Radiation Dose to the Thyroid and Gonads in Patients Undergoing Cardiac CT Angiography

Estimation and comparison of the effective dose and lifetime attributable risk of thyroid cancer between males and females in routine head computed tomography scans: a multicentre study

INTRODUCTION

A significant number of head computed tomography (CT) scans are performed annually. However, due to the close proximity of the thyroid gland to the radiation field, this procedure can expose the gland to ionising radiation. Consequently, this study aimed to estimate organ dose, effective dose (ED) and lifetime attributable risk (LAR) of thyroid cancer from head CT scans in adults.

METHODS

Head CT scans of 74 patients (38 males and 36 females) were collected using three different CT scanners. Age, sex, and scanning parameters, including scan length, tube current-time product (mAs), pitch, CT dose index, and dose-length product (DLP) were collected. CT-Expo software was used to calculate thyroid dose and ED for each patient based on scan parameters. LARs were subsequently computed using the methodology presented in the Biologic Effects of Ionizing Radiation (BEIR) Phase VII report.

RESULTS

Although the mean thyroid organ dose (2.66 ± 1.03 mGy) and ED (1.6 ± 0.4 mSv) were slightly higher in females, these differences were not statistically significant compared to males (mean thyroid dose, 2.52 ± 1.31 mGy; mean ED, 1.5 ± 0.4 mSv). Conversely, there was a significant difference between the mean thyroid LAR of females (0.91 ± 1.35) and males (0.20136 ± 0.29) (P = 0.001). However, the influencing parameters were virtually identical for both groups.

CONCLUSIONS

The study's results indicate that females have a higher LAR than males, which can be attributed to higher radiation sensitivity of the thyroid in females. Thus, additional care in the choice of scan parameters and irradiated scan field for female patients is recommended.

Spectra, fluence and absorbed doses in sensitive organs due to scattered X-rays during a chest CT

The use of ionizing radiation for the treatment and diagnosis of diseases is becoming more frequent. The technologies associated with diagnostic imaging are constantly evolving, allowing faster and cheaper diagnoses to benefit the patient. However, this has caused an increase in the exposure to ionizing radiation of patients and health professionals. One of the diagnostic techniques for obtaining high-resolution anatomical images of patients is computed tomography (CT). Due to the detail and quality of the images obtained with CT, its use is becoming more frequent. The information provided by these images allows the specialist to make better diagnoses; however, exposure to X-rays deposits a dose in the patient. CT represents approximately 20% of all X-ray examinations but it is responsible for 70% of the medical dose accumulated by the patient. During the acquisition of the images, the highest dose is deposited in the area of the body whose image is to be obtained. During the incidence of X-rays, there is dispersion of these that reach sensitive organs whose dose is not evaluated. The objective of this work was to estimate, using Monte Carlo methods, the fluence and X-ray spectra and to obtain a factor that allows knowing the absorbed dose in sensitive organs due to scattered radiation during a chest CT. With the MCNP5 code, the CT equipment and a hybrid anthropomorphic phantom, type BOMAB it was found that the absorbed dose in these organs depends on the size of the organ and the distance between the organ and the surface of the slice on the thorax where the X-rays are incident.

EVALUATION OF RADIATION ABSORBED DOSE AND IMAGE QUALITY IN DIFFERENT RETROSPECTIVE-ECG GATING ACQUISITION METHODS OF CARDIAC CT ANGIOGRAPHY

