sweden的可是有详细医疗记录/史的数据。
牙医的x光剂量是大于胸透，骨透的。而且是可能直接辐照到甲状腺的。所以他们的建议仍然是能用digital 的就用（相对剂量小），能要那个collar的也要。减少不必要的暴露是第一位的。
他不是说了么，
Even with a near tripling of the female incidence rate in the past 30 years,
it is small compared with the cancer rates for lung, colon, breast or prostate cancer.
Much of this increase is thought to be the result of the increased medical imaging of the thyroid. It is not so much that there are more thyroid cancers, as that more thyroid cancers are being discovered or diagnosed. Use of CAT scans, MRI scans and thyroid ultrasound has dramatically increased over the past 30 years. These tests can detect very small thyroid nodules that several decades ago would not have been found.
甲癌并没有显著增加，不管是同比还是相比。
协和的里面没有直接辐照甲状腺，而且还隔着楼板呢。不能把楼板当空气吧。