Estimation of Radiation Equivalent Dose and Lifetime Attributable Risk from Pediatric CAP CT Examination

Abstract

Aim: This study aims to estimate equivalent doses (EqDs) and life attributable risks (LARs) for pediatric patients who underwent chest–abdominal–pelvic (CAP) CT examinations in Madinah, Saudi Arabia. Methodology: This retrospective study collected data from 120 pediatric patients who underwent CAP CT examinations. The data were categorized by the age and gender of the pediatric patients. Then, the EqDs were computed using the NCICT (National Cancer Institute dosimetry system for computed tomography) program, and LARs were estimated from the equivalent dose (EqD) results using age- and gender-specific cancer risk models found in the Committee on the Biological Effects of Ionizing Radiation (BEIR) VII Phase 2 (2006). Results: The EqD range was 0.9 to 7.55 mSv for the prostate and colon (males and females), respectively. LARs for female breast and lung cancers were considered to have the highest values among the age groups. Nevertheless, LARs of the colon, liver, and leukemia cancers were higher for males than females. The LAR range of cancer incidence was 0.6 to 63.1 per 100,000 cases for prostate (aged 10–≤15 years) and breast (females aged 1≤–<5 years), respectively. The LAR range of cancer mortality was 0.1 to 41.9 per 100,000 cases for prostate (aged 10–≤15 years) and lung (females aged 1≤–<5 years). Conclusions: LARs of all cancer incidence and mortality from CAP CT examination were higher for pediatric females than males (with an average of 54%). This highlights the importance of considering pediatric patient gender and implementing optimization and protective measures in CAP CT examinations. LARs of breast and lung (for females) and colon (for males) cancers were found to have the highest values among the age groups. However, LARs of cancer incidence and mortality for colon, liver, and leukemia for males were higher than those for females.

1. Introduction

Computed tomography (CT) is used for imaging and diagnosing various body organ pathologies. Nevertheless, it includes ionizing radiation, which results in harmful biologic effectiveness. CT is considered one of the most frequent and highest radiation doses among the modalities used for diagnostic imaging for both workers and patients [1,2,3].

Thus, it is essential to estimate the radiation dose and the related cancer risks. This is to optimize the CT examinations and to minimize the related radiation cancer risks. Pediatric patients have higher radiosensitivity and a longer life expectancy compared to adult patients; therefore, the chance of radiation-induced cancer is higher for pediatric patients [4,5,6]. Moreover, it is necessary to work on minimizing ionizing exposure without compromising image quality to minimize the harmful effects of ionizing radiation [7,8,9].

Effective (EfD) and equivalent (EqD) radiation doses are common methods used to estimate radiation doses. The radiation weighting factor (W_R) was used to quantify the amount of absorbed energy of radiation in the human body tissue or organ. For instance, the amount of absorbed energy of X-rays and protons was given factors of 1 and 5, respectively. In the ICRP 103 recommendations, the concept of tissue weighting factor (W_T) was introduced to specify the radiosensitivity of each tissue or organ to radiation. For example, the highest W_T was for gonad tissues, and the next highest W_T was for breast and lung tissues. Theoretically, the EqD represents the absorbed radiation dose in the organ multiplied by the W_R that depends on the type and energy of the radiation (for X-rays, W_R = 1). (Equation (1)), whereas the EfD represents the total equivalent doses (EqDs) for all organs or tissues multiplied by the W_T for each organ or tissue (Equation (2)) [10,11,12,13].

EqD = Absorbed dose × W_R

(1)

EfD = ∑ EqDs × W_T

(2)

The estimation of related cancer risks can provide a more comprehensive understanding of the radiation that is harmful to pediatric patients. The radiation–response relationship was expressed as an absolute or relative relationship. With the absolute relationship, the additional risk of radiation to the lifetime baseline risk (LBR) is independent of the age of the exposed person, whereas with the relative relationship, the additional risk of radiation is dependent on the age and gender of the exposed person [14,15].

The linear no threshold model (LNT) provided in BEIR VII Phase 2 (2006) showed a reasonable relationship between low radiation doses and the incidence and mortality of cancers. The assumption of the LNT model is that “the smallest dose has the potential to cause a small increase in risk to humans”. This risk model was introduced to approximate the lifetime attributable risk (LAR) of radiation-induced cancers [16]. The risk is relative to both gender and age, with higher risks for females and young people, and it is an additional risk above and beyond the lifetime baseline risk (LBR) [17]. Incidence and mortality for LAR are classified as negligible, minimal, very low, low, or moderate [18,19].

