Evaluation of the impact of peak description on the quantitative capabilities of comprehensive two-dimensional liquid chromatography.

Comprehensive, two-dimensional liquid chromatography (LC × LC) is a powerful technique for the separation of complex mixtures. Most studies using LC × LC are focused on qualitative efforts, such as increasing peak capacity. The present study examined the use of LC × LC-UV/vis for the separation and quantitation of polycyclic aromatic hydrocarbons (PAHs). More specifically, this study evaluated the impact of different peak integration approaches on the quantitative performance of the LC × LC method. For well-resolved three-dimensional peaks, parameters such as baseline definition, peak base shape, and peak width determination did not have a significant impact on accuracy and precision. For less-resolved peaks, a dropped baseline and the summation of all slices in the peak improved the accuracy and precision of the integration methods. The computational approaches to three-dimensional peak integration are provided, including fully descriptive, select slice, and summed heights integration methods, each with its own strengths and weaknesses. Overall, the integration methods presented quantify each of the PAHs within acceptable precision and accuracy ranges and have comparable performance to that of single dimension liquid chromatography.

Metformin is not associated with improved biochemical free survival or cause-specific survival in men with prostate cancer treated with permanent interstitial brachytherapy.

PURPOSE: Several recent studies have suggested improved clinical outcomes in diabetic men with prostate cancer who also use metformin. We explore whether metformin use is associated with improved outcomes specifically in men undergoing prostate brachytherapy. MATERIAL AND METHODS: 2,298 consecutive patients underwent permanent interstitial brachytherapy by a single brachytherapist (GSM). The cohort included 2028 non-diabetic men, 144 men with diabetes who were not taking metformin, and 126 men with diabetes who were taking metformin. Median follow up was 8.3 years. Differences in biochemical free survival, cause specific survival, and overall survival between men taking metformin and those not taking metformin were compared using Kaplan-Meier curves and log rank tests. RESULTS: Fifteen year biochemical failure rate, cause specific mortality and overall mortality for non-diabetic men was 4.6%, 1.5%, 47.0%, respectively; for diabetic men taking metformin 4.8%, 2.0%, 37.2%; and for diabetic men not taking metformin was 2.8%, 0%, 72.7%, respectively. Metformin use was not predictive in multivariate analysis of biochemical failure or prostate cancer specific mortality. However, diabetic men not taking metformin had higher overall mortality than non-diabetic men. CONCLUSIONS: Metformin use was not associated with improved biochemical survival or cancer specific survival in this cohort of men treated with prostate brachytherapy.

Influence of glycosidic linkage on the solution conformational entropy of gluco- and mannobioses.

Employing size-exclusion chromatography, an entropically-controlled separation technique, we have determined the solution conformational entropy (-ΔS) of (1→2)-, (1→3)-, (1→4)-, and (1→6)-linked gluco- and mannobioses with an α anomeric configuration, at quasi-physiological conditions of solvent, temperature, and pH. The experiments allowed for comparison both among and between each series of disaccharides. Results included quantitative information on how the additional degrees of freedom of the (1→6) linkage influence -ΔS, as well as on the influence on solution conformational entropy of a single axial hydroxyl (OH) group and of the relative positioning of the glycosidic linkage and the anomeric hydroxyl group. We also contrasted the (1→4)-α-D-linked gluco- and mannobioses to their counterparts with a ß anomeric configuration. Comparison between (1→4)-ß-D-linked glucobiose (cellobiose) and (1→4)-ß-D-linked mannobiose showed that the restrictive effect on solution flexibility of the axial OH in the latter disaccharide is offset by the combined effect of hydroxyl group orientation and anomeric configuration on intramolecular hydrogen bonding.

Determining the solution conformational entropy of oligosaccharides by SEC with on-line viscometry detection.

