Abstract
The purpose of the present study was to investigate how the intention to participate in thyroid ultrasound examination (TUE) changed after reading an explanation of its merits and demerits among adolescents in Fukushima Prefecture following the nuclear disaster in a cross-sectional questionnaire study with a pre-post design. The study was conducted among adolescents eligible for TUE. In the pre-survey, data were collected on participants’ background characteristics, history of TUE participation, willingness to participate in TUE, and prior knowledge of the merits and demerits of TUE. Next, participants were provided with a written explanation of the merits and demerits of TUE. Following this, they were surveyed again regarding the understandability of the explanation and their willingness to participate in TUE after reading it. The primary outcome was the change in intention to participate in TUE between the pre- and post-surveys. The overall proportion of willingness to participate in TUE did not change dramatically after reading the explanation. However, 77.8% (367/472) of participants in the group that already knew the merits and demerits did not change their intention to participate in TUE, whereas only 70.5% (537/762) in the previously unaware group did not change their intention. The highest proportion of change was observed among those who initially responded as “undecided” regarding participation in TUE. Providing information on the merits and demerits of TUE was especially important for undecided individuals, as this group showed the greatest change in intention following the explanation.
Introduction
The health issues caused by a nuclear disaster are diverse and include acute radiation syndrome, internal radiation exposure, increased cancer incidence, and impacts on mental health. Among affected residents, careful and long-term follow-up is vital [1, 2]. In particular, following the Chernobyl nuclear disaster, the long-term incidence of thyroid cancer in children increased due to the uptake of radioactive iodine by the thyroid gland [3-6]. Ultrasound examination is the most important examination method for the early detection and long-term follow-up monitoring of thyroid cancer [7]. Therefore, conducting Thyroid Ultrasound Examinations (TUE), especially for young individuals potentially exposed to radioactive iodine following a nuclear disaster, is a crucial public health issue.
Various efforts have been made to ensure the appropriate administration of TUE for affected children and adolescents after a nuclear disaster. The nature and consequences of nuclear disasters vary, requiring different approaches for each event. For instance, following the Great East Japan Earthquake and the subsequent Fukushima Daiichi Nuclear Power Plant (FDNPP) accident in 2011, the release of radioactive material was limited, and contaminated food distribution was quickly contained, unlike the Chernobyl nuclear accident. In Fukushima, some patients with thyroid cancer were diagnosed after the disaster. However, after considering the overdiagnosis effect as well as the fact that the release of radioactive material was limited, the International Agency for Research on Cancer and other international organizations concluded that no considerable increase in thyroid cancer secondary to radiation effects has been observed to date [8, 9]. Conversely, in general medical care, thyroid cancer screening has been associated with a potential for overdiagnosis of thyroid cancer [10]. Overdiagnosis is defined as detecting cancers that would never have caused harm over the patient’s lifetime. We must consider overdiagnosis as a separate issue from the effects of radiation exposure. While we implemented countermeasures to reduce the risk of overdiagnosis, it is vital to explain this issue in advance to both adolescents and their guardians. Therefore, the merits and demerits of TUE after a nuclear disaster may differ depending on the specific context. It is crucial for residents eligible for such examinations to have a proper understanding of both the merits and demerits. Nevertheless, few studies have examined how awareness of these merits and demerits affects decision-making regarding participation in TUE.
The TUE, conducted as part of the Fukushima Health Management Survey, was in its seventh round as of 2025 [11-14]. To date, 350 cases of malignant or suspicious thyroid cancer have been identified by fine-needle aspiration cytology as of March 31, 2025 [14]. According to Matsumoto et al., postoperative complications in these cases did not differ from those observed in general clinical practice [15]. Moreover, although the estimated radiation doses differed by region in Fukushima, the detection rate of thyroid cancer did not vary by region [16, 17]. The TUE following the FDNPP accident was designed to minimize overdiagnosis and overtreatment, based on diagnostic criteria published by the Japan Society of Ultrasonics in Medicine [18, 19]. In addition, psychological support from specialists has been provided for individuals diagnosed with any disease during TUE [20]. The specific demerits of TUE identified in Fukushima include risk of overdiagnosis; psychological, social, and economic impacts associated with thyroid cancer diagnosis; and unnecessary interventions for nodules or cysts that do not require treatment [9, 13]. The specific merits of TUE identified in Fukushima include relief in the absence of abnormal findings, advantages of early diagnosis, and generation of accurate epidemiological information about radiation effects [13, 21].
