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Yttrium-90 microsphere brachytherapy of the liver exploits the distinctive features of the liver anatomy to treat liver malignancies with beta radiation and is gaining more wide spread clinical use. This report provides a general overview of microsphere liver brachytherapy and assists the treatment team in creating local treatment practices to provide safe and efficient patient treatment. Suggestions for future improvements are incorporated with the basic rationale for the therapy and currently used procedures. Imaging modalities utilized and their respective quality assurance are discussed. General as well as vendor specific delivery procedures are reviewed. The current dosimetry models are reviewed and suggestions for dosimetry advancement are made. Beta activity standards are reviewed and vendor implementation strategies are discussed. Radioactive material licensing and radiation safety are discussed given the unique requirements of microsphere brachytherapy. A general, team-based quality assurance program is reviewed to provide guidance for the creation of the local procedures. Finally, recommendations are given on how to deliver the current state of the art treatments and directions for future improvements in the therapy.

Estimates of radiation absorbed doses from radionuclides internally deposited in a pregnant woman and her fetus are very important due to elevated fetal radiosensitivity. This paper reports a set of specific absorbed fractions (SAFs) for use with the dosimetry schema developed by the Society of Nuclear Medicine's Medical Internal Radiation Dose (MIRD) Committee. The calculations were based on three newly constructed pregnant female anatomic models, called RPI-P3, RPI-P6, and RPI-P9, that represent adult females at 3-, 6-, and 9-month gestational periods, respectively. Advanced Boundary REPresentation (BREP) surface-geometry modeling methods were used to create anatomically realistic geometries and organ volumes that were carefully adjusted to agree with the latest ICRP reference values. A Monte Carlo user code, EGS4-VLSI, was used to simulate internal photon emitters ranging from 10 keV to 4 MeV. SAF values were calculated and compared with previous data derived from stylized models of simplified geometries and with a model of a 7.5-month pregnant female developed previously from partial-body CT images. The results show considerable differences between these models for low energy photons, but generally good agreement at higher energies. These differences are caused mainly by different organ shapes and positions. Other factors, such as the organ mass, the source-to-target-organ centroid distance, and the Monte Carlo code used in each study, played lesser roles in the observed differences in these. Since the SAF values reported in this study are based on models that are anatomically more realistic than previous models, these data are recommended for future applications as standard reference values in internal dosimetry involving pregnant females.

A new approach for calculating internal dose estimates was developed through the use of a more realistic computational model of the human body. The present technique shows the capability to build a patient-specific phantom with tomography data (a voxel-based phantom) for the simulation of radiation transport and energy deposition using Monte Carlo methods such as in the MCNP-4B code. MCNP-4B absorbed fractions for photons in the mathematical phantom of Snyder et al. agreed well with reference values. Results obtained through radiation transport simulation in the voxel-based phantom, in general, agreed well with reference values. Considerable discrepancies, however, were found in some cases due to two major causes: differences in the organ masses between the phantoms and the occurrence of organ overlap in the voxel-based phantom, which is not considered in the mathematical phantom.

Radiation dose distributions are developed for balloon and wire sources of radioactivity within coronary arteries. The Monte Carlo codes MCNP 4B and EGS4 were used to calculate dose distributions for photons and electrons at discrete energies around such sources, with and without the presence of a high-density atherosclerotic plaque. An interactive computer program was developed which then calculates dose distributions for many radionuclides by applying the emission spectra to the discrete energy grids calculated by the Monte Carlo codes, weighting appropriately for electron energy and abundance. Results for Re-186 and Re-188 balloon sources are shown in comparison to an Ir-192 wire source. The program provides dose distributions as well as estimates of activity levels needed to deliver prescribed doses to the vessel wall at selected distances from the lumen in a selected time interval. In addition, dose calculations are presented in this paper for other organs in the body, from photon radiation as well as from possible loss of liquid activity into the bloodstream in the case of a balloon rupture. These results, especially the interactive computer program permitting easy comparison of various radionuclides and their physical characteristics, will greatly facilitate the comparison process and aid in the selection of the best candidate(s) for clinical use.

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.

The MIRD scheme is not restricted to calculating mean absorbed doses in organs but can be extended to any tissue for which distribution and retention data can be obtained and for which a reasonably accurate mathematical description of the source and target tissues can be determined. The development of more accurate absorbed dose estimates and the correlation of these estimates with radiation effects will lead to a better understanding of the results from radiotherapeutic agents such as radiolabeled monoclonal antibodies. Therefore, radiobiologists and internal dosimetrists need to combine their efforts and work toward the common goal of improving the treatment of malignant diseases.