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Biomedical subjects

M G Stabin

Publications and source records attributed to M G Stabin.

At least 55 records · Page 3Linked to original sources
PubMed1998

Radiation absorbed doses to the walls of hollow organs.

UNLABELLED: Many radiopharmaceuticals are excreted from the body through the gastrointestinal (GI) tract. The doses to the walls of the organs involved often are very significant. As significant fractions of the administered activity pass through them, these organs may receive the highest doses in the body for many radiopharmaceuticals. The absorbed dose to these walled organs, from activity in their contents, is typically calculated as 50% of the average absorbed dose to the contents, for nonpenetrating emissions. The internal surface of the GI tract, and to a certain extent the urinary bladder, is lined with a variable thickness of mucus. In addition, the radiosensitive cell populations (crypt or stem cells) are located at some depth into the mucosa. These two factors suggest that the surface dose, often used to characterize the clinically relevant absorbed doses for walled organs, may represent an overestimate in some cases. METHODS: In this study, the radiation transport code MCNP was used to simulate the deposition of energy from nonpenetrating emissions of several radionuclides of interest: 90Y, 99mTc,123I and 131I. Absorbed doses as a function of distance from the wall-contents interface were calculated for three geometric shapes representing different organs along the routes of excretion. RESULTS: The absorbed dose from nonpenetrating emissions to the sensitive cell populations was consistently lower than estimated by the standard model assumption. The simulated absorbed doses to radiosensitive cells in the GI tract for 99mTc and 123I are tenfold lower; those for 131I are fivefold lower and those for 90Y are 20% lower. CONCLUSION: This study demonstrates that the normally reported dose to the walls of hollow organs probably should be modified to account for the attenuation of these nonpenetrating emissions in the linings of the walls. This study also demonstrates that Monte Carlo codes continue to be useful in the evaluation of the dose to sensitive cells in walled organs.

Colon↗
PubMed1997

Rhenium-188 hydroxyethylidene diphosphonate: a new generator-produced radiotherapeutic drug of potential value for the treatment of bone metastases.

The search for an ideal radioisotope for systemic radiotherapy continues. As a generator-produced radioisotope emitting both beta and gamma rays and having a short physical half-life of 16.9 h, rhenium-188 is a very good potential candidate for systemic radiotherapy. In this study, we labeled hydroxyethylidene diphosphonate (HEDP) with 188Re and analyzed the biodistribution and bone uptake following intravenous injection in rats to assess its potential for clinical use. The rats were injected with approximately 14.8 MBq (0.4 mCi) 188Re-HEDP in a volume of 0.1 ml intravenously and then sacrificed at 1 h, 24 h, or 48 h (four rats at each time). Samples (about 0.1 g) of lung, liver, kidney, spleen, testis, muscle, stool, and bone (thoracic vertebra) were taken and weighed carefully. In addition, a 1-ml sample of blood was drawn from the heart and 1 ml of urine was taken from the urinary bladder immediately after killing. Tissue concentrations were calculated and expressed as percent injected dose per gram or per milliliter (% ID/g or ml). Bone lesions were created in the right tibial bone in three rabbits to calculate the lesion to normal uptake ratio (L/N ratio). The biodistribution data showed that the radioactivity in the bone tissue was as high as 1.877% ID/g at 1 h and that it climbed to 2.017% ID/g at 4 h. The activity level in the kidney was highest at 1 h but declined rapidly throughout the study. The radioactivities in the lung, liver, muscle, spleen, testis, blood, and stool were all lower than 0.3% ID/g at 1 h and also declined rapidly. The biological half-life in bone was the longest (60.86 h). In contrast, the biological half-lives in muscle and blood were short (2.99 h and 6.21 h respectively). The concentrations of radioactivity in muscle, spleen, testis, and stool were quite low throughout the study. Most of the radiotracer was excreted by the urinary system. The L/N ratio was 4.23+/-0.21 in rabbits injected with 188Re-HEDP and 4.25+/-0.23 in those injected with technetium-99m methylene diphosphonate. In conclusion, we would suggest that 188Re-HEDP is a very good potential candidate for the treatment of bone metastases because of the following characteristics: (1) it is generator produced; (2) it has a short half-life; (3) it emits gamma rays suitable for imaging; (4) there is highly selective uptake in the skeletal system and bone lesions; and (5) it has a low non-target uptake and rapid clearance in nonosseous tissue.