Introduced here is a method for determining the solution conformational entropy of oligosaccharides (-ΔS) that relies on the on-line coupling of size-exclusion chromatography (SEC), an entropically-controlled separation technique, and differential viscometry (VISC). Results from this SEC/VISC method were compared, for the same injections of the same sample dissolutions and under identical solvent/temperature conditions, to results from a benchmark SEC/differential refractometry (SEC/DRI) method which has been applied successfully over the last decade to determining -ΔS of a variety of mono-, di-, and oligosaccharides. The accuracy (as compared to SEC/DRI) and precision of SEC/VISC were found to be excellent, as was the sensitivity of the viscometer in the oligomeric region. The experiments presented here contrast three sets of (1→4)-ß-d-oligosaccharides, namely manno-, cello-, and N-acetylchitooligosaccharides of degree of polymerization (DP) 2 through 6. For each series, the dependence of -ΔS on DP was found to be monotonic while, between series, differences at each DP could be ascribed to either the additional degrees of freedom imparted by large, multi-atomic substituent groups, or to the presence or absence of additional intramolecular hydrogen bonds, depending on the axial versus equatorial arrangement of particular hydroxyl groups. An hypothesis is advanced to explain the unexpectedly high sensitivity of viscometric detection for low-molar-mass analytes. The method presented can be extended to the analysis of oligosaccharides other than those studied here.

Does the "C3 effect" offset the Δ2 effect, as regards the solution flexibility of aldoses?

The solution flexibility of carbohydrates influences a variety of molecular recognition and regulatory processes. For aldoses and other monosaccharides, this flexibility is dictated by the orientations of the various hydroxyl (OH) groups present, which influences conformer and anomer ratios, interactions among these OH groups, and interactions between them and the surrounding solvent. Depending on the number and position of axial OH groups, a variety of structures can coexist in solutions at equilibrium. In 1950, as part of his pioneering studies on the shape of pyranoside rings, Reeves described the Δ2 effect, the greater destabilization of the pyranose ring conformation when the OH group on carbon 2 (C2 ) is in the axial position. It was later proposed by Angyal that the Δ2 effect could be cancelled by the presence of an axial OH on C3 , termed here the "C3 effect." Employing size-exclusion chromatography, an entropically-controlled separation technique, we have investigated whether or not the C3 and Δ2 effects indeed do compensate for one another with respect to their influence on the solution flexibility of select aldohexoses and aldopentoses. As will be seen, while qualitatively and semiquantitatively this mutual cancellation of effects does occur in aldohexoses, it does not appear to do so in aldopentoses. An explanation for the latter appears to lie in the variety of anomers and conformers present in equilibrium solutions of those aldopentoses studied and in the relative entropic contribution of individual conformers or anomers to the total solution flexibility.

Multisector prostate dosimetric quality: analysis of a large community database.

PURPOSE: To evaluate multi-institutional prostate brachytherapy dosimetric quality using multisector analysis. METHODS AND MATERIALS: In the database, 4547 patients underwent brachytherapy (3094 for (125)I, 1437 for (103)Pd, and 16 for (131)Cs). The original prostate postimplant dosimetry was reported using the maximum dose covering 90% of the prostate volume (D90) and the percentage of the prostate volume covered by the prescription dose (V100). Retrospectively, the dosimetry of all implants was recalculated after segmenting the prostate into 12 sectors (anterior, left and right lateral and posterior, about the center of gravity, and subdivided lengthwise into three-base, midgland, and apex). The dosimetric quality of each sector and combinations of sectors was compared across radionuclides. RESULTS: For each radionuclide, there was no significant difference between monotherapy and boost in terms of V100 or D90. When classified as excellent (V100 ≥ 90%), standard (V100 ≥ 80%), or minimal (V100 < 80%), 33.0%, 4.6%, and 10.5% of all base, midgland, and apical sectors, respectively, were of minimal quality. Specifically, 59.2% of the anterior base and 30.3% of the posterior base sectors were minimal. At the anterior midgland and apex, 22% and 19% of sectors were minimal. Excellent quality was observed in more than 90% of lateral and posterior midgland sectors and in >70% of lateral and posterior sectors. When stratified by (103)Pd vs. (125)I, sector analysis did not result in clinically significant dosimetric differences. CONCLUSIONS: Coverage of base sectors was inferior to midgland and apical sectors, and coverage of anterior sectors was notably inferior to lateral and posterior sectors. Further critique of brachytherapy planning and intraoperative technique is necessary for brachytherapists to minimize these dosimetric differences.

Permanent prostate brachytherapy extracapsular radiation dose distributions: analysis of a multi-institutional database.

