 μSv h-1 in the combined apron-and-glasses configuration; the value with the mobile screen was 2.8 μSv h-1. The eye-lens equivalent dose rate was 4.2 μSv h-1 without PPE and 3.6 μSv h-1 in the combined PPE configuration. Because apron-only and glasses-only scenarios were not simulated, the eye-lens reduction cannot be attributed exclusively to the glasses. For the patient, the highest values were in the breast (540 μSv h-1), liver (130 μSv h-1), lungs (96 μSv h-1), and esophagus (61 μSv h-1). These patient-phantom values represent an instantaneous stationary-source model and are not patient absorbed doses integrated over radiopharmaceutical kinetics. Within these limitations, the simulations support the use of PPE and distance optimization during ROLL procedures.