An investigation into internal exposure management needs for nuclear medicine practitioners and temporary visitors through I-131 internal dose assessment: Focusing on large hospitals in South Korea

Purpose

To investigate the internal exposure of nuclear medicine practitioners in South Korea.

Methods

This study selected nuclear medicine practitioners among domestic hospitals and quantitatively measured their degree of internal exposure to radioisotopes, and conducted a dose assessment based on the results. For the dose assessment, 35 nuclear medicine practitioners at seven large hospitals were selected as the measurement subjects, and the measurements were obtained using the thyroid count, total body count, and a urine sample analysis. The internal exposure was measured once every two weeks, and measurements were obtained three to 15 times according to the practitioners.

Results

As a result of measuring and analyzing the radionuclides with urine samples, one or more detections above the minimum detectable activity (MDA) was identified in 52 (15%) among all 340 cases for 14 of the practitioners (43%). The committed effective doses were evaluated as have a distribution of zero to 5.4 mSv, and were mostly 1 mSv or less. There were four practitioners exceeding 1 mSv based on the whole-body measurements, whose results from a urine sample analysis and thyroid monitoring all showed exposure of 1 mSv or less. All of the practitioners participated directly in the distribution and handling of radioactive sources, and none of the nurses exceeded 1 mSv. Furthermore, it was noteworthy that, among medical assistants who do not directly handle radioisotopes and are mainly involved in the transport of contaminated patients, there was one person who exceeded the whole-body measurement standard of 1 mSv.

Conclusions

The committed effective dose of most nuclear medicine practitioners who participated in the survey was lower than 1 mSv. However, because the possibility of overexposure under special circumstances cannot be completely excluded, new strict radiation protection rules on the handling of open-source radioisotopes in hospitals are required for non-handling workers.

Non-dehalogenation Mechanisms for Excretion of Radioiodine after Administration of Labeled Antibodies

In patients or mice with cancer the pharmacokinetic behavior of radioiodinated and radiometal chelated antibodies has been observed to be different. Rapid clearance from the tissues and excretion into the urine can occur after injection of radioiodinated antibodies. These observations have been interpreted to reflect in vivo dehalogenation of the antibody. This publication describes a variety of other mechanisms that can underlie these phenomena. These mechanisms include receptor uptake and catabolism of antibody and instability of the labeled antibody due to the labeling conditions. Specifically, the relative masses of chloramine-T and antibody in the iodination reaction mixture, the level of iodination of the antibody, and the amount of antibody administered to the recipient are all factors which can influence the clearance of radioiodinated antibody from the recipient. The final determinant for the different behavior of radioiodinated and In-111 metal chelated antibody relate to the different biologic pathways of indium when compared to iodine

Factors associated with serum thyroglobulin levels in a population living in Belarus

OBJECTIVE

Serum thyroglobulin (Tg) has been associated with a number of thyroid disorders and has been proposed as an indicator of iodine deficiency in a population. However, few studies have addressed the epidemiology of Tg in a population-based setting or in the context of exposure to radioactive iodine-131 (I-131). Our objective was to evaluate baseline levels of Tg in relation to sociodemographic characteristics, iodine status and thyroid function for individuals exposed to I-131.

DESIGN

A population-based cohort assembled in Belarus following the Chornobyl accident provided demographic factors, clinical data and physiological measurements.

PARTICIPANTS

Our analytical sample included 10,344 subjects of whom 7890 had no thyroid disease and 2454 had evidence of structural or functional thyroid abnormality.

MEASUREMENTS

Standardized assays were used to measure serum Tg, urinary iodine, TSH and antibodies to Tg and thyroid peroxidase. Ultrasound was used to assess the presence of nodules and estimate thyroid volume.

RESULTS

In the fully adjusted model, percent change in Tg was significantly increased among females, smokers and subjects of older age and Tg increased with decreasing urinary iodine concentration, increasing serum TSH and increasing thyroid volume (P-values for trend <0·0001), and presence of thyroid nodules (P < 0·05). We found a complex interaction between region of residence, rural/urban living, presence/absence of thyroid abnormalities and serum Tg (P < 0·0001).

CONCLUSIONS

In residents of Belarus, serum Tg is significantly related to presence of thyroid abnormalities as well as indicators of thyroid function and iodine deficiency and, therefore, could be used to characterize the iodine status and thyroid function of individuals in the context of epidemiological study.

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.

Estimation of intakes of 131I, 137Cs and 134Cs after the Chernobyl accident

Activities of (131)I and (137)Cs excreted in urine from two healthy males during May 1986, when contaminated air masses from Chernobyl arrived on the territory of the Czech Republic, were determined by bioassay. The data were used to estimate the intakes and committed effective doses from these radionuclides. The results for inhalation intakes are of particular interest, in the absence of sufficient contemporary data for airborne activity. They are found to be higher than initial estimates based on air sampling.

Tyrosine kinase inhibitors noncompetitively inhibit MCT8-mediated iodothyronine transport

CONTEXT

Tyrosine kinase inhibitors (TKI) are used for the treatment of various cancers. Case reports and clinical trials have reported abnormal thyroid function tests (TFT) after treatment with sunitinib, imatinib, sorafenib, dasatinib, and nilotinib. An increased requirement for levothyroxine was reported in thyroidectomized patients during TKI treatment.

OBJECTIVE

We hypothesized that abnormal TFT are compatible with inhibition of thyroid hormone (TH) transporters and subsequently reduced pituitary-TH feedback. Monocarboxylate transporter 8 (MCT8) is a TH transmembrane transporter in brain, pituitary, and other organs. MCT8 mutation leads to abnormal TFT in patients and respective mouse models. We tested whether TKI are able to inhibit MCT8-mediated TH uptake into cells.

DESIGN

Madin-Darby-canine kidney (MDCK1) cells stably expressing human MCT8 were exposed in vitro to TKI at increasing concentrations, and MCT8-mediated [(125)I]T(3) uptake and efflux were measured. The mode of inhibition was determined.

RESULTS

TKI exposure dose-dependently inhibited MCT8-dependent T(3) and T(4) uptake. IC(50) values for sunitinib, imatinib, dasatinib, and bosutinib ranged from 13-38 μm, i.e. similar to the Michaelis-Menten constant K(m) for T(3) and T(4), 4 and 8 μm, respectively. Kinetic experiments revealed a noncompetitive mode of inhibition for all TKI tested.

CONCLUSIONS

Partial inhibition by TKI of pituitary or hypothalamic TH feedback may increase TSH or increase the levothyroxine requirement of thyroidectomized patients. It is still possible that other mechanisms contribute to TKI-mediated impairments of TFT, e.g. altered metabolism of TH. Bosutinib was not previously reported to alter TFT.

131I activity in urine to the sewer system due to thyroidal treatments

In nuclear medicine, estimating the radioactivity contained in the urine of patients treated with I and discharged to the environment could prevent the exposure of a population to radioactive effluents and the pollution of the aquatic environment with ionizing radiation. This can be a regulatory requirement (as in Spain) or requested by the sewer authority. Seventy-nine differentiated thyroid cancer cases (undergone as inpatients) and 187 hyperthyroidism cases (undergone as outpatients) were treated in our hospital with I throughout the year 2009. In hyperthyroidism treatments, the effective elimination constant was used to calculate the corresponding discharged activity in the urine, giving an activity level always below 0.7 GBq. In differentiated thyroid cancer treatments, patient's urine was collected in storage tanks during the hospitalization. Measurements of external exposure at 1 m made every day were used to calculate the activity contained in the urine. The tank activity was always below 15 GBq, but always higher than 2 GBq. Obtained results show that effective doses to sewage workers, received from liquid discharges, can only be reduced to less than 10 μSv if storage tanks are installed. Without tanks, 157 μSv can be reached, above the constrain dose used in nuclear installations (100 μSv). Our calculations may be helpful to the regulatory authority to review the clinical radiation waste normative, especially in countries where the discharges are released directly into public sewage plants.

I-131 dose response for incident thyroid cancers in Ukraine related to the Chornobyl accident

BACKGROUND

Current knowledge about Chornobyl-related thyroid cancer risks comes from ecological studies based on grouped doses, case-control studies, and studies of prevalent cancers.

OBJECTIVE

To address this limitation, we evaluated the dose-response relationship for incident thyroid cancers using measurement-based individual iodine-131 (I-131) thyroid dose estimates in a prospective analytic cohort study.