Fukushima Prefecture and Fukushima Medical University have made ongoing efforts to inform residents about the above merits, demerits, and strategies to minimize the demerits through various media, including leaflets and animations [22]. However, a preliminary report in 2023 indicated that approximately half of the residents in the Fukushima Prefecture were unaware of these merits and demerits [23]. Therefore, Fukushima Prefecture was considered a suitable setting to investigate how recognition of the merits and demerits of TUE influences residents’ intentions to participate.
This study aimed to investigate how the intention to participate in TUE changed after reading explanations about its merits and demerits among adolescents eligible for TUE in Fukushima Prefecture following the nuclear disaster. Furthermore, we examined the factors that influenced changes in their intention to participate.
Methods
Study design and participants
This survey was conducted by Fukushima Prefecture, which outsourced the data analysis to Fukushima Medical University. A total of 16,000 paper-based questionnaires were distributed to residents, including children eligible for TUE and their parents or guardians [21]. Participants were informed of their rights and the survey details through a consent process before completing the questionnaire; they could also choose to respond using an online reply system [21]. The primary report was published online [21]. The database was sent from Fukushima Prefecture to Fukushima Medical University after the removal of personal information. The Ethics Committee of Fukushima Medical University waived the ethics review process because the project was outside the scope of the “Ethical Guidelines for Medical and Biological Research Involving Human Subjects” (Reference Number: REC2024-177).
This study was an observational cross-sectional study conducted among adolescents eligible for TUE. A total of 8,000 questionnaires were distributed; of these, 1,332 (16.7%) questionnaires were collected from adolescents. We excluded 92 participants who lacked data on age, sex, TUE experience, willingness to participate in TUE, and awareness of the merits and demerits. Ultimately, 1,234 participants were included in the final analysis (Supplementary Fig. 1A).
Survey tool
Participants were provided with a paper-based questionnaire and an online response link via email. First, background characteristics, history of participation in TUE, willingness to participate in TUE, and awareness of the merits and demerits were collected in the pre-survey. Second, participants read an explanation about the merits and demerits. Third, the understandability of the explanation and willingness to participate in TUE (after reading the explanation) were assessed in the post-survey (Supplementary Fig. 1B).
Primary outcome
The primary outcome was the change in intention to participate in TUE between the pre-survey and post-survey after reading the explanation about the merits and demerits of TUE. We also surveyed the factors that affected the change in intention to participate in TUE.
Statistical analysis
Firstly, children’s background characteristics were presented according to whether they knew or did not know about the merits and demerits. Secondly, multinomial logistic regression analyses were performed for the history of participation in TUE and willingness to participate in TUE.
To identify the change in intention to participate in TUE between the pre-and post-surveys, a Sankey diagram was used to visualize the intention before and after reading the explanation, according to groups with or without prior knowledge of the merits and demerits. Next, participants’ background characteristics were descriptively analyzed by the group that showed a change in willingness to participate in TUE after reading the explanation. Finally, a multinomial logistic regression analysis was conducted to evaluate factors associated with changes in willingness to participate in TUE after reading the explanation, among those who had expressed willingness to participate before reading.
The reasons for receiving or not receiving TUE were presented by the group, categorized based on their recognition of the merits and demerits. In addition, the understandability of the explanation about the merits and demerits was reported by the group with or without prior knowledge. Chi-square test was used for the analysis of categorical variables, and Fisher’s exact test was applied when the sample size in any cell was <five. All statistical analyses were conducted using Stata MP 18 (Lightstone, Texas, USA). The Sankey diagram was created using the online tool Flourish (Flourish, London, UK).
