Incorporation of patient immobilization, tissue compensation and matchline junction technique for three-field breast treatment.

A protocol for the treatment of the intact breast was developed to maximize dose homogeneity and reproducibility. This protocol uses patient and breast immobilization, three-dimensional tissue compensators, and a technique for geometric matching of fields when the supraclavicular area is treated. A series of phantom measurements and analysis of patient port films was performed to evaluate dose homogeneity and reproducibility using this technique, and the potential adverse effect of loss of skin sparing from the immobilization device was investigated. Dose homogeneity throughout the phantom breast was within +/- 6% of the prescribed central axis dose, and homogeneity at the supraclavicular match line was +/- 10%. This represented a significant improvement over techniques not using tissue compensation or geometrically matched fields. Reproducibility of patient treatments was not significantly improved from previous non-immobilized treatment techniques, but there was no loss of skin sparing from the device, and other advantages of immobilization were observed. Details of the protocol are discussed together with changes that are currently being made to improve the results obtained thus far.

Re-186(Sn) HEDP for treatment of multiple metastatic foci in bone: human biodistribution and dosimetric studies.

Investigation of the biodistribution of subtherapeutic amounts of a new, chromatographically purified rhenium-186(tin) hydroxyethylidene diphosphonate radiopharmaceutical have been completed in five patients with metastatic carcinoma to bone. The new agent localizes in metastatic foci in bone in the same manner as do standard technetium-99m diphosphonate bone-scanning agents and appears able to deliver therapeutic radiation doses of thousands of rads (tens of grays) to these metastatic foci while limiting the total red marrow dose to less than 75 rad (0.75 Gy). The simultaneous treatment of multiple metastatic foci in bone appears feasible with this new agent.

Noise analysis of scintillation camera images: stochastic and non-stochastic effects.

An analysis of noise was performed on scintillation camera images. The analysis was performed on sets of field floods, uniform exposures over the field of view, in such a way that stochastic and non-stochastic effects were separable. Stochastic noise for the digitally acquired images was found to approach the limit of Poisson count statistics. The non-stochastic component of the calculations dominated the results at the lower spatial frequencies. These results hold true even after standard methods of uniformity correction are applied, primarily due to the effects of Compton scatter events. The noise power spectrum calculations carry information about the patterns of the noise in flood images. Examples of digitisation, photomultiplier tube mottle and edge-packing artefacts are presented.

Gallium-67 lung uptake: conjugate-view technique.

A conjugate-view technique is derived for calculation of absolute gallium-67 (Ga-67) uptake from scintillation-camera images. The technique combines counts of posterior and anterior images of the lung with an attenuation correction obtained from cobalt-57 (Co-57) transmission imaging. The formulation is such that the effects of Compton scatter build-up are accounted for. Studies utilizing a canine model indicated that, normally, more activity is located in the chest wall than in the lungs. The quantitative technique must therefore accurately account for a variety of Ga-67 distributions, including that in the chest wall. Calculations were performed using a three-component model comparing results obtained with the conjugate-view approach to the actual uptake. These calculations suggest that an assumption of uniform activity distribution allows an accuracy of approximately +/- 10% over a broad range of body-part thicknesses and uptake by the lungs. It was concluded that the conjugate-view technique is necessarily approximate but can provide clinically useful results.

Accidental Cs-137 contamination.

Widespread use of radionuclides in medicine and industry poses the possibility of radiation accidents. We describe such an occurrence involving three industrial workers. The accident resulted from careless handling of a Cs-137 source. Evaluation of the Cs-137 whole body burden was carried out using stationary and scanning whole body counters. In addition, regional and whole body activity from contamination was assessed using an uncollimated gamma camera. This report emphasizes the value of the gamma camera for detection of radionuclide contamination in radiation accidents.

Comparison of superior vena caval and inferior vena caval access using a radioisotope technique during normal perfusion and cardiopulmonary resuscitation.

