Introduction
A diagnostic reference level (DRL) is an investigative benchmark used to help optimize
patient dose during medical exposures in diagnostic and interventional procedures.
Every imaging modality has its unique dose quantities. The air KERMA (kinetic energy
released in materials) is used for fluoroscopy, X-ray and mammography; similarly,
the dose quantities such as volume computed tomography (CT) dose index (CTDIvol) and
dose length product (DLP) are used in CT. All of these quantities are metrics that
can be physically measured, and the effective dose is not appropriate for DRLs because
the effective dose cannot be measured; it can only be calculated.[1 ]
The usage of multidetector-row CT in both diagnosis and treatment offers significant
advantages. Still, its use is believed to pose a potential risk of cancer and other
radiation-related effects.[2 ]
[3 ] Hence, the prudent use of multidetector CT demands strict compliance with the cardinal
principles of radiation protection to ensure that patient benefits outweigh any associated
risks.[4 ]
A significant variability in radiation exposure during CT scan examinations across
various facilities has been identified in many studies. Hence, it emphasized the importance
of establishing and applying DRLs as a standardized and optimized approach to improve
radiological protection for patients across all CT centers.[5 ] The International Commission on Radiological Protection recommends setting DRLs
at the 75th percentile to assist in identifying and minimizing excessively high radiation
doses in diagnostic procedures, thereby enhancing patient safety while maintaining
optimal image quality.[5 ]
[6 ]
DRLs are typically determined through surveys of patient doses collected from standard
procedures performed across multiple facilities within a country or region. An imaging
center might establish a local DRL by internal evaluation of patient doses. Similarly,
a group of imaging centers can develop a DRL based on patient dose assessments conducted
throughout the network.[7 ] Many studies establishing DRLs have been performed in India; most focus on a single
institution and are limited numbers for multiphase CT abdomen scans. In contrast,
this research investigates a broader cohort across multiple centers in the Mangalore
region, which includes various hospitals and diagnostic facilities. In this study,
we assessed the radiation doses for contrast-enhanced CT (CECT) of the abdomen and
pelvis across multiple centers in the Mangalore region of South India to establish
DRLs.
Materials and Methods
A cross-sectional study design was utilized, gathering data from various institutions
in the Mangalore region. The study encompassed all patients referred for multiphase
abdomen and pelvis CT examinations. Adult patients aged 18 to 60 years were included
for multiphase CT scans of the abdomen and pelvis, which included plain, arterial,
and portovenous phases. Body mass index (BMI) was categorized into different body
types: underweight (< 18.5 kg/m2 ), normal weight (18.5–24.9 kg/m2 ), and overweight (25–29.9 kg/m2 ), to analyze variations in dose descriptor values among these categories.[8 ] Bariatric patients and those undergoing single-slice CT scans were excluded from
the study. Ethical approval was obtained from the Institutional Ethics Committee,
with clearance number NU/CEC/2024/520.
Permission letters were obtained from each institution to access CT dose reports and
demographic data. Institutions and diagnostic centers were visited to complete the
permission process, adhering strictly to each institution's data collection policies.
Data collection was conducted prospectively, with all individual identities kept confidential.
Information gathered included patient height and weight for BMI calculation, CT dose
parameters including CTDIvol and DLP, CT machine specifications, and patient demographics.
CTDIvol and DLP values were recorded separately for plain, arterial, and portovenous
phases, as displayed on the CT console.
Results
This study analyzed 500 abdomen and pelvis CECT examinations. Statistical evaluations
were conducted using SPSS 23.0. Descriptive statistics were presented as mean, standard
deviation, median, minimum, and maximum values ([Table 1 ]). CTDIvol was compared across plain, arterial, and portovenous imaging phases, categorized
by BMI classification, using one-way analysis of variance with the Bonferroni post
hoc test ([Table 2 ]). Since the DLP data did not follow a normal distribution, the Kruskal–Wallis test
followed by a post hoc test was utilized to compare DLP among the plain, arterial,
and portovenous phases according to BMI classification ([Table 3 ]). The relationship between BMI, CTDIvol, and DLP was assessed using Pearson's correlation
coefficient. A p -value of less than 0.05 was deemed statistically significant.