METHODS

The cohort consists of individuals < 18 years of age on 26 April 1986 who resided in three contaminated oblasts (states) of Ukraine and underwent up to four thyroid screening examinations between 1998 and 2007 (n = 12,514). Thyroid doses of I-131 were estimated based on individual radioactivity measurements taken within 2 months after the accident, environmental transport models, and interview data. Excess radiation risks were estimated using Poisson regression models.

RESULTS

Sixty-five incident thyroid cancers were diagnosed during the second through fourth screenings and 73,004 person-years (PY) of observation. The dose-response relationship was consistent with linearity on relative and absolute scales, although the excess relative risk (ERR) model described data better than did the excess absolute risk (EAR) model. The ERR per gray was 1.91 [95% confidence interval (CI), 0.43-6.34], and the EAR per 10⁴ PY/Gy was 2.21 (95% CI, 0.04-5.78). The ERR per gray varied significantly by oblast of residence but not by time since exposure, use of iodine prophylaxis, iodine status, sex, age, or tumor size.

CONCLUSIONS

I-131-related thyroid cancer risks persisted for two decades after exposure, with no evidence of decrease during the observation period. The radiation risks, although smaller, are compatible with those of retrospective and ecological post-Chornobyl studies.

131I Biokinetics and cytogenetic dose estimates in ablation treatment of thyroid carcinoma

This study evaluated biokinetic behavior of radioiodine in the bodies of ten female adult patients, with well-differentiated thyroid cancer, treated with 131I post-near total thyroidectomy, for ablation of remnant thyroid. In vivo and in vitro bioassay analyses were performed from the first hour following radioiodine administration until minimum detection limits were reached. The retention of 131I in the body from day 1 to day 6 after the intake may be mathematically represented by an exponential decreasing curve, with an average biological half-life of approximately 0.81 d, with the exception of patients who presented thyroiditis. From day 6 to day 13, urinary excretion rates indicated an increased liberation of iodine. After 2 wk, the body retention of iodine followed an exponential decrease, with a half-life of about 15 d. The average whole-body dose for these patients was 0.27 Gy, as estimated through cytogenetic techniques.

Urinary excretion of radionuclides from Marshallese exposed to fallout from the 1954 Bravo nuclear test

Soon after the Bravo nuclear test at Bikini Atoll in the Marshall Islands on 1 March 1954, urine samples were collected for analysis of excreted radioactivity from native residents exposed to radioactive fallout on two atolls as well as from U.S. military personnel on a third atoll. The earliest acquired samples, obtained by the Los Alamos Scientific Laboratory (LASL), were assayed for various radionuclides and provided the first known measurements of (131)I in urine following exposure to fallout from a nuclear test. Over the course of 1954, many additional samples were collected by the LASL, as well as by the Atomic Energy Commission New York Operations Office's Health and Safety Laboratory and the Naval Radiological Defense Laboratory. Collectively, the groups sampled included Marshallese exposed on Rongelap and Ailinginae Atolls, American military weather observers temporarily resident on Rongerik Atoll, and sailors from the Japanese fishing vessel, the Lucky Dragon. While the bioassay measurement data and individual urine volumes have been crucial to various attempts to assess intakes of radioactivity and the related internal radiation doses among the Marshallese, those data have never been published in any peer-reviewed journal, but have been restricted to agency memoranda, laboratory reports, and summaries in some publications and book chapters. Reconstructions of internal doses to Marshallese in 1954 and in later years have depended on these data and, hence, they have considerable historical importance as well as importance to ongoing health risk projections for Marshallese. This paper presents much of the original data on urine volumes and radioactivity from the various assays of urine for radionuclides, and compares estimates of (131)I intakes made in 1954, 1985, 1987, and 2008.

Lack of association between urinary iodine excretion and successful thyroid ablation in thyroid cancer patients

BACKGROUND

Low-iodine diet is prescribed before (131)I administration in patients with differentiated thyroid cancer, although no study has properly quantified its clinical benefit.

OBJECTIVE

Our study aimed to evaluate the association between urinary iodine excretion (UIE) and (131)I ablation by correlating UIE with the rate of successful ablation.

PATIENTS

We retrospectively studied 201 differentiated thyroid cancer patients who had received (131)I therapy and posttherapy whole-body scan (WBS) for remnant ablation after either thyroid hormone withdrawal (THW group, n = 125) or recombinant human TSH (rhTSH group, n = 76). The outcome of thyroid ablation was assessed using two different criteria: no visible uptake at control WBS 8-12 months after ablation or no visible uptake plus undetectable stimulated serum thyroglobulin (Tg).

RESULTS

According to the criterion of no visible uptake, 84.6% of the patients were successfully ablated, with no significant difference between THW and rhTSH groups. Mean UIE at the time of ablation was 132 +/- 160 microg/liter, not significantly different between patients of the THW and rhTSH groups. There was no significant difference in UIE between ablated or nonablated patients both in the whole group and the rhTSH or THW groups. According to the criterion of no visible uptake plus undetectable stimulated serum Tg (in anti-Tg negative patients) at control WBS 8-12 months after ablation, UIE was not significantly different in ablated and nonablated patients.

CONCLUSIONS

Our study indicates that the body iodine content is not an important determinant of thyroid ablation, when preparing the patients with either THW or rhTSH.

Surgery and radioablation therapy combined: introducing a 1-week-condensed procedure bonding total thyroidectomy and radioablation therapy with recombinant human TSH

OBJECTIVE

The objective of this study was to determine whether the use of recombinant human TSH (rhTSH) to stimulate radioiodine uptake after thyroidectomy is as efficacious as a period of withholding thyroid hormones, while at the same time avoiding hypothyroidism, reducing sick leave time and shortening the hospital stay.

DESIGN

Our aim was to compare the standard procedure of differentiated thyroid cancer treatment, which consists of thyroidectomy followed by 4 weeks of hypothyroidism and a conclusive ablative activity of (131)iodine, with a new shortened treatment in which l-thyroxine (T(4)) medication is initiated a day after thyroidectomy, followed by application of rhTSH stimulation and subsequent ablation a few days after surgery. We presumed our treatment to represent the most sophisticated strategy for the reduction in sick leave days overall without any reduction in safety or the efficacy of ablative therapy.

METHODS

Patients (n=25) were randomized either for surgery and rhTSH stimulation or surgery and l-T(4) abstinence before the first application of radioiodine. Ablation success was determined by neck ultrasound and serum thyroglobulin during follow-up. RhTSH receivers were monitored for an average of 635 days (s.d.+/-289) and patients in l-T(4) abstinence for an average of 624 days (s.d.+/-205). Both groups were statistically compared for significant differences in treatment efficacy, safety and overall time of sick leave.

RESULTS AND CONCLUSIONS

Our shortened treatment proved to be equally efficacious and safe in comparison with the conventional therapy regimen. At the same time, it showed economic advantages through the reduction in average sick leave time from approximately 29 days (l-T(4) abstinence) down to approximately 6 days (rhTSH stimulation) as well as sustaining the patient's quality of life by the complete avoidance of hypothyroidism.

Unexpected effect of furosemide on radioiodine urinary excretion in patients with differentiated thyroid carcinomas treated with iodine 131

BACKGROUND

In patients receiving (131)I for therapeutic purposes, diuretics are frequently used in an attempt to accelerate elimination of unbound radioiodine, reduce its adverse effects, and shorten the hospital stay. The aims of our study were to investigate the influence of furosemide therapy on urinary excretion of (131)I in patients with differentiated thyroid cancer (DTC), referred to radioiodine ablation after thyroidectomy, and to investigate whether diuretics are useful in daily practice in patients with DTC.

METHODS

Forty-three patients with DTC who had normal renal function and low (131)I uptake in cervical region (3.55 +/- 3.45%) were included in this study. The furosemide (20 mg) and potassium chloride (250 mg) were given orally to 23 patients 3 hours after the (131)I administration, and then q8h for 3 days. Twenty patients did not receive either furosemide or potassium chloride. After (131)I administration, the patients collected their urine for 3 days, and radioactivity of urine sample from each micturition was expressed as percentage of the administered dose. Radioactivity of blood samples was measured after 72 hours, and the values were corrected for decay of (131)I and expressed in relation to the administered dose. Initial whole-body measurement (immediately after (131)I administration) and the whole-body measurement after 72 hours were recorded for all patients. The 72-hour whole-body measurement was corrected for decay of (131)I, and expressed as a percentage of the initial whole-body measurement.

