Thyroid Radiation Dose to Patients from Diagnostic Radiology Procedures over Eight Decades: 1930-2010

Radiation-Related Thyroid Cancer

Radiation is an environmental factor that elevates the risk of developing thyroid cancer. Actual and possible scenarios of exposures to external and internal radiation are multiple and diverse. This article reviews radiation doses to the thyroid and corresponding cancer risks due to planned, existing, and emergency exposure situations, and medical, public, and occupational categories of exposures. Any exposure scenario may deliver a range of doses to the thyroid, and the risk for cancer is addressed along with modifying factors. The consequences of the Chornobyl and Fukushima nuclear power plant accidents are described, summarizing the information on thyroid cancer epidemiology, treatment, and prognosis, clinicopathological characteristics, and genetic alterations. The Chornobyl thyroid cancers have evolved in time: becoming less aggressive and driver shifting from fusions to point mutations. A comparison of thyroid cancers from the 2 areas reveals numerous differences that cumulatively suggest the low probability of the radiogenic nature of thyroid cancers in Fukushima. In view of continuing usage of different sources of radiation in various settings, the possible ways of reducing thyroid cancer risk from exposures are considered. For external exposures, reasonable measures are generally in line with the As Low As Reasonably Achievable principle, while for internal irradiation from radioactive iodine, thyroid blocking with stable iodine may be recommended in addition to other measures in case of anticipated exposures from a nuclear reactor accident. Finally, the perspectives of studies of radiation effects on the thyroid are discussed from the epidemiological, basic science, and clinical points of view.

Comparison of Simulated Low-Dose and Conventional-Dose CT for Preoperative Planning in Shoulder Arthroplasty

BACKGROUND

Shoulder computed tomography (CT) is commonly utilized in preoperative planning for total shoulder arthroplasty. Conventional-dose shoulder CT may expose patients to more ionizing radiation than is necessary to provide high-quality images for this procedure. The purpose of this study was to evaluate the utility of simulated low-dose CT images for preoperative planning using manual measurements and common preoperative planning software.

METHODS

Eighteen shoulder CT scans obtained for preoperative arthroplasty planning were used to generate CT images as if they had been acquired at reduced radiation dose (RD) levels of 75%, 50%, and 25% using a simulation technique that mimics decreased x-ray tube current. This technique was validated by quantitative comparison of simulated low-dose scans of a cadaver with actual low-dose scans. Glenoid version, glenoid inclination, and humeral head subluxation were measured using 2 commercially available software platforms and were also measured manually by 3 physicians. These measurements were then analyzed for agreement across RD levels for each patient. Tolerances of 5° of glenoid version, 5° of glenoid inclination, and 10% humeral head subluxation were used as equivalent for preoperative planning purposes.

RESULTS

At all RD levels evaluated, the preoperative planning software successfully segmented the CT images. Semiautomated software measurement of 25% RD images was within tolerances in 99.1% of measurements; for 50% RD images, within tolerances in 96.3% of measurements; and for 75% RD images, within tolerances in 100% of measurements. Manual measurements of 25% RD images were within these tolerances in 95.1% of measurements; for 50% RD images, in 98.8% of measurements; and for 75% RD images, in 99.4% of measurements.

CONCLUSIONS

Simulated low-dose CT images were sufficient for reliable measurement of glenoid version, glenoid inclination, and humeral head subluxation by preoperative planning software as well as by physician-observers. These findings suggest the potential for substantial reduction in RD in preoperative shoulder CT scans without compromising surgical planning.

CLINICAL RELEVANCE

The adoption of low-dose techniques in preoperative shoulder CT may lower radiation exposure for patients undergoing shoulder arthroplasty, without compromising image quality.

Evaluation of thyroid radiation dose during abdominal Computed Tomography procedures and dose reduction effectiveness of thyroid shielding

INTRODUCTION

During abdominal Computed Tomography (CT) studies, vicinity organs receive a dose from scatter radiation. The thyroid is considered an organ at greater risk due to high radiosensitivity.