Recent studies of thoracic pressure changes during external cardiopulmonary resuscitation (CPR) suggest that there may be a significant difference in the rate of delivery of intravenous drugs when they are administered through the extrathoracic inferior vena cava (IVC) rather than the intrathoracic superior vena cava (SVC). Comparison of delivery of a radionuclide given using superior and inferior vena caval access sites was made during normal blood flow and during CPR. Mean times from injection to peak emission count in each ventricle were determined. There were no significant differences between mean peak times for SVC or IVC routes during normal flow or CPR. When peak times were corrected for variations in cardiac output, there were no significant differences between IVC and SVC peak times during normal flow. During CPR, however, mean left ventricular peak time, when corrected for cardiac output, was significantly shorter (P less than .05) when the SVC route was used. The mean time for the counts to reach half the ventricular peak was statistically shorter (P less than .05) in both ventricles with the SVC route during the low flow of CPR. This suggests that during CPR, increased drug dispersion may occur when drugs are infused by the IVC route and thus may modify the anticipated effect of the drug bolus. These results suggest that during CPR, both the cardiac output and the choice of venous access are important variables for drug delivery.

Effect of a pneumatic antishock garment on drug delivery via distal venous access.

We examined the effect of an inflated pneumatic antishock garment (PASG) on simulated drug delivery through a distally placed venous catheter, during both normal flow and cardiopulmonary resuscitation (CPR). A PASG device was applied to anesthetized mongrel dogs and was inflated to 60 mm Hg. A small bolus of radionuclide was injected through an intravenous catheter placed distal to the PASG. Emission counts were made over both ventricles during conditions of normal flow and then during CPR following cardiac arrest. Mean times from injection to peak counts were determined. A control group of animals with central venous catheters but no PASG was studied similarly. There were no clinically appreciable differences between groups during normal flow. During CPR the PASG animals showed a mean delay of 90 seconds to the left ventricle peak. This difference was not statistically significant. We conclude that, in this canine model, acceptable delivery of drugs can be obtained by venous infusion into a limb with a PASG inflated.

Central versus peripheral intravenous routes in cardiopulmonary resuscitation.

The central venous (CV) and peripheral venous (PV) routes of drug administration are generally considered to be equally effective during cardiopulmonary resuscitation (CPR). This canine study compared simulated drug delivery via CV and PV routes during CPR. The CV group dogs had a CV catheter placed via the external jugular vein, and the PV group dogs had a PV catheter placed in the distal forelimb. Thirty seconds after the induction of cardiac arrest with KCl, CPR was begun with a gas-powered chest compressor with ventilations after every fifth compression. Sixty seconds later, a 0.5 ml bolus of technetium 99m-labeled serum albumin was given. Time activity curves were obtained over the right and left ventricles. The mean time for the counts to rise to half the left ventricular peak (T1/2LV) was significantly less for the CV group than for the PV group (P less than 0.05), averaging 11 and 84 seconds, respectively. The time to left ventricular peak (TLV) was also statistically shorter for the CV group than the PV group, averaging 118 versus 258 seconds, respectively. This study demonstrates that central venous administration is more rapid than peripheral venous administration during CPR and supports the preferential use of the central venous route for drug administration clinically.

Low-level internal radionuclide contamination: use of gamma camera for detection.

The uncollimated gamma camera was evaluated as a screening tool for the detection of low levels of internal radionuclide contamination. The minimum detectable activity (MDA) is on the order of 1-4 nCi (37-148 Bq) for a 3-min sample and background counting time. Identification of unknown radionuclides at these low levels involves a systematic search and hence requires a more careful peaking method than organ imaging. Most gamma cameras are capable both of detecting a wide range (35 keV to 1.332 MeV) of gamma-ray energies in the presence of three to four radionuclides and also of distinguishing principal gamma-ray energies from Compton scatter. The differences in MDAs among gamma cameras are small, and vary primarily with the background activity. The actual contaminant activities lie between the calculated values based on measurements when the source is 10 cm away from the uncollimated detector head and using point sources both in air and with the tissue-equivalent scatter medium. The widely available gamma camera is capable of screening a large population, either suspected or actually contaminated, in the event of an emergency.

Thallium-201 imaging artifacts not detected by technetium-99m or cobalt-57 quality-control testing.

