Impact of the implementation of the new radiation quantities recommended by ICRU/ICRP for practical use in interventional radiology: a Monte Carlo study

Abstract

The International Commission on Radiation Units and Measurements (ICRU) proposed a new set of operational quantities for radiation protection for external radiation in its Report Committee 26. The new proposal aims to improve the coherence between the operational quantities and the definitions of the protection quantities in the recommendations of the International Commission on Radiological Protection (ICRP) in 2007. It is expected that this change in operational quantities will impact current dosimeter designs. Although for many photon energies, the conversion coefficients from physical field quantities to the new operational quantities will change relatively little, for radiation fields with low energy photon components, such as medical X-ray applications, there will be a significant decrease in the values of the conversion coefficients. This means that the numerical values of the new operational quantities will be much lower for the same radiation field. These values will be closer to the effective dose, but this change can still cause confusion for the workers. It is important to examine the effect of the new set of dose conversion coefficients on the personal dose in realistic radiation fields. We performed a study to assess the effect of changing the definition of the operational quantity, personal dose equivalent (Hp), in realistic radiation fields in IR workplaces. The X-ray tube Kilovoltage peak (kVp) in IR ranges between 60 and 120 kV. The medical staff is exposed to the scattered photons that have a wide range of energies depending on the beam configuration and the patient size. The objective of this study is to “quantitatively” estimate the impact of implementing the new ICRU quantities of Report 95 in IR radiation fields using Monte-Carlo simulations. Simulations of 560 different configurations in IR were performed using MCNPX to calculate fluence binned per energy and angle of incidence. Hp and Hp(10) were then calculated for each configuration using dose conversion coefficients from fluence given by ICRU Report 95 and 57, respectively. The results show that the mean of the ratio, Hp(10)/Hp, is 1.6 for all simulated scenarios. This reduction will correct the current overestimation of the effective dose and should result in better compliance with the dose limits in IR. However, it may also have negative consequences on the safety culture among the medical staff. Special care will be needed when interpreting these lower doses.