Rationale and Objectives
This study sought to more definitely illustrate the impact and feasibility of implementing a low-dose protocol for computed tomography (CT)-guided biopsies using size-specific dose estimates and multivariate analyses.
Materials and Methods
Fifty consecutive CT-guided lung and extrapulmonary biopsies were reviewed before and after implementation of a low-dose protocol (200 patients total, mean age 61 ± 15 years, 128 women). Analyses of variance with Bonferroni correction were used to compare standard and low-dose protocols in terms of patient demographics, physician experience, target lesion size, total dose-length product, total acquisitions, size-specific dose estimate, signal-to-noise ratio, contrast-to-noise ratio, and lesion conspicuity ratings. All procedures were performed on the same 16-slice CT scanner.
Results
Voluntary protocol adherence was 100% (lung) and 89% (extrapulmonary). The low-dose protocol achieved significantly lower total average dose-length product [(lung) 735.6 ± 599.4 mGy × cm to 252.1 ± 101.9 mGy × cm, P < .001; (extrapulmonary) 724.7 ± 545.0 mGy × cm to 392.9 ± 239.5 mGy × cm, P < .001] and size-specific dose estimate [(lung) 5.2 ± 0.8 mGy × cm to 4.3 ± 1.5 mGy, P < .001; (extrapulmonary) 10.1 ± 6.7 mGy to 6.5 ± 2.7 mGy, P < .001]. Only the change in protocol was independently associated with lower size-specific dose estimates when controlling for the other variables ( P < .0001). This was achieved with no significant differences in signal-to-noise ratio, contrast-to-noise ratio, or lesion conspicuity.
Conclusions
Implementation of a low-dose protocol for CT-guided biopsies resulted in 21% and 36% of size-specific dose estimate reduction for lung and extrapulmonary biopsies, respectively, with excellent adherence. Interventional and body radiologists should implement low dose CT-guidance protocols aiming to improve patient safety.
Introduction
Despite the many benefits of computed tomography (CT), its widespread use over the last several decades has dramatically increased patients’ average radiation exposure from medical imaging. Data supporting a cause-and-effect relationship are limited, but there is a general consensus that carcinogenesis is a stochastic effect of ionizing radiation, with a linear risk-dose relationship. As such, in 2007, it was estimated that 29,000 future cancers and 14,500 deaths would be related to CT scans performed in the United States .
Dose reduction has been an important focus in diagnostic radiology but less so for CT-guided procedures as adequate guidance can be prioritized over dose reduction efforts. Adoption of diagnostic appropriateness criteria and use of lower tube energies and iterative reconstruction techniques can each reduce dose while achieving similar image quality . Previous studies suggest similar techniques can significantly reduce radiation exposure during CT-guided biopsies, but most of these investigations did not control for important confounders or adjust dose parameters for patient size, limiting the strength of their findings.
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Materials and Methods
CT Guidance Protocols
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Table 1
CT Guidance Protocol Parameters
Protocol Acquisition Type Scan Type kVp mA mAs CTDI vol Gantry Rotation Pitch Collimation Low-dose lung protocol Planning Helical 120 120 60 4.2 0.5 0.8 1.5 Guiding Sequential 100 100 50 2.25 0.5 1 1.5 Standard lung protocol Planning Helical 120 120 60 4.2 0.5 0.8 1.5 Guiding Helical 120 120 60 4.2 0.5 0.8 1.5 Low-dose ex-pulm protocol Planning Helical 120 120 80 5.6 0.5 0.8 1.5 Guiding Sequential 100 100 80 3.6 0.5 1 1.5 Standard ex-pulm protocol Planning Helical 120 120 80 5.6 0.5 0.8 1.5 Guiding Helical 120 120 80 5.6 0.5 0.8 1.5
CT, computed tomography; CTDIvol, computed tomography dose index volume (mGy); ex-pulm, extrapulmonary; kVp, kilovolt potential peak; mA, milliamperes; mAs, milliampere seconds.