The NCICT (National Cancer Institute dosimetry system for computed tomography) program is a CT organ dose calculator. The program calculates the radiation dose for the total body EfD and various organ EqD using patient and CT scan data. NCICT uses a library of different pediatric and adult computational human phantoms [20]. NCICT was used in this study to compute the EfD and EqD radiation doses from the pediatric CAP CT examination.

The aim of this study was to estimate EqDs and life attributable risks (LARs) for pediatric patients who underwent chest–abdominal–pelvic (CAP) CT examination in Madinah, Saudi Arabia.

2. Methodology

2.1. Data Collection

In this retrospective study, the data of 120 pediatric patients who underwent CAP CT examination were collected. The data were obtained from the Picture Archiving and Communication System (PACS). Incomplete procedures or data were excluded from the study. The data were categorized into groups according to the age and gender of the pediatric patients. Thirty pediatric cases were collected for each age category. The age categories were defined as follows: <1 year, 1 ≤–<5 years, 5≤–<10 years, and 10≤–15 years. All procedures were performed using a Canon CT machine, Aquilion ONE/Genesis SP [21]. All procedures were performed using a Canon CT machine, Aquilion ONE/Genesis SP [21]. The CT machine and PACS were undergoing periodic quality control tests. The data used to estimate effective doses (EfDs) and EqDs from CAP CT examination of pediatric patients aged <1 year, 1≤–<5 years, 5≤–<10 years, and 10≤–15 years is shown in

Table 1. The data used to estimate EfDs and EqDs.

	<1	1≤–<5	5≤–<10	10–≤15
Mean age (year)	0.34	2.9	7.2	11.8
Current (mA)	135	152	170	170
Tube potential (kVp)	100	100	100	120
Scan length (cm)	22	33	36	46
Rotation time (sec.)	0.5	0.5	0.5	0.5
TCM strength	0	0	0	0
Pitch factor	0.65	0.65	1	1
CTDIvol (mGy)	3.2	3.5	5.9	6.4
Males–females (%)	47–53	37–63	24–76	64–36

.

2.2. Dose and Risk Assessment

EfDs and EqDs were computed using the NCIC program. This approach is straightforward, quick, and offers a convenient means of estimating EfD and EqD for CT scans. The LAR of cancer incidence and mortality from CAP CT examination were estimated using age- and gender-specific cancer risk models reported in the BEIR VII Phase 2 (2006). In the BEIR report, if the LAR for a certain age or gender was not found, it can be scaled or interpolated linearly based on the 0.1 Gray (Gy) radiation dose [17,22].

3. Results

Table 2. The EfD, EqD milli Sievert (mSv) and LAR estimation results from CAP CT examinations of pediatric patients aged <1 year.

	<1 Year		LAR of Cancer per 100,000 Cases (Males)		LAR of Cancer per 100,000 Cases (Females)
	Males	Females
Organ	EqD (mSv)		Incidence	Mortality	Incidence	Mortality
Stomach	4.14	4.14	3.1	1.6	4.1	2.3
Colon	4.27	4.27	14.3	6.9	9.3	4.3
Liver	4.22	4.22	2.5	1.8	1.1	1
Lung	4.08	4.08	12.8	12.8	29.9	26.2
Prostate	3.48	−−	3.2	0.5	−−	−−
Urinary bladder	3.97	4.03	8.2	1.7	8.5	2.3
Thyroid	2.23	2.23	2.5	−−	14.1	−−
Breast	3.79	3.79	−−	−−	44.3	10.3
Uterus	−−	3.48	−−	−−	1.7	0.3
Ovary	−−	3.56	−−	−−	3.7	1.9
All solid	−−	−−	73.7	32.5	155.6	58.2
Leukemia	−−	−−	7.5	2.2	6.2	1.7
All cancers	−−	−−	81.2	34.8	161.9	60
EfD (mSv)	3.17	3.39

,

Table 3. The EfD, EqD and LAR estimation results from CAP CT examination of pediatric patients aged 1≤–<5 years.

