It was a cross-sectional study relating to the doses delivered in CT-Pelvimetry, carried out with 03 radiology departments in the city of Douala-Cameroon, amongst which 01 in the public sector and 02 in the private sector; 02 Hitachi brand and 01 General Electric brand and having a 16-slice CT system commissioned in 2017 and 2018. The sample of 03 services was constituted after having solicited the 13 hospitals registered in the city of Douala with a functional CT scanner. One service did not respond to our request; two others were no longer operational after the beginning of the study because CT scan device were out of service. We did not have CT-Pelvimetry data in 7 other departments.

The collection of data was done manually over a period of 24 months (from May 2017 until May 2019). Part of the data was collected daily during CT scan procedures and the other part was extracted from the picture archiving and communication system (PACS) of the radiology units and was entered into an Excel file and verified. Pelvic CT examinations were performed in supine position. A lateral scout view was obtained, followed by helical acquisition from the antero-superior iliac spine to the ischial tuberosity. Following CT manufacturer recommendations, images were acquired at a thickness of 5 mm with the constants held at 120 kV and 17.80 - 18.80 mAS (Hitachi brand); 52.68 mAs (GE brand) and pitch 1.5. The different obstetrical diameters of the pelvis were measured on a dedicated computer equipped with a picture and archiving communication system, using multiplanar reconstruction.

In this study, we included all patients having benefited from a CT-Pelvimetry examination in the three services and providing required dosimetric data during the period of our study.

We carried out a sample of convenience, the total of 194 examinations was obtained during the period of the study. This examination exclusively concerning women of childbearing age.

The studied variables were: CT device brand, model and number of detector, installation date, date of completion of the examination, patient’s age, CT-Pelvimetry indication, pregnancy term, kilo voltage (kV), amperage (mA), time of tube rotation (s), tube current (mAs), the displayed CT dose index (CTDIvol) and the Dose Length Product (DLP). An average DLP for the examination was established to the DLP Data displayed on the CT console and the average Effective dose was evaluated using the International Commission on Radiological Protection (ICRP) conversion factor [9] [10].

( mGy ⋅ cm ) = CTDIvol × scan   length (1)

The average Effective Dose (ED) doses associated with the CT-Pelvimetry exam studied were assessed from the calculated DLP using a region- and age-specific coefficient:

E ( mSv ) = EDLP region,age × DLP (2)

where EDLP_region,age (mSv (mGy·cm)⁻¹) is the normalized value of effective dose per dose-length product over a specific body region for a particular standard patient age [11] [12] [13].

The fetal dose was calculated by the online software, called “Dose Fetal” Web [14] to estimate the radiation dose received by the fetus from CT. The algorithm employed by the tool is based on Monte Carlo simulations performed on computational phantoms and real data of pregnant patients at different gestational stages. The vendor-independent tool, can be used to calculate radiation dose exposure for any scanned body region, scan length and CT protocol. Its pull down-menu allows users to select gestational age and tube voltage. Additionally, users need to enter the volume CT dose index (CTDIvol), and select the upper and lower positions of the scan. The users can also add the maternal abdominal perimeter in millimetres to improve the accuracy of calculations, and the patient ID for their records. Calculations can be saved in PDF format.

The possible cancer risks caused by ionizing radiation doses of ~1 mSv or less are too small to be estimated directly from epidemiological data. The linear no-threshold (LNT) approach to estimating such risks involves using epidemiological data at higher (but still low) doses to establish an “anchor point”, and then extrapolating the excess cancer risk linearly down from this point to the low dose of interest [15].

We used FetDose program to calculate the risk to the fœtus [16] [17].

According to Osei et al., the fetal radiation risk (R) is calculated as

R = D f × RC (3)

where RC is the risk coefficient for the consequence of interest (Osei, et al., 2003). The risk of childhood cancer induction: risk coefficient used is 8.0 × 10⁻⁵  per mGy and hereditary effects: risk coefficient used is 0.5 × 10⁻⁵ per mGy [18] [19] [20].

Data analysis was carried out, first per service, then for all the 3 services. The dose metrics were analyzed and the proposed dose levels were established at 50th and 75th percentile of dose distribution. Our data were compared with other previous studies from France [21]; Sweden [22], and Canada [17]. The FetDose program was used to calculate all risk estimations.

This study was authorized by the Institutional Research Ethics Committee for Human Health at the University of Douala and by the Regional Health Delegation of the littoral Region of Cameroon. In order to respect confidentiality, all the data collected was studied anonymously, the services were coded by numbers (from 1 to 3).

03 radiology departments in Douala yielded information on a total of 194 CT protocols performed. 46.4% were collected in the first site, 41.2% in the second and 12.4% in the third. The CT machines were 16 multidetectors (General Electric Revolution and Hitachi Supria) (Table 1).

