Association of Radioactive Iodine Treatment With Cancer Mortality in Patients With Hyperthyroidism

IMPORTANCE

Radioactive iodine (RAI) has been used extensively to treat hyperthyroidism since the 1940s. Although widely considered a safe and effective therapy, RAI has been associated with elevated risks of total and site-specific cancer death among patients with hyperthyroidism.

OBJECTIVE

To determine whether greater organ- or tissue-absorbed doses from RAI treatment are associated with overall and site-specific cancer mortality in patients with hyperthyroidism.

DESIGN, SETTING, AND PARTICIPANTS

This cohort study is a 24-year extension of the multicenter Cooperative Thyrotoxicosis Therapy Follow-up Study, which has followed up US and UK patients diagnosed and treated for hyperthyroidism for nearly 7 decades, beginning in 1946. Patients were traced using records from the National Death Index, Social Security Administration, and other resources. After exclusions, 18 805 patients who were treated with RAI and had no history of cancer at the time of the first treatment were eligible for the current analysis. Excess relative risks (ERRs) per 100-mGy dose to the organ or tissue were calculated using multivariable-adjusted linear dose-response models and were converted to relative risks (RR = 1 + ERR). The current analyses were conducted from April 28, 2017, to January 30, 2019.

EXPOSURES

Mean total administered activity of sodium iodide I 131 was 375 MBq for patients with Graves disease and 653 MBq for patients with toxic nodular goiter. Mean organ or tissue dose estimates ranged from 20 to 99 mGy (colon or rectum, ovary, uterus, prostate, bladder, and brain/central nervous system), to 100 to 400 mGy (pancreas, kidney, liver, stomach, female breast, lung, oral mucosa, and marrow), to 1.6 Gy (esophagus), and to 130 Gy (thyroid gland).

MAIN OUTCOMES AND MEASURES

Site-specific and all solid-cancer mortality.

RESULTS

A total of 18 805 patients were included in the study cohort, and the mean (SD) entry age was 49 (14) years. Most patients were women (14 671 [78.0%]), and most had a Graves disease diagnosis (17 615 [93.7%]). Statistically significant positive associations were observed for all solid cancer mortality (n = 1984; RR at 100-mGy dose to the stomach = 1.06; 95% CI, 1.02-1.10; P = .002), including female breast cancer (n = 291; RR at 100-mGy dose to the breast = 1.12; 95% CI, 1.003-1.32; P = .04) and all other solid cancers combined (n = 1693; RR at 100-mGy dose to the stomach = 1.05; 95% CI, 1.01-1.10; P = .01). The 100-mGy dose to the stomach and breast corresponded to a mean (SD) administered activity of 243 (35) MBq and 266 (58) MBq in patients with Graves disease. For every 1000 patients with hyperthyroidism receiving typical doses to the stomach (150 to 250 mGy), an estimated lifetime excess of 19 (95% CI, 3-40) to 32 (95% CI, 5-66) solid cancer deaths could occur.

CONCLUSIONS AND RELEVANCE

In RAI-treated patients with hyperthyroidism, greater organ-absorbed doses appeared to be modestly positively associated with risk of death from solid cancer, including breast cancer. Additional studies are needed of the risks and advantages of all major treatment options available to patients with hyperthyroidism.

Estimation of Radiation Doses to U.S. Military Test Participants from Nuclear Testing: A Comparison of Historical Film-Badge Measurements, Dose Reconstruction and Retrospective Biodosimetry

Retrospective radiation dose estimations, whether based on physical or biological measurements, or on theoretical dose reconstruction, are limited in their precision and reliability, particularly for exposures that occurred many decades ago. Here, we studied living U.S. military test participants, believed to have received high-dose radiation exposures during nuclear testing-related activities approximately six decades ago, with two primary goals in mind. The first was to compare three different approaches of assessing past radiation exposures: 1. Historical personnel monitoring data alone; 2. Dose reconstruction based on varying levels of completeness of individual information, which can include film badge data; and 3. Retrospective biodosimetry using chromosome aberrations in peripheral blood lymphocytes. The second goal was to use the collected data to make the best possible estimates of bone marrow dose received by a group with the highest military recorded radiation doses of any currently living military test participants. Six nuclear test participants studied had been on Rongerik Atoll during the 1954 CASTLE Bravo nuclear test. Another six were present at the Nevada Test Site (NTS) and/or Pacific Proving Ground (PPG) and were believed to have received relatively high-dose exposures at those locations. All were interviewed, and all provided a blood sample for cytogenetic analysis. Military dose records for each test participant, as recorded in the Defense Threat Reduction Agency's Nuclear Test Review and Information System, were used as the basis for historical film badge records and provided exposure scenario information to estimate dose via dose reconstruction. Dose to bone marrow was also estimated utilizing directional genomic hybridization (dGH) for high-resolution detection of radiation-induced chromosomal translocations and inversions, the latter being demonstrated for the first time for the purpose of retrospective biodosimetry. As the true dose for each test participant is not known these many decades after exposure, this study gauged the congruence of different methods by assessing the degree of correlation and degree of systematic differences. Overall, the best agreement between methods, defined by statistically significant correlations and small systematic differences, was between doses estimated by a dose reconstruction methodology that exploited all the available individual detail and the biodosimetry methodology derived from a weighted average dose determined from chromosomal translocation and inversion rates. Employing such a strategy, we found that the Rongerik veterans who participated in this study appear to have received, on average, bone marrow equivalent doses on the order of 300-400 mSv, while the NTS/ PPG participants appear to have received approximately 250-300 mSv. The results show that even for nuclear events that occurred six decades in the past, biological signatures of exposure are still present, and when taken together, chromosomal translocations and inversions can serve as reliable retrospective biodosimeters, particularly on a group-average basis, when doses received are greater than statistically-determined detection limits for the biological assays used.

Longitudinal Positron Emission Tomography in Preventive Alzheimer's Disease Drug Trials, Critical Barriers from Imaging Science Perspective

Recent Alzheimer's trials have recruited cognitively normal people at risk for Alzheimer's dementia. Due to the lack of clinical symptoms in normal population, conventional clinical outcome measures are not suitable for these early trials. While several groups are developing new composite cognitive tests that could serve as potential outcome measures by detecting subtle cognitive changes in normal people, there is a need for longitudinal brain imaging techniques that can correlate with temporal changes in these new tests and provide additional objective measures of neuropathological changes in brain. Positron emission tomography (PET) is a nuclear medicine imaging procedure based on the measurement of annihilation photons after positron emission from radiolabeled molecules that allow tracking of biological processes in body, including the brain. PET is a well-established in vivo imaging modality in Alzheimer's disease diagnosis and research due to its capability of detecting abnormalities in three major hallmarks of this disease. These include (1) amyloid beta plaques; (2) neurofibrillary tau tangles and (3) decrease in neuronal activity due to loss of nerve cell connection and death. While semiquantitative PET imaging techniques are commonly used to set discrete cut-points to stratify abnormal levels of amyloid accumulation and neurodegeneration, they are suboptimal for detecting subtle longitudinal changes. In this study, we have identified and discussed four critical barriers in conventional longitudinal PET imaging that may be particularly relevant for early Alzheimer's disease studies. These include within and across subject heterogeneity of AD-affected brain regions, PET intensity normalization, neuronal compensations in early disease stages and cerebrovascular amyloid deposition.

Reference tissue normalization in longitudinal (18)F-florbetapir positron emission tomography of late mild cognitive impairment

BACKGROUND

Semiquantitative methods such as the standardized uptake value ratio (SUVR) require normalization of the radiotracer activity to a reference tissue to monitor changes in the accumulation of amyloid-β (Aβ) plaques measured with positron emission tomography (PET). The objective of this study was to evaluate the effect of reference tissue normalization in a test-retest (18)F-florbetapir SUVR study using cerebellar gray matter, white matter (two different segmentation masks), brainstem, and corpus callosum as reference regions.