METHODS

The primary objective of this study was to determine the entrances surface dose (ESD) to the thyroid during abdominal CT studies and to evaluate the efficiency of dose reduction by lead shielding. The calibrated thermoluminescence dosimeter (TLD) chips were used to measure the ESD during 180 contrast-enhanced (CE) and non-contrast-enhanced (NC) abdominal CT studies in the presence and absence of lead shielding.

RESULTS

Thyroid shielding reduces the ESD by 72.3% (0.55 mGy), 86.5% (2.95 mGy) and 64.0% (2.24 mGy) during NC, 3-phase and 4-phase abdominal CT scans. Also, the patient height was identified as a parameter that inversely influenced the thyroid dose, proving that the taller patients receive less dose to the thyroid. Regardless, the scan parameters such as time and display field of view (DFOV) positively impact the thyroid dose.

CONCLUSION

Lead shielding can prevent the external scatter reaching the thyroid region by 64%-87% during the non-vicinity scans such as abdomen CT. However, the actual dose saving lies between 0.2% and 0.4%, compared to the total effective dose of the whole CT procedure.

IMPLICATIONS FOR PRACTICE

The thyroid shield can effectively reduce external scatter radiation during abdominal CT procedures. However, the dose saving is insignificant compared to the total effective dose from the whole examination. Therefore, the use of thyroid shielding should be carefully evaluated during CT abdomen procedures.

Mean glandular dose in the mammary gland and dose of radiation in the thyroid gland and lens in women with and without breast implants during different modalities of mammography

There have always been concerns about the secondary effects of diagnostic methods that use ionizing radiation. During mammography, the parameters to be concerned about are the mean glandular dose and the scatter dose. We evaluated the dose of radiation to the breast, thyroid gland, and lens in digital mammography in women with and without implants, in tomosynthesis in women with and without implants, and in contrast-enhanced mammography.

MATERIALS AND METHODS

The study included 212 women with and without disease who were attended at the Centro Clínico de Estereotaxia, CECLINES, in Caracas, Venezuela, between June 2017 and August 2017; the women were classified into five groups according to the mammographic modality used to evaluate them and whether or not they had implants. The statistical analysis included descriptive statistics for the study population. We used the Mann-Whitney U to compare the mean glandular dose and dose in the thyroid gland and lens between groups.

RESULTS

The mean glandular dose and the dose of radiation received in the thyroid and lens were within the acceptable range. In a few exceptions, the mean glandular dose per view was slightly higher than 3 mGy. The scatter dose to the thyroid gland and the lens during mammography has a very small contribution to the annual dose equivalent.

CONCLUSION

The mean glandular dose and the scatter dose to the thyroid gland and lens delivered during tomosynthesis and 2D mammography in women with implants were higher than those delivered during other mammographic techniques in women without implants.

Parathyroid Imaging: Past, Present, and Future

The goal of parathyroid imaging is to identify all sources of excess parathyroid hormone secretion pre-operatively. A variety of imaging approaches have been evaluated and utilized over the years for this purpose. Ultrasound relies solely on structural features and is without radiation, however is limited to superficial evaluation. 4DCT and 4DMRI provide enhancement characteristics in addition to structural features and dynamic enhancement has been investigated as a way to better distinguish parathyroid from adjacent structures. It is important to recognize that 4DCT provides valuable information however results in much higher radiation dose to the thyroid gland than the other available examinations, and therefore the optimal number of phases is an area of controversy. Single-photon scintigraphy with 99mTc-Sestamibi, or dual tracer 99mTc-pertechnetate and 99mTc-sestamibi with or without SPECT or SPECT/CT is part of the standard of care in many centers with availability and expertise in nuclear medicine. This molecular imaging approach detects cellular physiology such as mitochondria content found in parathyroid adenomas. Combining structural imaging such as CT or MRI with molecular imaging in a hybrid approach allows the ability to obtain robust structural and functional information in one examination. Hybrid PET/CT is widely available and provides improved imaging and quantification over SPECT or SPECT/CT. Emerging PET imaging techniques, such as 18F-Fluorocholine, have the exciting potential to reinvent parathyroid imaging. PET/MRI may be particularly well suited to parathyroid imaging, where available, because of the ability to perform dynamic contrast-enhanced imaging and co-registered 18F-Fluorocholine PET imaging simultaneously with low radiation dose to the thyroid. A targeted agent specific for a parathyroid tissue biomarker remains to be identified.