Results
Participants’ background and factors affecting intention to participate in TUE at pre-survey
A total of 88.4% of participants had a history of participation in TUE, with a higher proportion observed in the group that already knew the merits and demerits (94.9%). A total of 28.9% of participants were undecided about participating in TUE; this proportion was higher in the group that did not know the merits and demerits (32.3%) (Table 1). The proportion of participants who answered “undecided” regarding participation in TUE at the pre-survey was 27.0% among those who had previously received TUE, 34.0% among those who had not received TUE, and 49.5% among those who did not remember their history of participation (Supplementary Table 1, p-value < 0.001). Regarding reasons for receiving TUE, the proportion of participants who answered “hope to cooperate in epidemiological studies” was significantly higher among those in the group that recognized the merits and demerits than among those in the unrecognized group (14.4% vs. 7.9%; Supplementary Table 2). Regarding reasons for refraining from TUE, the proportions of participants who answered “the examination might increase mental and health burden” and “may detect cancer that does not require treatment” were significantly higher in those in the recognized group than in those in the unrecognized group (15.7% vs. 6.0% and 10.8% vs. 3.3%, respectively; Supplementary Table 3). Understandability of the explanation of the merits (p-value = 0.005) and demerits (p-value = 0.001) was significantly higher in the group that previously recognized them (Supplementary Table 4).
Table 1 Participant background by recognition of the merits and demerits of TUE at the pre-survey (
n [%])
|
Already known (n = 472) |
Unknown (n = 762) |
Total (N = 1,234) |
p-value |
| Age |
|
|
|
0.32 |
| Over 17 years old |
166 (35.2) |
247 (32.4) |
413 (33.5) |
|
| 16–17 years old |
306 (64.8) |
515 (67.6) |
821 (66.5) |
|
| Sex |
|
|
|
0.119 |
| Female |
260 (55.1) |
385 (50.5) |
645 (52.3) |
|
| Male |
212 (44.9) |
377 (49.5) |
589 (47.7) |
|
| History of participation in TUE |
|
|
|
<0.001 |
| Received |
448 (94.9) |
643 (84.4) |
1,091 (88.4) |
|
| Not received |
10 (2.1) |
40 (5.2) |
50 (4.1) |
|
| Don’t remember |
14 (3.0) |
79 (10.4) |
93 (7.5) |
|
| Willingness to receive TUE |
|
|
|
0.001 |
| Yes |
278 (58.9) |
366 (48.0) |
644 (52.2) |
|
| No |
83 (17.6) |
150 (19.7) |
233 (18.9) |
|
| Undecided |
111 (23.5) |
246 (32.3) |
357 (28.9) |
|
TUE, Thyroid Ultrasound Examination.
The chi-square test was used for statistical analysis.
Multinomial logistic regression analysis showed that younger participants were less likely to belong to the group that did not participate in TUE and the group that did not remember participating in TUE (odds ratio [OR], 95% confidential intervals [CIs]: 0.19 [0.10–0.36] and 0.42 [0.27–0.65], respectively; Table 2). Participants who did not know the merits and demerits were positively associated with both the group that did not participate in TUE and the group that did not remember participation (OR [95% CI]: 3.02 [1.48–6.16] and 4.17 [2.32–7.48], respectively; Table 2). Not knowing the merits and demerits was also positively associated with having undecided intentions toward TUE participation (OR [95% CI]: 1.50 [1.13–1.98]), but not with refraining from participation (Table 3).