METHODS

We calculated the correlation between (18)F-florbetapir PET and concurrent cerebrospinal fluid (CSF) Aβ1-42 levels in a late mild cognitive impairment cohort with longitudinal PET and CSF data over the course of 2 years. In addition to conventional SUVR analysis using mean and median values of normalized brain radiotracer activity, we investigated a new image analysis technique-the weighted two-point correlation function (wS2)-to capture potentially more subtle changes in Aβ-PET data.

RESULTS

Compared with the SUVRs normalized to cerebellar gray matter, all cerebral-to-white matter normalization schemes resulted in a higher inverse correlation between PET and CSF Aβ1-42, while the brainstem normalization gave the best results (high and most stable correlation). Compared with the SUVR mean and median values, the wS2 values were associated with the lowest coefficient of variation and highest inverse correlation to CSF Aβ1-42 levels across all time points and reference regions, including the cerebellar gray matter.

CONCLUSIONS

The selection of reference tissue for normalization and the choice of image analysis method can affect changes in cortical (18)F-florbetapir uptake in longitudinal studies.

Organ Dose Estimates for Hyperthyroid Patients Treated with (131)I: An Update of the Thyrotoxicosis Follow-Up Study

The Thyrotoxicosis Therapy Follow-up Study (TTFUS) is comprised of 35,593 hyperthyroid patients treated from the mid-1940s through the mid-1960s. One objective of the TTFUS was to evaluate the long-term effects of high-dose iodine-131 ((131)I) treatment (1-4). In the TTFUS cohort, 23,020 patients were treated with (131)I, including 21,536 patients with Graves disease (GD), 1,203 patients with toxic nodular goiter (TNG) and 281 patients with unknown disease. The study population constituted the largest group of hyperthyroid patients ever examined in a single health risk study. The average number (± 1 standard deviation) of (131)I treatments per patient was 1.7 ± 1.4 for the GD patients and 2.1 ± 2.1 for the TNG patients. The average total (131)I administered activity was 380 ± 360 MBq for GD patients and 640 ± 550 MBq for TNG patients. In this work, a biokinetic model for iodine was developed to derive organ residence times and to reconstruct the radiation-absorbed doses to the thyroid gland and to other organs resulting from administration of (131)I to hyperthyroid patients. Based on (131)I data for a small, kinetically well-characterized sub-cohort of patients, multivariate regression equations were developed to relate the numbers of disintegrations of (131)I in more than 50 organs and tissues to anatomical (thyroid mass) and clinical (percentage thyroid uptake and pulse rate) parameters. These equations were then applied to estimate the numbers of (131)I disintegrations in the organs and tissues of all other hyperthyroid patients in the TTFUS who were treated with (131)I. The reference voxel phantoms adopted by the International Commission on Radiological Protection (ICRP) were then used to calculate the absorbed doses in more than 20 organs and tissues of the body. As expected, the absorbed doses were found to be highest in the thyroid (arithmetic means of 120 and 140 Gy for GD and TNG patients, respectively). Absorbed doses in organs other than the thyroid were much smaller, with arithmetic means of 1.6 Gy, 1.5 Gy and 0.65 Gy for esophagus, thymus and salivary glands, respectively. The arithmetic mean doses to all other organs and tissues were more than 100 times less than those to the thyroid gland. To our knowledge, this work represents the most comprehensive study to date of the doses received by persons treated with (131)I for hyperthyroidism.

Use of radiopharmaceuticals in diagnostic nuclear medicine in the United States: 1960-2010

To reconstruct reliable nuclear medicine-related occupational radiation doses or doses received as patients from radiopharmaceuticals over the last five decades, the authors assessed which radiopharmaceuticals were used in different time periods, their relative frequency of use, and typical values of the administered activity. This paper presents data on the changing patterns of clinical use of radiopharmaceuticals and documents the range of activity administered to adult patients undergoing diagnostic nuclear medicine procedures in the U.S. between 1960 and 2010. Data are presented for 15 diagnostic imaging procedures that include thyroid scan and thyroid uptake; brain scan; brain blood flow; lung perfusion and ventilation; bone, liver, hepatobiliary, bone marrow, pancreas, and kidney scans; cardiac imaging procedures; tumor localization studies; localization of gastrointestinal bleeding; and non-imaging studies of blood volume and iron metabolism. Data on the relative use of radiopharmaceuticals were collected using key informant interviews and comprehensive literature reviews of typical administered activities of these diagnostic nuclear medicine studies. Responses of key informants on relative use of radiopharmaceuticals are in agreement with published literature. Results of this study will be used for retrospective reconstruction of occupational and personal medical radiation doses from diagnostic radiopharmaceuticals to members of the U.S. radiologic technologists' cohort and in reconstructing radiation doses from occupational or patient radiation exposures to other U.S. workers or patient populations.

Nuclear medicine practices in the 1950s through the mid-1970s and occupational radiation doses to technologists from diagnostic radioisotope procedures

Data on occupational radiation exposure from nuclear medicine procedures for the time period of the 1950s through the 1970s is important for retrospective health risk studies of medical personnel who conducted those activities. However, limited information is available on occupational exposure received by physicians and technologists who performed nuclear medicine procedures during those years. To better understand and characterize historical radiation exposures to technologists, the authors collected information on nuclear medicine practices in the 1950s, 1960s, and 1970s. To collect historical data needed to reconstruct doses to technologists, a focus group interview was held with experts who began using radioisotopes in medicine in the 1950s and the 1960s. Typical protocols and descriptions of clinical practices of diagnostic radioisotope procedures were defined by the focus group and were used to estimate occupational doses received by personnel, per nuclear medicine procedure, conducted in the 1950s to 1960s using radiopharmaceuticals available at that time. The radionuclide activities in the organs of the reference patient were calculated using the biokinetic models described in ICRP Publication 53. Air kerma rates as a function of distance from a reference patient were calculated by Monte Carlo radiation transport calculations using a hybrid computational phantom. Estimates of occupational doses to nuclear medicine technologists per procedure were found to vary from less than 0.01 μSv (thyroid scan with 1.85 MBq of administered I-iodide) to 0.4 μSv (brain scan with 26 MBq of Hg-chlormerodin). Occupational doses for the same diagnostic procedures starting in the mid-1960s but using Tc were also estimated. The doses estimated in this study show that the introduction of Tc resulted in an increase in occupational doses per procedure.

Changes in radiation dose with variations in human anatomy: moderately and severely obese adults

The phantoms used in standardized dose assessment are based on a median (i.e., 50th percentile) individual of a large population, for example, adult males or females or children of a particular age. Here we describe phantoms that model instead the influence of obesity on specific absorbed fractions (SAFs) and dose factors in adults.

METHODS

The literature was reviewed to evaluate how individual organ sizes change with variations in body weight in mildly and severely obese adult men and women. On the basis of the literature evaluation, changes were made to our deformable reference adult male and female total-body models. Monte Carlo simulations of radiation transport were performed. SAFs for photons were generated for mildly and severely obese adults, and comparisons were made to the reference (50th) percentile SAF values.

RESULTS

SAFs studied between the obese phantoms and the 50th percentile reference phantoms were not significantly different from the reference 50th percentile individual, with the exception of intestines irradiating some abdominal organs, because of an increase in separation between folds caused by an increase in mesenteric adipose deposits. Some low-energy values for certain organ pairs were different, possibly due only to the statistical variability of the data at these low energies.

CONCLUSION

The effect of obesity on dose calculations for internal emitters is minor and may be neglected in the routine use of standardized dose estimates.