Role of DNA Repair Variants and Diagnostic Radiology Exams in Differentiated Thyroid Cancer Risk: A Pooled Analysis of Two Case-Control Studies

BACKGROUND

Given the increased use and diversity of diagnostic procedures, it is important to understand genetic susceptibility to radiation-induced thyroid cancer.

METHODS

On the basis of self-declared diagnostic radiology examination records in addition to existing literature, we estimated the radiation dose delivered to the thyroid gland from diagnostic procedures during childhood and adulthood in two case-control studies conducted in France. A total of 1,071 differentiated thyroid cancer (DTC) cases and 1,188 controls from the combined studies were genotyped using a custom-made Illumina OncoArray DNA chip. We focused our analysis on variants in genes involved in DNA damage response and repair pathways, representing a total of 5,817 SNPs in 571 genes. We estimated the OR per milli-Gray (OR/mGy) of the radiation dose delivered to the thyroid gland using conditional logistic regression. We then used an unconditional logistic regression model to assess the association between DNA repair gene variants and DTC risk. We performed a meta-analysis of the two studies.

RESULTS

The OR/mGy was 1.02 (95% confidence interval, 1.00-1.03). We found significant associations between DTC and rs7164173 in CHD2 (P = 5.79 × 10-5), rs6067822 in NFATc2 (P = 9.26 × 10-5), rs1059394 and rs699517 both in ENOSF1/THYS, rs12702628 in RPA3, and an interaction between rs7068306 in MGMT and thyroid radiation doses (P = 3.40 × 10-4).

CONCLUSIONS

Our results suggest a role for variants in CDH2, NFATc2, ENOSF1/THYS, RPA3, and MGMT in DTC risk.

IMPACT

CDH2, NFATc2, ENOSF1/THYS, and RPA3 have not previously been shown to be associated with DTC risk.

Mean glandular dose in the mammary gland and dose of radiation in the thyroid gland and lens in women with and without breast implants during different modalities of mammography

There have always been concerns about the secondary effects of diagnostic methods that use ionizing radiation. During mammography, the parameters to be concerned about are the mean glandular dose and the scatter dose. We evaluated the dose of radiation to the breast, thyroid gland, and lens in digital mammography in women with and without implants, in tomosynthesis in women with and without implants, and in contrast-enhanced mammography.

MATERIALS AND METHODS

The study included 212 women with and without disease who were attended at the Centro Clínico de Estereotaxia, CECLINES, in Caracas, Venezuela, between June 2017 and August 2017; the women were classified into five groups according to the mammographic modality used to evaluate them and whether or not they had implants. The statistical analysis included descriptive statistics for the study population. We used the Mann-Whitney U to compare the mean glandular dose and dose in the thyroid gland and lens between groups.

RESULTS

The mean glandular dose and the dose of radiation received in the thyroid and lens were within the acceptable range. In a few exceptions, the mean glandular dose per view was slightly higher than 3mGy. The scatter dose to the thyroid gland and the lens during mammography has a very small contribution to the annual dose equivalent.

CONCLUSION

The mean glandular dose and the scatter dose to the thyroid gland and lens delivered during tomosynthesis and 2D mammography in women with implants were higher than those delivered during other mammographic techniques in women without implants.

