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Dosimetric considerations relative to radionuclides for thyroid diagnosis and therapy
154
Abstracts
subsequently died and 11 developed chronic pericarditis. Others have reported endocardial fibrosis, hyalinization of small myocardial vessels with patchy myocardial necrosis and fibrosis following radiation. Dog hearts subjected to a single dose of 4000-8000 rads developed pericarditis, and there was evidence of myocardial destruction after 11-17 days. Compared to high-dosage radiation therapy, diagnostic radionuclide procedures result in relatively small radiation doses to the heart. Calculation of the dose to the heart and other organs, however, may be relevant, as such procedures are employed in the same patient. The dose of radiation absorbed by the heart is related to: (a) the specific radionuclide used, its physical charateristics and physical half-life; (b) its concentration, distribution and biological half-life in myocardium, blood and adjacent organs; and (c) the geometry and mass of the heart. Many of the radionuclides employed in cardiovascular nuclear medicine, however, do not concentrate exclusively in the heart, but distribute uniformly throughout the entire intravascular blood pool or even accumulate preferentially in other organs. Radiation to organs other than the heart, thus, becomes an important consideration in utilizing these procedures in the clinical routine. It is therefore the purpose of this communication: (1) to review briefly cardiac anatomy and physiology as they pertain to dosimetry; (2) to discuss currently employed radiopharmaceuticals with respect to their distribution between myocardium and the intracardiac blood pool; (3) to describe the possible effects of peripheral circulatory responses on the organ distribution of radionuclides; and (4) to report on the organ distribution of ““Tl in experimental animals and in man.
Absorbed Fractions for Radionuclides Uniformly Distributed in the Myocardium, by R. CHANDRA, S. Lo, M. E. Noz and G. Q. MAGUIRE, JR. New York University Medical Center, 550 First Avenue, New York, New York 10016, U.S.A. THE myocardium is approximated by 0.8- and l-cm thick spherical shells of varying radii. Absorbed fractions have been calculated for this model by numerical integration of the point-specific absorbed fractions following Berger’s approach. Results show that the absorbed fractions for a solid sphere or thick ellipsoid, depending upon the photon energy, are 60-110% higher than absorbed fractions for a similar sized spherical shell.
Dosimetric Considerations Relative to Radionuclides for Thyroid Diagnosis and Therapy, by HAROLD L. ATKINS.Brookhaven National Laboratory, Upton, New York 11973.
U.S.A.
RECENT changes have occurred in the radionuclidic approach to thyroid diagnosis and therapy. These changes have been directed toward reduction of radiation dose by the use of short-lived radionuclides for imaging and toward better control of late effects of therapy by substituting “‘1 for 13’I. Imaging of the thyroid is now widely performed following the administration of 99mTc or ‘?. Some problems exist relative to the use of 99mT~ in that the distribution of radioactivity in the thyroid is not always identical to the distribution of radioiodine. I231 represents a substantial advance over 1311,despite contamination of the former with small amounts of other radioiodines. The high incidence of induced hypothyroidism following “‘I therapy of thyrotoxicosis has spurred interest in the use of “‘1. The biological effectiveness of “‘1 is believed to be greater because of the high abundance of Auger electrons and possibly because of chemical effects following molecular disruption. Clinical results to date are inconsistent, however.
Dosimetry for Evaluation of the Biologic Effects of Radiation Treatment Using fnternally Deposited Radioeuclides and Labeled Compounds, by RODNEYE. BIGLER.Memorial Sloan-Kettering Cancer Center, 1267 York Avenue, New York 10021, U.S.A. THE concept of the Nominal Standard Dose (NSD) has achieved widespread utilization by radiotherapists for the purpose of comparing treatment regimes which differ in time, dose and fractionation patterns. For practical purposes, the NSD is a number which describes a complete course of radiotherapy that results in full connective tissue tolerance. Time, dose and fractionation (TDF) factors were introduced to simplify the analysis of “mixed” external beam and implant therapy procedures, since these two treatment modalities are frequently combined. In this report, the NSD concept with the TDF factor simplification is extended to radionuclides and labeled compounds internally distributed within the body by biologic processes.