Changes in radiation dose with variations in human anatomy: larger and smaller normal-stature adults

A systematic evaluation has been performed to study how specific absorbed fractions (SAFs) vary with changes in adult body size, for persons of different size but normal body stature.

METHODS

A review of the literature was performed to evaluate how individual organ sizes vary with changes in total body weight of normal-stature individuals. On the basis of this literature review, changes were made to our easily deformable reference adult male and female total-body models. Monte Carlo simulations of radiation transport were performed; SAFs for photons were generated for 10th, 25th, 75th, and 90th percentile adults; and comparisons were made to the reference (50th) percentile SAF values.

RESULTS

Differences in SAFs for organs irradiating themselves were between 0.5% and 1.0%/kg difference in body weight, from 15% to 30% overall, for organs within the trunk. Differences in SAFs for organs outside the trunk were not greater than the uncertainties in the data and will not be important enough to change calculated doses. For organs irradiating other organs within the trunk, differences were significant, between 0.3% and 1.1%/kg, or about 8%-33% overall.

CONCLUSION

The differences are interesting and can be used to estimate how different patients' dosimetry might vary from values reported in standard dose tables.

Convolution-Based Forced Detection Monte Carlo Simulation Incorporating Septal Penetration Modeling

In SPECT imaging, photon transport effects such as scatter, attenuation and septal penetration can negatively affect the quality of the reconstructed image and the accuracy of quantitation estimation. As such, it is useful to model these effects as carefully as possible during the image reconstruction process. Many of these effects can be included in Monte Carlo (MC) based image reconstruction using convolution-based forced detection (CFD). With CFD Monte Carlo (CFD-MC), often only the geometric response of the collimator is modeled, thereby making the assumption that the collimator materials are thick enough to completely absorb photons. However, in order to retain high collimator sensitivity and high spatial resolution, it is required that the septa be as thin as possible, thus resulting in a significant amount of septal penetration for high energy radionuclides. A method for modeling the effects of both collimator septal penetration and geometric response using ray tracing (RT) techniques has been performed and included into a CFD-MC program. Two look-up tables are pre-calculated based on the specific collimator parameters and radionuclides, and subsequently incorporated into the SIMIND MC program. One table consists of the cumulative septal thickness between any point on the collimator and the center location of the collimator. The other table presents the resultant collimator response for a point source at different distances from the collimator and for various energies. A series of RT simulations have been compared to experimental data for different radionuclides and collimators. Results of the RT technique matches experimental data of collimator response very well, producing correlation coefficients higher than 0.995. Reasonable values of the parameters in the lookup table and computation speed are discussed in order to achieve high accuracy while using minimal storage space for the look-up tables. In order to achieve noise-free projection images from MC, it is seen that the inclusion of the RT implementation for septal penetration increases the speed of the simulation by a factor of about 7,500 compared to the conventional SIMIND MC program.

A cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident: dose-response analysis of thyroid follicular adenomas detected during first screening in Ukraine (1998-2000)

The Chornobyl (Chernobyl) accident in 1986 exposed many individuals to radioactive iodines, chiefly (131)I, the effects of which on benign thyroid diseases are largely unknown. To investigate the risk of follicular adenoma in relation to radiation dose after Chornobyl, the authors analyzed the baseline data from a prospective screening cohort study of those exposed as children or adolescents. A stratified random sample was selected from all individuals who were younger than 18 years, had thyroid radioactivity measurements taken within 2 months after the accident, and resided in the three heavily contaminated areas in Ukraine. This analysis is based on the 23 cases diagnosed in 12,504 subjects for whom personal history of thyroid diseases was known. The dose-response relation was linear with an excess relative risk of 2.07 per gray (95% confidence interval: 0.28, 10.31). The risk was significantly higher in women compared with men, with no clear modifying effects of age at exposure. In conclusion, persons exposed to radioactive iodines as children and adolescents have an increased risk of follicular adenoma, though it is smaller than the risk of thyroid cancer in the same cohort. Compared with results from other studies, this estimate is somewhat smaller, but confidence intervals overlap, suggesting compatibility.

Accelerated SPECT Monte Carlo Simulation Using Multiple Projection Sampling and Convolution-Based Forced Detection

Monte Carlo (MC) is a well-utilized tool for simulating photon transport in single photon emission computed tomography (SPECT) due to its ability to accurately model physical processes of photon transport. As a consequence of this accuracy, it suffers from a relatively low detection efficiency and long computation time. One technique used to improve the speed of MC modeling is the effective and well-established variance reduction technique (VRT) known as forced detection (FD). With this method, photons are followed as they traverse the object under study but are then forced to travel in the direction of the detector surface, whereby they are detected at a single detector location. Another method, called convolution-based forced detection (CFD), is based on the fundamental idea of FD with the exception that detected photons are detected at multiple detector locations and determined with a distance-dependent blurring kernel. In order to further increase the speed of MC, a method named multiple projection convolution-based forced detection (MP-CFD) is presented. Rather than forcing photons to hit a single detector, the MP-CFD method follows the photon transport through the object but then, at each scatter site, forces the photon to interact with a number of detectors at a variety of angles surrounding the object. This way, it is possible to simulate all the projection images of a SPECT simulation in parallel, rather than as independent projections. The result of this is vastly improved simulation time as much of the computation load of simulating photon transport through the object is done only once for all projection angles.The results of the proposed MP-CFD method agrees well with the experimental data in measurements of point spread function (PSF), producing a correlation coefficient (r(2)) of 0.99 compared to experimental data. The speed of MP-CFD is shown to be about 60 times faster than a regular forced detection MC program with similar results.

Cervical lymph node metastases: diagnosis at sonoelastography--initial experience

PURPOSE

To prospectively estimate the accuracy of sonoelastography in the differentiation of benign and metastatic cervical lymph nodes (LNs) in patients suspected of having thyroid or hypopharyngeal cancer, with histologic nodal findings as the reference standard.

MATERIALS AND METHODS

The study protocol was approved by the hospital review board; each patient gave written informed consent. One hundred forty-one peripheral neck LNs (60 metastatic, 81 metastasis free) in 43 consecutive patients (22 men, 21 women; mean age, 58 years +/- 13 [standard deviation]) were examined. Patients referred for surgical treatment of suspected thyroid or hypopharyngeal cancer were examined with gray-scale ultrasonography (US), power Doppler US, and sonoelastography. At gray-scale and power Doppler US, the following LN characteristics were evaluated: short-axis diameter, short-to-long-axis diameter ratio, echogenicity, calcifications, and vascularity. A four-point rating scale was used to evaluate the US elastograms for LN visibility, relative brightness, margin regularity, and margin definition. In addition, strains of LN and surrounding neck muscles were measured on elastograms, and the muscle-to-LN strain ratio--that is, the strain index-was calculated. The diagnostic potential of the examined criteria for metastatic involvement was evaluated with univariate analysis and multivariate generalized estimating equation (GEE) regression. P < .05 indicated statistical significance.

RESULTS

A strain index greater than 1.5 had high utility in metastatic LN classification, with 98% specificity, 85% sensitivity, and 92% overall accuracy. These results were significantly better than those obtained by using the best gray-scale criterion--that is, a short-to-long-axis diameter ratio greater than 0.5-which had 81% specificity, 75% sensitivity, and 79% overall accuracy.

CONCLUSION

Sonoelastography had high accuracy (92%) in the differentiation of benign and metastatic cervical LNs in patients suspected of having thyroid or hypopharyngeal cancer.

Autoimmune thyroiditis and exposure to iodine 131 in the Ukrainian cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident: results from the first screening cycle (1998-2000)

CONTEXT

Due to the Chornobyl accident, millions were exposed to radioactive isotopes of iodine and some received appreciable iodine 131 (131I) doses. A subsequent increase in thyroid cancer has been largely attributed to this exposure, but evidence concerning autoimmune thyroiditis (AIT) remains inconclusive.