Table 2 Multinomial logistic regression analysis for history of participation in TUE (
N = 1,234)
|
Odds ratio (95% CI) |
p-value |
| Experience of TUE: Not received (vs. received) |
|
|
| Age (reference: Over 17 years old) |
|
|
| 16–17 years old |
0.19 (0.10–0.36) |
<0.001 |
| Sex (reference: female) |
|
|
| Male |
1.53 (0.85–2.74) |
0.156 |
| Merit awareness (reference: already known) |
|
|
| Unknown |
3.02 (1.48–6.16) |
0.002 |
| Experience of TUE: Don’t remember (vs. received) |
|
|
| Age (reference: Over 17 years old) |
|
|
| 16–17 years old |
0.42 (0.27–0.65) |
<0.001 |
| Sex (reference: female) |
|
|
| Male |
0.89 (0.57–1.37) |
0.59 |
| Merit awareness (reference: already known) |
|
|
| Unknown |
4.17 (2.32–7.48) |
<0.001 |
TUE, Thyroid Ultrasound Examination; CI, Confidence Interval.
Table 3 Multinomial logistic regression analysis for willingness to participate in TUE at pre-survey (
N = 1,234)
|
Odds ratio (95% CI) |
p-value |
| Willingness to participate in TUE: None (vs. yes) |
|
|
| Age (reference: Over 17 years old) |
|
|
| 16–17 years old |
0.42 (0.30–0.58) |
<0.001 |
| Sex (reference: female) |
|
|
| Male |
1.75 (1.28–2.39) |
<0.001 |
| History of participation in TUE (reference: received) |
|
|
| Not received |
5.47 (2.50–11.96) |
<0.001 |
| Don’t remember |
4.28 (2.30–7.97) |
<0.001 |
| Recognition of merits and demerits (reference: already known) |
|
|
| Unknown |
1.21 (0.87–1.67) |
0.260 |
| Willingness to participate in TUE: Undecided (vs. yes) |
|
|
| Age (reference: Over 17 years old) |
|
|
| 16–17 years old |
0.70 (0.53–0.94) |
0.017 |
| Sex (reference: female) |
|
|
| Male |
1.37 (1.05–1.79) |
0.019 |
| History of participation in TUE (reference: received) |
|
|
| Not received |
2.88 (1.29–6.44) |
0.010 |
| Don’t remember |
4.41 (2.52–7.72) |
<0.001 |
| Recognition of merits and demerits (reference: already known) |
|
|
| Unknown |
1.50 (1.13–1.98) |
0.005 |
TUE, Thyroid Ultrasound Examination; CI, Confidence Interval.
The proportion of children or adolescents who intended to participate in TUE was 52.2% in the “yes” group, 18.9% in the “no” group, and 28.3% in the “undecidable” group before reading the explanation about the merits and demerits. In contrast, after reading the explanation, the proportions were 49.7% in the “yes” group, 19.9% in the “no” group, and 30.5% in the “undecidable” group (Fig. 1A, B). Among the participants who had already known the merits and demerits, 234 participants did not change their mind for the participants who had willingness to participate before reading, 62 participants did not change their mind for the participants who did not have willingness before reading, and 71 participants did not change their mind for the participants who were undecided before reading (total n = 367). Among the participants who had not known the merits and demerits, 275 participants did not change their mind for the participants who had willingness to participate before reading, 103 participants did not change their mind for the participants who did not have willingness before reading, and 159 participants did not change their mind for the participants who were undecided before reading (total n = 537). The overall proportions did not dramatically change after reading the explanation. However, 77.8% (367/472) of participants in the group that already knew the merits and demerits did not change their intention to participate in TUE, whereas 70.5% (537/762) in the previously unaware group did not change their intention (Fig. 1A, B, Table 4).
