Radiation Exposure to Relatives of Patients Treated with Iodine-131 for Thyroid Cancer at Siriraj Hospital.

OBJECTIVE: Thyroid cancer patients treated with 1-131 are potential source of radiation exposure to relatives who are knowingly and willingly exposed to ionizing radiation as a result of providing comfort to patients undergoing I-131 therapy. This study aims to determine radiation dose received by relatives who care for non self-supporting 1-131 patients at Siriraj Hospital. MATERIAL AND METHOD: Twenty caregivers of 20 patients underwent I-131 therapy for thyroid cancer with a standard protocol were given specific instructions with regard to radiation safety and provided with electronic digital dosimeter to continuously measure radiation dose received on daily basis, three days in the hospital. On the day patient is released, thyroid uptake estimates were performed to assess internal radiation dose received by caregivers. RESULTS: The 3-day accumulative doses to caregivers to patients receiving 150 mCi (n = 11) and 200 mCi (n = 9) of I-131 ranged from 37 to 333 uSv and 176 to 1,920 pSv respectively depending on the level of supports required. Thyroid uptake estimates in all caregivers were undetectable. Dosimeter indicated a maximum whole-body dose of1.92 mSv was more than the public dose limit of] mSv but within the dose constraint of 5 mSv for caregivers. DISCUSSION: Radiation dose to caregivers of a non self-supporting hospitalized patient undergoing 1-131 therapy were well below the limits recommended by the ICRP. The patients can be comforted with confidence that dose to caregivers will be less than the limit. CONCLUSION: This study provides guidance for medical practitioners to obtain practical radiation safety concerns associated with hospitalized patients receiving I-131 therapy especially when patient needs assistance.

Total Effective Dose Equivalent to Caregivers from Hospitalized Patients Treated with High Dose Radioiodine for Thyroid Carcinoma.

Thyroid cancer patients treated with high-dose radioactive iodine (3.7-7.4 GBq) are different from other people because after the administration, the radionuclide I-131 is excreted via urine, feces, saliva and breathing, and also via exposure to other patients. Caregivers of the patient may receive higher radiation doses than normal. The purposes of this study were to estimate the total effective dose equivalent from internal and external exposure to caregivers of patients treated with high dose I-131 admitted at Siriraj Hospital, and to compare the estimated dose with the dose constraint of 5 mSv per annum for caregivers. Thirteen caregivers of 13 patients who underwent radioiodine therapy for thyroid cancers following a standard protocol were given specific instructions with regard to radiation safety and were attached to an electronic personal dosimeter and a personal air sampler pump continuously to measure received radiation dose on a daily basis over three days in the hospital. On discharge day, caregivers were asked to perform an in vivo bioassay by the thyroid uptake instrument. The results from the thirteen caregivers were divided into 3 groups. The total effective dose equivalent to caregivers of patients administered 3.7 GBq (n = 1), 5.55 GBq (n = 9), and 7.4 GBq (n = 3) were 0.159 mSv, 0.123 to 0.629 mSv, and 0.631 to 0.718 mSv, respectively. There values were well below 5 mSv per episode as proposed in the IAEA Safety Reports Series No. 63 and the ICRP Publication 103.

A comparison of the diagnostic performance of half-time SPECT and multiplanar pelvic bone scan in patients with significant bladder artifacts.

OBJECTIVES: The objective of this study was to evaluate the diagnostic performance of half-time single-photon emission computed tomography (SPECT) in the interpretation of bone scans in patients with bladder artifacts in comparison with multiplanar imaging. We also investigated whether SPECT could reduce the radiation dose to nuclear medicine personnel and shorten the acquisition time. MATERIALS AND METHODS: Data from 29 patients with significant bladder artifacts were assessed by two nuclear medicine physicians. The presence or absence of pelvic bone lesions was individually interpreted with both techniques, multiplanar imaging and half-time SPECT, using a three-point pelvic score as follows: 0=definitely no lesion, 1=indeterminate, 2=definite positive lesion. A comparison of the diagnostic performances between the two techniques was made. The radiation dose to personnel and acquisition time were also investigated. RESULTS: Using half-time SPECT, the incidence of studies interpreted without interference from bladder artifacts (artifact-free image) was 100% on both patient-based and lesion-based analyses of 29 patients, whereas multiplanar imaging revealed incidences of 52 and 90% on patient-based and lesion-based analyses, respectively. Ninety percent of technologists and 58% of assistants received 1 µSv/case radiation dose while performing multiplanar imaging. Only 10% of technologists received 1 µSv/case and none of the assistants received a detectable radiation dose from SPECT. The SPECT technique could also reduce the examination time, particularly when positioning time was included. CONCLUSION: Half-time SPECT can significantly improve the diagnostic confidence of interpreting equivocal pelvic lesions in patients with bladder artifacts, compared with multiplanar imaging. This technique also provides lower radiation dose to nuclear medicine staff and requires shorter examination time.

A prospective randomized study of the efficacy and cost-effectiveness of high and low dose regimens of I-131 treatment in hyperthyroidism.

OBJECTIVE: To compare the efficacy and cost-effectiveness of high and low dose regimens of I-131 treatment in patients with hyperthyroidism. MATERIAL AND METHOD: One hundred fifty patients with proven hyperthyroidism were randomly allocated into the high (74 patients) and low (76 patients) dose regimen of I-131 treatment. Four patients of the high dose group and one patient of the low dose group were excluded because of lost follow-up. A gland-specific dosage was calculated on the estimated weight of thyroid gland and 24-hour I-131 uptake. The high and low I-131 dose regimens were 150 microCi/gm and 100 microCi/gm, respectively. The first mean radioiodine activity administered to the high and low dose group was 10.2 and 8 mCi, respectively. Repeated treatment was given to 25 patients of the high dose group and 40 patients of the low dose group. Clinical outcome and calculated costs for outpatient attendances, and laboratory tests together with initial and subsequent treatments were evaluated for one year after I-131 treatment. Elimination of hyperthyroidism that resulted in either euthyroidism or hypothyroidism was classified as therapeutic success. The cost effectiveness was also compared. RESULTS: At 6 months after treatment, 45 (64.3%) patients receiving high dose and 59 (78.7%) patients receiving low dose were hyperthyroidism. Clinical outcome at one year showed persistence of hyperthyroidism in 21 (30%) patients of the high dose regimen and 36 (48%) patients of the low dose regimen. At one year post treatment, it was demonstrated that the high dose regimen could eliminate hyperthyroidism in a significantly shorter time than the low dose regimen, i.e., 259.6 days and 305.5 days, respectively, p = 0.008). For the persistent hyperthyroid patients, the average total cost of treatment in the low dose group was significantly higher than that of the high dose group, i.e., 13,422.78 baht and 10,942.79 baht, respectively; p = 0.050). CONCLUSION: A high dose regimen of radioactive iodine treatment is more effective than the low dose regimen. The successful outcome of a high dose regimen occurred significantly earlier than that of the low dose regimen. For the persistent hyperthyroid patients, the average total cost in the low dose group was significantly higher than that of the high dose group.