OBJECTIVE

The objective of the study was to quantify risk of AIT after 131I exposure.

DESIGN/SETTING/PARTICIPANTS

Baseline data were collected from the first screening cycle (1998-2000) of a large cohort of radiation-exposed individuals (n = 12,240), residents of contaminated, iodine-deficient territories of Ukraine. Study individuals were under the age of 18 yr on April 26, 1986, and had thyroid radioactivity measurements made shortly after the accident.

OUTCOMES

AIT was defined a priori based on various combinations of elevated antibodies to thyroid peroxidase (ATPO), TSH, and clinical findings; elevated ATPO were considered to be an indicator of thyroid autoimmunity.

RESULTS

No significant association was found between 131I thyroid dose estimates and AIT, but prevalence of elevated ATPO demonstrated a modest, significant association with 131I that was well described by several concave models. This relationship was apparent in individuals with moderately elevated ATPO and euthyroid, thyroid disease-free individuals.

CONCLUSIONS

Twelve to 14 yr after the Chornobyl accident, no radiation-related increase in prevalence of AIT was found in a large cohort study, the first in which 131I thyroid doses were estimated using individual radioactivity measurements. However, a dose-response relationship with ATPO prevalence raises the possibility that clinically important changes may occur over time. Thus, further follow-up and analysis of prospective data in this cohort are necessary.

A Cohort Study of Thyroid Cancer and Other Thyroid Diseases After the Chornobyl Accident: Thyroid Cancer in Ukraine Detected During First Screening

BACKGROUND

The Chornobyl accident in 1986 exposed thousands of people to radioactive iodine isotopes, particularly (131)I; this exposure was followed by a large increase in thyroid cancer among those exposed as children and adolescents, particularly in Belarus, the Russian Federation, and Ukraine. Here we report the results of the first cohort study of thyroid cancer among those exposed as children and adolescents following the Chornobyl accident.

METHODS

A cohort of 32 385 individuals younger than 18 years of age and resident in the most heavily contaminated areas in Ukraine at the time of the accident was invited to be screened for any thyroid pathology by ultrasound and palpation between 1998 and 2000; 13 127 individuals (44%) were actually screened. Individual estimates of radiation dose to the thyroid were available for all screenees based on radioactivity measurements made shortly after the accident and on interview data. The excess relative risk per gray (Gy) was estimated using individual doses and a linear excess relative risk model.

RESULTS

Forty-five pathologically confirmed cases of thyroid cancer were found during the 1998-2000 screening. Thyroid cancer showed a strong, monotonic, and approximately linear relationship with individual thyroid dose estimate (P<.001), yielding an estimated excess relative risk of 5.25 per Gy (95% confidence interval [CI] = 1.70 to 27.5). Greater age at exposure was associated with decreased risk of radiation-related thyroid cancer, although this interaction effect was not statistically significant.

CONCLUSION

Exposure to radioactive iodine was strongly associated with increased risk of thyroid cancer among those exposed as children and adolescents. In the absence of Chornobyl radiation, 11.2 thyroid cancer cases would have been expected compared with the 45 observed, i.e., a reduction of 75% (95% CI = 50% to 93%). The study also provides quantitative risk estimates minimally confounded by any screening effects. Caution should be exercised in generalizing these results to any future similar accidents because of the potential differences in the nature of the radioactive iodines involved, the duration and temporal patterns of exposures, and the susceptibility of the exposed population.

Normal Organ Radiation Dosimetry and Associated Uncertainties in Nuclear Medicine, with Emphasis on Iodine-131

In many medical applications involving the administration of iodine-131 ((131)I) in the form of iodide (I(-)), most of the dose is delivered to the thyroid gland. To reliably estimate the thyroid absorbed dose, the following data are required: the thyroid gland size (i.e. mass), the fractional uptake of (131)I by the thyroid, the spatial distribution of (131)I within the thyroid, and the length of time (131)I is retained in the thyroid before it is released back to blood, distributed in other organs and tissues, and excreted from the body. Estimation of absorbed dose to nonthyroid tissues likewise requires knowledge of the time course of activity in each organ. Such data are rarely available, however, and therefore dose calculations are generally based on reference models. The MIRD and ICRP have published metabolic models and have calculated absorbed doses per unit intake for many nuclides and radioactive pharmaceuticals. Given the activity taken into the body, one can use such models and make reasonable calculations for average organ doses. When normal retention and excretion pathways are altered, the baseline models need to be modified, and the resulting organ dose estimates are subject to larger errors. This paper describes the historical evolution of radioactive isotopes in medical diagnosis and therapy. We nonmathematically summarize the methods used in current practice to estimate absorbed dose and summarize some of the risk data that have emerged from medical studies of patients with special attention to dose and effects observed in those who received (131)I-iodide in diagnosis and/or therapy.

Thyroid gland tumor diagnosis at US elastography

PURPOSE

To prospectively evaluate the elastographic appearance of thyroid gland tumors and explore the potential sensitivity and specificity of ultrasonographic (US) elastography for differentiating benign and malignant tumors, with histopathologic analysis as the reference standard.

MATERIALS AND METHODS

The study was institutional review board approved, and each patient gave written informed consent. Fifty-two thyroid gland lesions (22 malignant, 30 benign) in 31 consecutive patients (six men, 25 women; mean age, 49.7 years +/- 14.7 [standard deviation]) were examined with real-time elastography in the elasticity imaging mode implemented on a clinical US scanner modified for research. In addition, the radiofrequency echo data stored during US were exported from the scanner and used for off-line strain image reconstruction. All elastograms were evaluated for the lesion visibility, relative brightness, and margin regularity and definition by using a four-point scale. In addition, normal thyroid gland tissue and thyroid gland tumor strains were measured on off-line processed elastograms, and the thyroid gland-to-tumor strain ratio (ie, strain index) was calculated. The potential of elastographic criteria for the diagnosis of thyroid gland cancer was evaluated with univariate analysis and multivariate logistic regression. Qualitative variables were compared by using the chi2 test, and quantitative variables were compared by using the Mann-Whitney U test. P < .05 was considered to indicate significance.

RESULTS

A strain index value greater than 4 on off-line processed elastograms was the strongest independent predictor of thyroid gland malignancy (P < .001); this criterion had 96% specificity and 82% sensitivity. Two other elastographic criteria, which were evaluated on real-time elastograms--a margin regularity score higher than 3 (88% specificity, 36% sensitivity) and a tumor area ratio higher than 1 (92% specificity, 46% sensitivity)--also were associated with malignancy (P < .05). However, the usefulness of these criteria was not considered to be high because of their low sensitivity.

CONCLUSION

Elastography is a promising imaging technique that can assist in the differential diagnosis of thyroid cancer.

Elastic moduli of thyroid tissues under compression

The aim of this study was to evaluate the elastic moduli of thyroid tissues under uniaxial compression and to establish the biomechanical fundamentals for accurate interpretation of thyroid elastograms. A total of 67 thyroid samples (24 samples of normal thyroid tissue, 2 samples of thyroid tissue with chronic thyroiditis, 12 samples of adenomatous goiter lesions and 7 samples of follicular adenoma, 19 samples of papillary adenocarcinoma (PAC) and 3 samples of follicular adenocarcinoma (FAC)) obtained from 36 patients who had received thyroid surgery were subjected to biomechanical testing within three hours after surgical resection at precompression strains of 5%, 10% and 20% and applied strains of 1%, 2%, 5% and 10% of sample height. As a result, the mean values of elastic moduli for benign thyroid lesions at all examined precompression levels were significantly higher than those for normal thyroid tissue measured at the same load (p<0.01). At low precompression (5%) and compression (1-2%) levels, benign thyroid nodule samples were 1.7 times harder than normal thyroid tissue. At high precompression (20%) and compression (10%) levels, this difference increased to 2.4 times. Stiffness of PAC samples was significantly higher than those for normal thyroid tissue and benign thyroid tumors measured at the same load (p<0.01). At low precompression (5%) and compression (1-2%) levels, PAC samples were 5.0 times harder than normal thyroid tissue. At high precompression (20%) and compression (10%) levels, this difference increased to 17.7 times. In contrast, samples of FAC were much softer than PAC (p<0.05) and were comparable in stiffness to normal thyroid tissues. The significant differences in the stiffness between normal thyroid tissue and thyroid tumors may provide useful information for accurate interpretation of thyroid elastograms.

A cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident: objectives, design and methods

The thyroid gland in children is one of the organs that is most sensitive to external exposure to X and gamma rays. However, data on the risk of thyroid cancer in children after exposure to radioactive iodines are sparse. The Chornobyl accident in Ukraine in 1986 led to the exposure of large populations to radioactive iodines, particularly (131)I. This paper describes an ongoing cohort study being conducted in Belarus and Ukraine that includes 25,161 subjects under the age of 18 years in 1986 who are being screened for thyroid diseases every 2 years. Individual thyroid doses are being estimated for all study subjects based on measurement of the radioactivity of the thyroid gland made in 1986 together with a radioecological model and interview data. Approximately 100 histologically confirmed thyroid cancers were detected as a consequence of the first round of screening. The data will enable fitting appropriate dose-response models, which are important in both radiation epidemiology and public health for prediction of risks from exposure to radioactive iodines from medical sources and any future nuclear accidents. Plans are to continue to follow-up the cohort for at least three screening cycles, which will lead to more precise estimates of risk.

A theoretical model for prescription of the patient-specific therapeutic activity for radioiodine therapy of Graves' disease

A fundamental function of the thyroid is to extract iodine from the blood, synthesize it into thyroid hormones, and release it into the circulation under feedback control by pituitary-secreted hormones. This capability of the thyroid, termed as functionality, can in principle be related to the severity of hyperthyroidism in individual patients. In this paper the uptake and release of 131I by the thyroid following the administration of 131I therapy for Graves' disease has been theoretically studied. The kinetics of iodine in the thyroid and blood have been evaluated using a two-compartment model. This simplified model appears to be adequate for dosimetry purposes and allows one to correlate levels of increased thyroid functionality (hyperthyroidism) with clinically measurable kinetic parameters. An expression has been derived for the rate of change of thyroid mass following therapy; this has the same form as an empirical relationship described in an earlier work. A method is presented for calculation of the amount of radioiodine activity to be administered to individual patients in order to achieve the desired final functionality of the gland. The activity to be administered is based on measurements of 131I kinetics after the administration of a 'low-activity' (1850 kBq) tracer for treatment planning.

Monoclonal antibodies in the treatment of hematologic malignancies: radiation dosimetry aspects

A number of therapeutic agents in nuclear medicine are currently attracting considerable interest, including several for the treatment of hematologic and nonhematologic malignancies. A knowledge of the radiation dose received by different organs in the body is essential to the optimization of the therapy for each patient; one wants to maximize the dose to the malignant tissue while minimizing the dose to critical healthy tissues and avoiding any toxic response therein. In this paper, current methods for calculating radiation doses will be discussed and evaluated. In almost all nuclear medicine therapy, and particularly in this application, dose to the active marrow is of paramount concern. Specific focus on current bone marrow dose models and their ability to predict observed marrow toxicity in patient populations to date will be discussed. The paper will focus on current and possible future dosimetry practice in therapeutic nuclear medicine, particularly as regards the treatment of hematologic malignancies.

Red marrow dosimetry for radiolabeled antibodies that bind to marrow, bone, or blood components

Hematologic toxicity limits the radioactivity that may be administered for radiolabeled antibody therapy. This work examines approaches for obtaining biodistribution data and performing dosimetry when the administered antibody is known to bind to a cellular component of blood, bone, or marrow. Marrow dosimetry in this case is more difficult because the kinetics of antibody clearance from the blood cannot be related to the marrow. Several approaches for obtaining antibody kinetics in the marrow are examined and evaluated. The absorbed fractions and S factors that should be used in performing marrow dosimetry are also examined and the effect of including greater anatomical detail is considered. The radiobiology of the red marrow is briefly reviewed. Recommendations for performing marrow dosimetry when the antibody binds to the marrow are provided.

Comparing filtered backprojection and ordered-subsets expectation maximization for small-lesion detection and localization in 67Ga SPECT

Iterative reconstruction of SPECT images has recently become clinically available as an alternative to filtered backprojection (FBP). However, there is conflicting evidence on whether iterative reconstruction, such as with the ordered-subsets expectation maximization (OSEM) algorithm, improves diagnostic performance over FBP. The study objective was to determine if the detection and localization of small lesions in simulated thoracic gallium SPECT images are better with OSEM reconstruction than with FBP, both with and without attenuation correction (AC).

METHODS

Images were simulated using an analytic projector acting on the mathematic cardiac torso computer phantom. Perfect scatter rejection was assumed. Lesion detection accuracy was assessed using localization receiver operating characteristic methodology. The images were read by 5 nuclear medicine physicians. For each reconstruction strategy and for each observer, data were collected in 2 viewing sessions of 100 images. Two-way ANOVA and, when indicated, the Scheffé multiple comparisons test were applied to check for significant differences.

RESULTS

Little difference in the accuracy of detection or localization was seen between FBP with and without AC. OSEM with AC extended the contrast range for accurate lesion detection and localization over that of the other methods investigated. Without AC, no significant difference between OSEM and FBP reconstruction was detected.

CONCLUSION

OSEM with AC may improve the detection and localization of thoracic gallium-labeled lesions over FBP reconstruction.

A new rectal model for dosimetry applications

A revised geometric representative model of the lower part of the colon, including the rectum, the urinary bladder and prostate, is proposed for use in the calculation of absorbed dose from injected radiopharmaceuticals. The lower segment of the sigmoid colon as described in the 1987 Oak Ridge National Laboratory mathematical phantoms does not accurately represent the combined urinary bladder/rectal/prostate geometry. In the revised model in this study, the lower part of the abdomen includes an explicitly defined rectum. The shape of sigmoid colon is more anatomically structured, and the diameters of the descending colon are modified to better approximate their true anatomic dimensions. To avoid organ overlap and for more accurate representation of the urinary bladder and the prostate gland (in the male), these organs are shifted from their originally defined positions. The insertion of the rectum and the shifting of the urinary bladder will not overlap with or displace the female phantom's ovaries or the uterus. In the adult male phantom, the prostatic urethra and seminal duct are also included explicitly in the model. The relevant structures are defined for the newborn and 1-, 5-, 10- and 15-y-old (adult female) and adult male phantoms.

METHODS

Values of the specific absorbed fractions and radionuclide S values were calculated with the SIMDOS dosimetry package. Results for 99mTc and other radionuclides are compared with previously reported values.

RESULTS

The new model was used to calculate S values that may be crucial to calculations of the effective dose equivalent. For 131I, the S (prostate<--urinary bladder contents) and S (lower large intestine [LLI] wall<--urinary bladder contents) are 6.7 x 10(-6) and 3.41 x 10(-6) mGy/MBq x s, respectively. Corresponding values given by the MIRDOSE3 computer program are 6.23 x 10(-6) and 1.53 x 10(-6) mGy/MBq x s, respectively. The value of S (rectum wall<--urinary bladder contents) is 4.84 x 10(-5) mGy/MBq x s. For 99mTc, we report S (testes<--prostate) and S (LLI wall<--prostate) of 9.41 x 10(-7) and 1.53 x 10(-7) mGy/MBq x s versus 1.33 x 10(-6) and 7.57 x 10(-6) mGy/MBq x s given by MIRDOSE3, respectively. The value of S (rectum wall<--prostate) for 99mTc is given as 4.05 x 10(-6) mGy/MBq x s in the present model.