PURPOSE: Periprostatic brachytherapy doses impact biochemical control. In this study, we evaluate extracapsular volumetric dosimetry following permanent prostate brachytherapy in patients entered in a multi-institutional community database. MATERIAL AND METHODS: In the database, 4547 patients underwent brachytherapy (3094 - (125)I, 1437 - (103)Pd and 16 - (131)Cs). Using the originally determined prostate volume, a 5 mm, 3-dimensional peri-prostatic anulus was constructed around the prostate (except for a 2 mm posterior margin), and evaluated in its entirety and in 90° segments. Prostate dosimetric parameters consisted of a V100 and D90 while the annular dosimetry was reported as a V100. RESULTS: The intraprostatic V100 and D90 for (103)Pd, and (125)I were statistically comparable when stratified by isotope and/or monotherapy vs. boost. The overall mean V100 for the periprostatic annulus was 62.8%. The mean V100 at the base (51.6%) was substantially less than the apex (73.5%) and midgland (65.9%). In addition, for all patients, the anterior V100 (45.7%) was less than the lateral (68.8%) and the posterior (75.0%). The geometric V100 annular differences were consistent when evaluated by isotope. Overall, the V100 was higher in the (125)I cohort. CONCLUSIONS: The optimal extracapsular brachytherapy dose and radial extent remains unknown, but will prove increasingly important with reductions and/or elimination of supplemental external beam radiation therapy. The large multi-institutional community database demonstrates periprostatic annular doses that are not as robust as those in selected high volume brachytherapy centers, and may be inadequate for optimal biochemical control following monotherapeutic brachytherapy, especially in higher risk patients.

Impact of small prostate size on postimplant prostate dosimetry: analysis of a large community database.

PURPOSE: Achieving high-quality permanent interstitial brachytherapy in smaller prostates is thought to be more difficult than in larger glands. This study evaluates 4547 implants in a large community database to test this hypothesis. METHODS AND MATERIALS: From January 2003 to October 2010, 4547 prostate brachytherapy implants from a large community database were analyzed. The cohort was divided into three groups based on size, namely smaller (<30cm(3), n=1301), medium (30-40cm(3), n=1861), and large (>40cm(3), n=1385). Postimplant dosimetry, including D90, V100, and V100 by prostate sector, was performed for each implant. Comparison of mean V100 among small, medium, and larger prostate volume cohorts was performed using a one-way analysis of variance test. RESULTS: For the overall cohort, the D90 was 105% and 104% for monotherapy and boost, respectively. Mean D90 for small prostates was 106% and 104% for monotherapy and boost, respectively. Mean V100 for small prostates was 91.1% and 90.0%, respectively. Coverage for small prostates was as good or slightly better than larger glands. V100 by prostate sector revealed that there were no sectors for which smaller glands had significantly inferior coverage compared with larger glands. CONCLUSION: Although smaller prostates may in some respects be more technically difficult to implant than larger glands, a review of community-based brachytherapists reveals that with current implant techniques, good quality implants are readily achievable in men with smaller glands.

Effect of body mass index on intrafraction prostate displacement monitored by real-time electromagnetic tracking.

PURPOSE: To evaluate, using real-time monitoring of implanted radiofrequency transponders, the intrafraction prostate displacement of patients as a function of body mass index (BMI). METHODS AND MATERIALS: The motions of Beacon radiofrequency transponders (Calypso Medical Technologies, Seattle, WA) implanted in the prostate glands of 66 men were monitored throughout the course of intensity modulated radiation therapy. Data were acquired at 10 Hz from setup to the end of treatment, but only the 1.7 million data points with a "beam on" tag were used in the analysis. There were 21 obese patients, with BMI ≥ 30 and 45 nonobese patients in the study. RESULTS: Mean displacements were least in the left-right lateral direction (0.56 ± 0.24 mm) and approximately twice that magnitude in the superior-inferior and anterior-posterior directions. The net vector displacement was larger still, 1.95 ± 0.47 mm. Stratified by BMI cohort, the mean displacements per patient in the 3 Cartesian axes as well as the net vector for patients with BMI ≥ 30 were slightly less (<0.2 mm) but not significantly different than the corresponding values for patients with lower BMIs. As a surrogate for the magnitude of oscillatory noise, the standard deviation for displacements in all measured planes showed no significant differences in the prostate positional variability between the lower and higher BMI groups. Histograms of prostate displacements showed a lower frequency of large displacements in obese patients, and there were no significant differences in short-term and long-term velocity distributions. CONCLUSIONS: After patients were positioned accurately using implanted radiofrequency transponders, the intrafractional displacements in the lateral, superior-inferior, and anterior-posterior directions as well as the net vector displacements were smaller, but not significantly so, for obese men than for those with lower BMI.