RESULTS

Urinary excretion of (131)I was significantly lower in the patients who were taking furosemide and potassium chloride compared with the control group. The whole-body measurements after 72 hours (13.22 +/- 6.55% vs. 8.24 +/- 3.39% of the initial; p < 0.01, respectively) and the blood radioactivity (34.66 +/- 24.84 vs. 11.64 +/- 8.32 cpm/mL per 1 MBq of administered (131)I, p < 0.01) were found to be unexpectedly higher in the patients who were taking furosemide and potassium chloride compared with the control group.

CONCLUSION

Our results demonstrated that furosemide given as an adjuvant medication in patients with DTC causes a significant decrease in urinary excretion of radioiodine and its higher blood concentration. Therefore, furosemide should not be recommended as an adjuvant therapy to radioiodine ablation in patients with DTC previously iodine depleted by low-iodine diet.

Contamination during a brachytherapy procedure

This paper describes an unusual contamination incident that occurred during the treatment of a prostate cancer patient with seeds containing 125I. The incident became particularly interesting as the radiation safety procedures in place prior to the incident were, in fact, inappropriate for the type of incident that occurred, resulting in a series of response errors. Strands containing 108 125I seeds with a total activity of 1.61 GBq (43.6 mCi) were implanted into a patient's prostate and the patient was sent to the recovery room. A radiation survey detected radiation levels of up to 15 microR h(-1), 10 cm from the surface of the implantation needles. Multiple individuals entered the room and were potentially exposed to contamination. Contamination was detected in a sample of the patient's urine, indicating that one or more implanted seeds were leaking. Initial test results for staff showed that 12 of 15 had thyroid levels potentially above their corresponding minimum detectable activity levels, with calculated thyroid burdens ranging from 0.17 kBq to 0.94 kBq, but, subsequent measurements, using each staff member's thigh counts as background, suggested that no staff member had been contaminated. The patient showed high uptake of 125I in his neck 10 d following the incident, estimated to correspond to an initial thyroid burden of 58 kBq. The possibility of contamination was not immediately considered due to the suspicion of the more common problem of a misplaced source. The initial measurements suggesting thyroidal contamination in staff point to an error in our thyroid screening method.

Iodine prophylaxis intensification. Influence on radioiodine uptake and activity of 131I used in the treatment of hyperthyroid patients with Graves' disease

Poland, a country with mild/moderate iodine deficiency introduced an obligatory iodination salt system in 1996.

AIM

To compare the results of radioiodine (131I) uptake after 5 h and 24 h with the activity of radioiodine used in the treatment of hyperthyroid patients with Graves' disease in the years 1995 and 2003.

PATIENTS, METHODS

The marker of iodine content in the diet was urinary iodine excretion. 1000 randomly chosen patients (average age: 46 +/- 12 years) were included in the study. Every patient had routinely estimated radioiodine uptake after 5 h and 24 h and the activity of 131I was calculated using scintigraphy and ultrasonography of the thyroid gland. Urinary iodine excretion in samples from year 1995 and 2003 was also determined in some patients and healthy volunteers.

RESULTS

The iodine load in the diet increased from 66 microg (average) in the year 1995 to 115 microg in the year 2003. Thyroid radioiodine uptake was 40% lower in comparison with the results from 1995. The average activity of 131I given in the year 2003 (10 mCi) was about 40% higher than in the year 1995 (7 mCi).

CONCLUSION

There was significant negative correlation between higher iodine content in the diet and lower values of radioiodine uptake, which led to the application of the higher activity of 131I during treatment.

Diagnostic 123I and 131I activities and radioiodine therapy. Effects on urinary iodine excretion in patients with differentiated thyroid carcinoma

AIM

Urinary iodine excretion (UIE) provides information about iodine supply and release. In the present study we investigated effects of the application of different radioiodine isotopes on UIE in patients with differentiated thyroid carcinoma (DTC).

PATIENTS, METHODS

In 91 consecutive patients with DTC UIE, measured as iodine/creatinine ratio, was determined before and after application of 123I and 131I for diagnostic or therapeutic purposes. Additionally, remnant volume (V) was determined prior to therapy. Group A consisted of 33 patients with supposed successful ablation of DTC. These patients received 370 MBq 131I for diagnostic use and served as controls. 58 patients (group B) with remnants, relapses and metastases received 370 MBq 123I for diagnostics prior to therapy with 1.5-22.2 GBq 131I. Factors influencing individual changes in urinary iodine excretion (deltaUIE) were investigated by using non-parametric tests.

RESULTS

In group A UIE did not change significantly after application of 131I. As well, UIE remained unchanged after diagnostic application of 123I in group B. In contrast, UIE increased significantly already 24 h after therapeutic application of 131I in this group. In patients with small remnants (V < 2.5 ml) a significant but only moderate increase of UIE could be observed (average increase: 47 microg I/g crea). In patients with larger remnants, with relapses or metastases increase of UIE values was significant and more pronounced.

CONCLUSIONS

It was confirmed that UIE increased significantly during radioiodine therapy in patients with DTC and radioiodine-accumulating tissue. The increase of UIE after therapeutic administration of radioiodine can be explained by the disintegrated thyroid follicles in thyroid remnants. The radioiodine-induced iodine release may be one reason for thyroid "stunning" even after application of diagnostic amounts of 131I.

PBPK model for radioactive iodide and perchlorate kinetics and perchlorate-induced inhibition of iodide uptake in humans

Detection of perchlorate (ClO4-) in several drinking water sources across the U.S. has lead to public concern over health effects from chronic low-level exposures. Perchlorate inhibits thyroid iodide (I-) uptake at the sodium (Na+)-iodide (I-) symporter (NIS), thereby disrupting the initial stage of thyroid hormone synthesis. A physiologically based pharmacokinetic (PBPK) model was developed to describe the kinetics and distribution of both radioactive I- and cold ClO4- in healthy adult humans and simulates the subsequent inhibition of thyroid uptake of radioactive I- by ClO4-. The model successfully predicts the measured levels of serum and urinary ClO4- from drinking water exposures, ranging from 0.007 to 12 mg ClO4-/kg/day, as well as the subsequent inhibition of thyroid 131I- uptake. Thyroid iodine, as well as total, free, and protein-bound radioactive I- in serum from various tracer studies, are also successfully simulated. This model's parameters, in conjunction with corresponding model parameters established for the male, gestational, and lactating rat, can be used to estimate parameters in a pregnant or lactating human, that have not been or cannot be easily measured to extrapolate dose metrics and correlate observed effects in perchlorate toxicity studies to other human life stages. For example, by applying the adult male rat:adult human ratios of model parameters to those parameters established for the gestational and lactating rat, we can derive a reasonable estimate of corresponding parameters for a gestating or lactating human female. Although thyroid hormones and their regulatory feedback are not incorporated in the model structure, the model's successful prediction of free and bound radioactive I- and perchlorate's interaction with free radioactive I- provide a basis for extending the structure to address the complex hypothalamic-pituitary-thyroid feedback system. In this paper, bound radioactive I- refers to I- incorporated into thyroid hormones or iodinated proteins, which may or may not be bound to plasma proteins.

Prediction of GFR in liver transplant candidates

BACKGROUND

Kidney function frequently is impaired in patients with cirrhosis; however, glomerular filtration rate (GFR) is difficult to estimate in these patients by using standard clinical markers. The aim of our study is to compare GFR calculated from renal clearance of iodine 125-labeled iothalamate ((125)I-iothalamate) with the plasma decay technique and the Modification of Diet in Renal Disease (MDRD) and Cockroft-Gault (CG) prediction equations.

METHODS

We performed a cross-sectional study of patients with liver cirrhosis being evaluated for transplantation (50% Child's class C); 89% had ascites or edema and 44% were men aged 55 +/- 2 years. Average pretest blood urea nitrogen level was 16 +/- 2 mg/dL (5.7 +/- 0.7 mmol/L); serum creatinine, 1.0 +/- 0.1 mg/dL (88 +/- 9 micromol/L; range, 0.6 to 1.7 mg/dL [53 to 150 micromol/L]); plasma albumin, 3.14 +/- 0.16 g/dL (31.4 +/- 1.6 g/L); and total bilirubin, 4.0 +/- 0.7 mg/dL (67 +/- 11.3 micromol/L). Kidney function was measured by means of simultaneous plasma and renal clearance of (125)I-iothalamate (Glofil-125; Cypros Pharmaceutical Corp, Carlsbad, CA) and the MDRD and CG equations.

RESULTS

GFRs were 58.2 +/- 5.1 mL/min/1.73 m(2) by renal clearance of (125)I-iothalamate and 76.7 +/- 7.2 mL/min/1.73 m(2) by the plasma decay technique (+18.5 mL/min, or 32%; P = 0.0004). GFR by the MDRD equation was 76.9 +/- 7.8 mL/min/1.73 m(2) (+18.7 mL/min, or 32%; P = 0.0004 versus renal iothalamate; r(2) = 0.57). GFR by the CG equation was the least accurate (+30.1 mL/min, or 52%; P = 0.0001 versus renal iothalamate).