Early stages of hydration in a sodium iodide crystal may cause artifactual "hot" spots on thallium-201 heart images. This phenomenon was observed when a mobile gamma camera was used even though the daily quality-control flood-field views revealed no apparent abnormalities. Nevertheless, hot spots were visible on thallium-201 and xenon-133 flood-field images. With asymmetric photopeak positioning using a technetium-99m source, hot spots were noted in addition to phototube nonuniformities. Subsequently, the camera head was disassembled, the crystal was inspected visually, and the crystal seal was found to be broken. Hydration of the crystal was confirmed by the camera manufacturer. Quality-control procedures should test for hydration-induced artifacts on a regular basis.

Basal kinetic studies of Tc-99m DMPE as a myocardial imaging agent in the dog.

Newly synthesized Tc-99m dichlorobis(1,2-dimethylphosphino)ethane (DMPE) was investigated as a myocardial imaging agent with respect to its kinetics (dependent on both time and regional coronary blood flow), its percent organ uptake, and its imaging characteristics in the anesthetized dog. Most of these data are compared with those of Tl-201. Blood clearance of the two agents is essentially the same. Compared with Tl-201, Tc-99m DMPE shows faster overall kinetics, higher heart-to-lung ratio, equally good correlation with a wide range of regional blood flows, and higher liver uptake. At the time of peak myocardial uptake, the mean heart uptake of Tl-201 is 4.3%, compared with 2.9% for Tc-99m DMPE, yet only 0.9% uptake of Tc-99m DMPE is found in the lung as compared with 3.3% for Tl-201. These differences result in a heart-to-lung ratio of 2:1 for Tc-99m DMPE and 1:1 for Tl-201, based on the data obtained from the time-activity curve. The quantitative findings are supported by the superior quality of Tc-99m DMPE images of both normal and infarcted dog heart. The high hepatic uptake of Tc-99m DMPE is not a serious problem if images are obtained within 5-60 min after dose. These basic kinetic studies suggest that Tc-99m DMPE is a promising myocardial imaging agent.

Effect of coronary blood flow on uptake and washout of Tc-99m DMPE and Tl-201.

After intravenous administration of Tc-99m DMPE the flow-dependent kinetics were studied in dogs during induced ischemia and during induced maximal reactive hyperemia. A control group was also studied. Mean time-activity curves obtained from the myocardial wall were compared within the same intervention group and also with other groups. During reactive hyperemia, there was a rapid and absolute increase in uptake followed by a rapid washout, whereas during ischemia there was a slow and decreased uptake followed by a slow washout. The magnitude of Tc-99m DMPE uptake during reactive hyperemia was slightly less than that of Tl-201, but the decreased uptake with ischemia was about equal for the two agents. Following maximal uptake in the myocardium the effective half-life of Tc-99m DMPE was one-third to one-fourth that of Tl-201. The similar kinetics of Tc-99m DMPE compared to Tl-201 suggests its usefulness in the evaluation of ischemic heart disease.

Exposure to Xenon 133 in the nuclear medicine laboratory.

Exposure of nuclear medicine personnel to 133X was examined quantitatively at three area hospitals during ventilation-perfusion studies in which the technologists breathed through a specially made xenon-trapping apparatus. The accumulated mean xenon activity varied a great deal from hospital to hospital, ranging from 52 nCi (1.92 kBq) to over 5 microCi (185 kBq) during a typical 20-minute lung study. The observed difference largely depended on the xenon exhaust and trapping systems, which could make a 100-fold difference in exposure rates. The air flow and its exchange rate in the room were additional factors contributing to the different exposure rates. Although the patient continued to be a source of xenon contamination throughout the study, the xenon-trapping system, while operational, could exhaust substantial quantities of xenon. The exhaust duct system, on the other hand, left little contaminated air in the room, resulting in the least exposure to personnel.

Effect of coronary blood flow on thallium-201 uptake and washout.