Low Radiation X-rays: Benefiting People Globally by Reducing Cancer Risks

Modern medical imaging facilitates the diagnosis and treatment of human diseases. However, few people are aware of the cons of radiation exposure from medical imaging. Emerging evidence reveals that cumulative doses of radiation exposure will increase the morbidity and mortality of pertaining cancer. As a special young population, patients with adolescent idiopathic scoliosis (AIS) suffer more radiation harms from repeated diagnostic imaging, most of which can be avoided in clinical practice. Accumulating evidence highlights reduced cancer risks of radiation exposure for AIS patients with low/zero radiation imaging modalities proposed, amongst which easy conversion from anterior-posterior (AP) to posterior-anterior (PA) projection for whole-spine radiographs should be stressed. It can greatly reduce radiation doses without compromising the quality of diagnostic imaging. Tight collimation combined with PA projection can further reduce radiation harms, and need to be spread to benefit people globally.

Trends in Estimated Thyroid, Salivary Gland, Brain, and Eye Lens Doses From Intraoral Dental Radiography Over Seven Decades (1940 TO 2009)

The purpose of this study is to support retrospective dose estimation for epidemiological studies by providing estimates of historical absorbed organ doses to the brain, lens of the eye, salivary glands, and thyroid from intraoral dental radiographic examinations performed from 1940 to 2009. We simulated organ doses to an adult over 10 y time periods from 1940 to 2009, based on commonly used sets of x-ray machine settings collected from the literature. Simulations to estimate organ dose were performed using personal computer x-ray Monte Carlo software. Overall, organ doses were less than 1 mGy for a single intraoral radiograph for all decades. From 1940 to 2009, doses to the brain, eye lens, salivary glands, and thyroid decreased by 86, 96, 95, and 89%, respectively. Of these four organs, the salivary glands received the highest doses, with values decreasing from about 0.23 mGy in the 1940s to 0.025 mGy in the 2000s for a single intraoral radiograph. Based on simulations using collected historical data on x-ray technical parameters, improvements in technology and optimization of the technical settings used to perform intraoral dental radiography have resulted in a decrease in absorbed dose to the brain, eye lens, salivary glands, and thyroid over the period from 1940 to 2009.

Dental X-Rays and the Risk of Thyroid Cancer and Meningioma: A Systematic Review and Meta-Analysis of Current Epidemiological Evidence

Background: Exposure to moderate-to-high doses of ionizing radiation is the only established environmental risk factor for thyroid cancer and brain and central nervous system tumors. Considering the high lifetime prevalence and frequency of exposure to dental X-rays, the most common source of diagnostic radiation exposure in the general population, even a small associated increase in cancer risk would be of considerable public health importance. With the objective to inform clinical practice and guidelines, we synthesized the current epidemiological evidence on the association between dental X-rays and the risk of thyroid cancer, meningioma, and other cancers of the head and neck region. Methods: The Medline, Embase, and Web of Science databases were searched to identify eligible studies. Summary odds ratio/relative risk estimates and confidence intervals were extracted, and pooled risk ratios (RRs) for each cancer were calculated using random effects meta-analysis. Results: The literature search identified 5537 publications; of these, 26 studies including 10,868 cancer patients were included in the synthesis. The random effects meta-analyses, based on seven studies of thyroid cancer (six case/control, one cohort) and eight studies of meningioma (all case/control), showed that multiple (or repeated) exposures to dental X-rays were significantly associated with an increased risk of thyroid cancer (pooled RR = 1.87 [95% confidence interval, CI 1.11-3.15]) and meningioma (pooled RR = 1.53 [CI 1.26-1.85]). There was no association with glioma, and there were too few studies of other cancers of the head and neck region to conduct a meaningful meta-analysis. Conclusions: Based on a meta-analysis of retrospective case/control studies, these findings provide some support to the hypothesis that multiple (or repeated) exposures to dental X-rays may be associated with an increased risk of thyroid cancer and meningioma. These studies did not include individual organ doses and ages at exposure, and are subject to recall bias and other limitations. Furthermore, the thyroid exposure has decreased dramatically over time from the use of thyroid shields and improved technology/equipment. Prospective studies, based on dental X-ray records and patient follow-up, are needed to test the hypothesis further and clarify the possible cancer risk associated with dental radiography, as although the risk at the individual level, particularly with improved technology/equipment, is likely to be very low, the proportion of the population exposed is high. Considering that about one-third of the general population in developed countries is routinely exposed to one or more dental X-rays per year, these findings manifest the need to reduce diagnostic radiation exposure as much as possible.