Table 1
Descriptive statistics for CTDIvol and DLP
Dose descriptors
Scan phases
75th percentile
Mean
Median
Standard deviation
Minimum
Maximum
CTDIvol (mGy)
Plain
8.30
7.86
8.00
1.35
3.40
11.60
Arterial
9.20
8.44
8.10
1.99
3.00
20.20
Portovenous
10.00
8.69
8.20
2.33
3.30
20.30
DLP (mGy.cm)
Plain
460.50
425.76
414.10
117.40
143.00
935.43
Arterial
524.25
457.54
428.00
142.96
143.80
1040.50
Portovenous
464.45
383.15
348.00
162.02
139.00
1052.20
Abbreviations: CTDIvol, volumetric computed tomography dose index; DLP, dose length
product.
Table 2
Comparison of CTDIvol (mGy) at plain, arterial, and portovenous phases of imaging
based on BMI classification
Scan phases
BMI classification
Mean ± SD
95% confidence interval for mean
Min
Max
F
Significance
Lower bound
Upper bound
Plain
Underweight
7.42 ± 1.41
7.075
7.770
3.40
9.10
20.495
p < 0.001
Normal weight
7.67 ± 1.33
7.507
7.822
3.40
10.80
Overweight
8.41 ± 1.21
8.217
8.598
3.60
11.60
Arterial
Underweight
7.52 ± 1.56
7.131
7.899
3.90
13.50
36.357
p < 0.001
Normal weight
8.09 ± 1.69
7.890
8.288
3.00
13.60
Overweight
9.46 ± 2.26
9.105
9.818
4.35
20.20
Portovenous
Underweight
7.45 ± 1.69
7.036
7.867
3.30
13.50
35.845
p < 0.001
Normal weight
8.35 ± 2.08
8.102
8.591
3.40
15.20
Overweight
9.85 ± 2.55
9.446
10.253
3.80
20.30
Abbreviations: BMI, body mass index; CTDIvol, volumetric computed tomography dose
index; SD, standard deviation.
Table 3
Comparison of DLP (mGy.cm) with plain, arterial, and portovenous phase of imaging
based on BMI classification
Median
(mGy.cm)
IQR
Kruskal–Wallis statistics
p -Value
Plain
Underweight
400.00
(352.8–416.5)
51.576
p < 0.001
Normal weight
400.90
(376.7–433.4)
Overweight
450.55
(404.5–510.35)
Arterial
Underweight
386.60
(346.8–410.8)
97.523
p < 0.001
Normal weight
409.50
(370.7–475.05)
Overweight
513.65
(447.1–620.55)
Portovenous
Underweight
253.60
(219.4–355.6)
83.184
p < 0.001
Normal weight
316.70
(247.3–424.1)
Overweight
437.90
(349.5–534.0)
Abbreviations: BMI, body mass index; DLP, dose length product; IQR, interquartile
range.
The 75th percentile CTDIvol values are 8.30, 9.20, and 10.00, respectively, for plain,
arterial, and portovenous. Mean values are 7.86, 8.44, and 8.69, respectively—the
median ranges from 8.00 (plain) to 8.20 (portovenous).
The 75th percentile DLP values are 460.50 (plain), 524.25 (arterial), and 464.45 (portovenous).
Mean values are 425.76, 457.54, and 383.15, respectively. Averages range from 348.00
(portovenous) to 428.00 (arterial).
