41Thyroid Cancers in Fukushima: Critical Review and Analysis of the 1st and 2nd Round Examination

Background After the Fukushima–Daiichi nuclear power plant (NPP) disaster, thyroid ultrasound examination (TUE) has been performed in subjects who were aged ≤18 years. Previous studies reported controversial results. Through critical review, three limitations were identified: arbitrary grouping of 59 municipalities, 2) usage of region as proxy of dose, and 3) separate analyse of the 1st and 2nd round data. Methods To overcome these limitations, this study examined the relationship between radiation dose and the number of participants with thyroid malignancy, using publicly available municipality level data (N = 59). To analyse two wave screening data, multi-level random-effect Poisson regression model was applied. The number of participants with thyroid malignancy was explained by dose estimates. Interaction between dose and screening round dummy (0 for the 1st and 1 for the 2nd) was also introduced to take into account latency. Results Interaction terms between external dose (Akahane et al. 2013) and screening round dummy were positive and significant (β = 0.681, z = 2.05). Similar results were obtained for UNSCEAR estimated thyroid dose (UNSCEAR 2013) (β = 0.128, z = 2.24) and re-estimated thyroid dose (Suzuki et al. 2018) (β = 0.215, z = 2.42). Conclusions These robust results are consistent with the conjecture that the 1st round TUE is the “baseline” that will not correlated with radiation level and the 2nd round TUE detected thyroid cancer caused by radiation from Fukushima NPP that distributed heterogeneously among regions. Key messages This was an ecological study at the municipality level, the results should be examined with individual level data.

Assessment of Thyroid Cancer Risk After Cervical Computed Tomography: The Impact of Bismuth Shielding

Background: Computed tomography (CT) is vastly applied in X-ray procedures because of its high quality in detecting the anatomical structures of the body. However, it leads to an increase in patient dose, resulting in carcinogenesis. In the head and neck CT, the thyroid is the most important at-risk organ. The aim of this study was to estimate thyroid cancer risk in cervical CT with and without a bismuth shield. Materials and Methods: After obtaining permission from the authors, data related to the thyroid dose of patients undergoing cervical CT in the study by Santos et al (2019) were used, and then thyroid cancer risk was calculated for different ages at exposure in male and female patients using the biological effects of the ionizing radiation (BEIR) VII model. Results: Using bismuth shielding reduced thyroid dose by 37% and 39% in male and female phantoms, respectively. Thyroid cancer estimation demonstrated that the risk was nearly two-fold in females compared to males. Finally, bismuth shielding reduced 40% of cancer risk, and it decreased in both genders by increasing age at exposure. Conclusion: According to our findings, excess relative risk (ERR) up to 0.06% was associated with cervical CT. Although ERR amounts were low, the effect of radiation on thyroid cancer risk should not be neglected. Accordingly, it is suggested that future trials use bismuth shielding to reduce thyroid cancer risk.

Comparison of thyroid doses to the public from radioiodine following the Chernobyl and Fukushima accidents

Estimates of thyroid doses to the public from radioiodine intake following the accidents at Chernobyl and Fukushima Daiichi nuclear power plants are compared. The basis for thyroid dose estimates after the Chernobyl accident was a large set of measurements of 131I thyroidal content for approximately 400,000 residents in Belarus, Ukraine, and Russia. Due to a lack of direct thyroid measurements after the Fukushima accident (just over 1000 residents were measured), thyroid doses were estimated based on ecological models and are therefore associated with much higher uncertainty than those based on direct thyroid measurements. Thyroid dose estimates for evacuees were up to 50,000 mGy for Chernobyl and up to approximately 100 mGy for Fukushima. This large difference in thyroid dose to the public is mainly due to the different dominant pathways of radioiodine intake: ingestion of fresh, locally produced cows’ milk (Chernobyl) and inhalation of contaminated air (Fukushima).

A comparison of thyroidal protection by iodine and perchlorate against radioiodine exposure in Caucasians and Japanese