Table 4 Participant backgrounds by group for change in willingness to participate in TUE after reading the explanation of merits and demerits (
n = 1,224)
|
Willingness to participate in TUE after reading paragraph |
Total |
p-value |
| Yes |
None |
Undetermined |
| Participants who had willingness to participate before reading |
509 (79.4) |
30 (4.7) |
102 (15.9) |
641 (100.0) |
|
| 16–17 years old |
371 (72.9) |
22 (73.3) |
78 (76.5) |
471 (73.5) |
0.76 |
| Male |
213 (41.8) |
17 (56.7) |
46 (45.1) |
276 (43.1) |
0.25 |
| Unknown about merits and demerits |
275 (54.0) |
16 (53.3) |
74 (72.5) |
365 (56.9) |
0.002 |
| All explanations easy to understand |
493 (97.2) |
29 (96.7) |
91 (89.2) |
613 (95.9) |
<0.001 |
| Participants who did not have willingness before reading |
22 (9.6) |
165 (72.4) |
41 (18.0) |
228 (100.0) |
|
| 16–17 years old |
12 (54.5) |
82 (49.7) |
20 (48.8) |
114 (50.0) |
0.90 |
| Male |
11 (50.0) |
89 (53.9) |
28 (68.3) |
128 (56.1) |
0.21 |
| Unknown about merits and demerits |
14 (63.6) |
103 (62.4) |
29 (70.7) |
146 (64.0) |
0.61 |
| All explanation easy to understand |
22 (100.0) |
153 (93.3) |
38 (92.7) |
213 (93.8) |
0.44 |
| Participants who were undecided before reading |
77 (21.7) |
48 (13.5) |
230 (64.8) |
355 (100.0) |
|
| 16–17 years old |
46 (59.7) |
33 (68.8) |
150 (65.2) |
229 (64.5) |
0.55 |
| Male |
34 (44.2) |
19 (39.6) |
127 (55.2) |
180 (50.7) |
0.062 |
| Unknown about merits and demerits |
52 (67.5) |
34 (70.8) |
159 (69.1) |
245 (69.0) |
0.93 |
| All explanation easy to understand |
76 (98.7) |
41 (85.4) |
206 (89.6) |
323 (91.0) |
0.019 |
TUE, Thyroid Ultrasound Examination.
The chi-square test was used for categorical variables.
Ease of understanding the explanation about the merits and demerits was significantly associated with willingness to participate in TUE after reading the explanation, both among those who were already willing before reading (p < 0.001) and those who were undecided before reading (p = 0.019; Table 4). Furthermore, 20.6% of those who answered “yes” before reading the explanation changed their intention afterward. Conversely, 27.6% of those who answered “no” and 35.2% of those who were “undecided” changed their intention after reading, respectively (Table 4). Among those who had expressed willingness to participate in TUE before reading, the proportion of participants who were previously unaware of the merits and demerits was higher in the group whose intention changed from “yes” to “undecidable” (OR [95% CI]: 2.07 [1.29–3.33], Table 5). Conversely, the proportion of participants who reported ease of understanding the explanation was lower in the group that changed their intention from “yes” to “undecidable” (OR [95% CI]: 0.38 [0.22–0.64], Table 5).
Table 5 Multinomial logistic regression analysis for change in willingness to participate in TUE after reading the explanation about merits and demerits among those initially willing to participate in TUE (
n = 641)
|
Odds ratio (95% CI) |
p-value |
| Change to “not willing” (reference: no change) |
|
|
| Age (reference: Over 17 years old) |
|
|
| 16–17 years old |
1.04 (0.45–2.42) |
0.92 |
| Sex (reference: female) |
|
|
| Male |
1.81 (0.86–3.82) |
0.119 |
| Informed about merits (reference: already known) |
|
|
| Unknown |
0.88 (0.42–1.87) |
0.75 |
| Impression of explanation (reference: vague) |
|
|
| All explanations easy to understand |
0.41 (0.17–1.01) |
0.052 |
| Change to “undecided” (reference: no change) |
|
|
| Age (reference: Over 17 years old) |
|
|
| 16–17 years old |
1.26 (0.76–2.10) |
0.37 |
| Sex (reference: female) |
|
|
| Male |
1.09 (0.70–1.69) |
0.70 |
| Informed about merits (reference: already known) |
|
|
| Unknown |
2.07 (1.29–3.33) |
0.003 |
| Impression of explanation (reference: vague) |
|
|
| All explanations easy to understand |
0.38 (0.22–0.64) |
<0.001 |
TUE, Thyroid Ultrasound Examination; CI, Confidence Interval.