Animals↗
PubMed1997

Tissue distribution and radiation dosimetry of astatine-211-labeled chimeric 81C6, an alpha-particle-emitting immunoconjugate.

A paired-label study was performed in athymic mice bearing subcutaneous D-54 MG human glioma xenografts to compare the localization of human/mouse anti-tenascin chimeric antibody 81C6 labeled by reaction with N-succinimidyl 3-[211At]astatobenzoate and N-succinimidyl 3-[131I]iodobenzoate. Over the 48-h observation period, the distribution of 211At- and 131I-labeled antibody were quite similar in tumor and normal tissues except stomach. These data were used to calculate human radiation doses for both intravenously and intrathecal administered 211At-labeled chimeric 81C6 using a quality factor of 5 for alpha-emissions.

Animals↗
PubMed1997

Review of the fetal radiation doses received from 59Fe kinetic studies at Vanderbilt University in the 1940's.

Fetal radiation dose estimates were calculated for women who received oral administrations of 59Fe at Vanderbilt University in the 1940's. A similar dosimetry analysis was performed by Dyer and Brill in 1972; the availability of recently developed physical models of the pregnant female at different stages of gestation and of a new kinetic model for iron metabolism afforded an opportunity to re-evaluate these doses. Radiation dose estimates for the fetus (and fetal liver in three cases) were calculated for a number of oral and intravenous studies using these new models and the available data about the original experiments. The total fetal doses do not appear to have exceeded a few hundred microgray (a few tens of millirad) for the majority of the study subjects. Considerable uncertainty exists, however, in the amount of activity administered to these subjects.

Administration, Oral↗
PubMed1997

Placental transfer of radiopharmaceuticals and dosimetry in pregnancy.

The calculation of radiation dose estimates to the fetus is often important in nuclear medicine. To obtain the best estimates of radiation dose to the fetus, the best biological and physical models should be employed. In this paper the most recent data available on the placental crossover of many radiopharmaceuticals are presented. This information was used with standard kinetic models describing the maternal distribution and retention and with the best available physical models to obtain fetal dose estimates for these radiopharmaceuticals at all stages of pregnancy (presented in a separate paper). The literature yielded information on placental crossover of 15 radiopharmaceuticals, from animal or human data. From these data, radiation dose estimates were developed in early pregnancy and at 3, 6, and 9 mo gestation for these radiopharmaceuticals, as well as for many others used in nuclear medicine (the latter considering only maternal organ contributions to fetal dose).

Adult↗
PubMed1997

Radiation absorbed dose to the embryo/fetus from radiopharmaceuticals.

Radiation protection practice requires the knowledge of estimated absorbed radiation doses to aid in the understanding of the potential detriment of various exposures. In nuclear medicine, the radiation doses to the internal organs of the subject are commonly calculated using the MIRD methods and equations. The absorbed dose to the embryo or fetus has long been an area of concern. The recent release of the pregnant female phantom series, and its incorporation into the MIRDOSE 3 computer software, has made possible the estimation of absorbed doses from radionuclides in the body to the fetus in early pregnancy and at 3, 6, and 9 mo gestation. A survey of several major medical institutions was made to determine the radiopharmaceuticals which might be given, whether intentionally or not, to women of childbearing years. Biokinetic data for these radiopharmaceuticals were gathered from various documents and other resources, and the absorbed doses to the embryo and fetus at these different stages of gestation from radiations originating within the mother's organs were estimated. In addition, information about activity distributed within the placenta and fetus was included where quantitative data were available. These absorbed dose estimates can be used to evaluate the risk associated with the use of different radiopharmaceuticals so that a more informed evaluation of the risks and benefits of the different procedures may be made. Further research is needed into the mechanisms and quantitative aspects of the placental transfer of many radiopharmaceuticals.