Gantry rotation time expressed in seconds, pitch expressed as a ratio of the table feed to the detector width, and collimation expressed in millimeters.
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Biopsy Cohorts and Technique
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Data Collection
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SSDE=a×e−b×AP×LAT√×CTDIvol SSDE
=
a
×
e
−
b
×
A
P
×
L
A
T
×
C
T
D
I
v
o
l
where a = 3.70 and b = 0.0367 are previously defined constants ; AP and LAT are in cm; and SSDE is in mGy. Lesion density, density standard deviation, and the attenuation of the adjacent parenchyma were measured for lung biopsies to calculate contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) values according to the technique by Heyer et al. :
CNR=(DensityLesion−DensityLung Parenchyma)/Standard DeviationLesion CNR
=
(
Density
Lesion
−
Density
Lung Parenchyma
)
/
Standard Deviation
Lesion
SNR=DensityLesion/Standard DeviationLesion SNR
=
Density
Lesion
/
Standard Deviation
Lesion
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Data Analysis
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Results
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Table 2
Lung Biopsy Statistics
Parameter Standard-dose Protocol (n = 50) Low-dose Protocol (n = 50)P Value Gender (M/F) 14/36 17/33 .52 Age (y) 65 ± 15 67 ± 13 .43 Lesion size (cm) 2.0 ± 1.6 2.1 ± 1.2 .97 Physician (T/A) 40/10 36/14 .35 Total DLP (mGy × cm) 735.6 ± 599.4 252.1 ± 101.9 <.001 Total acquisitions 17 ± 8 15 ± 6 .13 Planning SSDE (mGy) 5.6 ± 0.8 5.6 ± 0.9 .99 Guidance SSDE (mGy) 4.7 ± 0.7 3.0 ± 0.4 <.001
DLP, dose-length product; M/F, male/female; SSDE, size-specific dose estimate; T/A, trainee/attending.
Data reported as mean ± standard deviation unless indicated otherwise. P values are for univariate comparisons.
Table 3
Extrapulmonary Biopsy Statistics
Parameter Standard-dose Protocol (n = 50) Low-dose Protocol (n = 50)P Value Gender (M/F) 16/34 25/25 .07 Age (y) 56 ± 16 57 ± 16 .84 Physician (T/A) 39/11 33/17 .19 Total DLP (mGy × cm) 724.7 ± 545.0 392.9 ± 239.5 <.001 Total acquisitions 13 ± 6 14 ± 7 .48 Planning SSDE (mGy) 10.1 ± 6.7 7.7 ± 2.9 .02 Guidance SSDE (mGy) 10.1 ± 6.7 5.2 ± 1.7 <.001
DLP, dose-length product; M/F, male/female; SSDE, size-specific dose estimate; T/A, trainee/attending.
Data reported as mean ± standard deviation unless indicated otherwise. P values are for univariate comparisons.
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SNR:−0.5±7.1(standard dose)vs0.2±3.0(low dose),P=.52 SNR
:
−
0.5
±
7.1
(
standard dose
)
vs
0.2
±
3.0
(
low dose
)
,
P
=
.52
CNR:33.7±19.5(standard dose)vs33.3±26.2(low dose),P=.93 CNR
:
33.7
±
19.5
(
standard dose
)
vs
33.3
±
26.2
(
low dose
)
,
P
=
.93
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SNR:0.2±3.0(120kVp)vs0.3±2.8(100kVp),P=.43 SNR
:
0.2
±
3.0
(
120
kVp
)
vs
0.3
±
2.8
(
100
kVp
)
,
P
=
.43
CNR:33.3±26.2(120kVp)vs25.8±18.9(100kVp),P=.11 CNR
:
33.3
±
26.2
(
120
kVp
)
vs
25.8
±
18.9
(
100
kVp
)
,
P
=
.11
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Discussion
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Conclusions
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Acknowledgments
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