	1≤–<5 Years		LAR of Cancer per 100,000 Cases (Males)		LAR of Cancer per 100,000 Cases (Females)
	Males	Females
Organ	EqD (mSv)		Incidence	Mortality	Incidence	Mortality
Stomach	6.96	6.96	5.1	2.7	6.8	3.8
Colon	7.55	7.55	24.5	11.9	16.1	7.4
Liver	6.72	6.72	3.9	2.8	1.8	1.5
Lung	6.75	6.76	20.4	20.4	47.8	41.9
Prostate	1.16	−−	1	0.1	−−	−−
Urinary bladder	4.12	4.5	8.3	1.7	9.2	2.5
Thyroid	3.07	3.07	3.2	−−	18.1	−−
Breast	5.53	5.64	−−	−−	63.1	14.7
Uterus	−−	5.17	−−	−−	2.5	0.5
Ovary	−−	5.55	−−	−−	5.5	2.9
All solid	−−	−−	107.2	47.8	231	87.1
Leukemia	−−	−−	10.7	3.4	9	2.8
All cancers	−−	−−	118	51.3	240.1	90
EfD (mSv)	4.89	5.34

,

Table 4. The EfD, EqD and LAR estimation results from CAP CT examination of pediatric patients aged 5≤–<10 years.

	5≤–<10 Years		LAR of Cancer per 100,000 Cases (Males)		LAR of Cancer per 100,000 Cases (Females)
	Males	Females
Organ	EqD (mSv)		Incidence	Mortality	Incidence	Mortality
Stomach	5.87	5.87	3.8	1.9	4.9	2.8
Colon	6.54	6.54	18.6	9	12.2	5.6
Liver	5.64	5.64	2.8	2	1.2	1.1
Lung	5.75	5.75	15	15	34.9	30.7
Prostate	1.23	−−	0.9	0.1	−−	−−
Urinary bladder	4.31	4.8	7.6	1.6	8.6	2.4
Thyroid	2.61	2.61	1.9	−−	10.9	−−
Breast	4.8	4.91	−−	−−	44.8	10.5
Uterus	−−	4.55	−−	−−	1.9	0.4
Ovary	−−	4.88	−−	−−	4.2	2.2
All solid	−−	−−	70.1	32.8	150.1	59.5
Leukemia	−−	−−	6.2	2.9	5.1	2.3
All cancers	−−	−−	76.4	35.8	155.3	61.9
EfD (mSv)	4.21	4.6

and

Table 5. The EfD, EqD and LAR estimation results from CAP CT examination of pediatric patients aged 10≤–15 years.

	10–≤15 Years		LAR of Cancer per 100,000 Cases (Males)		LAR of Cancer per 100,000 Cases (Females)
	Males	Females
Organ	EqD (mSv)		Incidence	Mortality	Incidence	Mortality
Stomach	5.85	5.85	3.2	1.7	4.2	2.3
Colon	6.52	6.52	15.7	7.6	10.3	4.7
Liver	5.63	5.63	2.4	1.7	1.1	0.9
Lung	5.42	5.42	11.7	11.7	27.3	23.9
Prostate	0.9	−−	0.6	0.1	−−	−−
Urinary bladder	2.88	3.41	4.3	0.9	5.1	1.4
Thyroid	3.97	3.97	1.9	−−	10.9	−−
Breast	4.6	4.68	−−	−−	33.3	7.8
Uterus	−−	3.89	−−	−−	1.4	0.3
Ovary	−−	4.24	−−	−−	3	1.6
All solid	−−	−−	55.3	26.7	114.6	47.7
Leukemia	−−	−−	5	2.9	3.9	2.4
All cancers	−−	−−	60.4	29.7	118.5	50.1
EfD (mSv)	4.18	4.54

show the EfD, EqD, and LAR results from CAP CT examination of pediatric patients aged <1 year, 1≤–<5 years, 5≤–<10 years, and 10≤–15 years, respectively. The EqD and LAR were estimated for 10 human body organs: stomach, colon, liver, lung, prostate, urinary bladder, thyroid, breast, uterus, and ovary. In addition, the LARs for all solids, leukemia, and all cancers were estimated. The estimated radiation dose and LARs show a noticeable variation in radiation dose and cancer incidence and mortality, based on both age and gender. The results for the EfDs and EqDs were computed using the NCICT program, and the results for the LARs were estimated using the BEIR VII Phase 2 (2006) report.

4. Results and Discussion

CT is considered one of the most frequent and highest radiation dose sources among the modalities used for diagnostic imaging, for both workers and patients. Several studies have highlighted a concern about the high EfDs included in pediatric CT examinations, as they have higher radiosensitivity and a longer life expectancy compared to adult patients. Consequently, the probability of radiation-induced cancer increases [23,24]. The NCICT is a CT organ dose calculator used in this study to estimate the EfD and EqD from CAP CT examinations of pediatric patients. The LAR of cancer incidence and mortality from CAP CT examinations was estimated using age- and gender-specific cancer risk models reported in the BEIR VII Phase 2 (2006).