Embryo, Mammalian↗
PubMed1997

Health concerns related to radiation exposure of the female nuclear medicine patient.

The female nuclear medicine patient is of special concern in evaluating radiation dose and risk in nuclear medicine. The female's overall body size and organ sizes generally are smaller than those of her male counterpart (thus her radiation doses will be higher, given the same amounts of administered activity and similar biokinetics); female gonads are inside the body instead of outside and are near several organs often important as source organs in internal dosimetry (urinary bladder, liver, kidneys, intestines); risk of breast cancer is significantly higher among females than males; and in the case of pregnancy, exposure to radiation of the embryo/fetus and the nursing infant are of special concern in such an analysis. All these concerns are addressed in this study through a comparative study of radiation doses for males and females over a large number (approximately 60) of nuclear medicine studies and through a study of what is known about radiation dosimetry in pregnancy and breast feeding. It was found that women's critical organ doses and effective doses (as defined by the International Commission on Radiological Protection 60 [ICRP 60] are about 25% higher than those for men across all these studies. Women's gonad doses, however, may be as much as 10 to 30 times higher than those in men, although 2- to 3-fold differences are common. Many radiopharmaceuticals are administered to women of childbearing age; however, little is known about how much activity crosses the placenta and about the biokinetics in the fetus should it occur. Nonetheless, dose estimates are provided at four stages of pregnancy (early, 3-month, 6-month, and 9-month gestation) for a large number of radiopharmaceuticals, whether or not quantitative estimates of placental crossover can be made. Many radiopharmaceuticals are also excreted in breast milk of nursing mothers. Breast feeding interruption schedules are suggested through analysis of the observed kinetics of these pharmaceuticals and an assumed dose limit of 1 mSv (effective dose equivalent) to the infant.

Female↗
PubMed1997

Radiation dosimetry for indium-111-pentetreotide.

UNLABELLED: We present radiation dose estimates for 111In-pentetreotide. METHODS: Kinetic data were gathered in 10 subjects at two different sites. A compartmental model was used to fit the data, including retention, in three major organs and excretion. RESULTS: The data were consistent for the subjects at both sites. The organ receiving the highest dose was the kidneys (0.52 mGy/MBq); the effective dose equivalent was 0.1 mSv/MBq, and the effective dose was 0.073 mSv/MBq. CONCLUSION: The results of this study provide the basis for evaluation of radiation safety of this drug.

Adult↗
PubMed1996

Radiation dose from breastfeeding following administration of thallium-201.

UNLABELLED: Radiation exposure to a breast feeding infant was estimated when the mother underwent a nuclear medicine procedure using 201Tl. METHODS: A lactating mother was administered 111 MBq of 201Tl for a brain scan. Breast milk samples were collected over a period of three days, and the rate of 201Tl secretion was determined. The infant was not breast fed during that time. Based on our data, we determined the time-activity function for radioactivity in the breast milk. From these data, and assuming an intake of 1000 ml/day, we calculated the fraction of administered activity that might be taken in by the infant. We also calculated the intake assuming breastfeeding delays of 2, 24, 48, 72, 96 and 500 hr. RESULTS: We calculated the radiation dose to various organs and the effective dose to an infant and a 1-yr-old for breastfeeding delays of 2 to 500 hr. The effective dose to a 1-yr-old from an administration of 111 MBq of 201Tl to the mother ranged from 0.90 mSv to 0.00072 mSv, and the effective dose to a newborn ranged from 1.6 mSv to 0.0013 mSv depending on delay time. CONCLUSION: Our estimates of radiation exposure to an infant from breastfeeding indicate that in this case, a 1-yr-old would have received less than the NCRP's proposed limit on annual effective dose to members of the general public of 1 mSv with a 48-hr delay and no restrictions on holding the child. A newborn would have received less than the proposed infrequent exposure limit of 5 mSv without any delay or restrictions in breastfeeding.

Adult↗
PubMed1995

Specific absorbed fractions of energy from internal photon sources in brain tumor and cerebrospinal fluid.

