Saturday, May 24, 2014

Dental X-rays and Thyroid Cancer

In my first blog, I talked about the increased risk of thyroid cancer from childhood therapeutic radiation. This therapeutic radiation was used for acne treatment, lymphoma, Hodgkin’s, and tonsil cancers. I mentioned however that since the 1950’s, therapeutic radiation has only been used in children in cases of morbidity and mortality. But if these therapeutic radiations have decreased, why is the incidence increasing?
As I mentioned in another blog, the increase in incidence numbers seems to result mostly from an increase and advancement in diagnostic technology, however the author of that research does not completely rule out the possibility that there could be other health determinants that are also contributing to this rise. Because of this I looked into other forms of radiation that patients of all ages are subjected to and I came across and article that looked into the effects of dental x-rays on thyroid cancer.
The article written by Memnon et al. described a case-control study, which looks back into causal attributes of two groups (disease and not diseased), that was performed to observe this relationship. Patients in Kuwait, a country with a relatively high incidence of thyroid cancer , were used for this study. Cases were identified as patients who were residents of Kuwait with primary thyroid cancer who were alive and entered into the cancer registry via the International Classification of Disease for Oncology. Population Controls, who were selected form local primary health clinics, were individually matched to a Case. The data was collected through a questionnaire which included medical histories of any type of diagnostic x-rays (including Dental x-ray) and the number of exposures, reproductive history, family history, diet, and any other sociodemographic characteristics. Dose response patterns for number of dental x-ray exposures was generates as well as an analysis of odds ratios. The study found that there was a two-fold increase risk of thyroid cancer in patients who were exposed to dental x-rays (Table II).They also saw a dose response pattern which showed an increase risk of thyroid cancer with an increase in number of exposures to dental x-ray (Table II).

            While these results are intriguing, in studies such as this case-control study, there can be many biases that come into play such as recall bias, in which the patient with the disease may know more about there medical history that those without the disease because of their health situation. The large sample size of thyroid cancer patients in Kuwait, however, gives this study a leg up.  Even so, it is very difficult to be completely certain of causality, therefore the study can conclude that dental x-rays can only be considered a risk factor of thyroid cancer. Nonetheless, perhaps merely identifying risk factors and becoming aware of them in our present environment could contribute to lowering incidence rates and mortality rates of thyroid cancer.

Memon, Anjum, Sara Godward, Dillwyn Williams, Iqbal Siddique, and Khalid Al-Saleh. "Dental X-rays and the Risk of Thyroid Cancer: A Case-control Study." PubMed. NCBI, 2010. Web. 22 May 2014.