CONCLUSION

The current clinically used CG and MDRD equations to estimate kidney function in patients with cirrhosis and volume excess and the (125)I-iothalamate plasma decay technique are inaccurate because they overestimate GFR. It seems very unlikely that accurate and reliable formulas will be developed that are able to replace the formal measurement of GFR in patients with liver cirrhosis. Therefore, we conclude that despite the additional complexity, renal clearance techniques should be used to assess GFR accurately in patients with liver cirrhosis and ascites.

Iodine excretion during stimulation with rhTSH in differentiated thyroid carcinoma

AIM

Elevated iodine intake is a serious problem in the diagnostic and therapeutic application of (131)iodine in patients with differentiated thyroid cancer. Therefore, iodine avoidance is necessary 3 months in advance. Additionally, endogenous stimulation requires withdrawal of thyroid hormone substitution for 4 weeks. Exogenous stimulation using recombinant human TSH (rhTSH) enables the continuous substitution of levothyroxine, which contains 65.4% of its molecular weight in iodine. Thus, a substantial source of iodine intake is maintained during exogenous stimulation. Although this amount of stable iodine is comparable to the iodine intake in regions of normal iodine supply, it may reduce the accumulation of radioiodine in thyroid carcinoma tissue. The aim of this study was to assess the iodine excretion depending on different ways of stimulation.

METHODS

Iodine excretion was measured in 146 patients in the long term follow up after differentiated thyroid carcinoma. Patients were separated into 2 groups, those on hormone withdrawal (G I) and rhTSH-stimulated patients on hormone substitution (G II).

RESULTS

Iodine excretion was significantly lower in hypothyroid patients (G I, median 50 micro g/l, range: 25-600 micro g/l) than in those under levothyroxine medication (G II, median 75 micro g/l, 25-600 micro g/l, p <0.027). TSH in G I (median 57.0 micro U/ml, range: 14.4-183 micro U/ml) was significantly lower (p <0.001) than in G II (117 micro U/ml, 32.2-281 micro U/ml).

CONCLUSION

Iodine excretion was higher in patients under rhTSH-stimulation than after hormone withdrawal. This may indicate an increased iodine pool in rhTSH-stimulated patients (deiodination of levothyroxine), thus limiting the sensitivity of radioiodine scanning to the level of endogenous stimulation despite significantly higher TSH levels during rhTSH-stimulation.

Relationship between orally administered dose, surface emission rate for gamma radiation, and urine radioactivity in radioiodine-treated hyperthyroid cats

OBJECTIVE

To determine the relationship between surface emission rate of gamma radiation and urine concentration of I131 (urine radioactivity) during the period 7 to 21 days after oral or SC administration of I131 to hyperthyroid cats.

ANIMALS

47 hyperthyroid cats administered I131 PO and 24 hyperthyroid cats administered I131 SC.

PROCEDURE

A dose of I131 (1.78 to 2.04 X 10(2) MBq [4.8 to 5.5 mCi]) was administered orally. Surface emission at the skin adjacent to the thyroid gland on days 7, 10, 14, 18, and 21 and number of counts/30 s in a urine sample (1 mL, obtained via cystocentesis) on days 7, 14, and 21 after oral administration were measured. Effective half-life (T1/2E) was derived for each point. Surface emission thresholds for maximum urine radioactivity values were established. A dose of I131 (1.48 X 10(2) MBq [4.0 mCi]) was administered SC. Urine radioactivity and surface emission rates for SC administration were compared with values for oral administration.

RESULTS

The T1/2E for surface emissions and urine radioactivity progressively increased toward values for physical T1/2 over time. The T1/2E for surface emissions was 2.19 to 4.70 days, and T1/2E for urine radioactivity was 2.16 to 3.67 days. Surface emission rates had a clinically useful threshold relationship to maximum urine concentrations of I131.

CONCLUSIONS AND CLINICAL RELEVANCE

Surface emission rates for cats administered I131 appeared useful in determining upper limits (threshold) of urine radioactivity and are a valid method to assess the time at which cats can be discharged after I131 administration.

Seed loss through the urinary tract after prostate brachytherapy: examining the role of cystoscopy and urine straining post implant

This study describes one institution's experience with seed retrieval through the urinary tract and makes recommendations for cystoscopy and urine straining post prostate brachytherapy (PB). 1794 patients from two separate cohorts covering different time periods (early versus late) were analyzed. All patients were preplanned with a modified peripheral loading technique and implanted with preloaded needles (125I or 103Pd) under ultrasound guidance. A catheter was used to delineate the urethra during the volume study but was not used during the implant. All patients underwent post implant cystoscopy. All patients were instructed to strain their urine for seven days post implant and return any seeds to our center. In our experience, seed loss through the urinary tract is a common event after PB, occurring in 29.7% of patients and was more common in patients from the early cohort, those implanted with 125I seeds or those patients with prior transurethral resection of the prostate. Average seed loss per case, however, represents only 0.58% of total activity. We continue to recommend routine post implant cystoscopy for seed retrieval and periprocedural management. We no longer recommend that patients strain their urine at home after documenting a low rate of seed loss after discharge.

Effects of diuretics on iodine uptake in non-toxic goitre: comparison with low-iodine diet

Low-iodine diet has been employed to achieve iodine depletion prior to radioiodine (RI) therapy. However, treatment with diuretics may be more effective than low-iodine diet in causing iodine depletion and subsequent increase in RI uptake by the thyroid. Fifty-five patients with non-toxic goitre were given 0.20 MBq RI p.o. on the first day of the study and thyroid uptake was measured. In 15 patients, a low-iodine diet was started and continued for 14 days. The remaining 40 patients received furosemide 40 mg/day orally for 5 days with an unrestricted diet. On the 15th day of the study, all patients were given 0.20 MBq RI p.o. and thyroid RI uptake was measured again. Additionally, 24-h urinary iodine excretion and RI clearance were measured on the 1st and 6th days in 21 patients from the furosemide group and on the 1st and 15th days in eight patients from the diet group. Furosemide administration led to a 58.40% increase in iodine uptake over the baseline value, which was significantly higher than the increase caused by low-iodine diet (17.22%) ( P<0.0001). Urinary excretion of RI decreased in both groups similarly (furosemide, 29.45%; low-iodine diet, 21.06%; P=0.33). Iodine clearance also decreased in each group similarly (10.61% vs 7.53%, P=0.53). Treatment with furosemide prior to administration of RI increases the uptake of RI by the thyroid more effectively than does low-iodine diet.

Synthesis of dendrimer-based biotin radiopharmaceuticals to enhance whole-body clearance

To synthesize a biotin radiopharmaceutical that clears rapidly, dendrimer was used as a carrier and conjugated with succinimidyl 3-[(125)I]iodobenzoate and tetrafluorophenyl norbiotinamidosuccinate. Then, succinic anhydride was used to reduce its pI. In mice, the non-succinylated product showed high liver (67% ID/g) and kidney (44% ID/g) uptakes and whole-body retention (94% ID) at 20 min that persisted for 12 hr. The corresponding organ uptakes (22% and 11% ID/g) and the whole-body retention (47% ID) were drastically reduced by succinylation (p<0.0001). Lysine co-injection further lowered renal uptake.

Low-molecular-weight polyethylenimine as a non-viral vector for DNA delivery: comparison of physicochemical properties, transfection efficiency and in vivo distribution with high-molecular-weight polyethylenimine

Low-molecular-weight polyethylenimine (LMW-PEI) was synthesized by the acid-catalyzed, ring-opening polymerization of aziridine and compared with commercially available high-molecular-weight PEI (HMW-PEI) of 25 kDa. Molecular weights were determined by size-exclusion chromatography in combination with multi-angle laser light scattering. The weight average molecular weight (M(w)) of synthesized LMW-PEI was determined as 5.4+/-0.5 kDa, whereas commercial HMW-PEI showed a M(w) of 48+/-2 kDa. DNA polyplexes of LMW-PEI and HMW-PEI were characterized with regard to DNA condensation (ethidium bromide fluorescence quenching), size (photon correlation spectroscopy) and surface charge (laser Doppler anemometry). Compared with HMW-PEI, DNA condensation of LMW-PEI was slightly impaired at lower N/P ratios. Complexes with plasmid DNA at a N/P ratio of 6.7 showed significantly increased hydrodynamic diameters (590+/-140 vs. 160+/-10 nm), while the zeta-potential measurements were similar (23+/-2 vs. 30+/-3 mV). The cytotoxicity of LMW-PEI in L929 fibroblasts was reduced by more than one order of magnitude compared with HMW-PEI, as shown by MTT assay. LMW-PEI exhibited increased transfection efficiency in six different cell lines. Reporter gene expression was found to be increased by a factor of 2.1-110. The pharmacokinetics and biodistribution of 125I-PEI in mice were similar for both molecular weights with an AUC of ca. 330+/-100% ID/ml min. Approximately half of the injected dose accumulated in the liver. LMW-PEI proved to be an efficient gene delivery system in a broad range of cell lines. Due to differences in polyplex structure, as well as its relatively low cytotoxicity, which makes the application of high N/P ratios possible, LMW-PEI appears to possess advantageous qualities with regard to transfection efficiency over PEI of higher molecular weight.

