Introduction

Investigation of deformity in spinal and bone structures via radiological techniques is a vital tool in the diagnosis of pathological changes in body and surgeons use this tool to select the best treatment with least invasive procedures. In conventional radiography with X-ray, computed tomography and digital radiography are standard modalities for obtaining imaging information from skeletal deformities [ 1 ].

Euronext Paris Advanced Orthopedic Solutions (EOS) system is a new imaging system with capability of obtaining two-dimensional (2D) anteroposterior (AP) and lateral images from the whole body. These 2D images can then be used for the three-dimensional (3D) reconstruction of bony structures in the body as a stereo radiography tool [ 2 ]. This new radiography modality is a slot-scanning X-ray, presented by EOS (EOS Imaging, Paris, France) and also adopted by radiology community, and has advantage of imaging with very low radiation dose as well. In this system, two sets of X-ray tubes are installed at right angles as a biplanar configuration. A multi-wire proportional chamber (MWPC) is used for the detection of the radiation and acquisition of the images, simultaneously, from different views. By this modality, it is possible to measure and analyze spine curvature, bone fracture, torsion, orientation and alignment of spine and lower limb in body. The evaluation of the accuracy, reliability and reproducibility of this system showed advantages compared to manual 2D and computed tomography (CT) modalities [ 3 ].

During recent years, various researchers have performed studies on the determination of the patient dose or risk due to EOS imaging [ 4 - 6 ]. These studies were performed by calculation or measurement of the patient dose or the cancer risk. There are also studies on the comparison of the patient dose or the cancer risk from different X-ray imaging modalities, including EOS, digital radiography (DR) and computed tomography (CT) [ 7 - 10 ]. However, to the best of our knowledge, there is not any study on the risk of the exposure induced cancer death (REID) determination for different body organs due to EOS imaging of the patients with different imaging techniques. The aim of this study is to estimate the equivalent dose and REID for different organs of body due to radiography of the patients by an EOS imaging system.

Material and Methods

In the present experimental study, 120 patients were evaluated and the techniques for imaging of the patients were whole body, full spine and lower limb. Equivalent dose and REID for colon, liver, lung, stomach, breast, bladder, ovary, blood cells (leukemia) and other organs were calculated using PCXMC (a PC Program for X ray Monte Carlo) software (version 2.0.1.2).

The patient data, including kVp, dose area product (DAP), mA, focus to detector distance, field size, imaging technique, imaging view, age, height, weight and sex of patients were collected. Then the patient data were introduced as the input of this software and REID was calculated based on Monte Carlo simulation of X-ray and human phantoms.

Patients and EOS system

Patients referred to an EOS (EOS Imaging, Paris, France) imaging department were evaluated based on REID for different organs due to radiation received by this imaging system. In this system, the gas ionization detectors and thin grid ionization chambers are used for detection of X-ray. To decrease the effect of scattered radiation, the detector has a collimator. The detectors are perpendicular to each other to have the capability of three-dimensional imaging.

The total number of patients was 120 and in each technique, 40 patients were included in the study (20 male and 20 female). The ages of patients were in the range of 3-80 years.

The imaging techniques were full spine, lower limb, and full body. Images were acquired in lateral, anterior-posterior (AP) and posterior-anterior (PA) views, but the results were averaged for both views for each patient. The imaging was performed in Shahid Sadoughi Hospital (Yazd, Iran). The patient and the imaging technique information, including, age, sex, height, weight, kVp, focal to detector distance, dose area product (DAP), field size, filter type and thickness, and patient descent were noted and introduced in the PCXMC software for the calculation of the equivalent dose and REID for different organs. The organs included the colon, liver, lung, stomach, breast, bladder, ovary, blood cells (leukemia) and other organs.

Ethical guidelines by Shahid Beheshti University of Medical Sciences (ethics code: IR.SBMU.MSP.REC.1399.236) were followed in different steps of this research, including patient information collection, dose calculation and report of the result data. kVp and mA for different techniques (lower limb, full spine, full body) for male and female are tabulated in Table 1.

Organ dose calculation using PCXMC software

A PCXMC (version 2.0.1.2) software (STUK, Finland) [ 11 ] was used for the estimation of REID for different organs. The data of each imaging technique (including age, weight, height, imaging view, kVp, mA, field size, focus to detector distance, dose area product) are introduced as the input of this software. The software calculates effective dose, REID and other dose or risk quantities, based on Monte Carlo simulation of X-rays and human phantoms. The equivalent dose (mSv) for different organs (based on International Commission on Radiological Protection (ICRP) 103 report [ 12 ]), kinetic energy released per unit mass (kerma), and REID for different organs can be calculated using this software. In Figure 1, a part of this software is illustrated as a sample.

Figure 1. A part of PCXMC software. (a) For introduction of input parameters. (b) Calculated organ equivalent doses (mSv) and the risk of the exposure induced cancer death (REID).

Results

Mean equivalent dose (mSv) for different organs for lower limb, full spine and full body techniques are presented in Tables 2, 3 and 4, respectively. The results were distinguished for the males and the females. The maximum equivalent dose (mSv) due to EOS imaging system, was estimated in bladder 0.240±0.066 for the full body technique and 0.240±0.093 in the lower limb technique, respectively, for both the males and the females.

