Absorbed dose distributions from beta-decaying radionuclides: Experimental validation of Monte Carlo tools for radiopharmaceutical dosimetry.

PURPOSE: This study aims to experimentally validate the Monte Carlo generated absorbed doses from the beta particles emitted by 90 Y and 177 Lu using radiochromic EBT3 film-based dosimetry. METHODS: Line sources of 90 Y and 177 Lu were inserted longitudinally through blocks of low-density polyethylene and tissue-equivalent slabs of cortical bone and lung equivalent plastics. Radiochromic film (Gafchromic EBT3) was laser cut to accommodate orthogonal line sources of radioactivity, and the film was sandwiched intimately between the rectangular blocks to achieve charged particle equilibrium. Line sources consisted of plastic capillary tube of length (13 ± 0.1) cm, with 0.42-mm inner diameter and a wall thickness of 0.21 mm. 90 Y line sources were prepared from a solution of dissolved 90 Y resin microspheres. 177 Lu line sources were prepared from an aliquot of 177 Lu-DOTATATE. Film exposures were conducted for durations ranging from 10 min to 38 h. Radiochromic film calibration was performed by irradiation with 6-MV-bremsstrahlung x rays from a calibrated linear accelerator, in accordance with literature recommendations. Experimental geometries were precisely simulated within the GATE Monte Carlo toolkit, which has previously been used for the generation of dose point kernels. RESULTS: The mean percentage difference between measured and simulated absorbed doses were 5.04% and 7.21% for 90 Y and 177 Lu beta absorbed dose in the range of (0.1-10) Gy. Additionally, 1D gamma analysis using a local 10%/1 mm gamma criterion was performed to compare the absorbed dose distributions. The percentage of measurement points passing the gamma criterion, averaged over all tests, was 93.5%. CONCLUSIONS: We report the experimental validation of Monte Carlo derived beta absorbed dose distributions for 90 Y and 177 Lu, solidifying the validity of using Monte Carlo-based methods for estimating absorbed dose from beta emitters. Overall, excellent agreement was observed between the experimental beta absorbed doses in the linear region of the radiochromic film and the GATE Monte Carlo simulations demonstrating that radiochromic film dosimetry has sufficient sensitivity and spatial resolution to be used as a tool for measuring beta decay absorbed dose distributions.

Low-Cost Fetal Magnetocardiography: A Comparison of Superconducting Quantum Interference Device and Optically Pumped Magnetometers.

Background Fetal magnetocardiography (fMCG) is a highly effective technique for evaluation of fetuses with life-threatening arrhythmia, but its dissemination has been constrained by the high cost and complexity of Superconducting Quantum Interference Device (SQUID) instrumentation. Optically pumped magnetometers (OPMs) are a promising new technology that can replace SQUIDs for many applications. This study compares the performance of an fMCG system, utilizing OPMs operating in a person-sized magnetic shield, to that of a conventional fMCG system, utilizing SQUID magnetometers operating in a magnetically shielded room. Methods and Results fMCG recordings were made in 24 subjects using the SQUID system with the mother lying supine in a magnetically shielded room and the OPM system with the mother lying prone in a person-sized, cylindrical shield. Signal-to-noise ratios of the OPM and SQUID recordings were not statistically different and were adequate for diagnostic purposes with both technologies. Although the environmental noise was higher using the small open-ended shield, this was offset by the higher signal amplitude achieved with prone positioning, which reduced the distance between the fetus and sensors and improved patient comfort. In several subjects, fMCG provided a differential diagnosis that was more precise and/or definitive than was possible with echocardiography alone. Conclusions The OPM-based system was portable, improved patient comfort, and performed as well as the SQUID-based system at a small fraction of the cost. Electrophysiological assessment of fetal rhythm is now practical and will have a major impact on management of fetuses with long QT syndrome and other life-threatening arrhythmias.

Methods for functional assessment after C7 spinal cord hemisection in the rhesus monkey.

BACKGROUND: Reliable outcome measures are essential for preclinical modeling of spinal cord injury (SCI) in primates. MEASURES: need to be sensitive to both increases and decreases in function in order to demonstrate potential positive or negative effects of therapeutics. OBJECTIVES: To develop behavioral tests and analyses to assess recovery of function after SCI in the nonhuman primate. METHODS: In all, 24 male rhesus macaques were subjected to complete C7 lateral hemisection. The authors scored recovery of function in an open field and during hand tasks in a restraining chair. In addition, EMG analyses were performed in the open field, during hand tasks, and while animals walked on a treadmill. Both control and treated monkeys that received candidate therapeutics were included in this report to determine whether the behavioral assays were capable of detecting changes in function over a wide range of outcomes. RESULTS: The behavioral assays are shown to be sensitive to detecting a wide range of motor functional outcomes after cervical hemisection in the nonhuman primate. Population curves on recovery of function were similar across the different tasks; in general, the population recovers to about 50% of baseline performance on measures of forelimb function. CONCLUSIONS: The behavioral outcome measures that the authors developed in this preclinical nonhuman primate model of SCI can detect a broad range of motor recovery. A set of behavioral assays is an essential component of a model that will be used to test efficacies of translational candidate therapies for SCI.