8th Baltic Congress of Radiology

Nuclear Medicine

oral abstract

Thyroid cancer and thyrotoxicosis can be treated with radioactive iodine therapy using the radiopharmaceutical I-131, but successful treatment requires thyroid uptake measurements. Thyroid uptake measurements in I–131 therapy planning are non-invasive measurements that are used to determine the fraction of I-131 taken up by the thyroid at selected times after ingestion. The measurements provide support in determining the activity of I-131 to be administered to patients for therapy.The concentration of I-131 in the thyroid is impacted by such factors as medication (e.g., thyroid hormones, antithyroid medication, amiodarone, and betadine) and food that contains iodine (e.g., kelp).

Although most measurements are observed with uptake within the expected range, there are exceptions. It is therefore important to look at both measurements where there are no problems and measurements where there are apparent deviations. In the case of Riga East University Hospital, the approximate number of measurements per month is 100, where the measurements are performed using a planar small-field gamma camera with thyroid uptakes of the I-131 examination method. The representations of the uptakes are based on several measurement points of reference I-131 and patient-thyroid image pairs. The uptake is calculated by applying different algorithms, which use such parameters as half-life, geometric values, and count rate. The analysis of previous measurements also examined whether the treatment is planned for thyrotoxicosis or thyroid oncology. This has implications for the activity of I-131 used in the measurements, the measurement process, and the expected uptake. This breakdown provided additional information on possible causes for deviations. All examinations were carefully evaluated, and additional information was collected from patients if any abnormalities were observed. All the information collected was recorded and prepared for further evaluation and summarization.

In the case of I-131 uptake measurements made in advance of radioiodine ablation of residual thyroid tissues after thyroidectomy, as expected the uptake in most cases was largely decreased. Another less prevalent factor (a few cases a year) that impacted the thyroid uptake measurements was the size of the thyroid, which lead to incorrect centering. In order to assess the location of the thyroid gland and obtain an anatomical reference, it is necessary to mark the fossa jugularis as accurately as possible with a radioactive marker. But this cannot always be perfectly assessed due to the anatomical characteristics of the patient where it is difficult to feel the jugular fossa and mark it correctly. Another factor affecting the measurements that were observed in clinical practice was that the neck was not being stretched enough or being overstretched. Some measurements showed an effect of motion on the measurement results. Although all patients are informed in advance about the preparation before the measurements, there were cases where the patient had taken iodine-containing medication shortly before the measurements. Patients do not always realize that the medicaments they are taking may contain iodine, so it is necessary to pay close attention to the medications they are taking. In one case, the uptake was very low precisely because the patient was taking a medicine for neck pain that contained iodine. Occasionally, a CT scan using an iodine-containing contrast medium is performed recently and thus the I-131 uptake is impacted. The same is true for diet: although it is less common to see cases where dietary instructions are not followed, it is still essential to pay attention to them. In some cases, shifts were observed in the gamma chamber uniformity and hence there was a shift in the measured values.

To prevent decreased I-131 uptake, it is important to inform patients about the preparation for measurement and the measurement procedure. It is also necessary to clarify in advance what medications have been taken in the last month, whether iodine-containing contrast media have been used and whether iodine-containing foods have been consumed in the last two weeks. It is also important to pay attention to the technical condition of the equipment and to carry out regular repairs and maintenance. As in some cases, shifts were observed in the gamma chamber uniformity and hence there were shifts in the measurements. It is important to record all cases where deviations are observed to reduce the likelihood of preventable recurrences.

Thyroid cancer and thyrotoxicosis can be treated with radioactive iodine therapy, but successful treatment requires thyroid uptake measurements. To improve the effectiveness of the measurements, patients are informed about the preparatory procedure, but the measurements do not always show an I-131 uptake, so it is necessary to identify all of the factors. The results show that one of the most common preventable factors affecting I-131 uptake is iodine-containing medicines and foods.

1227