Mean REID for different organs for lower limb, full spine and full body techniques are presented in Table 5. The results were distinguished for the male and female patients. Due to EOS imaging radiography, the maximum organ REID (incidence per million) estimated for lungs as 2.59±1.0 and 2.53±0.9 in the full body technique for both males and females, respectively.

Discussion

In the present study, the equivalent dose and REID were estimated for different organs of body due to imaging of the patients using an EOS imaging system. There was difference in the equivalent dose and REID for different organs in EOS imaging. Based on the results in Table 2, the maximum equivalent dose values are obtained for bladder (0.258 mSv) and prostate (0.231 mSv) in the lower limb technique. The minimum values are for thyroid (0.017 mSv), active bone marrow and lung (0.063 mSv for both) for this technique. For the full spine technique, the maximum equivalent dose values are obtained for stomach (0.173mSv) and breast (0.175 mSv) and the minimum values are related to active bone marrow (0.072 mSv) and prostate (0.132 mSv) (Table 3). According to Table 4, in the full body technique, the maximum values are related to bladder, stomach and breast (0.237, 0.185 and 0.181 mSv, respectively).

Based on the data in Table 5, the maximum and minimum REID (estimated death in the population per million) are related to colon (1.46 %) and ovaries (0.13 %) in the lower limb technique. Moreover, for the full spine technique, the maximum and minimum values were obtained for lungs (2.35 %) and ovaries (0.1 %), respectively. For the full body technique, the maximum REID (estimated deaths in population per million) is estimated for lung (2.56 %) and the minimum is related to ovaries (0.34 %) (Table 5). The comparison of equivalent dose and REID values shows that those organs with the maximum or minimum equivalent dose are not the same as those organs with the maximum or minimum REID. This can be due to the fact that there are some limitations in calculation of REID by the PCXMC software. In other words, this software presents REID only for some specific organs. Additionally, the risk coefficients vary for different organs and therefor while an organ has the maximum equivalent dose, it may not have the maximum REID. For example, for the full body technique, the maximum equivalent dose values are related to bladder and stomach, but the maximum REID are related to lung and colon.

For male patients, in the lower limb imaging, the maximum and minimum equivalent dose (mSv) values are for bladder and thyroid, respectively (Table 2). The same trend is observed for the females in this technique. This trend can be explained by considering this fact that in the lower limb technique, bladder is very close to the radiation field while thyroid is far.

For both male and female patients, in the full spine imaging technique, the maximum and minimum equivalent dose values are related to stomach and active bone marrow, respectively (Table 3). For the full body imaging technique, the maximum and minimum equivalent dose is related to bladder and active bone narrow, respectively (Table 4). For female patients, in full spine and full body technique, the breast equivalent dose was among the highest values. This can be explained by the fact that in full body technique, breast is in the radiation field. Generally, the equivalent dose in different organs of the body is low due to the radiation received by the body during EOS imaging in different imaging techniques and views.

For male patients, among these organs, in the lower limb imaging, the maximum and minimum REID values are for colon and leukemia, respectively (Table 5). For the same cases in female, the maximum and minimum REID values are related to colon and ovaries, respectively.

According to ICRP-103 commission [ 12 ], tissue weighting factor (W_T) for tissues such as colon, lung and breast is 0.12 while this value for gonads is 0.08; thus, in the lower limb technique for both the males and the females, the highest REID is related to colon and it can be also explained based on the fact that colon is in the radiation field and is among the highest equivalent doses for both gender based on Table 2 (0.188 mSv for male and 0.203 mSv for female).

As it was stated, the highest equivalent dose in lower limb technique is bladder in the males and the females (0.236 mSv and 0.240 mSv, respectively), but its W_T is 0.04, which is lower than colon thus the REID for colon is the highest.

For full spine technique, in the males, the maximum REID is related to lungs and the minimum is related to leukemia (Table 5). For the same conditions in females, the maximum and minimum are related to lungs and ovaries, respectively. For the full body technique, in males, the maximum and minimum REID values are related to lung and leukemia, respectively (Table 5). For the same conditions in females, the maximum value is related to lung and the minimum values are for ovaries and leukemia, respectively.

In the full spine and the full body techniques, lungs are located in radiation field with W_T of 0.12, which is the highest value among different body tissues, while W_T of liver, which is among the highest values of equivalent dose in full spine and full body technique, is 0.04.

Generally, the REID value by radiation in different organs of body is related to W_T, radiation field and exposure settings in different imaging techniques and views.

Different studies have shown that the patient dose in EOS radiography is lower than other radiography techniques such as CT and digital radiography [ 13 - 15 ]. For example, Alrehily et al. [ 13 ] reported that EOS has lower radiation exposure in scoliosis patients, in comparison with CT and normal radiography. In the study by Escott et al. [ 14 ] it was observed that radiography with EOS protocols delivers lower radiation to the patients, while it is more efficient in CT scan and routine radiography to assess length.

Conclusion

There was difference in equivalent dose and the risk of the exposure induced cancer death by radiation in different organs in various techniques of EOS imaging system. Generally, due to the low radiation dose received by the body during EOS imaging in different imaging techniques and views, the equivalent dose and the risk of the exposure induced cancer death for different organs of body are low.

References

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