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This paper reports on the initial performance evaluation of a bedside cardiac PET/SPECT system. The system was designed to move within a hospital to image critically-ill patients, for example, those in intensive care unit (ICU) or emergency room settings, who cannot easily be transported to a conventional SPECT or PET facility. The system uses two compact (25 cm x 25 cm) detectors with pixilated NaI crystals and position sensitive PMTs. The performance is evaluated for both 140 keV (Tc-99m) and 511 keV (F-18) emitters with the system operating in single photon counting (SPECT) mode. The imaging performance metrics for both 140 keV and 511 keV included intrinsic energy resolution, spatial resolution (intrinsic, system, and reconstructed SPECT), detection sensitivity, count rate capability, and uniformity. Results demonstrated an intrinsic energy resolution of 31% at 140 keV and 23 % at 511 keV, a planar intrinsic spatial resolution of 5.6 mm full width half-maximum (FWHM) at 140 keV and 6.3 mm FWHM at 511 keV, and a sensitivity of 4.15 counts x [mu][Ci.sup.-1] x [s.sup.-1] at 140 keV and 0.67 counts x [mu][Ci.sup.-1] x [s.sup.-1] at 511 keV. To further the study, a SPECT acquisition using a dynamic cardiac phantom was performed, and the resulting reconstructed images are presented. Index Terms--Cardiac SPECT, mobile SPECT, 511 keV SPECT.

Background: 99mTc-macroaggregated albumin (99mTc-MAA) scintigraphy is utilized in treatment planning for Yttrium-90 (90Y) Selective Internal Radiation Therapy (SIRT) of liver tumors to evaluate hepatopulmonary shunting by calculating the lung shunt fraction (LSF). The purpose of this study was to evaluate if LSF calculation using SPECT/CT instead of planar gamma camera imaging is more accurate and if this can potentially lead to more effective treatment planning of hepatic lesions while avoiding excessive pulmonary irradiation. Results: LSF calculation was obtained using two different methodologies in 85 cases from consecutive patients intended to receive 90Y SIRT. The first method was based on planar gamma camera imaging in the anterior and posterior views with geometric mean calculation of the LSF from regions of interest of the liver and lungs. The second method was based on segmentation of the liver and lungs from SPECT/CT images of the thorax and abdomen. The differences in planar imaging versus SPECT/CT derived LSF values along with the estimated absorbed lung mean dose (LMD) were evaluated. The LSF values were higher in planar imaging versus SPECT/CT in 81/85 cases, with a mean value of 8.5% vs. 4.6% respectively; the difference was statistically significant using a paired t-test (alpha = 0.05). In those patients who received SIRT, the estimated absorbed LMD calculated with planar imaging was significantly higher than with SPECT/CT (t-test, P < 0.005). Repeated phantom experiments using an anthropomorphic torso phantom with variable 99mTc activity concentrations for the liver and lungs were performed with the standard patient protocol, demonstrated improved accuracy of the LSF calculation based on SPECT/CT than planar imaging (mean overestimated value of 6% vs. 26%). Conclusions: This study demonstrates that LSF calculation using planar imaging can be significantly overestimated while calculation using SPECT/CT imaging and appropriate segmentation tools can be more accurate. Minimizing the errors in obtaining the LSF can lead to more effective 90Y SIRT treatment planning for hepatic tumors while ensuring the lung dose will not exceed the standard acceptable safety thresholds. [ABSTRACT FROM AUTHOR]

Background: Source modeling is an approach to reduce computational burden in Monte Carlo simulations but at the cost of reduced accuracy. Although this method can be effective, one component of the source model that is exceptionally difficult to model is the electron contamination, a significant contributor to the skin and shallow dose. Aims and Objectives: To improve the accuracy for the electron contamination component of the overall source model, we have generated a spatial mesh based surface source model. Methods and Materials: The source model is located downstream from the flattening filter and mirror but upstream from the movable jaws. A typical phase space file uses around ten parameters per particle, but this method simplifies this number to five components. By using only the electron distance from the central axis, angles from the central axis and energy, the computational time and disk space required is greatly reduced. Results and Conclusion: Despite the simplification in the source model, the electron contamination is still accurate to within 1.5%. [ABSTRACT FROM AUTHOR]

From the classical radiobiology course in a medical physics graduate program, we learned the most important principle in terms of cell behavior under different radiotherapy dose-fractionation schemes: repair, reassortment, reoxygenation, and repopulation (a.k.a. "4 Rs"). Various immunotherapies are now approved for use in cancer patients as not only secondary options to conventional therapies but also as first-line treatment.[7] The impact of these recent developments of cancer immunotherapy in the field of medical physics is inevitable. Biological therapy is a type of therapy that uses substances from living organisms to treat cancer".[16] Based on this definition, immunotherapy is not a physics topic and therefore should not be included in the medical physics curriculum. [Extracted from the article]

The article discusses the design and shielding of a room dedicated to 137Cs irradiation. Regulations require that the exterior areas of any radiation facility must be restricted unless the dose equivalent is less than 0.02 mSv in any one hour. Two Monte Carlo radiation transport simulation codes, MCNPS and Mercurad, were used to design a facility to shield a 3.48 x 105 MBq 137Cs irradiator that meets these requirements. Simulations showed that the dose equivalent rates were below the legal limit for unrestricted access. The facility was constructed using available concrete block and student labor to minimize costs. To verify the accuracy of the Monte Carlo radiation transport codes, an ion chamber was used to characterize the facility.