An artificial amino acid, 4-iodo-L-meta-tyrosine: biodistribution and excretion via kidney

We evaluated the use of radiolabeled 4-iodo-L-meta-tyrosine as an amino acid transport marker. The pharmacologic features of this compound, particularly the biodistribution and excretion, were examined by conducting in vivo and in vitro studies using 4-(125)I-iodo-L-meta-tyrosine (4-(125)I-mTyr). Results obtained for L-(14)C-Tyr and 3-(125)I-iodo-alpha-methyl-L-tyrosine ((125)I-IMT) were used for comparison.

METHODS

In vivo biodistribution studies of 4-(125)I-mTyr were performed in male ddY mice. Urinary excretion of 4-(125)I-mTyr and (125)I-IMT with administration of probenecid was studied. Local distribution of 4-(125)I-mTyr and (125)I-IMT in kidney was visualized by autoradiography. We performed metabolite analysis of 4-(125)I-mTyr in mice. For in vitro studies, reabsorption mechanisms of 4-(125)I-mTyr were compared with those of (125)I-IMT and the parent L-(14)C-Tyr using superconfluent monolayers of the porcine kidney epithelial cell line LLC-PK(1) in medium containing inhibitor (L-Tyr, D-Tyr, and 2,4-dinitrophenol), in Na(+)-free medium, and at 4 degrees C.

RESULTS

4-(125)I-mTyr demonstrated high accumulation in the pancreas and kidney and comparable brain uptake to that of (125)I-IMT. Blood clearance of 4-(125)I-mTyr was faster than that of (125)I-IMT. Three hours after administration, >70% of 4-(125)I-mTyr was excreted via the urine, whereas <5% was found in the feces. Renal autoradiography revealed moderate accumulation of 4-(125)I-mTyr and high accumulation of (125)I-IMT in the renal cortex. Probenecid further reduced accumulation of 4-(125)I-mTyr and (125)I-IMT in the kidney as well as urinary excretion. At 30 min after tracer injection, intact free 4-(125)I-mTyr accounted for >98.1% of the total present in kidney and >96.3% in urine. Protein incorporation was not observed. Uptake of 4-(125)I-mTyr into LLC-PK(1) cell monolayers was remarkably reduced by 5 mmol/L L-Tyr (4.6%) and incubation at 4 degrees C (15.6%) but was reduced by 5 mmol/L D-Tyr (50.0%). L-(14)C-Tyr and (125)I-IMT showed similar results; however, uptake of (125)I-IMT was enhanced by 0.1 mmol/L 2,4-dinitrophenol (165.1%), an inhibitor of generation of energy-rich phosphates.

CONCLUSION

The artificial amino acid 4-(125)I-mTyr demonstrated high metabolic stability, rapid blood clearance, rapid urinary excretion, and similar biodistribution to other radiolabeled L-Tyr analogs. 4-(125)I-mTyr can be a competitive substrate of L-Tyr reabsorption. However, 4-(125)I-mTyr demonstrates different pharmacologic features than those of (125)I-IMT, particularly in renal handling. 4-(125)I-mTyr may potentially be applied as a new amino acid transport marker.

Radiation safety issues with high activities of liquid I-125: techniques and experience

The handling of a liquid radioactive source is a procedure that is uncommon for the average clinical medical physicist. A newly approved treatment device utilizes high activities of liquid I-125 solution as the source of radiation. The radiation safety issues and our experience utilizing high activity liquid I-125 sources are presented. To date we have treated 22 patients with infused activities ranging up to 26.8 GBq (724 mCi). The careful manipulation of such solutions is important to maintain a safe environment for the patients and the involved medical staff.

Iodine-129 in thyroid and urine in Ukraine and Denmark

Human thyroids collected from Gomel in Belarus, sheep thyroid from Jutland and human urine from Zealand in Denmark were analysed for 129I and 127I concentrations. The ratios of 129I/127I in human thyroid in Gomel are 2.65-11.0 x 10(-9) with an average of 7.21 x 10(-9), which is one order of magnitude higher than those from Asia and South America (10(-10)), but significantly lower than those observed in west Europe (10(-8)). A weak negative correlation (P < 0.05) between 129I/127I ratio in human thyroid and the age of the subjects was observed in Gomel. The average ratio of 129I/127I in sheep thyroids from Jutland of Denmark is 1.81 x 10(-7), which is two orders of magnitude higher than those in south hemisphere, and Asia. It is also significantly higher than those observed in other west European countries before 1984 and that in human thyroid in Gomel. The high thyroid 129I level in Jutland is attributed to the release of reprocessing plants in France and UK. The 129I/127I ratios in human urine in Zealand of Denmark are 0.86-2.86 x 10(-8). The possibility of using urine 129I to evaluate the thyroid exposure to 129I is investigated.

Uptake of radiolabelled herceptin by experimental mammary adenocarcinoma

BACKGROUND

The aim of this study was to examine the biodistribution of (131)I-herceptin in C3H/Bi mice with transplantable mammary adenocarcinoma with a high frequency of C-erbB2 receptor expression.

MATERIAL AND METHODS

Mice C3H/Bi with subcutaneously transplanted mammary adenocarcinoma were used as animal model to study the interaction between C-erbB2 receptor and hercepin, a humanized anti-C-erbB2 monoclonal antibody. The expression of the gene encoding C-erbB2 receptor in the tumours was studied by the RT-PCR technique.

RESULTS

Expression of this gene was found in 66% of the studied cases. Similarly, the presence of the C-erbB2 receptor in 77% of the tumours was detected by a Western blot analysis with the use of herceptin. Biodistribution experiments of iodine-labelled herceptin in mice C3H/Bi with adenocarcinoma revealed its maximal accumulation in the tumours at 48 hours since the i.v. injection (7% ID/g). The tumour/muscle radioactivity ratio reached its highest value (above 20) also at 48 hours after the injection.

CONCLUSIONS

C3H/Bi mice with this adenocarcinoma may be a good experimental model to study herceptin, or its fragments, labelled with different radionuclids for preliminary evaluation of their usefulness in the therapeutic and diagnostic aspects of breast cancer.

Retrospective study of the iodine-131 contamination of workers in the radiopharmaceutical industry

A dose reconstruction study was performed for personnel occupationally exposed to 131I in radiopharmaceutical production, during the years 1981 to 1994, with the objective of estimating committed effective doses and critically reviewing the main causes of their exposures. The workers were selected from a group responsible for the production, labelling and distribution of all radiopharmaceutical material in Brazil. Best estimates of intakes and doses were derived from the examination of the individual monitoring records and the reports from the radiation protection supervisor, complemented by interviews with the workers and with radiation protection officers. Over this time period workers had chronic as well as acute intakes of 131I. Committed effective doses were found to be dependent on the task performed by the worker and the site of operation and inversely correlated with the amounts of iodine handled. Intakes in general were a consequence of inadequate radiation protection control.