Transferrin, when injected intracranially into glioblastoma multiforme lesions, acts as a cytotoxic substance. Transferrin, radiolabeled with In-111, can be coinjected and subsequent scintigraphic imaging can demonstrate the biokinetics of the cytotoxic transferrin. The administration of 111In transferrin into a brain tumor results in distribution of radioactivity in the brain, brain tumor, and the cerebrospinal fluid (CSF). Information about absorbed radiation doses to these regions, as well as other nearby tissues and organs, is important for evaluating radiation-related risks from this procedure. The radiation dose is usually estimated for a mathematical representation of the human body. We have included source/target regions for the eye, lens of the eye, spinal column, spinal CSF, cranial CSF, and a 100-g tumor within the brain of an adult male phantom developed by Cristy and Eckerman. The mathematical models of the spinal column, spinal CSF, and the eyes were developed previously, however, these source/targets have not been routinely included in photon transport simulations. Specific absorbed fractions (SAFs) as a function of photon energy were calculated using the ALGAMP computer code, which utilizes Monte Carlo techniques for simulating photon transport. The ALGAMP code was run three times, with the source activity distributed uniformly within the tumor, cranial CSF, and the spinal CSF volumes. These SAFs, which were generated for 12 discrete photon energies ranging from 0.01 to 4.0 MeV, were used with decay scheme data to calculate S-values needed for estimating absorbed doses. S-values for 111In are given for three source regions (brain tumor, cranial CSF, and spinal CSF) and all standard target regions/organs, the eye and lens, as well as to tissues within these source regions. S-values for the skeletal regions containing active marrow are estimated. These results are useful in evaluating the radiation doses from intracranial administration of 111In transferrin. The SAFs are also generally useful for calculation of absorbed dose from any radionuclide in these source regions.

Adult↗
PubMed1994

Bremsstrahlung radiation dose in yttrium-90 therapy applications.

UNLABELLED: The bremsstrahlung component of the decay scheme of beta emitters has been traditionally ignored in internal dosimetry calculations. METHODS: We have estimated the radiation dose from the bremsstrahlung component of the decay scheme of 90Y as a function of distance from a point source in a liquid medium and to body organs from distributed sources of 90Y in the liver and spleen. RESULTS: These estimates agree with measurements of bremsstrahlung dose measured in a Rando phantom, and give an estimate of the importance of this contribution to the overall dosimetry. CONCLUSIONS: The bremsstrahlung radiation absorbed dose contribution from an organ to itself is very small compared to that from the beta dose, but the contribution to other organs is not always negligible, especially when large amounts of 90Y may be involved, as in therapy applications.

Beta Particles↗
PubMed1994

A model of the prostate gland for use in internal dosimetry.

UNLABELLED: Several radionuclides or radiolabeled pharmaceuticals may be taken up by the prostate gland. METHODS: A model of the prostate gland has been developed and implemented in the adult male mathematical phantom within software which calculates absorbed fractions of energy from activity in source regions within the phantom. RESULTS: Specific absorbed fractions are reported for all target regions within the phantom for 12 discrete source energies from 0.01 to 4.0 MeV. S-values for all target regions for six radionuclides are also reported. CONCLUSIONS: This work provides another organ useful for internal dose calculations within the 70-kg phantom.

Algorithms↗
PubMed1994

Absorbed fractions for electrons and beta particles in spheres of various sizes.

UNLABELLED: The use of electron-emitting radionuclides in tumor imaging and therapy has presented some new challenges to conventional radiation dosimetry. The fraction of electron energy absorbed in most source regions has usually been assumed to be unity. In small structures such as localized tumors or isolated regions containing moderate to high energy electron emitters, however, this may not always be the case. METHODS: Using an extension of Berger's scaled absorbed dose distributions for point sources to represent a spherical geometry, absorbed fractions of electron energy for sources uniformly distributed in spheres of various sizes have been calculated. RESULTS: Beta particle and monoenergetic electron energies studied range from 0.025 to 4.0 MeV and sphere masses range from 0.01 to 1000 g. S values have also been calculated for 90Y, 123I and 131I based on the results of the absorbed fraction calculations. CONCLUSION: These calculated absorbed fractions are valuable in estimating electron energy loss from small spherical structures and may be useful in estimating the radiation dose to these small volumes.

