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Now, two new studies find that a safer, lower dose of radioactive iodine is just as effective as the higher dose at getting rid of any such cells that remain after surgery.
The research also found that patients were just as likely to have their thyroid shrunk away if they took a drug called Thyrogen (thyrotropin) as if they underwent thyroid hormone withdrawal -- which leads to fatigue, pain and weight gain -- before embarking on the radioiodine treatment.
The two studies, published in the May 3 issue of the New England Journal of Medicine, compared low- and high-dose radioactive iodine in a total of more than 1,000 patients. The participants, from Britain and France, also received either Thyrogen or thyroid hormone withdrawal as part of the therapy.
In either study, the researchers found that patients who received the low-dose (30 millicuries) of radioactive iodine in combination with Thyrogen were just as apt to have their remaining thyroid cells mopped up -- with fewer side effects -- than patients who received higher-dose (100 millicuries ) radioiodine along with either Thyrogen or hormone withdrawal.
However, the researchers say they plan on monitoring the patients for several years to see if rates of cancer recurrence are similar in the different groups.
"We try to give the lowest possible effective radiation dose so that we cure the current cancer, but we do not increase the risk of producing a second cancer resulting from the radiation itself," explained Dr. Ujjal Mallick, an oncologist at the Northern Centre for Cancer Care in Newcastle upon Tyne, in England, and lead author of the UK study.
"Our study shows that clinicians can consider low-dose radioactive iodine in selected patients that have up to a four-centimeter tumor in the thyroid gland that has not spread outside the neck and have been operated on by expert surgeons," Mallick said.
The number of people diagnosed with thyroid cancer has been on the rise in the past decade, and there will be more than 56,000 new cases in the United States in 2012, according to the American Cancer Society's estimate. The disease, which is highly curable if caught early, affects more women than men, with patients tending to be diagnosed in their 40s and 50s.
The new studies suggest that, "we can spare a lot of young patients by using low-dose radioactive iodine," Mallick said.
However, Dr. David Cooper, an endocrinologist at Johns Hopkins School of Medicine in Baltimore, said that patients under 45 probably can probably avoid radioactive iodine altogether if their tumors are small (less than 2 centimeters) and the cancer has not spread to other parts of their body. Cooper was not involved in the new studies.
In fact, some of the low-risk patients in the current studies might not have needed radioactive iodine treatment at all, Cooper said.
"The chance that a person with low-risk thyroid cancer is going to come back in a year or two with recurrence is no different whether they got radioactive iodine or not," Cooper said.
In low-risk cases, the whole point of radiation treatment is more about getting rid of the normal tissue, which makes monitoring patients for recurrence easier, and less about wiping out disease, which surgery usually takes care of, Cooper said. However tests are usually sensitive enough to pick out recurrence even in patients who do not receive radiation to help eliminate their thyroid.
The research, led by Mallick and his colleagues, involved 421 patients at 29 centers in the U.K. who had thyroid cancer that had not spread outside the neck. The other study looked at 684 patients in France who had small thyroid tumors that had not metastasized (spread) beyond the neck.
All of the patients had undergone surgery to remove the bulk of their thyroid gland and were receiving thyroid hormone therapy to replace the natural thyroid hormone.
In both studies, researchers found that the rates of effective thyroid reduction in the months after treatment were similar in both the low- and high-dose groups.
Mallick and his colleagues found that about 84 percent of patients who received low-dose radioactive iodine along with Thyrogen had undetectable levels of thyroid tissue six to nine months later, compared with about 90 percent in the high-dose-plus-Thyrogen group and about 88 percent in the high-dose-plus-hormone-withdrawal group.
"These studies are not all that earth shattering" because smaller studies have shown that low-dose therapy is effective, Cooper said. "However these studies add something because they involve hundreds of people that were monitored carefully."
Many doctors in the United States are already using Thyrogen for thyroid ablation because patients feel awful during the weeks of thyroid hormone withdrawal leading up to radioactive iodine therapy, Cooper said.
However, a major problem with radioactive iodine treatment in the United States is that doctors use it in patients outside of the 2009 American Thyroid Association recommendations, which state that radioiodine should be used for certain people with tumors larger than 1 centimeter that have other properties, such as invasiveness, Cooper said. (Cooper was the lead author of these recommendations).
The current studies could help doctors at least see that a large dose of radioactive iodine is not necessary, Cooper said.
For his part, Mallick said, "In our hospital, we are going to start to implement the low-dose radioactive iodine for patients who match the criteria in the study."
He and his collaborators are about to start a new trial comparing low-dose with no radioiodine to see if radiation is necessary in selected low-risk patients after surgery. "This will answer a question that has plagued clinicians for several decades," he said.
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