Pitfalls in interventional X-ray organ dose assessment—combined experimental and computational phantom study: application to prostatic artery embolization

Abstract

Purpose With X-ray radiation protection and dose management constantly gaining interest in interventional radiology, novel procedures often undergo prospective dose studies using anthropomorphic phantoms to determine expected reference organ-equivalent dose values. Due to inherent uncertainties, such as impact of exact patient positioning, generalized geometry of the phantoms, limited dosimeter positioning options, and composition of tissue-equivalent materials, these dose values might not allow for patient-specific risk assessment. Therefore, first the aim of this study is to quantify the influence of these parameters on local X-ray dose to evaluate their relevance in the assessment of patientspecific organ doses. Second, this knowledge further enables validating a simulation approach, which allows employing physiological material models and patient-specific geometries.Methods Phantom dosimetry experiments using MOSFET dosimeters were conducted reproducing imaging scenarios in prostatic arterial embolization (PAE). Associated organequivalent dose of prostate, bladder, colon and skin was determined. Dose deviation induced by possible small displacements of the patient was reproduced by moving the X-ray source. Dose deviation induced by geometric and material differences was investigated by analyzing two different commonly used phantoms. We reconstructed the experiments using Monte Carlo (MC) simulations, a reference male geom-1 Pattern Recognition Lab, FAU Erlangen-Nürnberg, etry, and different material properties to validate simulations and experiments against each other. ResultsOverall, MC simulated organ dose values are in accordance with the measured ones for the majority of cases. Marginal displacements of X-ray source relative to the phantoms lead to deviations of 6 % to 135 % in organ dose values, while skin dose remains relatively constant. Regarding the impact of phantom material composition, underestimation of internal organ dose values by 12 % to 20 % is prevalent in all simulated phantoms. Skin dose, however, can be estimated with low deviation of 1 % to 8 % at least for two materials.Conclusions Prospective reference dose studies might not extend to precise patient-specific dose assessment. Therefore online organ dose assessment tools, based on advanced patient modeling and MC methods are desirable.

XDose: toward online cross-validation of experimental and computational X-ray dose estimation

“…For example, it can be difficult to accurately map clinical imaging settings to MC simulations unless the underlying X-ray physics as well as the patient's anatomy and position relative to the X-ray device are known. Empiric methods often lack reproducibility and are prone to measurement uncertainties [21].…”

“…Our MC code is based on the Geant4 toolkit [32]. To provide physical plausibility, we employed the Geant4 configuration used in the TG-195 report [19] and a previous study [21]. Besides accurately capturing the spatial relationship between all components of the imaging settings, mapping the Fig.…”

“…Sophisticated algorithms are needed to solve the photon transport equation, such as Monte Carlo (MC) methods [16], finite differences [17], or deep-learningbased approaches [18]. While the task group report 195 (TG-195) of the American Association of Physicists in Medicine (AAPM) proposes a protocol to ensure the validity of such algorithms [19], uncertainties concerning patient anatomy and alignment, or material composition remain [20,21]. Unfortunately, the high inter-and intra-procedure variance of organ dose values concerning complicated FGIs, therefore, demands for individualized patient-specific dose metrics [22,23] and procedure-specific dose studies.…”

“…Unfortunately, the high inter-and intra-procedure variance of organ dose values concerning complicated FGIs, therefore, demands for individualized patient-specific dose metrics [22,23] and procedure-specific dose studies. Consequently, for most procedures, a high uncertainty remains when estimating organ or effective dose from the total air kerma using either simulation or experimental phantom studies [21,24,25].…”

“…In contrast, simulation approaches are easy to repeat, but it is difficult to model the imaging setting accurately. This is why we propose to combine both approaches to arrive at a more accurate result by leveraging the specific advantages of each technique [21]. However, joint experimental and computational studies often require manual effort to adapt simulation parameters and to properly account for the imaging settings.…”