Assessment of thyroid cancer risk associated with radiation dose from personal diagnostic examinations in a cohort study of US radiologic technologists, followed 1983-2014

OBJECTIVE

To assess whether personal medical diagnostic procedures over life, but particularly those associated with exposure in adulthood, were associated with increased thyroid cancer risk.

DESIGN

Participants from the US Radiologic Technologists Study, a large, prospective cohort, were followed from the date of first mailed questionnaire survey completed during 1983-1989 to the earliest date of self-reported diagnosis of thyroid cancer or of any other cancer than non-melanoma skin cancer (NMSC) in any of three subsequent questionnaires up to the last in 2012-2014.

SETTING

US nationwide, occupational cohort.

PARTICIPANTS

US radiologic technologists with exclusion of: those who reported a previous cancer apart from NMSC on the first questionnaire; those who reported a cancer with an unknown date of diagnosis on any of the questionnaires; and those who did not respond to both the first questionnaire and at least one subsequent questionnaire.

PRIMARY OUTCOME MEASURE

We used Cox proportional hazards models with age as timescale to compute HRs and 95% CI for thyroid cancer in relation to cumulative 5-year lagged diagnostic thyroid dose.

RESULTS

There were 414 self-reported thyroid cancers (n=275 papillary) in a cohort of 76 415 persons. Cumulative thyroid dose was non-significantly positively associated with total (excess relative risk/Gy=2.29 (95% CI -0.91 to 7.01, p=0.19)) and papillary thyroid cancer (excess relative risk/Gy=4.15 (95% CI -0.39, 11.27, p=0.08)) risk. These associations were not modified by age at, or time since, exposure and were independent of occupational exposure.

CONCLUSION

Our study provides weak evidence that thyroid dose from diagnostic radiation procedures over the whole of life, in particular associated with exposure in adulthood, influences adult thyroid cancer risk.

Assessment of PCXMC for patients with different body size in chest and abdominal x ray examinations: a Monte Carlo simulation study

A PC Program for x ray Monte Carlo (PCXMC) has been used to calculate organ doses in patient dosimetry and for the exposure assessment in epidemiological studies of radiogenic health related risks. This study compared the dosimetry from using the built-in stylized phantoms in the PCXMC to that of a newer hybrid phantom library with improved anatomical realism. We simulated chest and abdominal x ray projections for 146 unique body size computational phantoms, 77 males and 69 females, with different combinations of height (125-180 cm) and weight (20-140 kg) using the built-in stylized phantoms in the PCXMC version 2.0.1.4 and the hybrid phantom library using the Monte Carlo N-particle eXtended transport code 2.7 (MCNPX). Unfortunately, it was not possible to incorporate the hybrid phantom library into the PCXMC. We compared 14 organ doses, including dose to the active bone marrow, to evaluate differences between the built-in stylized phantoms in the PCXMC and the hybrid phantoms (Cristy and Eckerman 1987 Technical Report ORNL/TM-8381/V1, Oak Ridge National Laboratory, Eckerman and Ryman 1993 Technical Report 12 Oak Ridge, TN, Geyer et al 2014 Phys. Med. Biol. 59 5225-42). On average, organ doses calculated using the built-in stylized phantoms in the PCXMC were greater when compared to the hybrid phantoms. This is most prominent in AP abdominal exams by an average factor of 2.4-, 2.8-, and 2.8-fold for the 10-year-old, 15-year-old, and adult phantoms, respectively. For chest exams, organ doses are greater by an average factor of 1.1-, 1.4-, and 1.2-fold for the 10-year-old, 15-year-old, and adult phantoms, respectively. The PCXMX, due to its ease of use, is often selected to support dosimetry in epidemiological studies; however, it uses simplified models of the human anatomy that fail to account for variations in body morphometry for increasing weight. For epidemiological studies that use PCXMC dosimetry, associations between radiation-related disease risks and organ doses may be underestimated, and to a greater degree in pediatric, especially obese pediatric, compared to adult patients.