CONCLUSION

The new revised rectal model describes an anatomically realistic lower abdomen region, thus giving improved estimates of absorbed dose. Due to shifting the prostate gland, a 30%-45% reduction in the testes dose and the insertion of the rectum leads to 48%-55% increase in the LLI wall dose when the prostate is the source organ.

MIRD pamphlet no. 16: Techniques for quantitative radiopharmaceutical biodistribution data acquisition and analysis for use in human radiation dose estimates

This report describes recommended techniques for radiopharmaceutical biodistribution data acquisition and analysis in human subjects to estimate radiation absorbed dose using the Medical Internal Radiation Dose (MIRD) schema. The document has been prepared in a format to address two audiences: individuals with a primary interest in designing clinical trials who are not experts in dosimetry and individuals with extensive experience with dosimetry-based protocols and calculational methodology. For the first group, the general concepts involved in biodistribution data acquisition are presented, with guidance provided for the number of measurements (data points) required. For those with expertise in dosimetry, highlighted sections, examples and appendices have been included to provide calculational details, as well as references, for the techniques involved. This document is intended also to serve as a guide for the investigator in choosing the appropriate methodologies when acquiring and preparing product data for review by national regulatory agencies. The emphasis is on planar imaging techniques commonly available in most nuclear medicine departments and laboratories. The measurement of the biodistribution of radiopharmaceuticals is an important aspect in calculating absorbed dose from internally deposited radionuclides. Three phases are presented: data collection, data analysis and data processing. In the first phase, data collection, the identification of source regions, the determination of their appropriate temporal sampling and the acquisition of data are discussed. In the second phase, quantitative measurement techniques involving imaging by planar scintillation camera, SPECT and PET for the calculation of activity in source regions as a function of time are discussed. In addition, nonimaging measurement techniques, including external radiation monitoring, tissue-sample counting (blood and biopsy) and excreta counting are also considered. The third phase, data processing, involves curve-fitting techniques to integrate the source time-activity curves (determining the area under these curves). For some applications, compartmental modeling procedures may be used. Last, appendices are included that provide a table of symbols and definitions, a checklist for study protocol design, example formats for quantitative imaging protocols, temporal sampling error analysis techniques and selected calculational examples. The utilization of the presented approach should aid in the standardization of protocol design for collecting kinetic data and in the calculation of absorbed dose estimates.

MIRD pamphlet No. 17: the dosimetry of nonuniform activity distributions--radionuclide S values at the voxel level. Medical Internal Radiation Dose Committee

The availability of quantitative three-dimensional in vivo data on radionuclide distributions within the body makes it possible to calculate the corresponding nonuniform distribution of radiation absorbed dose in body organs and tissues. This pamphlet emphasizes the utility of the MIRD schema for such calculations through the use of radionuclide S values defined at the voxel level. The use of both dose point-kernels and Monte Carlo simulation methods is also discussed. PET and SPECT imaging can provide quantitative activity data in voxels of several millimeters on edge. For smaller voxel sizes, accurate data cannot be obtained using present imaging technology. For submillimeter dimensions, autoradiographic methods may be used when tissues are obtained through biopsy or autopsy. Sample S value tabulations for five radionuclides within cubical voxels of 3 mm and 6 mm on edge are given in the appendices to this pamphlet. These S values may be used to construct three-dimensional dose profiles for nonuniform distributions of radioactivity encountered in therapeutic and diagnostic nuclear medicine. Data are also tabulated for 131I in 0.1-mm voxels for use in autoradiography. Two examples illustrating the use of voxel S values are given, followed by a discussion of the use of three-dimensional dose distributions in understanding and predicting biologic response.

The MIRD perspective 1999. Medical Internal Radiation Dose Committee

The MIRD schema is a general approach for medical internal radiation dosimetry. Although the schema has traditionally been used for organ dosimetry, it is also applicable to dosimetry at the suborgan, voxel, multicellular and cellular levels. The MIRD pamphlets that follow in this issue and in coming issues, as well as the recent monograph on cellular dosimetry, demonstrate the flexibility of this approach. Furthermore, these pamphlets provide new tools for radionuclide dosimetry applications, including the dynamic bladder model, S values for small structures within the brain (i.e., suborgan dosimetry), voxel S values for constructing three-dimensional dose distributions and dose-volume histograms and techniques for acquiring quantitative distribution and pharmacokinetic data.

Cancer mortality following treatment for adult hyperthyroidism. Cooperative Thyrotoxicosis Therapy Follow-up Study Group

CONTEXT

High-dose iodine 131 is the treatment of choice in the United States for most adults with hyperthyroid disease. Although there is little evidence to link therapeutic (131)I to the development of cancer, its extensive medical use indicates the need for additional evaluation.

OBJECTIVE

To evaluate cancer mortality among hyperthyroid patients, particularly after (131)I treatment.

DESIGN

A retrospective cohort study.

SETTING

Twenty-five clinics in the United States and 1 clinic in England.

PATIENTS

A total of 35 593 hyperthyroid patients treated between 1946 and 1964 in the original Cooperative Thyrotoxicosis Therapy Follow-up Study; 91 % had Graves disease, 79% were female, and 65% were treated with (131)I.

MAIN OUTCOME MEASURE

Standardized cancer mortality ratios (SMRs) after 3 treatment modalities for hyperthyroidism.

RESULTS

Of the study cohort, 50.5% had died by the end of follow-up in December 1990. The total number of cancer deaths was close to that expected based on mortality rates in the general population (2950 vs 2857.6), but there was a small excess of mortality from cancers of the lung, breast, kidney, and thyroid, and a deficit of deaths from cancers of the uterus and the prostate gland. Patients with toxic nodular goiter had an SMR of 1.16 (95% confidence interval [CI], 1.03-1.30). More than 1 year after treatment, an increased risk of cancer mortality was seen among patients treated exclusively with antithyroid drugs (SMR, 1.31; 95% CI, 1.06-1.60). Radioactive iodine was not linked to total cancer deaths (SMR, 1.02; 95% CI, 0.98-1.07) or to any specific cancer with the exception of thyroid cancer (SMR, 3.94; 95% CI, 2.52-5.86).

CONCLUSIONS

Neither hyperthyroidism nor (131)I treatment resulted in a significantly increased risk of total cancer mortality. While there was an elevated risk of thyroid cancer mortality following (131)I treatment, in absolute terms the excess number of deaths was small, and the underlying thyroid disease appeared to play a role. Overall, (131)I appears to be a safe therapy for hyperthyroidism.

Childhood cancer 10 years after the Chernobyl accident

Ten years have passed since the Chernobyl disaster. Five years ago, reports began to appear suggesting an increase in the frequency of thyroid cancer in children living or born in the areas with highest exposure to radioactive contamination. During the past year, data have been published, presented, or submitted that demonstrate the magnitude of the increase in incidence. No increase in childhood leukemia or other cancers has been documented. However, anxiety about the future persists. A rapid government response, including the distribution of potassium iodide to the highest-risk groups, pregnant women and young children, could have prevented the majority of the cases of thyroid cancer.

Radiation absorbed dose from indium-111-CYT-356

Indium-CYT-356 is an agent developed by CYTOGEN Inc. (CYT) (Princeton, NJ) for the use in staging patients with prostate cancer. This investigation was performed to provide the human dosimetry needed for Food and Drug Administration approval for routine use in patients.