Biodistribution and kinetics of (131)I-labelled anti-CD20 MAB IDEC-C2B8 (rituximab) in relapsed non-Hodgkin's lymphoma

The native chimeric human-mouse anti-CD20 antibody IDEC-C2B8 (rituximab) is therapeutically applied in relapsed non-Hodgkin's lymphoma (NHL). The purpose of this study was to evaluate the distribution and pharmacokinetics of iodine-131 labelled rituximab in humans for radioimmunotherapy of relapsed CD20-positive NHL. Thirty-five patients with relapsed NHL were administered 20-40 mg rituximab labelled with 250 MBq (131)I. Biodistribution was determined by the gamma camera whole-body scans, whole-body probe measurements and the analysis of serial blood and urine samples. Dosimetry was performed using the MIRDOSE 3 program. Antibody administration was well tolerated. The whole-body activity showed a mono-exponential decrease with a wide range of effective half-lives, the mean value (88 h) being significantly longer than the half-life of its murine counterpart, tositumomab. This led to appropriately higher dose factors for the whole body and organs. Activity was excreted mainly through the kidneys. Normal organs showed decreasing ratios of organ to whole-body activity over time, whereas the tumour tissue presented different kinetics, with increasing ratios of tumour to whole-body activity as evidence for specific antibody binding. It is concluded that (131)I-labelled rituximab is suitable for pretherapeutic dosimetry. Due to the wide range of whole-body and organ dose factors, individual dosimetry is necessary for radioimmunotherapy with (131)I-labelled rituximab. The therapeutic activities of (131)I-labelled rituximab required to deliver similar doses should be lower than those of its murine counterpart.

Improved renal clearance and tumor targeting of 99mTc-labeled anti-Tac monoclonal antibody Fab by chemical modifications

This study was undertaken to improve the renal clearance and tumor targeting properties of 99mTc-labeled humanized anti-Tac (HuTac) monoclonal antibody Fab fragments using two chemical approaches: 1) labeling with a renal secretion agent 99mTc-mercaptoacetyltriglycine (MAG3) and 2) lowering its isoelectric point (pI) by acylation. HuTac Fab (3.3 mg/mL) was reacted with a trifluorophenyl ester (TFP) of 99mTc-MAG3 alone or was additionally reacted with TFP-glycolate to reduce the pI. In Balb/c mice, 99mTc-MAG3-Fab (pI > 9.3) rapidly accumulated in the kidneys (177% injected dose [ID]/g at 15 min) and then gradually cleared out of the kidneys. In contrast, the glycolation (pI 4.6 approximately 6.6) drastically reduced the renal uptake (31% ID/g) and also the whole-body retention (82% ID vs 101% for the nonglycolated) at 15 min, indicating that the glycolated 99mTc-MAG3-Fab (pI 4.6 approximately 6.6) was rapidly excreted. The glycolated remained in the blood longer than the nonglycolated (1.2% vs 0.3% ID/g at 360 min), but this effect was less drastic than the effect shown on the renal uptake. In nude mice bearing receptor-positive (ATAC4) tumors, the glycolated 99mTc-MAG3-Fab increased the peak tumor uptake to 14.8% ID/g from 8.3% ID/g for 99mTc-MAG3-Fab, whereas the glycolation resulted in a drastic reduction of the renal uptake at 15 min. We demonstrated that the renal clearance and the tumor targeting of Fab could be optimized by chemical modifications.

Thyroidal uptake and radiation dose after repetitive I-131-MIBG treatments: influence of potassium iodide for thyroid blocking

BACKGROUND

In I-131-MIBG therapy, I-131-iodide can be released from the I-131-MIBG molecule. Hypothyroidism might result from the undesirable irradiation of the thyroid gland. To prevent this, stable iodide such as potassium iodide (KI) is given to oversaturate the thyroid before I-131-MIBG is administered.

PROCEDURE

In the present study, the incidence of hypothyroidism (elevated TSH) was correlated with the thyroidal uptake of I-131 and dose (MIRD dosimetry) after 35 individual treatments in ten patients. Iodine-131-MIBG therapy was performed using a modified dosage of 1.9-11.1 GBq (50-300 mCi) IV. Premedication with KI was done as recommended with a dose of 100 mg KI orally from 2 days before until 4 weeks after I-131-MIBG.

RESULTS

The absorbed thyroidal dose amounted to a very variable range of 0.2 (patient # 1) up to 30.0 (patient 3) Gy with 7.1 +/- 7.9 Gy per treatment and 24.1+/- 19.2 Gy per patient (mean+/- SD), despite the same and compliantly taken KI premedication protocol. Up to now, 4/10 or 40% of patients have developed hypothyroidism after a mean follow-up period of 11 months and a mean total administered dose of 18.7 GBq (505 mCi). A trend towards higher thyroidal doses was seen in the hypothyroid patients.

CONCLUSIONS

This study observes a general high inter- and intra-individual variability in radio-iodide uptake in the thyroid after I-131-MIBG therapy despite KI premedication, as well as possible occurrence of hypothyroidism. A dose-response relationship needs confirmation on a larger cohort of patients to reach statistical value. An alternative thyroid cytoprotection strategy for possible long-term survivors may be considered.

[A study on the isolation period of patients with metastatic thyroid cancer treated by 131I according to a new guideline]

In Japan, a new guideline for the release of patients administered 131I was issued by the Ministry of Welfare on June, 1998: The dose rate is under 30 microSv/h at 1 m or the activity in the body is under 500 MBq. This study was designed to set the appropriate isolation period enough to satisfy these limits. A total of 28 patients with the history of total thyroidectomy and metastasis were selected for this study. In these patients, 28 patients were treated with oral administration of 3.7 GBq of Na131I (72 times), and one of 28 patients was once treated with 5.55 GBq of Na131I. Two of them were also received a total of 4 courses of a split dose therapy of 3.7 GBq of Na131I (740 MBq once a week for 5 consecutive weeks = one course). Measurements of the external exposure dose (microSv/h) at 1 m and the urinary excretory radioactivity (MBq) were performed at various times. There was a good correlation of the external exposure dose between standing (x microSv/h) and sitting (y microSv/h) postures (y = 0.99x + 0.406, r = 0.99, p < 0.0001, n = 169). The difference in the external exposure dose before and after urination (x microSv/h) had a significant correlation with the urinary excretory radioactivity (y MBq); y = 16.6x + 24.8, r = 0.96, p < 0.001, n = 41. Also, there was a significant correlation between the predicted value of residual radioactivity in the body (y' MBq) and the external exposure dose (x' microSv/h); y' = 20.8x' + 31.5, r = 0.98, p < 0.001, n = 77. In the patients treated with 3.7 GBq of Na131I, the mean and S.D. values of the external exposure dose (microSv/h) changed as follow: After 6 hr, 168 +/- 40; 24 hr, 52 +/- 23; 48 hr, 20 +/- 15; 72 hr, 10 +/- 9; and 96 hr, 8 +/- 9. The percentages of the patients satisfied the new guideline were as follow; 21.7% at 24 hr, 81.2% at 48 hr and 100% after 72 hr. Therefore the 3-day isolation is sufficient for the patients administered 3.7 GBq of Na131I.

Some experiences with treating thyroid cancer patients

U.S. NRC Regulatory Guide 8.39 provides for the release of patients treated with 131I provided that predetermined calculations indicate that no member of the public will receive a total dose equivalent in excess of 5 mSv (500 mrem). When this condition cannot be met or there are other reasons for keeping the patient hospitalized after treatment, control of contamination and exposure from the patient must be taken into consideration. If the patients are hospitalized following treatment, decontaminating the patient's room after discharge and controlling the exposure potential from the patient are considerations for the hospital radiation safety staff. This paper reviews the experiences from fifty patients treated as inpatients over the past two years.

Evaluation of radioiodinated histamine as isotope carrier in vivo

The iodo derivative of histamine labelled with 125I has been used for many years to prepare tracers used in RIA systems. The aim of this study was to evaluate radioiodinated histamine as a potential isotope carrier for in vivo applications. The biological behaviour of radioiodinated histamine has been investigated in rodents. The observed absence of any specific iodohistamine uptake by a critical organ or tissue promises a very quick distribution of the iodohistamine in soft tissues, and a rapid rate of whole-body clearance via the urinary tract (e.g. over 50% of the injected dose (ID) during the first hour after administration). In spite of moderately low in vitro stability of iodohistamine in serum, biodistribution studies in rodents have not shown any significant release of iodine from the parent molecule in the whole animal. Low uptake was observed in the thyroid (e.g. 0.22 and 0.11% ID at 1 and 2 h after administration to rats), and not more than 3% of injected activity was detected in the stomach in all of the biodistribution experiments. Moreover, our results refute any possibility of competition between histamine and iodohistamine for receptor binding sites, and suggest that radioactive mono-iodohistamine may be used successfully to develop some new radiolabelled bioactive molecules with potential application in vivo.