Discussion
Investigating how the intention to receive TUE changed after reading the explanation of its merits and demerits among eligible adolescents following a nuclear disaster is a crucial public health issue. We surveyed changes in the intention to participate in TUE before and after reading the explanation.
Although the overall proportions in each intention group did not change dramatically after reading the explanation, some participants did change their intention, with the highest proportion of change observed among those who had initially responded as “undecided.” Among those who answered “yes” before reading the explanation, 20.6% changed their intention afterward. Among those who answered “no,” 27.6% changed their intention, and among those who were “undecided,” 35.2% changed their intention after reading. Previous studies have reported that understanding concepts such as overdiagnosis is challenging [24]. It is essential to ensure that individuals who are “undecided” about TUE participation can easily access clear and understandable information about its merits and demerits.
In this survey, 61.8% (762/1,234) of participating adolescents were unaware of the merits and demerits of TUE, a higher percentage than that reported among parents or guardians [21]. This may be attributed to better comprehension of complex information and a greater likelihood of carefully reading explanatory materials among parents or guardians. Further, the questionnaire survey among adolescent included a generation with low participation rates to TUE (the over 17 years old group), and it was thought that the lack of opportunities to read the merits and demerits led to low awareness. The survey results also showed that some adolescents changed their intention from “yes” to “no,” or from “no” to “yes” after reading the explanation. In Fukushima Prefecture, various efforts have been made to disseminate the information on the merits and demerits of TUE in an accessible manner, including the creation of child-friendly materials and animated videos. However, further efforts, including using stable media for adolescents or on-site classes, are necessary to improve understanding and support informed decision-making among adolescents.
Among those who were willing to participate in TUE, the proportion of individuals whose intentions changed to “undecided” after reading the explanation about the merits and demerits was several times higher in those who were previously unaware of the merits and demerits compared to those who were previously aware. Additionally, the proportion of individuals whose intentions changed to “undecided” after reading the explanation was also higher in those who felt the explanation was vague compared to those who felt the explanation was clear. Among those who were willing to participate in TUE before reading the explanation, the ratio of unawareness about the merits and demerits was 2.07 times higher in those who changed their intention from “willing to participate” to “undecided” than in those whose intention remained unchanged. The odds ratio of those who had the impression that the explanation was easy was 0.38 (95% CI: 0.22–0.64) in those who changed their intention from “willing to participate” to “undecided” compared to those whose intention remained unchanged (Table 5). These results may indicate the need for repeated and easy-to-understand explanations about the merits and demerits of TUE. A previous review showed that the most effective methods for conveying complex information vary among individuals [25]. Further research is needed to better understand the factors influencing decision-making regarding participation in TUE.
The present study has some limitations regarding generalizing the results to the broader public. First, the survey was conducted among a population that experienced only the FDNPP accident; caution is required when applying these findings to other nuclear accidents. Second, the post-test was conducted immediately after reading the explanation; further surveys are needed to assess middle- to long-term changes in intention. Third, the response rate was 16.7%, which may affect the validity of the results. Nevertheless, this study is the first to assess changes in intention after reading the explanation about the merits and demerits of TUE among adolescents affected by the nuclear disaster.
In conclusions, after reading the explanation about the merits and demerits, a portion of adolescents changed their intention to participate in TUE (Graphical Abstract). The proportion of change was highest among those who answered “undecided” before reading the explanation. It is vital to ensure that information about the merits and demerits of TUE reaches those who are “undecided” about participation.
Graphical Abstract
Acknowledgments
We acknowledge the staff of Fukushima Prefecture, Fukushima Medical University, and the residents who participated in this survey.
Author contribution
Conception of the work: all authors
Data analysis and interpretation: all authors
Data curation: all authors
Drafting of the article: YK
Critical revision of the article: all authors
Final approval of the version to be published: all authors
Conflict of interest
The authors declare no conflicts of interest in relation to this study.
Funding sources
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
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