Comparison of CTDIvol with Three CT Phases (Based on BMI Classification)
The mean CTDIvol values increased with weight across all imaging phases, with significant
differences observed among BMI groups (p < 0.001). In the plain phase, the mean CTDIvol was 7.42 ± 1.41 for underweight, 7.67 ± 1.34
for normal weight, and 8.41 ± 1.21 for overweight individuals (F = 20.495). Similarly, in the arterial phase, the mean CTDIvol values were 7.52 ± 1.56,
8.09 ± 1.69, and 9.46 ± 2.26, respectively (F = 36.357). In the portovenous phase, the trend persisted, with mean CTDIvol values
of 7.45 ± 1.69, 8.35 ± 2.08, and 9.85 ± 2.55, respectively (F = 35.845). These findings underscore the substantial influence of body weight on
CTDIvol across all imaging phases.
In the plain phase, there was no significant difference in the mean values between
the underweight and normal weight categories (p = 0.531). However, the overweight category had a significantly higher mean than the
underweight and normal weight groups (p < 0.001). In the arterial phase, while the difference between the underweight and
normal weight categories was not statistically significant (p = 0.076), the overweight category showed significantly higher mean values compared
with both the underweight and normal weight groups (p < 0.001). In the portovenous phase, significant differences were observed across
all weight categories: the underweight group had a significantly lower mean than the
normal and overweight groups (p < 0.001), and the normal weight group had a significantly lower mean compared with
the overweight group (p < 0.001) ([Table 4 ] and [Fig. 1 ]).
Table 4
Pairwise comparison in CTDIvol across different body types
Dependent variable
Mean difference (I-J)
Standard error
Significance
95% confidence interval
Lower bound
Upper bound
Plain
Underweight
Normal weight
–0.24186
0.17892
0.531
–0.6716
0.1879
Overweight
–0.98484*
0.19194
0.000
–1.4459
–0.5238
Normal weight
Overweight
–0.74298*
0.13068
0.000
–1.0569
–0.4291
Arterial
Underweight
Normal weight
–0.57395
0.25568
0.076
–1.1881
0.0402
Overweight
–1.94671*
0.27428
0.000
–2.6056
–1.2879
Normal weight
Overweight
–1.37276*
0.18674
0.000
–1.8213
–0.9242
Portovenous
Underweight
Normal weight
–0.89490*
0.29979
0.009
–1.6150
–0.1748
Overweight
–2.39804*
0.32161
0.000
–3.1706
–1.6255
Normal weight
Overweight
–1.50314*
0.21896
0.000
–2.0291
–0.9772
Abbreviation: CTDIvol, volumetric computed tomography dose index.
Note: All significant differences are marked with an asterisk (*).
Fig. 1 Representing the volumetric computed tomography dose index (CTDIvol) changes with
three body mass index (BMI) categories in all computed tomography (CT) phases.
Comparison of DLP with Three CT Phases (Based on BMI Classification)
In the plain phase, the DLP averages and interquartile ranges increased with weight:
400.00 (352.8–416.5) for underweight, 400.9 (376.7–433.4) for normal weight, and 450.55
(404.5–510.35) for overweight individuals. A comparable trend was noted during the
arterial phase, with DLP averages of 386.60 (346.8–410.8) for underweight, 409.50
(370.7–475.05) for normal weight, and 513.65 (447.1–620.55) for overweight individuals.
In the portovenous phase, the DLP averages further highlighted this pattern: 253.60
(219.4–355.6) for underweight, 316.70 (247.3–424.1) for normal weight, and 437.90
(349.5–534.0) for overweight individuals. The p -values (p < 0.001) for all phases confirm statistically significant differences in DLP across
weight groups, and the Kruskal–Wallis statistics demonstrate an apparent increase
in averages and interquartile ranges with higher weight categories ([Table 3 ] and [Fig. 2 ]).
Fig. 2 Representing the dose length product (DLP) changes with three body mass index (BMI)
categories in all computed tomography (CT) phases.
In the plain phase, pairwise comparisons revealed significant differences in DLP between
normal and overweight (p < 0.001) and underweight and overweight groups (p < 0.001). However, there was no significant difference between the underweight and
normal weight groups (p = 0.403).
