Dose estimation of ultra-low-dose chest CT to different sized adult patients
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To evaluate the effect of patient size on radiation dose for standard CT (SD-CT), ultra-low-dose CT (ULD-CT) and two-view digital radiography (DR).
Dosimeters were distributed within the lungs of chest phantoms representing males of 65 kg and 82 kg (body mass indices 23 and 29). In contrast to SD-CT and DR which include automatic exposure control (AEC), the ULD scan employs a fixed mAs value. The phantoms were exposed to SD, ULD and DR while recording lung doses. Projected dose data were calculated from the phantoms. The resulting exposure settings were used in Monte Carlo programs to determine the effective dose for a standard-sized (BMI 24.2) adult male (170 cm/70 kg) and female (160 cm/59 kg). Patients previously examined by both ULD- and SD-CT were identified to determine post hoc size-specific dose estimates (SSDEs).
ULD-CT dose was inversely related to patient size; average lung doses summarised in terms of patient size BMI23/29 are 5.2/8.1 (SD-CT), 0.56/0.35 (ULD-CT) and 0.05/0.13 mGy (DR), while the effective doses for these techniques on a standard-sized male were 2.9, 0.16 and 0.03 mSv and 2.3, 0.247 and 0.024 mSv for a standard-sized female respectively. SSDEs for 15 patients (averages: BMI 26, range 18–37) averaged 5.5 mGy (3.6–10) for SD-CT and 0.35 mGy (0.42–0.27) for ULD-CT.
The effective doses for a standard-sized male and female examined by ULD-CT are (respectively) ~ 6%/~ 11% of SD-CT and ~ 5/~ 10 times higher than DR. ULD-CT gave a lower radiation dosage to larger patients than DR. AEC is warranted in ULD-CT for improved dose consistency.
• For standard-sized patients, ULD-CT dose level is ~ 6%/~ 11% of SD-CT, and ~ 5/~ 10 times higher than DR. For larger patients, ULD-CT is currently being used clinically at lower dose levels than DR.
• Using ULD-CT should greatly reduce the risk of late effects from ionising radiation.
• AEC in ULD-CT is desirable for increased consistency in patient dose.
KeywordsTomography Thoracic radiography Digital radiography Radiation dosage
Automatic exposure control
As low as reasonably achievable
Body mass index
Volume CT dose index
Dose length product
Size-specific dose estimate
The authors would like to thank Prof. Hans Dieter Nagel at the Science & Technology for Radiology, Germany; Dr. Teemu Siiskonen, at the Finnish Radiation Authority (STUK); and Dr. Yoko Kagaku, Kyoto Kagaku Co., Ltd., for their support and assistance with this project.
The authors state that this work has not received any funding.
Compliance with ethical standards
The scientific guarantor of this publication is Tony Martin Svahn.
Conflict of interest
The authors of this manuscript declare no relationships with any companies, whose products or services may be related to the subject matter of the article.
Statistics and biometry
One of the authors has significant statistical expertise.
No complex statistical methods were necessary for this paper.
Written informed consent was not required for this study because only exposure data and parameter settings were extracted from examinations in retrospect, in addition to phantom data.
Institutional Review Board approval was not required because for this study because only exposure data and parameter settings were extracted from examinations in retrospect, in addition to phantom data.
• Observational and experimental
• Performed at one institution
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