METHODS

Biodistribution data collected from three sites were obtained from prostate cancer patients who received diagnostic doses of 111In-CYT-356. Data included blood and urine collections, and the organ uptake value was measured from sequential conjugate whole-body and planar images over a 7-10 day period. Dose contributions from radioactivity in transit through the GI tract were estimated using a compartmental model. The calculations used the MIRD methodology and MIRDOSE 3.

RESULTS

The total-body dose observed was 0.14 mGy/MBq, and the effective dose was found to be 0.25-0.29 mSv/MBq. The largest organ doses were found for the liver (1.0 mGy/MBq), kidneys (0.67 mGy/MBq) and spleen (0.88 mGy/MBq).

CONCLUSION

The radiation dose to the patient from a typical 185 MBq administration of 111In-CYT-356 is comparable to the dose from other 111In-labeled whole antibodies used in the diagnosis and management of cancer patients. The inclusion of the GI tract as a source organ increases the effective dose by 18%.

Human recombinant TNF-alpha on localization of 90Y-radioantibody in human tumour xenografts

The effect of recombinant human tumour necrotic factor-alpha (TNF-alpha) on the intratumour and whole-body distributions of 90Y-labelled C110 anticarcinoembryonic antigen (CEA) monoclonal antibody (MAb) was studied using nude mice bearing two different tumours. The nude mice were injected subcutaneously with the CEA-positive LS174T colorectal cancer xenograft and the CEA-negative H-MESO-1 malignant mesothelioma xenograft. One hour before injection of radiolabelled MAb, mice were injected intravenously with human recombinant TNF-alpha (3 mg per mouse) or saline, and biodistributions of radiolabel were determined by tissue counting and whole-body autoradiography (ARG). Twenty-four hours after injection, TNF-alpha administration increased radioactivity in the LS174T tumour by 57% (17.30 +/- 1.61 vs. 9.83 +/- 1.55% ID g-1, P < 0.01), while decreasing radioactivity in blood and other normal organs. Diminished but similar effects on radioantibody biodistribution were seen at 48 and 72 hours. TNF-alpha did not affect specific MAb localization in the control H-MESO xenograft. Tumour:blood ratios were increased from 0.7 to 1.7 at 24 h with TNF-alpha administration. Pretreatment with TNF-alpha may be of value in increasing specific localization of monoclonal antibodies in tumour tissue.

Radon update: facts concerning environmental radon: levels, mitigation strategies, dosimetry, effects and guidelines. SNM Committee on Radiobiological Effects of Ionizing Radiation

The risk from environmental radon levels is not higher now than in the past, when residential exposures were not considered to be a significant health hazard. The majority of the radon dose is not from radon itself, but from short-lived alpha-emitting radon daughters, most notably 218Po(T1/2 3 min) and 214Po (T1/2 0.164 msec) along with beta particles from 214Bi (T1/2 19.7 min). Radon gas can penetrate homes from many sources and in various fashions. Measuring radon in homes is simple and relatively inexpensive and may be accomplished in a variety of ways. Although it is not possible to radon-proof a house, it is possible to reduce the level. In high radon areas, if the average level is higher than 4-8 pCi/liter (NCRP recommended level is 8 pCi/liter; EPA recommended level is 4 pCi/liter), appropriate action is advised. The shape of the dose response curves for miners exposed to alpha-emitting particles in the workplace is consistent with current biologic knowledge. It is linear in the low dose range and saturates in the high dose range. No detectable increase in lung cancer frequency is seen in the lowest exposed miners (those with exposures < 120 WLM, the relevant dose interval for most homes). Evidence for a health effect from radon exposure is based on data from animal studies and epidemiologic studies of mines. Extensive radiobiologic data predict a linear dose-response curve in the low dose region due to poor biological repair mechanisms for the high density of ionizing events that alpha particles create. However, no compelling evidence for increased cancer risks has yet been demonstrated from "acceptable" levels (< 4-8 pCi/liter).

Dosimetry of intraperitoneally administered radiolabeled antibodies

Intraperitoneal and intracavitary radioimmunotherapy differ from other approaches of radioimmunotherapy in that high activity and dose gradients exist near the solution/tumor interface. Dose to tumor and normal tissue at the interface is a function of depth and is due to three major components: (1) the activity concentration of the administered radiolabeled antibody solution as a function of time within the compartment; (2) the spatial distribution of antibody/radionuclide complex as a function of depth and time as the biomolecules bind to and permeate tumor/normal tissues; and (3) the physical characteristics of the radionuclide in relation to depth of antibody penetration. In this review, the biological and physical aspects of intraperitoneally administered radiolabeled antibodies are discussed, and the state of experimental and calculational studies for this site is described. Areas requiring future investigation are examined, and recommendations are made regarding the type of measurements and calculations which are required for accurate dosimetry.

Pharmacokinetics of the FO23C5 anti-CEA antibody fragment labelled with 99Tcm and 111In: a comparison in patients

The FO23C5 anti-carcinoembryonic antigen (CEA) F(ab')2 antibody was radiolabelled with 111In via diethylenetriaminepentaacetic acid (DTPA) and directly with 99Tcm by stannous ion and mercaptoethanol antibody reduction to compare the pharmacokinetics of these three agents. Four patients received 15 mCi 99Tcm-Fab' 1 week before receiving 1 mCi 111In-F(ab')2. Five additional patients received only the 99Tcm-Fab'. Radiochromatograms by high-performance liquid chromatographic (HPLC) analysis of serum and urine samples from patients receiving 111In were typical of those observed by us previously in connection with other antibodies. The identical analyses of samples from patients receiving 99Tcm showed no differences with the method of reduction and more complex radiochromatograms. In addition to peaks due to a mixture of labelled F(ab')2 and Fab' fragments and, occasionally, immune complexes, there were several peaks due to labelled cysteine and other small labelled species present in both serum and urine. The biodistribution of 99Tcm was as expected for a labelled Fab' fragment: relative to 111In, 99Tcm cleared rapidly from circulation and into kidneys and urine. Liver levels of 111In and 99Tcm were surprisingly similar at 1 day (12 versus 9% ID) although initial 111In levels were lower and increased while 99Tcm levels were higher and decreased. Spleen levels were also similar. In 4/9 patients receiving 99Tcm, hepatobiliary clearance was observed at levels which could confuse interpretation whereas this mode of clearance was observed in only 1/4 patients receiving 111In. Image quality was superior with 111In versus 99Tcm at 1 day postadministration as judged by counting rates and background activity whereas the opposite was true at 2-3 h postadministration.

Intratumoral and whole-body distributions of C110 anti-carcinoembryonic antigen radioimmunotoxin after intraperitoneal and intravenous injection: a quantitative autoradiographic study

The intratumoral and whole-body distributions of 90Y-labeled C110 anticarcinoembryonic antigen immunotoxin after i.p. and i.v. injection were compared by quantitative autoradiography. During in vitro incubation of spherical tumor nodules of LS174T human colon cancer (about 5 mm in diameter) in a medium containing C110 radioimmunotoxin (RIT), the direct penetration of the immunotoxin increased with time but was limited to the outer 300 microns of the tumor nodule after 12 h of incubation. In vivo experiments were performed in nude mice bearing LS174T xenografts as i.p. tumor nodules. Injection of C110 RIT i.p. resulted in a ring-like distribution, i.e., high uptake at the tumor periphery and considerably lower uptake at the tumor center (ratio of peripheral to central concentration, 7:1 at 1 day and 2:1 at 5 days). In contrast, i.v. injection provided a much smaller gradient in C110 RIT distribution from peripheral to central regions (ratio of peripheral to central concentration, 3:1 at 1 day and 1:1 at 5 days). Estimates of total tumor uptake of C110 RIT by quantitative autoradiography demonstrated almost equivalent tumor uptake after either i.p. or i.v. injection, while i.v. injection was associated with increased C110 RIT uptake in various normal organs, especially in the liver, as compared to i.p. injection. The results in this study suggest that (a) i.v. injection may produce more homogeneous distribution of C110 RIT in i.p. tumor nodules of LS174T but may also result in increased liver toxicity, and (b) i.p. injection may decrease C110 RIT exposure of normal tissues, which can reduce systemic toxicity, but may also produce more restricted intratumoral distribution of C110 RIT. In addition, current methods using a nude mouse model of i.p. tumor nodules and quantitative autoradiography allow us to assess intratumoral and whole-body distributions of radiolabeled immunoconjugates from various administration routes.

