Assessment of scatter radiation dose and absorbed doses in eye lens and thyroid gland during digital breast tomosynthesis.

Thunyarat Chusin,Kosuke Matsubara,Rena Okubo,Yoshinori Ogawa,Akihiro Takemura

doi:10.1002/acm2.12486

Thunyarat Chusin, Kosuke Matsubara + Show 3 more

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https://doi.org/10.1002/acm2.12486

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Abstract

Digital breast tomosynthesis (DBT) is an alternative tool for breast cancer screening; however, the magnitude of peripheral organs dose is not well known. This study aimed to measure scattered dose and estimate organ dose during mammography under conventional (CM) and Tomo (TM) modes in a specific DBT system. Optically stimulated luminescence dosimeters (OSLDs), whose responses were corrected using a parallel‐plate ionization chamber, were pasted on the surface of custom‐made polymethyl methacrylate (PMMA) and RANDO phantoms to measure entrance surface air kerma (ESAK). ESAK measurements were also acquired with a 4.5‐cm thick breast phantom for a standard mammogram. Organ dose conversion factors (CFD) were determined as ratio of air kerma at a specific depth to that at the surface for the PMMA phantom and multiplied by the ratio of mass energy absorption coefficients of tissue to air. Normalized eye lens and thyroid gland doses were calculated using the RANDO phantom by multiplying CFD and ESAK values. Maximum variability in OSLD response to scatter radiation from the DBT system was 33% in the W/Rh spectrum and variations in scattered dose distribution were observed between CM and TM. The CFD values for eye lens and thyroid gland ranged between 0.58 to 0.66 and 0.29 to 0.33, respectively. Mean organ doses for two‐view unilateral imaging were 0.24 (CM) and 0.18 (TM) μGy/mAs for the eye lens and 0.24 (CM) and 0.25 (TM) μGy/mAs for the thyroid gland. Higher organ doses were observed during TM compared to CM as the automatic exposure control (AEC) system resulted in greater total mAs values in TM.

Highlights

Another study used Monte‐Carlo simulations on organ doses from a specific Digital breast tomosynthesis (DBT) system and reports an increase of up to 21% in thyroid gland and 9% in lung during DBT acquisition compared to digital mammography (DM) acquisition.[7]
While the x‐ray tube rotates across a compressed breast within a limited angle range during DBT acquisition, it remains fixed during DM acquisition,[8] and the absorbed dose at each acquisition mode varies when used with the automatic exposure control (AEC) system.[7,9]
The organ doses tended to be higher during Tomo mode (TM) compared to conventional mode (CM), because of higher total mAs values observed during TM under AEC operation

Summary

Introduction

While the x‐ray tube rotates across a compressed breast within a limited angle range during DBT acquisition, it remains fixed during DM acquisition,[8] and the absorbed dose at each acquisition mode varies when used with the automatic exposure control (AEC) system.[7,9]. These differences should be taken into account for estimating scattered dose at organs of interest during DBT imaging. DM acquisition was used in the conventional mode (CM) while the DBT acquisition was specified as Tomo mode (TM) which acquires 25 projections of breast tissue from different tube angles between −25° and +25° at 2° intervals

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