Radioactive iodine released in nuclear accidents may accumulate in the thyroid and by irradiation enhances the risk of cancer. Radioiodine uptake into the gland can be inhibited by large doses of stable iodine or perchlorate. Nutritional iodine daily intake may impact thyroid physiology, so that radiological doses absorbed by the thyroid as well as thyroid blocking efficacy may differ in Japanese with a very rich iodine diet compared to Caucasians. Based on established biokinetic–dosimetric models for the thyroid, we derived the parameters for Caucasians and Japanese to quantitatively compare the effects of radioiodine exposure and the protective efficacy of thyroid blocking by stable iodine at the officially recommended dosages (100 mg in Germany, 76 mg in Japan) or perchlorate. The maximum transport capacity for iodine uptake into the thyroid is lower in Japanese compared to Caucasians. For the same radioiodine exposure pattern, the radiological equivalent thyroid dose is substantially lower in Japanese in the absence of thyroid blocking treatments. In the case of acute radioiodine exposure, stable iodine is less potent in Japanese (ED50 = 41.6 mg) than in Caucasians (ED50 = 2.7 mg) and confers less thyroid protection at the recommended dosages because of a delayed responsiveness to iodine saturation of the gland (Wolff–Chaikoff effect). Perchlorate (ED50 = 10 mg in Caucasians) at a dose of 1000 mg has roughly the same thyroid blocking effect as 100 mg iodine in Caucasians, whereas it confers a much better protection than 76 mg iodine in Japanese. For prolonged exposures, a single dose of iodine offer substantially lower protection than after acute radioiodine exposure in both groups. Repetitive daily iodine administrations improve efficacy without reaching levels after acute radioiodine exposure and achieve only slightly better protection in Japanese than in Caucasians. However, in the case of continuous radioiodine exposure, daily doses of 1000 mg perchlorate achieve a high protective efficacy in Caucasians as well as Japanese (> 0.98). In Caucasians, iodine (100 mg) and perchlorate (1000 mg) at the recommended dosages seem alternatives in case of acute radioiodine exposure, whereas perchlorate has a higher protective efficacy in the case of longer lasting radioiodine exposures. In Japanese, considering protective efficacy, preference should be given to perchlorate in acute as well as prolonged radioiodine exposure scenarios.

Effect of change in neck position on thyroid dose and volume in supraclavicular irradiation for breast cancer using conformal technique

Background and aim: Radiation exposure to the thyroid gland during breast irradiation can lead to hypothyroidism and this can impact on the quality of life. The aim of this study was to analyse if there is any difference in the radiation dose received by the thyroid gland during supraclavicular irradiation for breast cancer, with two different neck positions—straight or when the head is turned to the contralateral side to the breast being treated, when using a conformal technique. Materials and methods: All patients who received chest wall/breast and supraclavicular irradiation for breast cancer in 2019 in our department were divided into two groups based on the neck position as SN (neck positioned straight) and TN (neck tilted to contralateral side). The volume of thyroid gland, the radiation dose and volume parameters for Dmax, Dmean, and V5 to V40 of the thyroid were tabulated. Results: There were 72 patients included in the study with a mean age of 59 years, with 39 in the SN group and 33 in the TN group. There was no significant difference in thyroid volume between the two groups. Dmean, V15, V20, V25, V30 and V35 were significantly lower in tilted neck patients as compared to straight neck patients. Conclusion: Neck positioned to the contralateral side of the breast primary may be recommended for conformal CT-based radiation planning.

Radiation Exposure to the Thyroid After the Chernobyl Accident

IntroductionThe Chernobyl accident resulted in a considerable release of radioactivity to the atmosphere, particularly of Iodine-131 (131I), with the greatest contamination occurring in Belarus, Ukraine, and western part of Russia.Material and MethodsIncrease in thyroid cancer and other thyroid diseases incidence in population exposed to Chernobyl fallout in these counties was the major health effect of the accident. Therefore, a lot of attention was paid to the thyroid doses, mainly, the 131I intake during two months after the accident. This paper reviews thyroid doses, both the individual for the subjects of radiation epidemiological studies and population-average doses. Exposure to 131I intake and other exposure pathways to population of affected regions and the Chernobyl cleanup workers (liquidators) are considered.ResultsIndividual thyroid doses due to 131I intake varied up to 42 Gy and depended on the age of the person, the region where a person was exposed, and their cow’s milk consumption habits. Population-average thyroid doses among children of youngest age reached up to 0.75 Gy in the most contaminated area, the Gomel Oblast, in Belarus. Intake of 131I was the main pathway of exposure to the thyroid gland; its mean contribution to the thyroid dose in affected regions was more than 90%. The mean thyroid dose from inhalation of 131I for early Chernobyl cleanup workers was estimated to be 0.18 Gy. Individual thyroid doses due to different exposure pathways varied among 1,137 cleanup workers included in the epidemiological studies up to 9 Gy. Uncertainties associated with dose estimates, in terms of mean geometric standard deviation of individual stochastic doses, varied in range from 1.6 for doses based on individual-radiation measurements to 2.6 for “modelled” doses.ConclusionThe 131I was the most radiologically important radionuclide that resulted in radiation exposure to the thyroid gland and cause an increase in the of rate of thyroid cancer and other thyroid diseases in population exposed after the Chernobyl accident.