Significant differences in DLP were observed across all weight group comparisons in
the arterial phase. Overweight individuals had significantly higher DLP compared with
both normal weight (p < 0.001) and underweight groups (p < 0.001). A notable difference was also found between underweight and normal weight
groups (p = 0.006), indicating a progressive increase in DLP with body weight during this phase.
The portovenous phase also demonstrated significant differences in DLP between normal
and overweight (p < 0.001) and underweight and overweight groups (p < 0.001). Additionally, a statistically significant difference was observed between
underweight and normal weight groups (p = 0.001). These results confirm that the portovenous phase shows the most significant
variability, with DLP rising markedly as weight increases ([Table 5 ]).
Table 5
Pairwise comparison in DLP across different body types
Test statistics
Standard error
p -Value
Plain
Normal and overweight
–92.397
14.468
< 0.001
Under and overweight
–122.066
21.251
< 0.001
Under- and normal weight
–29.668
19.809
0.403
Arterial
Normal and overweight
–119.379
14.473
< 0.001
Under- and overweight
–180.406
21.257
< 0.001
Under- and normal weight
–61.026
19.815
0.006
Portovenous
Normal and overweight
–102.279
14.473
< 0.001
Under- and overweight
–175.860
21.258
< 0.001
Under- and normal weight
N73.581
19.816
0.001
Abbreviation: DLP, dose length product.
Correlation between BMI and Dose Descriptors
The correlation between BMI and CTDIvol across the scan phases shows significant positive
relationships. For CTDIvol, a moderate positive correlation was found in all phases:
plain (r = 0.333, p < 0.001), arterial (r = 0.429, p < 0.001), and portovenous (r = 0.410, p < 0.001). Similarly, for DLP, there was a significant positive correlation across
all phases as well: plain (r = 0.338, p < 0.001), arterial (r = 0.486, p < 0.001), and portovenous (r = 0.460, p < 0.001) ([Table 6 ] and [Fig. 3 ]). These results indicate that CTDIvol and DLP also increase as BMI increases.
Table 6
Correlation between BMI and CT dose descriptors
Correlation
Plain
Arterial
Portovenous
BMI-CTDIvol
r -value
0.333**
0.429**
0.410**
p- value
< 0.001
< 0.001
< 0.001
BMI-DLP
r -value
0.338**
0.486**
0.460**
p -value
< 0.001
< 0.001
< 0.001
Abbreviations: BMI, body mass index; CT, computed tomography; CTDIvol, volumetric
computed tomography dose index; DLP, dose length product.
Note: ** indicates that the correlations are statistically significant at p value < 0.001.
Fig. 3 Represents the correlation between (A ) volumetric computed tomography dose index (CTDIvol) and body mass index (BMI) in
three phases and (B ) dose length product (DLP) and body mass index (BMI) in three phases.
Discussion
This study gathered data from 500 patients across five health care facilities in the
Mangalore region in South India. It aimed to establish reference benchmarks for CT
scans of the abdomen and pelvis, providing standard dose descriptors to guide clinical
practice and improve diagnostic accuracy.
The data obtained in the present study, in terms of CTDIvol and DLP, were compared
with findings from several modern studies published globally over the past 10 to 15
years[3 ]
[4 ]
[5 ]
[9 ]
[10 ]
[11 ]
[12 ]
[13 ]
[14 ]
[15 ]
[16 ] ([Table 7 ]). The present study demonstrated the lowest radiation exposure for both dose descriptors.