Of the 194 examinations, 38.66% were for scar uterus; 29.9% were for clinically contracted pelvis; 28.35% were for breech presentation and 3.09% were for deformation of the pelvis indication. Mean age of pregnant women was 30 years (range: 19 - 40 years, median = 30 years). The mean term and the time of imaging examinations was 36 weeks of amenorrhea (Table 2(a), and Table 2(b)). All these clinical indications were justified [23].

In the three services, all protocols were performed according helical acquisition with a voltage of 120 kV, 32.31 mAs average. The mean radiation dose of helical acquisitions, CTDIw and DLP were 1.97 mGy (range: 1.00 - 2.46 mGy) and 56.17 mGy·cm (range: 51.69 - 59.21 mGy·cm) respectively. The mean effective dose was 0.78 mSv (Table 3).

The mean fetal dose calculated was 1.5 mGy (range: 0.76 - 1.87). The risk of Childhood Cancer calculated was 1 in 16,000 - 1 in 10,000 and 1 in 260,000 - 1 in 106,000 to the risk of Hereditary Disease, respectively (see Table 4).

CT-Pelvimetry doses and fetal dose from our work were compared with others studies (Table 5).

The mean fetal dose (1.50 mGy) equivalent to 5 chest X-rays examination if we consider the minimum dose of 0.3 mGy for a frontal chest X-ray. Doses, CTDIvol and DLP from our study were 1.97 mGy (range: 1.00 - 2.46 mGy) and 56.17 mGy·cm (range: 51.69 - 59.21 mGy·cm) respectively, the mean effective dose was 0.78 mSv. These doses were globally higher than those in other studies [21] [22]. The DLP value from our pelvimetry examinations was 1.5 to 3.8 higher compared to these studies. Thibaut et al. doses were estimates generated by CT scan software while the measurements in the Phexell et al. study were executed on an anthropomorphic phantom and thermos-luminescent dosimeters (TLD) were used for the dose measurements, and bags of sodium chloride were chosen for simulation of the pregnancy in the third trimester, especially lower than 36 weeks. But CTDIvol, effective dose and fetal dose from our study was lower than that value found by Slimane et al. [24] (Table 5).

These doses were the same as those in our previous study [25].

The fetal dose and risks from our work concerning CT-Pelvimetry exclusively are lower compared to the E.K. Osei et al. study which concerned CT-pelvis examination.

The radiation doses received by the 194 foetuses ranges from 0.76 to 1.87 mGy (1.5 mGy mean foetal dose) from CT-Pelvimetry examination (see Table 3, Table 4 and Table 6). According to the conclusions of the studies carried out by the ICRP, there is no deterministic effect of practical importance in humans below a dose of at least 100 mGy [26]. Doll and Wakeford showed that radiation doses of the order of 10 mGy received by the fetus in utero produce a consequent increase in the risk of childhood cancer. The excess absolute risk coefficient at this level of exposure is approximately 6% per gray [27].

The probability of induced hereditary effect on the basis of the doses received by the fetuses (Table 4 and Table 6) in this study shows that the risk to the individual fetuses was 1 in 140,000 (range: 1 in 260,000 - 1 in 106,000) from CT-Pelvimetry examination. The risks values are very low compared to the natural incidence. The natural frequency of genetic disorders and congenital abnormalities occur in about 2% - 5% of all live births [28]. Thus, the increased genetic risk of 1 in 10,714 for an individual fetus associated with the fetal dose in this study is very small compared with the natural risk of genetic disease.

The risk of 1 in 9000 (range: 1 in 16,000 - 1 in 10,000) associated with the mean absorbed dose of 1.5 mGy from our study is very law comparable to the natural baseline risk of childhood cancer 1 in 650 (1.5 × 10⁻³) [20] [29]. The BM estimated 360,114 total childhood cancers occurring worldwide in 2015; 54% in Asia and 28% in Africa. BM estimated standardised rates ranged from ~178 cases per million in Europe and North America, through to ~218 cases per million in West and Middle Africa [30].

The risk for the fetus to develop cancer after the mother has undergone any kind of radiological examination during pregnancy has been investigated and found to be minimal by Bailey et al. [32], and has also been reported in ICRP 84 (Table 7). The radiation dose in the spiral method was lower than 1.97 mGy. The absorbed mean radiation dose to the fetus (1.50 mGy) using the spiral method is considered low, especially when the dose is related to the 99.7% probability that a child (0 - 19 years) will not develop a malignancy from the absorbed doses ≤5 mGy [32]. Consequently, all such CT-Pelvimetry examination can be carried out on pregnant women, as long as they have been clinically justified and the dose is kept to minimum consist with the diagnostic requirement.

Our study had some limitations. The CTDIvol or its derivative the DLP data were estimates generated by CT scan software, which depend on scan acquisition parameters. They should be taken as an index of radiation output by the system for comparison purposes. We do not have gold standard direct dosimetry data to compare. Perhaps, the next step is to compare our data with CTDIvol and DLP estimates using an anthropomorphic phantom with dosimeters (phantom study).

The fetal dose and risks from our work concerning CT-Pelvimetry exclusively are lower compared to the E.K. Osei et al. study which concerned CT-pelvis examination.