Radiation dose to the testes after 131I therapy for ablation of postsurgical thyroid remnants in patients with differentiated thyroid cancer

Radioiodine-131 is used in differentiated thyroid cancer (DTC) for ablation of postsurgical thyroid remnants and destruction of metastases. The question may be raised of whether 131I treatment of DTC in male patients may give an irradiation dose to the testes that could impair fertility. Few data in the literature concern the dose absorbed by the testes after 1311 therapy for DTC. Because 131I kinetics may be altered by the hypothyroid condition commonly present at the time of treatment and by the radioiodinated iodoproteins released by the damaged thyroid tissue, the dose values reported in the International Commission on Radiological Protection (ICRP) tables for euthyroid men may not be appropriate. To clarify this problem, three male subjects undergoing 131I therapy for ablation of thyroid remnants shortly after thyroidectomy for DTC were studied.

METHODS

The mean administered activity was 1256 MBq, and the duration of the study was 2 wk. The gamma dose was measured by thermoluminescent dosimeters (TLDs) applied to the lower poles of the testes. Correction factors were calculated for the distance of the TLD from the center of the testes and for attenuation by the testes of the gamma rays reaching the TLD. After correction, the gamma dose to the testes ranged from 21 to 29 mGy. The gamma dose calculated by the Medical Internal Radiation Dose (MIRD) method from blood and urine samples was similar (18-20 mGy) to that measured by TLDs. The beta dose was estimated by the MIRD method from blood activity and testicular volume and ranged between 14 and 31 mGy.

RESULTS

The total (beta and gamma) doses to testes were 30, 33 and 43 microGy/MBq in the three subjects.

CONCLUSION

These values are close to those derived from the ICRP tables (26-37 microGy/MBq 131I) for euthyroid subjects. The present data indicate that significant irradiation is delivered to the testes after the administration of the 131I ablative dose to thyroidectomized patients. The relevance of the radiation absorbed by testes on fertility remains to be established.

Elimination of nonspecific radioactivity from [76Br]bromide in PET study with [76Br]bromodeoxyuridine

[76Br]Bromodeoxyuridine ([76Br]BrdU) might allow a determination of proliferation in vivo using positron emission tomography (PET), but only with consideration of organ nonspecific radioactivity constituted by [76Br]bromide. A first study assessed the potential of diuretics to eliminate [76Br]bromide. [76Br]Bromide was injected in the vein of rats and different diuretic combinations were given. Urine was collected and radioactivity measured. Torasemide plus sodium chloride gave better 76Br elimination than the other diuretics. In a second experiment, rats were given [76Br]BrdU. After the radioactivity injection, the rats of the treatment group were given torasemide plus NaCl. At 44 h after the radioactivity injection, the radioactivity concentration and the fraction incorporated into DNA were measured in different organs. Using diuretics, the elimination of [76Br]bromide was increased. The radioactivity decreased 30-50% in most of the organs but the highest radioactivity uptake was found in the organs with more active DNA synthesis. This method may facilitate the use of [76Br]BrdU as a tracer for DNA synthesis using PET.

The use of delay tanks in the management of radioactive waste from thyroid therapy

An underground system of tanks was installed to delay the discharge of 131I waste from the thyroid therapy unit to the on-site sewage treatment plant. As a consequence, the level of radioactivity discharged to sewage has fallen by a factor of 530, reducing the radiation dose to hospital and auxiliary service staff. Cancer patients are no longer required to collect their urine, hence increasing the hygiene for all concerned. A model was developed of iodine waste which estimates the dose rate above the delay tanks and the activity of iodine discharged. The maximum effective dose to a member of the public due to the holding tanks is 40 microSv.year-1. There is now better management of the radioactive waste from the iodine therapy ward.

Use of radioiodine urinalysis for effective thyroid blocking in the first few hours post exposure

A useful correlation between maximum thyroid uptake and radioiodine urine levels at different times after exposure was developed in order to determine when the intervention with an adequate blocking agent might still be effective. In an animal model (dog), six different doses were administered in the range of 100-600 kBq. The best correlation was found between the 125I uptake after 48 h (T-48) and urine radioactivity 4-6 h (U-4, U-5, U-6) after exposure. For the case of U-4, the equation Y(T-48) = 0.790 X(U-4) + 2.973 (r = 0.974 with a level of significance of p < 0.001) was obtained. An analogous study, carried out in humans (n = 20) to whom 1311 was administered, showed a similar correlation and level of significance: Y(T-24) = 1.162 X(U-4)+3.263 (r = 0.926; p < 0.001). The validity of this correlation was confirmed in four volunteers who received small doses of 125I(25-100 kBq), with good agreement between measured and extrapolated thyroid uptake and a mean difference of less than 10% (CV = 16.2%). Three different blocking agents were then tested in the same dog: potassium iodide, potassium perchlorate, and a thionamide (Tapazole). The blocking action of the first two compounds was about 90%, as opposed to only 48% for the third compound. Potassium iodide was chosen for its limited side effects and more universal utilization. The final study, carried out with four different doses, indicated that 25 mg of KI is the ideal amount to be administered to the dog. This corresponds to approximately 100 mg for a 70 kg human being (i.e., 1.4 mg kg(-1)). This dose, when administered to a volunteer 4 h after exposure, provided a thyroid blocking of 68%.

Disposal of therapeutic 131I waste using a multiple holding tank system

Therapeutic application of 131I for the treatment of thyroid cancer generates a significant amount of liquid radioactive waste. Discharge of this waste into the public sewage system is governed by local regulations. In Canada, the permissible concentration is such that only a few patients can be treated in modern water-efficient buildings if this waste is discharged directly through the toilet to the public sewage system. If the toilet discharge is first collected into a holding tank for physical decay before it is released, a large patient load can be handled without exceeding the permissible concentration. In this paper, the principles of operation and the design parameters are discussed, and a multiple holding tank system installed in the Princess Margaret Hospital/Ontario Cancer Institute is described.

Pharmacokinetics of [125I]-recombinant human interleukin-11: 1. Absorption, distribution and excretion after subcutaneous administration to male rats

Absorption, distribution, metabolism and excretion of [125I]-rhIL-11 (recombinant human interleukin-11) after subcutaneous administration in rats were investigated. After a single administration, the concentration of radioactivity in the tissues was 2-6-fold higher in the liver and kidneys, and slightly higher in the gastrointestinal tract as compared to the plasma concentration. However, since the concentration in the other tissues was lower than the plasma concentration, the transport of rhIL-11 into tissues appeared to be low. Tissue radioactivity rapidly diminished, thus accumulation of rhIL-11 in tissues was thought to be low. Excretion of radioactivity into urine and feces was almost complete 72 h after administration, with 88.5% of the dosed radioactivity being found in urine and 7.9% in feces. When [125I]-rhIL-11 was administered to bile-duct cannulated rats, 44.4% of the dosed radioactivity was excreted into bile up to 48 h after administration. Most radioactivity in bile and urine was found in the TCA supernatant and low molecular weight fraction by HPLC analysis, indicating that rhIL-11 was eliminated from the body by metabolism.

Prediction of urinary excretion of technetium-99m-MAG3

The urinary excretion of 99mTc-mercaptotriacetylglycine (MAG3), like that of 131I-orthoiodohippurate (OIH), can be used to identify acute renal transplant rejection and measure its severity. This parameter is often quantitated as the excretory index (observed excretion/predicted excretion). A new method for predicting the urinary excretion of 99mTc-MAG3 is presented.

METHODS

The expected excretion was calculated from multisample plasma time-activity curves in 122 subjects, with correction for the first pass of the initial bolus. The resulting formula was tested prospectively against actual urine measurements in an additional 466 subjects.

RESULTS

Least-squares fitting led to the following equation: Predicted excretion = 0.79(1-exp(-0.0066CMAG3), with residual s.d. 0.06, where CMAG3 is MAG3 clearance in ml/min and the predicted excretion is expressed as a fraction of the administered dose. Tested prospectively in the additional 466 subjects, the s.d. was 0.09.

CONCLUSION

A new formula to predict the urinary excretion of 99mTc-MAG3 has been developed and prospectively validated. Based on our data, the normal range for the excretory index using MAG3 is the same as that of 131I-OIH, 0.8-1.2.

Direct determination of urinary iodine by inductively coupled plasma mass spectrometry using isotope dilution with iodine-129

An inductively coupled mass spectrometric method was developed for the direct determination of iodine in urine. The application of isotope dilution analysis with added 129I offers new possibilities for automatic and accurate determinations. The sample preparation consists of dilution with an ammonia solution containing 129I. The validation was made by comparison with the results obtained in another laboratory by a spectrophotometric method based on the Sandell-Kolthoff reaction. Different regression models, including maximum likelihood estimation, were used to compare the methods. None of the models revealed analytical bias between the two methods. The urine samples analyzed for validation were from three persons previously exposed to an iodine bath and covered a concentration range of 0.2 to 2.8 micromol/L. A detection limit of 0.02 micromol/L, a within-run CV of 2.5%, and a between-run CV of 11.9% were estimated for the proposed method.