Abstracts
subsequently died and 11 developed chronic pericarditis. Others have reported endocardial fibrosis, hyalinization of small myocardial vessels with patchy myocardial necrosis and fibrosis following radiation. Dog hearts subjected to a single dose of 4000-8000 rads developed pericarditis, and there was evidence of myocardial destruction after 11-17 days. Compared to high-dosage radiation therapy, diagnostic radionuclide procedures result in relatively small radiation doses to the heart. Calculation of the dose to the heart and other organs, however, may be relevant, as such procedures are employed in the same patient. The dose of radiation absorbed by the heart is related to: (a) the specific radionuclide used, its physical charateristics and physical half-life; (b) its concentration, distribution and biological half-life in myocardium, blood and adjacent organs; and (c) the geometry and mass of the heart. Many of the radionuclides employed in cardiovascular nuclear medicine, however, do not concentrate exclusively in the heart, but distribute uniformly throughout the entire intravascular blood pool or even accumulate preferentially in other organs. Radiation to organs other than the heart, thus, becomes an important consideration in utilizing these procedures in the clinical routine. It is therefore the purpose of this communication: (1) to review briefly cardiac anatomy and physiology as they pertain to dosimetry; (2) to discuss currently employed radiopharmaceuticals with respect to their distribution between myocardium and the intracardiac blood pool; (3) to describe the possible effects of peripheral circulatory responses on the organ distribution of radionuclides; and (4) to report on the organ distribution of ““Tl in experimental animals and in man.
Absorbed Fractions for Radionuclides Uniformly Distributed in the Myocardium, by R. CHANDRA, S. Lo, M. E. Noz and G. Q. MAGUIRE, JR. New York University Medical Center, 550 First Avenue, New York, New York 10016, U.S.A. THE myocardium is approximated by 0.8- and l-cm thick spherical shells of varying radii. Absorbed fractions have been calculated for this model by numerical integration of the point-specific absorbed fractions following Berger’s approach. Results show that the absorbed fractions for a solid sphere or thick ellipsoid, depending upon the photon energy, are 60-110% higher than absorbed fractions for a similar sized spherical shell.
Dosimetric Considerations Relative to Radionuclides for Thyroid Diagnosis and Therapy, by HAROLD L. ATKINS.Brookhaven National Laboratory, Upton, New York 11973.
U.S.A.
RECENT changes have occurred in the radionuclidic approach to thyroid diagnosis and therapy. These changes have been directed toward reduction of radiation dose by the use of short-lived radionuclides for imaging and toward better control of late effects of therapy by substituting “‘1 for 13’I. Imaging of the thyroid is now widely performed following the administration of 99mTc or ‘?. Some problems exist relative to the use of 99mT~ in that the distribution of radioactivity in the thyroid is not always identical to the distribution of radioiodine. I231 represents a substantial advance over 1311,despite contamination of the former with small amounts of other radioiodines. The high incidence of induced hypothyroidism following “‘I therapy of thyrotoxicosis has spurred interest in the use of “‘1. The biological effectiveness of “‘1 is believed to be greater because of the high abundance of Auger electrons and possibly because of chemical effects following molecular disruption. Clinical results to date are inconsistent, however.
Dosimetry for Evaluation of the Biologic Effects of Radiation Treatment Using fnternally Deposited Radioeuclides and Labeled Compounds, by RODNEYE. BIGLER.Memorial Sloan-Kettering Cancer Center, 1267 York Avenue, New York 10021, U.S.A. THE concept of the Nominal Standard Dose (NSD) has achieved widespread utilization by radiotherapists for the purpose of comparing treatment regimes which differ in time, dose and fractionation patterns. For practical purposes, the NSD is a number which describes a complete course of radiotherapy that results in full connective tissue tolerance. Time, dose and fractionation (TDF) factors were introduced to simplify the analysis of “mixed” external beam and implant therapy procedures, since these two treatment modalities are frequently combined. In this report, the NSD concept with the TDF factor simplification is extended to radionuclides and labeled compounds internally distributed within the body by biologic processes.