Myocardial uptake and washout of thallium-201 (201TI) were studied in an experimental dog model in which regional blood flow to the posterior wall was varied by transient 2-minute occlusion of the circumflex coronary artery to produce transient ischemia and reactive hyperemia. Thallium-201 myocardial activity in a region of interest was determined continuously after i.v. administration by a gamma camera and computer program. Activity in the posterior wall was compared with that in the anterior wall in the same dog and the posterior wall of control dogs. Thallium-201 uptake was directly related to blood flow. With reactive hyperemia, there was a rapid and absolute increase in uptake followed by rapid washout; with ischemia, there was slow and decreased uptake followed by a slow washout. The calculated myocardial activity during washout in both ischemic and hyperemic areas approached values in control dogs long after blood flow had returned to baseline levels. Significant differences in washout slopes were found between the three groups of dogs (-0.156%/min in control dogs, -0.244%/min after reactive hyperemia, and -0.076%/min after transient ischemia, with half-washout times of 5.3 hours, 3.4 hours and 11.0 hours, respectively). These data suggest that both the initial decrease in activity in the ischemic area and the initial excess in the hyperemic area are corrected by different washout rates of ischemic and hyperemic cells during redistribution.

Cationic Tc-99m complexes as potential myocardial imaging agents.

Nineteen cationic Tc-99m complexes, based upon four different ligand series, have been synthesized under "no carrier added" conditions and qualitatively evaluated as myocardial imaging agents in a dog model. Of these complexes, the four halogen derivatives of the diars series [diars = o-phenylenebis(dimethylarsine)] successfully concentrate in the myocardium. These Tc-99m diars complexes are shown by thin-layer chromatography to be identical to the Tc-99 analogs that have been fully characterized as trans octahedral complexes of Tc(III) by classical chemical techniques. Tissue distribution studies in rats show a definite difference in the biodistributions of [99mTc(diars)2Cl2]+ and [99mTc(diars)2Br2]+, despite the similar size, shape, charge, and lipophilicity of these two complexes. A tissue distribution study in resting beagle dogs shows that [99mTc(diars)2Br2]+ accumulates in the normal myocardium about half as well as TI-201 (0.022 compared with 0.038% dose/g).

Heart imaging with cationic complexes of technetium.

The cationic technetium-99 complex trans-[99TC(dmpe)2Cl2]+, where dmpe is bis(1,2-dimethylphosphino)ethane or (CH3)2P-CH2-P(CH3)2, has been prepared and characterized by single-crystal, x-ray structural analysis. The technetium-99m analog, trans-(99mTc(dmpe) 2Cl2]+, has also been prepared and shown to yield excellent gamma-ray images of the heart. The purposeful design, characterization, and synthesis of this technetium-99m radiopharmaceutical represents a striking application of fundamental inorganic chemistry to a problem in applied nuclear medicine.

Internal contamination of laboratory personnel by 131I1.

Internal contamination by 131I among the personnel in a nuclear medicine laboratory was surveyed from January to July, 1979. Because of the formulation change made by the manufacturer in April to reduce volatility, it was possible to study two different therapeutic solutions of 131I. Internal contamination of personnel who administered 131I was found to be 90 times less after the reformulation. Compliance with a recent NRC regulatory guide of less than 40 nCi (1.48 kB1) of 131I thyroid burden as a quarterly average should not be difficult using the new, less volatile 131I; however, strict precautionary measures are essential to minimize contamination, which is common in the nuclear medicine environment.

Survey of 99mTc contamination of laboratory personnel: hand decontamination.

Decontamination after exposure to various 99mTc radiopharmaceuticals was tested with serial hand washings both with and without soap. All radiopharmaceuticals were removed more effectively with soap and the degree of decontamination related closely to the number of washings. The affinity of the radiopharmaceuticals for the skin varied, depending upon the labeled material, and only macroaggregated albumin was effectively removed to less than 1% of its original activity with soap. Activity transfer to the opposite hand could be substantial with macroaggregated albumin and sulfur colloid if soap is not used.

Survey of 99mTc contamination of laboratory personnel: its degree and routes.

Internal contamination of personnel preparing 99mTc labeled radiopharmaceuticals was confirmed by detection of radioactivity in urine. Observation of work habits, whole-body scanner studies, nose swabs, and wipe tests in the hot laboratory demonstrated that: (a) contamination of the laboratory coat occurred during radiopharmaceutical preparation; (b) the degree of personnel contamination appeared to be higher among the short in stature; and (c) no gross evidence was found to indicate that internal contamination took place through an air-borne route. While the calculated internal radiation dose is minimal, even this could be avoided if particular precautionary practices are observed.