Long-term biodistribution in tumored mice of murine and chimeric B72.3-IgG antibody radiolabeled with 114mIn via both DTPA and a macrocyclic chelator

To assess the possibilities of using 114mIn as a therapeutic agent, the long-term biodistribution of 114mIn was studied, in tumor-bearing nude mice, after injection of labeled monoclonal antibody (MoAb) B72.3 IgG, either DTPA-coupled murine, DTPA-coupled chimeric, or macrocycle-coupled chimeric antibody. Although the biodistributions in all cases were similar, there were important differences. The use of DTPA-coupled chimeric antibody led to higher concentrations of radioactivity in tumor, and to lower concentrations in liver and bone, as compared to DTPA-coupled murine antibody. The use of macrocycle-coupled chimeric antibody led to higher concentrations of radioactivity in the liver and in bone as compared to the DTPA-coupled chimeric antibody. However, in this case there were no significant differences in tumor uptake or clearance. Radiation doses were calculated based on the organ retention and by neglecting source-to-target contributions. Radiation dose distribution was marginally favorable for therapy in the group injected with DTPA-coupled chimeric antibody.

Pulmonary nuclear medicine

The major nuclear medicine contribution to the pulmonary imaging literature for the past year was the inaugural report from the Prospective Investigation of Pulmonary Embolism Diagnosis study. Investigations focusing on the role of thrombolytic agents for the management of pulmonary thrombosis have advanced to the stage in which different therapeutic regimens are being tested along with new agents that continue to emerge. Ongoing research and clinical trials are evaluating newer radiolabeled aerosols in patients with airways and interstitial lung disease using imaging and clearance measurements. Positron-emission tomography continues to be utilized in a few research centers for tumor localization and characterization.

SPECT volume quantitation: influence of spatial resolution, source size and shape, and voxel size

A number of factors influence the accuracy of estimation of source volume with single-photon emission computed tomography (SPECT) imaging. This study investigated the role of a number of factors including system spatial resolution (which includes the influence of low-pass filters applied to suppress noise), source size and shape, and voxel size in determining volume. A rectangular parallelepiped (bar), a right cylinder, and a sphere were mathematically modeled as being imaged with a SPECT system by calculating the three-dimensional (3-D) convolution of them with symmetric Gaussian functions of 20 different full widths at half maximums (FWHM's). The resulting activity profiles were analyzed to determine the location of the edges as a function of the source size relative to the FWHM of the system. The edge definition criteria studied were (1) the location of the 50% count threshold and (2) the maximum in the local gradient. In addition, the threshold which yielded the correct edge location was also determined. A nonstationary computer simulation of SPECT imaging, based on the serial model of the system transfer function, was used to test the predictions of the mathematical model and investigate the influence of (1) voxel size and sampling with a discrete array of voxels; (2) attenuation; (3) scatter; (4) variable spatial resolution; (5) low-pass filtering; and (6) noise. The mathematical model predicted that both the 50% threshold and the maximum in the local gradient methods of estimating edge location would show either an under- or overestimate of source volume depending on both the ratio of source diameter to system FWHM and the source shape.(ABSTRACT TRUNCATED AT 250 WORDS)

Initial clinical study of indium-111-labeled clone 110 anticarcinoembryonic antigen antibody in patients with colorectal cancer

A murine monoclonal antibody directed against carcinoembryonic antigen (CEA) was labeled with indium-111 (111In) by means of a benzylisothiocyanate derivative of diethylenetriamine penta-acetic acid (DTPA) and used for clinical radioimmunodetection studies. Twenty-one patients having a history of surgically resected colorectal cancer and rising serum CEA levels suggestive of tumor recurrence were studied. Patients were infused over 20 minutes with 5, 10, or 20 mg of the monoclonal antibody labeled with 5 mCi of 111In. The mean radiochemical purity was greater than 96%. No toxicity was seen. The stability of the radiolabel on antibody in patient serum was demonstrated by high-performance liquid chromatography (HPLC), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) with autoradiography, and immunoprecipitation for up to 96 hours after infusion. Tumor sites were identified in 20 of 21 patients. Sites of antibody accumulation in 20 patients were confirmed as tumor either by resection at laparotomy (16 patients) or fine-needle biopsy (four patients). Nine patients who had the identified lesion resected or irradiated showed return of the serum CEA antigen level to normal or near normal values. In the absence of high levels of circulating CEA (greater than 500 ng/mL), the disappearance of radioactivity from patient serum demonstrated first order elimination kinetics, with a mean half-life of 38 hours. The serum half-life was not affected by the dose of antibody administered or by serum CEA titers below 500 ng/mL. Despite a mean liver uptake of 18% injected dose (ID) 24 hours after administration, hepatic metastases were easily visualized as areas of increased uptake of radioactivity. Radioimmunodetection of recurrent colorectal cancer, not detected by computed tomographic (CT) scans, appears achievable with this agent. This may allow successful clinical intervention in selected patients.

Preclinical assessments of 90Y-labeled C110 anti-carcinoembryonic antigen immunotoxin: a therapeutic immunoconjugate for human colon cancer

We have synthesized 90Y-labeled immunotoxin (IT) containing ricin A chain and C110 anti-carcinoembryonic antigen monoclonal antibody (MAb) to produce a therapeutic immunoconjugate for human colon cancer. The C110 IT was labeled with 90Y via a benzylisothiocyanate derivative of diethylenetriaminepentaacetic acid. The efficiency of 90Y labeling was consistently 90 to 98%, with a specific activity of about 1 microCi/microgram. In in vitro stability studies, more than 80% of 90Y remained bound to the C110 IT for up to 5 days after incubation. The percentage of binding of 90Y-labeled C110 IT to carcinoembryonic antigen-coated microbeads was 86%, indicating good retention of the initial immunoreactivity of the C110 MAb. In in vitro protein synthesis inhibition assays, 90Y-labeled C110 IT was approximately 3.7-fold more toxic to the LS174T human colon carcinoma cell line than unmodified C110 IT and 1380-fold more toxic than 90Y-labeled C110 MAb. Biodistribution studies of 90Y-labeled C110 IT in LS174T tumor-bearing mice showed that, at 24 h following i.p. injection, high accumulation of radioactivity was seen in the i.p. tumor and liver and, thereafter, high accumulation in these tissues remained almost unchanged until up to 168 h, with percentage of injected dose/g ranging from 15 to 18% in the tumor and 10 to 15% in the liver. The radioactivity in the spleen and bone gradually increased with time and reached their highest levels (approximately 8% of injected dose/g) at 168 h. Estimation of absorbed radiation doses to the tissues showed that i.p. tumor would have received an approximately 1.5 to 7 times higher radiation dose than normal organs. In in vivo therapeutic trials, 90Y-labeled C110 IT provided survival prolongation of LS174T tumor-bearing mice superior to that with either unmodified C110 IT or 90Y-labeled C110 MAb (4 less than 0.01; Mann-Whitney U test). These results indicate that 90Y-labeled C110 anti-carcinoembryonic antigen IT may be a potent therapeutic immunoconjugate for human colon cancer and that it may have direct relevance for i.p. treatment of peritoneal carcinomatosis from colon cancers.