In this study, the lowest values for the EqDs and LARs were found in the area of interest (out of the primary X-ray beam direction). For example, in the brain, oral cavity, and testes. For all age groups, the EqD range of the brain, oral cavity, and testes was 0.1 to 0.14, 0.26 to 0.49, and 0.45 to 0.8 mSv, respectively. These values were found to be insignificant; therefore, the LARs of cancers, out of the primary X-ray beam, were insignificant and were not taken into consideration [18,19].

The EfD results, obtained in this study, from CAP CT examinations of pediatric patients aged <1 year, 1≤–<5 years, 5≤–<10 years, and 10≤–15 years were found to be within >75% agreement with the results found in the literature [25,26,27,28]. For example, the EfDs obtained in this study and in Kanal et al. (2022) [24] for male pediatric patients aged 1≤–<5 and 5≤–<10 years were 4.89 and 4.4 and 4.21 and 4.7, respectively. However, the results in this study differed from other results found in the literature. The reason could be related to the assessment method or the CT parameters and protocols used. These differences in results were logically accepted; thus, the CT parameters and protocols can be considered optimum or require optimization.

In this study, the EfD results of pediatric patients aged 1≤–<5 years were higher than those of pediatric patients aged <1 year, 5≤–<10 years, and 10≤–15 years, with 35%, 13%, and 14%, respectively. The high EfDs for this age group (aged 1≤–<5 years) compared to the other age groups were related to the CT parameters collected (showed in Table 1) from the PACS system and used to estimate the EfD. Thus, optimization of the CAP CT protocol might be required for this age group (1≤–<5 years) to minimize the EfD [29,30].

The EqD range for the area of interest (area exposed to the primary X-ray beam) for all age groups was 0.9 to 7.55 mSv for the prostate and colon (males and females), respectively. The LAR range of cancer incidence was 0.6 to 63.1 per 100,000 cases for prostate (10–≤15 years old) and breast (females aged 1≤–<5 years), respectively. The LAR range of cancer mortality was 0.1 to 41.9 per 100,000 cases, for prostate (10–≤15 years old) and lung (female aged 1≤–<5 years).

Table 2, Table 3, Table 4 and Table 5 reveal that the LARs of all cancer incidence and mortality for females were higher than those for males, with an average of 54% higher. This is because females were given higher LARs in the BEIR VII Phase 2 (2006) (incidence and mortality per 100,000 cases from 0.1 Gy), except for colon, liver, and leukemia cancers, where higher LARs were given to males.

Good agreement (>75%) was found between the results of the EqDs and LARs obtained in this study and the results found in the literature for patients aged <1 year, 1≤–<5 years, 5≤–<10 years, and 10≤–15 years (males and females) [27,31,32,33,34,35,36]. Additionally, a significant difference (>50%) was found between the EqDs and LARs results obtained in this study and some results found in the literature [37,38,39]. The difference is related to the method used (measurement or simulation) and the CT parameters (helical or axial scanning, slice thickness and width, exposure factors, and the type of CT machine).

In this study, the LARs of cancer incidence and mortality for female breast and lung were considered to have the highest values among the studied age groups. The LARs of female breast cancer incidence and mortality were 44.3 and 10.3 for <1 year old, 63.1 and 14.7 for 1≤–<5 years old, 44.8 and 10.5 for 5≤–<10 years old, and 33.3 and 7.8 for 10≤–15 years old (per 100,000 cases). The LARs of female lung cancer incidence and mortality were 29.9 and 26.2 for <1 year old, 47.8 and 41.9 for 1≤–<5 years old, 34.9 and 30.7 for 5≤–<10 years old, and 27.3 and 23.9 for 10≤–15 years old (per 100,000 cases).

Nevertheless, LARs of incidence and mortality for the colon, liver, and leukemia cancers were higher for males than females. The highest LARs for male cancer incidence and mortality is colon cancer, with incidence and mortality of 14.3 and 6.9 for <1 year old, 24.5 and 11.9 for 1≤–<5 years old, 18.6 and 9 for 5≤–<10 years old, and 15.7 and 7.6 for 10≤–15 years old (per 100,000 cases). The main reason for the high LARs of breast, lung, and colon cancers, compared to other cancers, is the high LARs in the BEIR VII Phase 2 (2006) (incidence and mortality per 100,000 cases from 0.1 Gy) that are given to these organs.

Previous studies have found that female and pediatric patients are at higher risk of LARs cancer incidence and mortality compared to males and adult individuals. In addition, the LARs of breast and lung cancers for females were reported to be higher than those for males, whereas the LARs of colon cancers for males were reported to be higher than those for females [33,40,41]. These findings are consistent with the findings in this study.

