Long-term fade study of the DT-702 LiF: Mg,Cu,P TLD.

LiF thermoluminescent dosemeters (TLDs) are used by the US Navy to record radiation exposure of personnel. The Model DT-648 LiF:Mg,Ti TLD has been replaced by a new Model DT-702 LiF:Mg,Cu,P TLD. The DT-648 was used for many years and has undergone extensive testing to identify its pre- and post-irradiation fade operating characteristics. Studies have shown that the addition of copper increases the thermoluminesence sensitivity of the TLD for improved low-level radiation monitoring. This study evaluates various fading characteristics of the new copper-doped dosemeter using current equipment for processing of TLDs and calibrating to a National Institute of Standards and Technology standard source. The 57-week study took place at the Naval Dosimetry Center, Bethesda, MD, USA. TLDs were stored for various lengths of time before and after being exposed to a National Institute of Standards and Technology calibrated radiation sources. TLDs were then processed using current US Navy instructions and the resulting dose compared with the calibrated exposure. Both loss of signal and loss of sensitivity were evaluated. The results of this study have shown that the DT-702 TLD has no statistically significant change in sensitivity or change in signal with up to 57 weeks of pre- or post-irradiation time. The results of this study will increase the accuracy of exposure record keeping for the Navy and will allow longer issue periods. This will increase flexibility with international and domestic shipping procedures, as well as reduce workload requirements for dosimetry processing.

Technical note: the calibration of 90Y-labeled SIR-Spheres using a nondestructive spectroscopic assay.

90Y-labeled SIR-Spheres are currently used to treat patients with hepatic metastases secondary to colorectal adenocarcinoma. In general, the prescribed activity is based on empirical data collected during clinical trials. The activity of the source vial is labeled by the manufacturer as 3.0 GBq +/- 10% and is not independently verified by the end user. This technical note shows that the results of a nondestructive spectroscopic assay of a SIR-Spheres sample was 26% higher than the activity stated by the manufacturer. This difference should not impact the current empirical prescription method but may be problematic for patient-specific dosimetry applications, such as image-based dosimetry.

Sustainable production of orphan radionuclides at Wisconsin.

Over a hundred proton-induced reactions have been studied at the University of Wisconsin Medical Physics department since the installation of the first CTI RDS 112 in 1985. The focus has been to measure thick target yields at 11 MeV, in an effort to concentrate on the practical production of positron emitting radionuclides that have favorable decay characteristics, high yields and the potential for labeling pivotal biological tracers. This review covers our recent advances to scale-up the production of the heavy halogens and transition metals as feed-stock for non-conventional PET tracers that are currently attracting increased attention in oncology.

18F-labeled resin microspheres as surrogates for 90Y resin microspheres used in the treatment of hepatic tumors: a radiolabeling and PET validation study.

(90)Y-labeled resin microspheres (SIR-Spheres) are currently used to treat patients with primary and metastatic solid liver tumors. This treatment is typically palliative since patients have exhausted all other standard treatment options. Improving the quality of life and extending patient survival are typical benchmarks for tracking patient response. However, the current method for predicting microsphere biodistributions with (99m)Tc-labeled macroaggregated albumin (MAA) does not correlate well with patient response. This work presents the development of a new (18)F-labeled resin microsphere to serve as a surrogate for the treatment microsphere and to employ the superior resolution and sensitivity of positron emission tomography (PET). The (18)F microsphere biodistributions were determined in a rabbit using PET imaging and histological review. The PET-based uptake ratio was shown to agree with the histological findings to better than 3%. In addition, the radiolabeling process was shown to be rapid, efficient and relatively stable in vivo.

A new internal pair production branching ratio of 90Y: the development of a non-destructive assay for 90Y and 90Sr.

(90)Y is utilized as a therapeutic radioisotope in radiolabeled monoclonal antibodies and in microspheres for targeted radiation therapy of the liver. Currently, the widely used dose calibrator assay of (90)Y can have uncertainties exceeding +/-10%. A non-destructive assay using spectroscopy is possible by reducing the currently published uncertainty (+/-12%) in the internal pair production branching ratio for the 0(+)-0(+) transition of (90)Zr. A high-purity germanium detector was used to determine the branching ratio to be (31.86+/-0.47) x 10(-6).

Heterogeneity of serum tryptophan concentration and availability to the brain in patients with the chronic fatigue syndrome.

We assessed the serotonin status of patients with the chronic fatigue syndrome (CFS). Tryptophan (Trp) availability to the brain, expressed as the ratio of concentration of serum Trp to the sum of those of its five competitors (CAA), and other parameters of Trp disposition were compared in 23 patients with the CFS and 42 healthy controls. The serum [free Trp]/[CAA] ratio was 43% higher in CFS patients, due to a 48% higher [free Trp]. [Total Trp] was also significantly higher (by 19%) in CFS patients, and, although the [total Trp]/[CAA] ratio did not differ significantly between the control and patient groups, the difference became significant when the results were co-varied with age and gender. [CAA] was not significantly different between groups, but was significantly lower in females, compared to males, of the CFS patient group. We have established normal ranges for Trp disposition parameters and propose criteria for defining the serotonin-biosynthetic status in humans. We have provisionally identified two subgroups of CFS patients, one with normal serotonin and the other with a high serotonin status. The relevance of our findings to, and their implications for, the pharmacological and other therapies of the chronic fatigue syndrome are discussed.