Human biodistribution and dosimetry of iodine-123-fluoroalkyl analogs of beta-CIT

Two new N-omega-fluoroalkyl analogs of [123I]2beta-carbomethoxy-3beta-(4-iodophenyl)tropane ([123I]beta-CIT), the fluoroethyl and fluoropropyl compounds ([123I]FE-CIT and [123I]FP-CIT, respectively), have been shown to have faster kinetics and better selectivity for the dopamine transporter than [123I]beta-CIT. We examined the organ biodistribution and radiation safety of these two compounds in six healthy volunteers who received an injection with each of the two compounds 2 weeks apart. Data were obtained on the Strichman 860 whole-body scanner. Transmission scans were obtained in all subjects prior to the injection of the radiotracer with a line source and used to derive organ-specific attenuation correction factors. Whole-body planar images were acquired every hour for the first 6 h, and at 24 h. Attenuation-corrected regional conjugate counts were converted into units of activity using a calibration factor obtained for each subject by dividing whole-body conjugate decay-corrected counts from the first acquisition by the injected activity. Radiation dose estimates were on average higher for [123I]CIT-FE than for [123I]CIT-FP, with the lower large intestine receiving the highest exposure: 0.15+/-13% mGy/MBq (mean +/-COV) and 0.12+/-14% mGy/MBq for [123I]FE-CIT and [123I]FP-CIT, respectively, followed by the upper large intestine and the spleen.

Determination of glomerular filtration rate using technetium-99m-DTPA with differing degrees of renal function

Glomerular filtration rate (GFR) is an important index of renal function. Twenty-four-hour creatinine clearance overestimates GFR in patients with poor renal function. Inulin and iothalamate clearances are accepted reference standards for determining GFR but are expensive and laborious. We have previously reported that GFRs obtained by measuring the disappearance of 99mTc-DTPA from ultrafiltered (protein-free) samples of plasma were virtually identical to those obtained by the iothalamate method. However, the subjects used in that study had normal to only moderately decreased renal function.

METHODS

The accuracy of measuring GFR by plasma clearance of 99mTc-DTPA was determined in subjects where renal function varied from normal to severely impaired. In all subjects, GFR was established by clearance of 125I-iothalamate from urine and serum and was used as the standard of reference.

RESULTS

For subjects with normal to moderately diminished renal function (GFR > 20 ml/min), the correlation between values of GFR obtained by the DTPA and iothalamate methods was high (n = 18, r = 0.966). The difference between the pairs of GFR values obtained by the two methods was not statistically significant (p > 0.1). In patients with severe renal insufficiency (GFR < 20 ml/min), the correlation between the DTPA and iothalamate methods was poor (n = 11, r = 0.236), and the GFR values obtained by the two methods were statistically different (p < 0.01).

CONCLUSION

These results suggest that GFR can be determined accurately by plasma clearance of 99mTc-DTPA in all patients except those with severe renal insufficiency.

Renal excretion of iodine-131 labelled meta-iodobenzylguanidine and metabolites after therapeutic doses in patients suffering from different neural crest-derived tumours

Iodine-131 labelled meta-iodobenzylguanidine ([131I]MIBG) is used for diagnostic scintigraphy and radionuclide therapy of neural crest-derived tumours. After administration of therapeutic doses of [131I]MIBG (3.1-7.5 GBq) to 17 patients (n=32 courses), aged 2-73 years, 56%+/-10%, 73%+/-11%, 80%+/-10% and 83%+/-10% of the dose was cumulatively excreted as total radioactivity in urine at t=24 h, 48 h, 72 h and 96 h, respectively. Except for two adult patients, who showed excretion of 14%-18% of [131I]meta-iodohippuric acid ([131I]MIHA), the cumulatively excreted radioactivity consisted of >85% [131I]MIBG, with 6% of the dose excreted as free [131I]iodide, 4% as [131I]MIHA and 2.5% as an unknown iodine-131 labelled metabolite. Cumulative renal excretion rates of total radioactivity and of [131I]MIBG appeared to be higher in neuroblastoma and phaeochromocytoma patients than in carcinoid patients. Based on the excretion of small amounts of [131I]meta-iodobenzoic acid in two patients, a possible metabolic pathway for [131I]MIBG is suggested. The degree of metabolism was not related to the extent of liver uptake of radioactivity.

Radiation dose rates from patients receiving iodine-131 therapy for carcinoma of the thyroid

Patients treated with radioiodine present a radiation hazard and precautions are necessary to limit the radiation dose to family members, nursing staff and members of the public. The precautions advised are usually based on instantaneous dose rates or iodine retention and do not take into account the time spent in close proximity with a patient. We have combined whole-body dose rate measurements taken from 86 thyroid cancer patients after radioiodine administration with published data on nursing and social contact times to calculate the cumulative dose that may be received by an individual in contact with a patient. These dose estimates have been used to calculate restrictions to patients behaviour to limit received doses to less than 1 mSv. We have also measured urinary iodide excretion in 19 patients to estimate the potential risk from the discharge of radioiodide into the domestic drainage system. The dose rate decay was biexponential for patients receiving radioiodine to ablate the thyroid after surgery (the ablation group, A) and monoexponential for these receiving subsequent treatments for residual or recurrent disease (the follow-up group, FU). The faster clearance in the follow-up patients generally resulted in less stringent restrictions than those advised for ablation patients. For typical activities of 1850 MBq for the ablation patients and 3700 MBq or 7400 MBq for the follow-up patients, the following restrictions were advised. Patients could travel in a private car for up to 8h on the day of treatment (for an administered activity of 1850 MBq in group A) or 4 and 2h (for activities of 3700 or 7400 MBq in group FU) respectively. Patients should remain off work for 3 days (1850 MBq/group A) or 2 days (up to 7400 MBq/group FU). Partners should avoid close contact and sleep apart for 16 days (1850 MBq/group A) or 4-5 days (3700 or 7400 MBq/group FU). Contact with children should be restricted according to their age, ranging from 16 days (1850 MBq/group A) or 4-5 days (3700 or 7400 MBq in group FU) for younger children, down to 10 days (1850 MBq/group A) or 4 days (up to 7400 MBq/group FU) for older children. The cumulative dose to nursing staff for the week after treatment was dependent on patient mobility and was estimated at 0.08 mSv for a self-caring patient to 6.3 mSv for a totally helpless patient (1840 MBq/group A). Corresponding doses to nurses looking after patients in group FU were 0.18-12.3 mSv (3700 MBq) or 0.36-24.6 mSv (7400 MBq). Sensible guidelines can be derived to limit the dose received by members of the public and staff who may come into contact with cancer patient treated with radioiodine to less than 1 mSv. The rapid clearance of radioiodine in patients treated on one or more than one occasion means that therapy could be administered at home to selected patients with suitable domestic circumstances. In most cases the restriction times, despite the high administered activities, are less than those for patients treated for thyrotoxicosis. The concentration of radioiodide in domestic drainage systems should not pose a significant risk.

Targeting disseminated melanoma with radiolabelled methylene blue: Comparative bio-distribution studies in man and animals

Targeted radiotherapy for pigmented melanoma with 3,7-(dimethylamino) phenazathionium chloride [methylene blue (MTB)] labelled with Astatine-211 (211At; alpha-particle emitter) proved to be very effective in animal model systems. Since the results justified an introduction of the treatment to the clinic, the aim of the bio-distribution studies using [123I]-MTB and [131I]-MTB in patients was to confirm selectiveness of radiolabelled MTB uptake in melanoma lesions. The investigations were carried out using planar and SPECT (single photon emission computed tomography) gamma-cameras. A stable uptake of radioiodinated MTB was found in pigmented melanomas in man, with tumour/surrounding tissue and tumour/blood ratios amounting to 9 at 19 h after a single i.v. injection. A time-dependent kinetics of radioiodinated MTB distribution was similar to that observed in human melanoma-bearing athymic mice. Blood radioactivity decreased by about 90% during the first 2.5 min after i.v. injection of the compound (T1/2biol = 0.58 min). Its retention time in various organs was either the same or very similar to that characteristic of the blood. A rapid uptake of radioiodinated MTB in the liver and kidneys confirmed the importance of these organs in excreting the compound: 25-30% of the radioactivity administered was expelled with urine over the first 24 h after the injection. There was no obvious retention of radioiodinated MTB in the brain over the observation period and in the eyes for at least the first 14 h.