Red bone marrow dose estimation using several internal dosimetry models for prospective dosimetry-oriented radioiodine therapy.

The aim of the present study was to review the available models developed for calculating red bone marrow dose in radioiodine therapy using clinical data. The study includes 18 patients (12 females and six males) with metastatic differentiated thyroid cancer. Radioiodine tracer of 73 ± 16 MBq 131I was orally administered, followed by blood sampling (2 ml) and whole-body scans (WBSs) done at several time points (2, 6, 24, 48, 72, and ≥ 96 h). Red bone marrow dose was estimated using the OLINDA/EXM 1.0, IDAC-Dose 2.1, and EANM models, the models developed by Shen and co-workers, Keizer and co-workers and Siegel and co-workers, and Traino and co-workers, as well as the single measurement model (SMM). The results were then compared to the standard reference model Revised Sgouros Model (RSM) reported by Wessels and co-workers. The mean dose deviations of the Traino, Siegel, Shen, Keizer, OLINDA/EXM, EANM, SMM, and IDAC-Dose 2.1 models from the RSM were - 17%, - 24%, 6%, - 29%, - 15%, 40%, 48%, and - 8%, respectively. The statistical analysis demonstrated no significant difference between the results obtained with the RSM and with those obtained with the Shen, Traino, OLINDA/EXM, and IDAC-Dose 2.1 models (t test; pvalue > 0.05). However, a significant difference was found between RSM doses and those obtained with the EANM, SMM, and Keizer models (t test; pvalue < 0.05). The correlation between red marrow dose from the SMM and EANM models was modest (R2 = 0.65), while the crossfire dose calculated with the OLINDA/EXM and IDAC-Dose 2.1 models were in good agreement with each other and with the reference model. The findings obtained indicate that most of the dosimetry models can be used for a reliable dosimetry, and the calculated total body doses can be considered as a reliable non-invasive option for a conservative activity planning. In addition, the excellent performance of the IDAC-Dose 2.1 model will be of particular importance for a practical and accurate dosimetry, with the advantages of allowing for the use of realistic advanced phantoms and updated dose fractions, and of providing information about the blood dose contribution to the red bone marrow.

Evaluation of radiation safety in (177)Lu-PSMA therapy and development of outpatient treatment protocol.

The aim of this study is to investigate the outpatient treatment protocol and radiation safety of a new-emerging lutetium-177 ((177)Lu) prostate specific membrane antigen (PSMA) therapy. This work analyzed the dose rate of 23 patients treated with 7400 MBq (177)Lu-PSMA at different distances (0, 0.25, 0.50, 1.0 and 2.0 m) and variable time marks (0, 1, 2, 4, 18, 24, 48 and 120 h) after the termination of infusion. Blood samples were withdrawn from 17 patients within the same group at 3, 10, 20, 40, 60 and 90 min and 2, 3, 24 h after termination of infusion. Seven different patients were asked to collect urine for 24 h and a gamma well counter was used for counting samples. Family members were invited to wear an optically stimulated luminescence dosimeter whenever they were in the proximity of the patients up to 4-5 d. The total dose of the medical team including the radiopharmacist, physicist, physician, nurse, and nuclear medicine technologist was estimated by an electronic personnel dosimeter. The finger dose was determined using a ring thermoluminescent dosimeter for the radiopharmacist and nurse. The mean dose rate at 1 m after 4 h and 6 h was 23 ± 6 µSv h(-1) and 15 ± 4 µSv h(-1) respectively. The mean total dose to 23 caregivers was 202.3 ± 42.7 µSv (range: 120-265 µSv). The radiation dose of the nurse and radiopharmacist was 6 and 4 µSv per patient, respectively, whereas the dose of the physicist and physician was 2 µSv. The effective half life of blood distribution and early elimination was 0.4 ± 0.1 h and 5 ± 1 h, respectively. Seven patients excreted a mean of 45% (range: 32%-65%) from the initial activity in 6 h. Our findings demonstrate that (177)Lu-PSMA is a safe treatment modality to be applied as an outpatient protocol, since the dose rate decreases below the determined threshold of <30 µSv h(-1) after approximately 5 h and degrades to 20 µSv h(-1) after 6 h.

Indirect assessment of the maximum empirical activity (250 mCi) with respect to dosimetry concepts in radioiodine therapy of metastatic differentiated thyroid cancer.