The LARs for all cancer incidence and mortality of pediatric patients aged 1≤–<5 years were higher than those of pediatric patients aged <1 year, 5≤–<10 years, and 10≤–15 years, with 32%, 33%, and 46%, respectively. The high LARs for this age group (aged 1≤–<5 years) compared to other age groups were related to the CT data (shown in Table 1) collected from the PACS system and used to estimate the EfD and LARs. In addition, significant variation in pediatric patient size was noticed for this age group (1≤–<5 years), and this could affect the accuracy of the results for this age group. This variation is considered a limitation of this study. However, optimization of the CT protocol and parameters of the CAP examination could be required for this age group.

Nonetheless, several studies reported that the LAR from low radiation doses was significantly lower than the lifetime baseline risk (LBR) values. For example, LARs from CT examinations with a radiation dose of 1–10 mSv were considered to be “very low or small” and the ratio of LAR to LBR was 0.0001 and 0.001, respectively [24,25,26]. Other studies reported that the LAR from the radiation dose of 2.7 mSv was associated with 0.07% of the lifetime attributable risk of cancer, and the brain dose of 20 to 40 mGy would result in a LAR of cancer incidence of one per 6300 cases [42,43]. Even though most of the assessed EfDs, EfDs, and LARs were found to be comparable with the values found in the literature, radiation dose optimization should be continued to reduce the radiation dose received by pediatric patients undergoing CT procedures. Moreover, a revision of CT protocols and parameters is recommended. However, setting an optimal CT protocol with high image quality was reported as a demanding technique due to the variation in pediatric patient size [44].

Some caveats to this study deserve to be mentioned; firstly, there were no age sub-groups where this could influence the precision of the obtained results. The variation in pediatric patient size was noticed, especially for patients aged <5 years.

However, in this study, the division of data into age groups followed the American Association of Physicists in Medicine (AAPM) No. 96 and the International Commission on Radiological Protection (ICRP) publication 102 report [45,46]. Nevertheless, it is recommended to use smaller increments for pediatric age groups, such as month for pediatric patients aged <1 year and year for pediatric patiets aged 1 to <5 years. In addition, the percentage of pediatric gender was similar for patients aged <1 (47% and 53% for males and females, respectively), whereas the pediatric females were higher than males for patients aged 1≤–<5 and 5≤–<10, and lower than males for pediatric patietnts aged 10–≤15. More investigation could be required in the future work to accurately examine the effect of pediatric gender on the radiation dose estimation. However, the computed EfDs values using the NCICT3.0.20211123 for Windows and based on the pediatric patient gender were 6%−8% higher for pediatric females (shown in Table 2, Table 3, Table 4 and Table 5). In addition, the high LARs for females were mainly related to female LARs reported in the BEIR VII Phase 2 (2006) and were used to estimate the LARs (for pediatric females and males) in this study.

5. Conclusions

LARs of all cancer incidence and mortality from pediatric CAP CT examination were higher for females than males (with an average of 54%). This highlights the importance of considering pediatric patient gender and implementing optimization and protective measures in CAP CT examinations. LARs (incidence and mortality) for breast and lung cancers (females) and colon cancer (males) had the highest values among the age groups. The main reason for high LARs for breast, lung, and colon cancers compared to others is the high LARs reported in the BEIR VII Phase 2 (2006) (i.e., LAR of cancer incidence and mortality per 100,000 cases from 0.1 Gy) that are given to these organs. LARs of cancer incidence and mortality for colon, liver, and leukemia for males were higher than those for females, with values of 34% and 38% (colon cancer), 50% and 43% (liver cancer), and 18% and 20% (leukemia). In addition, slightly higher values of EfD, EqD, and LAR for pediatric patients aged 1≤–<5 years were found compared to the other age groups. Thus, the CAP CT examinations for this age group could require optimization.

Even though the low radiation dose from the CAP CT examination resulted in a “very low” LAR of cancer incidence and mortality, justifying and applying the lowest reasonably achievable principle (ALARA) is essential for minimizing possible radiation-induced cancer risks. This principle is applied to obtain the best possible medical diagnostic image while exposing the patient to the lowest possible radiation dose. This can be accomplished by optimizing the CT protocol, CT parameters, and following the guidelines for radiation protection [47,48].

In addition, periodic updating of exposure levels for pediatric CT procedures is valuable to monitor radiation doses and to minimize radiation risks for patients undergoing these procedures.