PubMed · 10259388
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J Harshbarger. 1982. Testing for scan linearity.. https://pubmed.ncbi.nlm.nih.gov/10259388/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
PURPOSE: Electron beam radiotherapy is frequently administered based on clinical setups without formal treatment planning. We felt, therefore, that it was important to monitor electron beam treatments by in vivo dosimetry to prevent errors in treatment delivery. In this study, we present our clinical experience with patient dose verification using electron diodes and quantitatively assess the dose perturbations caused by the diodes during electron beam radiotherapy. METHODS AND MATERIALS: A commercial diode dosimeter was used for the in vivo dose measurements. During patient dosimetry, the patients were set up as usual by the therapists. Before treatment, a diode was placed on the patient's skin surface and secured with hypoallergenic tape. The patient was then treated and the diode response registered and stored in the patient radiotherapy system database via our in-house software. A customized patient in vivo dosimetry report showing patient details, expected and measured dose, and percent difference was then generated and printed for analysis and record keeping. We studied the perturbation of electron beams by diodes using film dosimetry. Beam profiles at the 90% prescription isodose depths were obtained with and without the diode on the beam central axis, for 6-20 MeV electron beams and applicator/insert sizes ranging from a 3-cm diameter circular field to a 25 x 25 cm open field. RESULTS: In vivo dose measurements on 360 patients resulted in the following ranges of deviations from the expected dose at the various anatomic sites: Breast (222 patients) -20.3 to +23.5% (median deviation 0%); Head and Neck (63 patients) -21.5 to +14.8% (median -0.7%); Other sites (75 patients) -17.6 to +18.8% (median +0.5%). Routine diode dosimetry during the first treatment on 360 patients (460 treatment sites) resulted in 11.5% of the measurements outside our acceptable +/-6% dose deviation window. Only 3.7% of the total measurements were outside +/-10% dose deviation. Detailed investigations revealed that the dose discrepancies, overwhelmingly, were due to inaccurate diode orientation and positioning, especially in the regions with rapidly changing contours and/or sloping surfaces. The presence of a diode in the treatment field was found, in some cases, to cause significant dose reduction, most noticeable with smaller fields and lower energy beams. The reduction in dose ranged from 16% (for a 6 MeV beam and a 3 cm diameter circular field) to 4% (for a 12 MeV beam and a 10 x 10 cm field). CONCLUSIONS: Diode dosimetry was found to be convenient and valuable for verifying in real time the dose delivery accuracy of electron beam treatments, but with some caveats. When treating a small field by low energy electrons, frequent use of diodes is undesirable, because it might result in appreciable reduction of dose to the target volume.
We describe the first results of a quantitative LC-tandem mass spectrometry method for urinary C-peptide with the use of [2H14]C-peptide as internal standard. LC was based on gradient elution of a Hypersil PEP C18 column. Mass spectrometry was performed in the negative electrospray ionization mode and by monitoring of the transitions at m/z 1514/1334 ([2H14]C-peptide) and 1507/1320 (C-peptide). For sample preparation, we applied ultrafiltration. The analytical performance of the method in terms of measurement precision gave an RSD of <2% (n=10). The overall imprecision was investigated from independent analysis of two urine samples in six-fold and resulted in an RSD<5%. The limit of detection, expressed as signal-to-noise ratio 3, was approximately 0.15 ng C-peptide injected. Analysis of 10 random urine samples from laboratory volunteers showed interference-free ion chromatograms at a signal-to-noise ratio of approximately 75 on average. The C-peptide concentrations calculated from quantification by the bracketing calibration technique ranged from 32 to 165 ng/ml.
A rapid and highly sensitive LC-MS-MS method using deuterium-labelled internal standards was developed and evaluated for the simultaneous determination of deramciclane and its pharmacologically active metabolite (N-desmethylderamciclane). The sample preparation based on liquid-liquid extraction was carried out with an off-line robotic system. Evaluation of this analytical method shows that samples can be assayed with acceptable accuracy and precision in the 0.1 to 50 ng/ml concentration range for both compounds. The method was applied for the quantitative determination of deramciclane and its metabolite in human plasma samples during a food interaction pharmacokinetic study.