Table 7
Comparison of diagnostic reference levels of CT abdomen and pelvis in terms of CTDIvol
and DLP with the present study
Articles
Country
Year
CTDIvol (mGy)
DLP (mGy.cm)
Foley et al[4 ]
Ireland
2012
12.3
598
Santos et al[9 ]
Portugal
2014
18
800
Saravanakumar et al[10 ]
India (South India)
2015
12
550
Roch et al[11 ]
France
2018
13
650
Varghese et al[12 ]
India (Kerala)
2018
10.6
509.3
Sohrabi et al[13 ]
Iran
2018
13.8
643.6
Matsunaga et al[14 ]
Japan
2019
18.2
870.9
Lee et al[3 ]
Australia
2020
13
600
Erem et al[5 ]
Uganda
2022
12.5
1418.3
Kumsa et al[15 ]
Ethiopia (Addis Ababa)
2023
16
822
Kahraman et al[16 ]
Türkiye
2024
11.2
588.9
Present study
India, Mangalore
2024
8.3
460.5
Abbreviations: CT, computed tomography; CTDIvol, volumetric computed tomography dose
index; DLP, dose length product.
By analyzing dose metrics such as CTDIvol and DLP, the study highlights significant
variations in radiation exposure across different BMI classifications. It provides
a comparative perspective with international and national benchmarks.
The DRLs derived in this study (CTDIvol: 8.3 mGy, DLP: 460.5 mGy·cm) are notably lower
than most international and national DRLs reported in the literature. For instance,
studies conducted in Portugal (CTDIvol: 18 mGy, DLP: 800 mGy·cm) and Japan (CTDIvol:
18.2 mGy, DLP: 870.9 mGy·cm) reflect significantly higher dose levels.[9 ]
[14 ] Among Indian studies, the present DRL values are lower than those from Kerala (CTDIvol:
10.6 mGy, DLP: 509.3 mGy·cm) and South India (CTDIvol: 12 mGy, DLP: 550 mGy·cm).[10 ]
[12 ] These results underscore the advancements in CT protocols and radiation safety practices
in the study region.
When comparing national or international benchmarks with local or institutional DRLs,
it is common to find elevated radiation exposure values for National Diagnostic Reference
Level (NDRL) and Regional Diagnostic Reference Level (RDRL). This difference may be
attributed to substantial variations in sample populations and the variability in
CT machines used across broader geographic regions.
The current study demonstrates a clear correlation between BMI and dose descriptors.
Higher BMI categories were associated with increased radiation doses across all CT
phases. For example, the CTDIvol values for the portovenous phase increased from 7.45
mGy in underweight individuals to 9.85 mGy in overweight individuals (p < 0.001). This trend aligns with existing literature, which attributes the increase
in dose to the greater attenuation of X-rays in individuals with higher body mass.
Such findings emphasize the need for tailored dose optimization strategies based on
patient-specific parameters. A study by Inoue et al examined various body size indices,
including water equivalent diameter, effective diameter, weight, weight-to-height
ratio, BMI, and body surface area. All these indices demonstrated a strong positive
correlation with CTDIvol and DLP.[17 ]
Setting DRLs at the 75th percentile offers a strong basis for dose optimization. Moreover,
sophisticated CT technology and improved imaging methods are responsible for the reduced
radiation doses, and these recommendations may be used as a model by other regions
seeking to create or improve DRLs. The factors, including iterative reconstruction
techniques, automated exposure management, and careful scan parameter selection, help
optimize radiation dose. These methods preserve optimum image quality with dose reduction.[18 ]
Limitations and Future Directions
The study has few limitations even though it offers insightful information. The exclusion
of bariatric patients and single-slice CT systems may limit the applicability of the
findings to all patient populations and older technologies. Additionally, the study
focuses on a single region, and further research is needed to establish DRLs at a
national level. Future research should focus on how other variables, such as scan
indications and contrast delivery, affect radiation dosage. Future research should
also focus on continuous dose monitoring and include advanced imaging technologies
to refine these benchmarks further.
Conclusion
This study across multiple centers set up local DRLs for CT scans of the abdomen and
pelvis in adults in South India's Mangalore area. It shows significant differences
in radiation doses for three BMI groups, helping to optimize radiation doses and showing
how body type affects radiation exposure. These results highlight the need to use
DRLs as a standard to improve patient safety while maintaining optimum diagnostic
quality. The outcomes serve as a helpful guide for other areas looking to fine-tune
CT protocols and create their local DRLs.
