A HPLC-SRM-MS based method for the detection and quantification of methotrexate in urine at doses used in clinical practice for patients with rheumatological disease: a potential measure of adherence.

Rheumatoid arthritis (RA) is a common autoimmune disease that causes significant disability and reduced life expectancy. The folate antagonist methotrexate (MTX) is first-line therapy for RA when used weekly at low doses (5-25 mg). However, the true rate of adherence to MTX is uncertain. This is in part due to the different methods of measurement of adherence employed with no biochemical test currently available to determine adherence to low dose MTX. Common methods of MTX measurement include immunoassays in patients with high dose therapy, but these assays cross-react with MTX metabolites and lack the sensitivity required to measure adherence to low dose MTX. HPLC-SRM-MS (selected reaction monitoring-mass spectrometry) has several theoretical advantages over immunoassays with improved specificity, minimal cross-reaction and higher sensitivity. The aim of this study was to develop an assay to measure MTX and its major metabolite 7-OH-MTX in urine as a tool to monitor adherence to low dose MTX in clinic. As a proof of concept, urine samples from 4 participants with RA were measured after directly observed therapy. The assay showed improved sensitivity compared to that reported by immunoassays, with low carryover and high within-run precision. In participant samples, MTX was measurable in the urine for up to 105 hours after administration and 7-OH-MTX was detectable up to 98 hours after administration, suggesting that this assay is suitable for the measurement of adherence to therapy. The assay requires minimal sample preparation and can be adopted by other laboratories with minimal study set up.

Association of a complement receptor 1 gene variant with baseline erythrocyte sedimentation rate levels in patients starting anti-TNF therapy in a UK rheumatoid arthritis cohort: results from the Biologics in Rheumatoid Arthritis Genetics and Genomics Study Syndicate cohort.

Eligibility for anti-tumour necrosis factor (TNF) therapy in most European countries is restricted to severe, active rheumatoid arthritis (RA). The DAS28 score is a marker of disease severity and incorporates one of two inflammatory markers, erythrocyte sedimentation rate (ESR) or C-reactive protein. We aimed to determine the relation between genetic variants known to affect ESR and levels of ESR in patients with active RA. DNA samples were genotyped for four single-nucleotide polymorphisms (SNPs) rs7527798 (CR1L), rs6691117 (CR1), rs10903129 (TMEM57) and rs1043879 (C1orf63). The association between SNPs and baseline ESR, baseline DAS28-ESR, and change in DAS28-ESR was evaluated. Baseline ESR was significantly associated with CR1 rs6691117 genotype (P=0.01). No correlation was identified between baseline DAS28-ESR or change in DAS28-ESR. In conclusion, genetic variation in the gene encoding CR1 may alter ESR levels but not DAS28-ESR, indicating no adjustment for CR1 genotype is required in the assessment of patients with severe active RA.

SU-E-T-575: To Analyze the Clinical Impact of Esophageal Sparing on Treatment Plans for Patients with Grade 3 Esophagitis.

PURPOSE: To analyze the clinical impact of esophageal sparing on treatment plans for patients with grade 3 esophagitis. METHODS: The treatment plans of 8 patients (project total: 20 patients) who were treated with IMRT and exhibited stage 3 esophagitis were re-planned to give a simulated clinical plan with dose distribution that mirrored our current clinical practice (74Gy to the target, and 5mm margins), and a plan that emphasized esophageal sparing. Doses to the esophagus, heart, cord, lung and PTV were compared. RESULTS: Comparing the esophageal sparing plan to the simulated clinical plan, the mean reduction in esophageal volume receiving 50, 55, 60, 65, and 70Gy were 2.0, 3.2, 5.0, 7.2, and 10.9 cm3 , respectively. The mean reduction in the continuous length of esophagus receiving 50, 55, 60, 65, and 70Gy were 12, 24, 38, 40, and 47mm, respectively. The associated reduction in dose to 90% and 95% of the PTV was 2.2 and 3.8Gy, respectively. Of the 8 patients examined, 2 showed a significant decrease in PTV coverage (4.6Gy, 12.3Gy for 90% of PTV), 4 showed decreases under 1.1Gy, but 2 showed an increase of 1.4Gy and 0.5Gy for 90% PTV. Cord dose was maintained below 50Gy, and there was a slight increase in mean heart dose and mean lung dose of 2.4Gy, and 2.7Gy, respectively. Data will also be presented comparing these plans with the actual treated plans (for which the patients had grade 3 esophagitis) and plans that emphasize PTV coverage. CONCLUSIONS: Treatment planning to emphasize esophageal sparing can reduce the volume and continuous length of the esophagus which receives high doses. There is some associated modest reduction in PTV coverage. In summary, in many cases esophageal sparing can be accomplished for lung cancer cases while maintaining adequate PTV coverage, although there is variability between patients.

SU-E-T-558: Assessing the Effect of Inter-Fractional Motion in Esophageal Sparing Plans.

PURPOSE: To compare esophageal dose distributions in esophageal sparing IMRT plans with predicted dose distributions which include the effect of inter-fraction motion. METHODS: Seven lung cancer patients were used, each with a standard and an esophageal sparing plan (74Gy, 2Gy fractions). The average max dose to esophagus was 8351cGy and 7758cGy for the standard and sparing plans, respectively. The average length of esophagus for which the total circumference was treated above 60Gy (LETT60) was 9.4cm in the standard plans and 5.8cm in the sparing plans. In order to simulate inter-fractional motion, a three-dimensional rigid shift was applied to the calculated dose field. A simulated course of treatment consisted of a single systematic shift applied throughout the treatment as well a random shift for each of the 37 fractions. Both systematic and random shifts were generated from Gaussian distributions of 3mm and 5mm standard deviation. Each treatment course was simulated 1000 times to obtain an expected distribution of the delivered dose. RESULTS: Simulated treatment dose received by the esophagus was less than dose seen in the treatment plan. The average reduction in maximum esophageal dose for the standard plans was 234cGy and 386cGY for the 3mm and 5mm Gaussian distributions, respectively. The average reduction in LETT60 was 0.6cm and 1.7cm, for the 3mm and 5mm distributions respectively. For the esophageal sparing plans, the average reduction in maximum esophageal dose was 94cGy and 202cGy for 3mm and 5mm Gaussian distributions, respectively. The average change in LETT60 for the esophageal sparing plans was smaller, at 0.1cm (increase) and 0.6cm (reduction), for the 3mm and 5mm distributions, respectively. CONCLUSIONS: Interfraction motion consistently reduced the maximum doses to the esophagus for both standard and esophageal sparing plans.

Unexpected behavior of the near-threshold double-photoionization cross section of beryllium.

The threshold region of the double-photoionization cross section of atomic beryllium was investigated using monochromatized synchrotron radiation. The photon energy dependence of the double-photoionization cross section can be described by the Wannier power law up to 1.7 eV above threshold. However, we unexpectedly find oscillations in the cross section, which are in excellent agreement with a modulated threshold law based on the Coulomb-dipole theory [Phys. Rev. Lett. 49, 365 (1982)]]. This new finding casts some doubts on the general applicability of the Wannier power law.

Oscillations in the double-photoionization cross section of Li near threshold.

The threshold region of the double-photoionization cross section of lithium was investigated using monochromatized synchrotron radiation and ion time-of-flight spectrometry. While the overall energy dependence can be described by the Wannier power law, we found oscillations in the cross section which are in good agreement with a modulated threshold law as proposed by Temkin [Phys. Rev. Lett. 49, 365 (1982)]]. This behavior may be due to the unequal binding energies of the electrons involved in the double-photoionization process.