Beta Particles↗
PubMed1993

Biodistribution and dosimetry of iodine-123-IBF: a potent radioligand for imaging the D2 dopamine receptor.

Iodine-123-labeled iodo-benzofuran (IBF) is a potent D2 dopamine receptor antagonist that has been developed as a potential SPECT imaging agent. This report documents its biodistribution and radiation dosimetry in seven healthy humans. Approximately 100 MBq of IBF were administered to each volunteer. Urine was collected to measure the fraction of the activity that was voided by the renal system. Conjugate images were serially acquired over 24 hr to determine the fraction of activity in the other organs. Standard image analysis techniques were used to measure the geometric mean count rates in the brain, GI tract, heart, liver, lungs and thyroid at each time point. Corrections for attenuation were made with 123I transmission scans. Multicompartmental modeling was used to stimulate and predict the biokinetic behavior of 123I-IBF in the rest of the body. The absorbed doses for 24 organs were then estimated with the MIRD formalism. Rapid biological washout minimized the absorbed dose to most tissues. The excretory organs were exposed to the most radiation. The lower large intestine received about 0.13 mGy/MBq (0.48 rad/mCi), and the urinary bladder received 0.11 mGy/MBq. This low radiation burden will allow more than 370 MBq (10 mCi) to be administered to healthy research subjects during each study of the D2 receptor. Since high quality images of the brain can be obtained with half this amount, the findings suggest that 123I-labeled IBF has a large margin of radiation safety in humans. Its stability in vivo and its high target-to-background contrast ratio in the human brain may make it a useful SPECT imaging agent.

Adult↗
PubMed1993

Radiation dose to the upper spine from therapeutic administrations of iodine-131-sodium iodide.

Thyroid cancer patients sometimes receive conventional external irradiation to the neck in addition to radioactive iodine therapy. In these situations, knowledge of the radiation dose already received by the spine in the neck area from the radioiodine administration can be an aid in treatment planning. This paper gives an estimate of the radiation dose to the upper spine from administration of 3700 MBq of 131I-sodium iodide. Monte Carlo codes used to estimate radiation dose from internal emitters usually give absorbed doses to the whole spine or marrow. One such code was modified to give a dose only to the upper spine region near the thyroid. Calculations assumed a thyroid uptake of 10% of administered activity and retention with a 35-hr effective half-time. Activity in the remainder of the body was assumed to clear with a 6-hr half-time to urine. Under these assumptions, the dose to this upper spine region was about 200 mGy.

Adult↗
PubMed1992

MIRD Pamphlet No. 14: a dynamic urinary bladder model for radiation dose calculations.

The constant-volume urinary bladder model in the standard MIRD phantom has recognized limitations. Various investigators have developed detailed models incorporating more physiologically realistic features such as expanding bladder contents and residual volume, and variable urinary input rate, initial volume and first void time. We have reviewed these published models and have developed a new model incorporating these factors. The model consists of a spherical source with variable volume to simulate the bladder contents and a wall represented by a spherical shell of constant volume. The wall thickness varies as the source expands or contracts. The model provides for variable urine entry rate (three different hydration states), initial bladder contents volume, residual volume and first void time. The voiding schedule includes an extended nighttime gap during which the urine entry rate is reduced to one-half the daytime rate. Radiation dose estimates have been calculated for the bladder wall surface (including photon and electron components) and at several depths in the wall (electron component) for [18F]FDG, 99mTc-DTPA, 99mTc-HEDP, [99mTc]pertechnetate 99mTc-RBCs, 99mTc-glucoheptonate, 99mTc-MAG3, [123I]/[124I]/[131I]OIH and sodium [131I]iodide(Nal). The initial bladder volume and first void time that provide the lowest radiation dose to the bladder wall are determined separately for each compound to give guidance for establishing dose reduction protocols.

Algorithms↗