Cardiac computed tomography angiography (CCTA) studies have risen concern of radiobiological effects over the patients. Therefore, estimating radiation doses absorbed during CCTA is important. In this study, we compared radiation dose and image quality by using three different retrospective electrocardiography (ECG) protocols. A total of 123 patients undergoing CCTA were divided in three different groups. We used full-dose modulation (CareDose4D) technique in group (1); fixed tube current 200 mAs for group (2); and in group (3), chest circumference was used to adapt tube current (180-200 mAs) and tube potential (100-120 kVp). For groups (1) and (2), tube potential adapted depends on body mass index (BMI) in which it was 100 kVp for BMI < 27 kg/m2, and 120 kVp for BMI ≥ 27 kg/m2. Quantitive assessment of image quality was calculated by measuring signal intensity (SI) and image noise (IN) in the proximal segments of aorta root on left and right coronary arteries. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were also calculated by using SI and IN. Two experienced radiologists using a 4-point scale assessed the subjective image quality. Our results show that in group (1), the mean effective dose was 4.46 mSv (range: 1.75-8.6 mSv) and for group (2), the mean effective radiation dose was 5.07 mSv (range: 2.57-9.74 mSv) and in group (3), the mean effective dose was 5.85 mSv (range: 3.36-12.17 mSv). Group (1) representing 12% and 23% decrease in radiation dose comparing by groups (2) and (3). In multivariate analysis, adjusting for BMI, radiation dose for patients with BMI < 27 kg/m2 was significantly different; 2.53 mSv for group (1) compared to 3.54 mSv in group (2) and 5.207 in group (3) (p < 0.0001). In addition, lowering tube potential from 120 to 100 kVp in 200 mAs fixed tube current, represents 27% decrease in radiation dose. The quantitative image quality (IN, SI, SNR and CNR) was not statistically significant among the groups. To sum up, Retrospective-ECG gating may reduce radiation dose by using automatic tube current modulation and 100kVp tube potential with preservation of image quality in patient's whose BMI < 27 kg/m2.

Direct Anterior Hip Replacement Does Not Pose Undue Radiation Exposure Risk to the Patient or Surgeon

BACKGROUND

The fluoroscopically assisted direct anterior approach for total hip arthroplasty has gained interest in recent years. One of the perceived advantages is the use of fluoroscopy to aid in the positioning of implants. The purpose of this study was to measure the radiation entrance surface dose to anatomically important areas of both patients and surgeons during direct anterior approach total hip arthroplasty.

METHODS

Radiation dosimetry badges were placed at the sternal notch and pubic symphysis of 50 patients undergoing direct anterior approach total hip arthroplasty. Badges were also placed on the surgeons outside of their lead aprons at the level of the thyroid. Three fellowship-trained arthroplasty surgeons were involved in the study. Radiation exposure of each badge was measured after each case (surgeon and patient). The cumulative dose was also calculated for the surgeons. To limit surgeon bias during the study, 50 consecutive direct anterior approach total hip arthroplasties that occurred prior to this study were analyzed for total fluoroscopic dose and time and served as a control group.

RESULTS

Forty-five subjects met study criteria. In the study group, 1 patient had a detectable thyroid exposure equal to 1 mrem. Seven patients had a detectable radiation entrance surface dose at the pubic symphysis (range, 1 to 7 mrem). No radiation entrance surface dose was detectable in the remaining 44 patients at the sternal notch and 38 patients at the pubic symphysis. Surgeons in the study did not experience a detectable radiation entrance surface dose. The mean fluoroscopic time was 13.72 seconds (range, 6.7 to 28.7 seconds). The mean patient radiation exposure was 178 mrem (range, 54 to 526 mrem).

CONCLUSIONS

This study demonstrates that during direct anterior approach total hip arthroplasty, the mean patient entrance surface dose at the pubic symphysis and the sternal notch is not detectable in most patients. The mean patient exposure in this study during direct anterior approach total hip arthroplasty was 178 mrem, which is less than a single pelvic radiograph (600 mrem). No surgeon in our study demonstrated a detectable radiation entrance surface dose. Our data suggest that direct anterior approach total hip arthroplasty typically results in a negligible or very low dose of absorbed radiation exposure to the patient and the surgeon.

CLINICAL RELEVANCE

We believe this study to have clinical relevance because both patients and surgeons have evidence that utilization of fluoroscopy during direct anterior total hip replacement places both parties at a relatively low radiation exposure risk.

Radiobiology in Cardiovascular Imaging

The introduction of ionizing radiation in medicine revolutionized the diagnosis and treatment of disease and dramatically improved and continues to improve the quality of health care. Cardiovascular imaging and medical imaging in general, however, are associated with a range of radiobiologic effects, including, in rare instances, moderate to severe skin damage resulting from cardiac fluoroscopy. For the dose range associated with diagnostic imaging (corresponding to effective doses on the order of 10 mSv [1 rem]), the possible effects are stochastic in nature and largely theoretical. The most notable of these effects, of course, is the possible increase in cancer risk. The current review addresses radiobiology relevant to cardiovascular imaging, with particular emphasis on radiation induction of cancer, including consideration of the linear nonthreshold dose-response model and of alternative models such as radiation hormesis.