AIM: The development of reliable dosimetry models promotes the individualized therapy concept toward more success and less complications. This paper evaluates the traditional maximum empirical activity (250 mCi) and the benefit of joining two dosimetry approaches to optimize the therapeutic activity and radioiodine efficacy in metastatic differentiated thyroid cancer. MATERIALS AND METHODS: Nineteen (12 females and seven males) patients with metastatic differentiated thyroid cancer were included in the present study. The mean age of the patients was 46±16 years. The mean height and weight were 1.67±0.11 m and 76±18 kg, respectively. Radioiodine treatment was given by recombinant human thyrotropin stimulation in seven patients, and thyroxine withdrawal was successful for the rest 12 patients. The mean thyroid-stimulating hormone value was 68±34 µIU/ml, and the mean thyroglobulin value was 408±356 ng/ml before therapy. After radiotracer administration, lesion-absorbed dose was calculated in addition to red marrow dose estimation via two different models. RESULTS: Total body and blood residence time was found to be 30±17 and 4.5±1.9 h, respectively. Red marrow absorbed dose was 0.535±0.262 Gy/100 mCi using the model accounts for red marrow dose surrogated by blood, and it was 0.398±0.212 Gy/100 mCi using a modified model with mean deviation of -24% (range: -19 to -31%). Red marrow absorbed dose was found to be 0.50±0.15 Gy/100 mCi in the levothyroxine withdrawal group, whereas it was 0.46±0.2 Gy/100 mCi for the patients who received recombinant human thyrotropin. Mean lesion-absorbed dose was 0.16±0.14 Gy/g/mCi. The speculated dose from 250 mCi iodine-131 was evaluated, as 65% of all lesions (n=27) would receive at least 100 Gy, whereas the percentage of bone lesions that would receive at least 100 Gy was only 55%. CONCLUSION: Upon to this study, red marrow dose varies with type of preparation as that of medication withdrawal cases was slightly higher than exogenous thyroid-stimulating hormone. Involvement of lesion and red marrow dose assessment through dosimetry protocol seems indeed valuable to optimize safe and effective activity compared with the conventional regime with 250 mCi as maximum empirical activity.

Effects of hemodialysis on iodine-131 biokinetics in thyroid carcinoma patients with end-stage chronic renal failure.

OBJECTIVES: Radioiodine therapy could be challenging in chronic renal failure patients requiring hemodialysis. The aim of this study was to establish the effects of hemodialysis on elimination of radioiodine from the body in thyroid carcinoma patients with end-stage chronic renal failure and to determine its effects on environmental radiation dose. MATERIALS AND METHODS: Three end-stage chronic renal failure patients (four cases) diagnosed with differentiated thyroid carcinoma requiring radioiodine therapy were included in our study. Each patient was given 50-75 mCi (1850-2775 MBq) iodine-131 with 50% dose reduction. Dose rate measurement was performed at the 2nd, 24th, and 48th hour (immediately before and after hemodialysis) after radioiodine administration. The Geiger-Müller probe was held at 1 m distance at the level of the midpoint of the thorax for the dose rate measurement. RESULTS AND CONCLUSION: The effective half-life of iodine-131 for three patients was found to be 44 h. In conclusion, the amount of radioiodine excreted per hemodialysis session was calculated to be 51.25%.

Determining and Managing Fetal Radiation Dose from Diagnostic Radiology Procedures in Turkey.

OBJECTIVE: We intended to calculate approximate fetal doses in pregnant women who underwent diagnostic radiology procedures and to evaluate the safety of their pregnancies. MATERIALS AND METHODS: We contacted hospitals in different cities in Turkey where requests for fetal dose calculation are usually sent. Fetal radiation exposure was calculated for 304 cases in 218 pregnant women with gestational ages ranging from 5 days to 19 weeks, 2 days. FetDose software (ver. 4.0) was used in fetal dose calculations for radiographic and computed tomography (CT) procedures. The body was divided into three zones according to distance from the fetus. The first zone consisted of the head area, the lower extremities below the knee, and the upper extremities; the second consisted of the cervicothoracic region and upper thighs; and the third consisted of the abdominopelvic area. Fetal doses from radiologic procedures between zones were compared using the Kruskal-Wallis test and a Bonferroni-corrected Mann-Whitney U-test. RESULTS: The average fetal doses from radiography and CT in the first zone were 0.05 ± 0.01 mGy and 0.81 ± 0.04 mGy, respectively; 0.21 ± 0.05 mGy and 1.77 ± 0.22 mGy, respectively, in the second zone; and 6.42 ± 0.82 mGy and 22.94 ± 1.28 mGy, respectively, in the third zone (p < 0.001). Our results showed that fetal radiation exposures in our group of pregnant women did not reach the level (50 mGy) that is known to increase risk for congenital anomalies. CONCLUSION: Fetal radiation exposure in the diagnostic radiology procedures in our study did not reach risk levels that might have indicated abortion.

The evaluation of urine activity and external dose rate from patients receiving radioiodine therapy for thyroid cancer.

The aim of this study was to determine the external dose rate of iodine retention as a function of time in the bodies of thyroid cancer patients during their isolation period in the hospital. Urine samples were collected at 6th, 12th, 18th, 24th h and 2nd, 3rd, 4th, 5th d from 83 patients after oral administration of (131)I and counted. The external dose rates were also simultaneously determined at the same time points. Then, it was expressed as retained radioiodine body activity versus dose rate. Effective half life calculated from urine sample measurements was found as 18.4±1.8 h within the first 24 h and 64±2.7 h between 48 and 120 h. According to this results, the external dose rate (<20 µSv h(-1)), which patients could be discharged, was achieved after 48 h for 3700 and 5550 MBq, and after 72 h for 7400 MBq of (131)I treatments.