Radioembolization and the Dynamic Role of (90)Y PET/CT.

Before the advent of tomographic imaging, it was postulated that decay of (90) Y to the 0(+) excited state of (90)Zr may result in emission of a positron-electron pair. While the branching ratio for pair-production is small (~32 × 10(-6)), PET has been successfully used to image (90) Y in numerous recent patients and phantom studies. (90) Y PET imaging has been performed on a variety of PET/CT systems, with and without time-of-flight (TOF) and/or resolution recovery capabilities as well as on both bismuth-germanate and lutetium yttrium orthosilicate (LYSO)-based scanners. On all systems, resolution and contrast superior to bremsstrahlung SPECT has been reported. The intrinsic radioactivity present in LYSO-based PET scanners is a potential limitation associated with accurate quantification of (90) Y. However, intrinsic radioactivity has been shown to have a negligible effect at the high activity concentrations common in (90) Y radioembolization. Accurate quantification is possible on a variety of PET scanner models, with or without TOF, although TOF improves accuracy at lower activity concentrations. Quantitative (90) Y PET images can be transformed into 3-dimensional (3D) maps of absorbed dose based on the premise that the (90) Y activity distribution does not change after infusion. This transformation has been accomplished in several ways, although the most common is with the use of 3D dose-point-kernel convolution. From a clinical standpoint, (90) Y PET provides a superior post-infusion evaluation of treatment technical success owing to its improved resolution. Absorbed dose maps generated from quantitative PET data can be used to predict treatment efficacy and manage patient follow-up. For patients who receive multiple treatments, this information can also be used to provide patient-specific treatment-planning for successive therapies, potentially improving response. The broad utilization of (90) Y PET has the potential to provide a wealth of dose-response information, which may lead to development of improved radioembolization treatment-planning models in the future.

Intraprocedural yttrium-90 positron emission tomography/CT for treatment optimization of yttrium-90 radioembolization.

Radioembolization with yttrium-90 ((90)Y) microspheres relies on delivery of appropriate treatment activity to ensure patient safety and optimize treatment efficacy. We report a case in which (90)Y positron emission tomography (PET)/computed tomography (CT) was performed to optimize treatment planning during a same-day, three-part treatment session. This treatment consisted of (i) an initial (90)Y infusion with a dosage determined using an empiric treatment planning model, (ii) quantitative (90)Y PET/CT imaging, and (iii) a secondary infusion with treatment planning based on quantitative imaging data with the goal of delivering a specific total tumor absorbed dose.

Online training on the safe use of fluoroscopy can result in a significant decrease in patient dose.

RATIONALE AND OBJECTIVES: Concerns over medical radiation exposure have received national press in recent years, and training in the appropriate use of radiation has become an essential component of every radiology residency program. Appropriate training is particularly important in fluoroscopy because it is commonly used by inexperienced radiology residents and has the potential to impart relatively high patient radiation doses. In an effort to minimize the radiation doses received by patients, our institution has recently initiated an online training program in the safe use of fluoroscopy. This course is required and must be completed by new radiology residents before their first fluoroscopy rotation. The goal of this study was to determine if the use of an online course in the safe use of fluoroscopy could result in decreased patient dose without affecting diagnostic quality. MATERIALS AND METHODS: Four years of retrospective procedural data for residents performing gastrointestinal and genitourinary fluoroscopic procedures without specialized training were reviewed. Incoming residents took an American Medical Association-accredited online training program in the safe use of fluoroscopy the week before their first fluoroscopy rotation. Patient dose and diagnostic quality data, inferred from the frequency of attending physician intervention necessary to complete the procedure, were collected for all exams performed by the new group of residents after completion of the training course. This was then compared to data from prior classes and stratified by procedure type. RESULTS: Statistically significant reductions in both average fluoroscopy time (FT) or dose-area-product (DAP) were found for many of the fluoroscopic procedures performed by residents who participated in the online fluoroscopy training program. Specifically, statistically significant reductions in FT for barium enema, cystogram, defecogram, and esophagram procedures (P < .001) were found. Esophagram and upper gastrointestinal studies were completed with a significantly lower DAP (P < .001). The average reduction in DAP across all procedures performed by first-year residents was 38%, whereas the average reduction in FT was 25%. Based on a review of data from all procedures performed, there was no statistically significant loss in diagnostic quality. CONCLUSION: An online training program can be effectively used to provide radiation safety instruction immediately before the start of a resident's fluoroscopy rotation, decreasing patient dose without affecting diagnostic quality.

Role of positron emission tomography/computed tomography in breast cancer.

Although positron emission tomography (PET) imaging may not be used in the diagnosis of breast cancer, the use of PET/computed tomography is imperative in all aspects of breast cancer staging, treatment, and follow-up. PET will continue to be relevant in personalized medicine because accurate tumor status will be even more critical during and after the transition from a generic metabolic agent to receptor imaging. Positron emission mammography is an imaging proposition that may have benefits in lower doses, but its use is limited without new radiopharmaceuticals.

Positron emission tomography/computed tomography in melanoma.

Fludeoxyglucose F 18 positron emission tomography/computed tomography (PET/CT) has been invaluable in the assessment of melanoma throughout the course of the disease. As with any modality, the studies are incomplete and more information will be gleaned as our experience progresses. Additionally, it is hoped that a newer PET agent in the pipeline will give us even greater success in the identification and subsequent treatment of melanoma. This article aims to examine the utilization of PET/CT in the staging, prognostication, and follow-up of melanoma while providing the physicians who order and interpret these studies practical guidelines and interpretive pitfalls.

Treatment modification of yttrium-90 radioembolization based on quantitative positron emission tomography/CT imaging.

Treatment activity for yttrium-90 ((90)Y) radioembolization when calculated by using the manufacturer-recommended technique is only partially patient-specific and may result in a subtumoricidal dose in some patients. The authors describe the use of quantitative (90)Y positron emission tomography/computed tomography as a tool to provide patient-specific optimization of treatment activity and evaluate this new method in a patient who previously received traditional (90)Y radioembolization. The modified treatment resulted in a 40-Gy increase in absorbed dose to tumor and complete resolution of disease in the treated area within 3 months.

Complementarity and clustering in a simple model mixed bilayer.

A bilayer of uniform thickness containing a mixture of long and short lipids is simulated using a parallel hard-rod model to illustrate the effect of transbilayer repulsions between the tails of the long component. Monte Carlo simulations show considerable entropy-driven clustering within each layer. Demixing reaches a maximum at the highest packing fraction of the liquid state and decreases as the system orders. The formation of complementary clusters of long and short rods on opposite sides of the bilayer increases translational freedom within each cluster by reducing constraints imposed by the opposing leaflet, an effect that becomes less important as rods lock into facing hexagonally ordered arrays.