Establishing Diagnostic Reference Level for Adult Abdomen and Pelvis CT Scans: A Benchmarking Study across BMI Groups

Abstract

Objective This study aims to establish local diagnostic reference levels (DRLs) for contrast-enhanced computed tomography (CECT) abdomen and pelvis scans in adult patients within the Mangalore region, emphasizing variations in radiation dose metrics across body mass index (BMI) categories.

Materials and Methods A prospective multicenter study was conducted across five health care facilities and analyzed data from 500 patients (18–60 years) undergoing multiphase CECT abdomen and pelvis scans. CT dose descriptors, volumetric CT dose index (CTDIvol), and dose length product (DLP) were recorded separately for plain, arterial, and portovenous phases. Descriptive statistics, analysis of variance, and correlation analyses assessed dose variations across BMI categories.

Results The 75th percentile CTDIvol and DLP values for the plain phase were 8.30 mGy and 460.50 mGy·cm, respectively. Significant variations in radiation dose indices were observed across BMI groups (p < 0.001). CTDIvol for the plain phase increased from 7.42 ± 1.41 mGy in underweight individuals to 8.41 ± 1.21 mGy in overweight individuals. Corresponding DLP values ranged from 400.00 to 450.55 mGy·cm.

Conclusion The study established DRLs at the 75th percentile, demonstrating lower radiation doses than national and international benchmarks. These results highlight the significance of optimizing doses according to BMI to improve patient safety and the quality of diagnoses.

Keywords

body mass index - diagnostic reference levels - dose descriptors - radiation dose optimization - multiphase CT

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.

Conflict of Interest

None declared.

Acknowledgments

The authors sincerely appreciate the contributions of the CT technologists at each of the surveyed sites to this study.

Data Availability Statement

The data sets used and/or analyzed during the current study are accessible from the corresponding author upon reasonable request.

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Publication History

Article published online:
01 April 2025