Development of BNBSL: A β-ν spectra library for spectrometry applications

While modern nuclear decay data can provide many details of a given nuclides β-decay modes (branching ratios, decay heating etc.), knowledge of the emitted β-energy spectrum is often not included. This limitation hampers the use of decay data in some analysis, such as β-spectrometry of irradiated material, prediction of β-decay Bremsstrahlung or antineutrino, ν̄, detection. To address this deficiency, and for increased ease of β-spectrometry studies of complex samples, a library of β, ν and Bremsstrahlung-spectra, called BNBSL (Beta-Neutrino-Bremsstrahlung spectra library), has been produced. It has been found that the content compares favourably with experimental data and methodologies for its application to complex nuclear inventories have been developed. BNBSL contains spectra for over 1500 nuclides, which is hoped will benefit applied nuclear, radiation and materials science studies.

A COMPARISON OF OXIDE DECAY HEAT SIMULATIONS AND NUCLEAR DATA LIBRARIES WITH FUSION IRRADIATION EXPERIMENTS

We compare existing experimental decay heat data sets measured at the JAEA fusion neutron source (FNS), which employed a fast extraction rabbit system that in certain cases allowed the measurements to capture, at short cooling times, the decay profile of 16N in a range of oxides. Focussing on those data points and timescales that can be attributed to 16N, we compare measurements to simulations performed using the FISPACT-II inventory code together with evaluated nuclear data libraries. Making small corrections for other contributions at these short times, we derive integral cross section data estimates for 16O(n,p)16N from 12 oxide sample measurements and compare with previously obtained measurements in the IAEA EXFOR database and evaluations in the nuclear data libraries themselves.

Phase I-II clinical trial design: a state-of-the-art paradigm for dose finding

Background

Conventional phase I algorithms for finding a phase-2 recommended dose (P2RD) based on toxicity alone is problematic because the maximum tolerated dose (MTD) is not necessarily the optimal dose with the most desirable risk-benefit trade-off. Moreover, the increasingly common practice of treating an expansion cohort at a chosen MTD has undesirable consequences that may not be obvious.

Patients and methods

We review the phase I-II paradigm and the EffTox design, which utilizes both efficacy and toxicity to choose optimal doses for successive patient cohorts and find the optimal P2RD. We conduct a computer simulation study to compare the performance of the EffTox design with the traditional 3 + 3 design and the continuous reassessment method.

Results

By accounting for the risk-benefit trade-off, the EffTox phase I-II design overcomes the limitations of conventional toxicity-based phase I designs. Numerical simulations show that the EffTox design has higher probabilities of identifying the optimal dose and treats more patients at the optimal dose.

Conclusions

Phase I-II designs, such as the EffTox design, provide a coherent and efficient approach to finding the optimal P2RD by explicitly accounting for risk-benefit trade-offs underlying medical decisions.

A phase II study of bevacizumab and erlotinib after radiation and temozolomide in MGMT unmethylated GBM patients

Survival for glioblastoma (GBM) patients with an unmethyated MGMT promoter in their tumor is generally worse than methylated MGMT tumors, as temozolomide (TMZ) response is limited. How to better treat patients with unmethylated MGMT is unknown. We performed a trial combining erlotinib and bevacizumab in unmethylated GBM patients after completion of radiation (RT) and TMZ. GBM patients with an unmethylated MGMT promoter were trial eligible. Patient received standard RT (60 Gy) and TMZ (75 mg/m2 × 6 weeks) after surgical resection of their tumor. After completion of RT they started erlotinib 150 mg daily and bevacizumab 10 mg/kg every 2 weeks until progression. Imaging evaluations occurred every 8 weeks. The primary endpoint was overall survival. Of the 48 unmethylated patients enrolled, 46 were evaluable (29 men and 17 women); median age was 55.5 years (29-75) and median KPS was 90 (70-100). All patients completed RT with TMZ. The median number of cycles (1 cycle was 4 weeks) was 8 (2-47). Forty-one patients either progressed or died with a median progression free survival of 9.2 months. At a follow up of 33 months the median overall survival was 13.2 months. There were no unexpected toxicities and most observed toxicities were categorized as CTC grade 1 or 2. The combination of erlotinib and bevacizumab is tolerable but did not meet our primary endpoint of increasing survival. Importantly, more trials are needed to find better therapies for GBM patients with an unmethylated MGMT promoter.

Interatomic potentials for modelling radiation defects and dislocations in tungsten

We have developed empirical interatomic potentials for studying radiation defects and dislocations in tungsten. The potentials use the embedded atom method formalism and are fitted to a mixed database, containing various experimentally measured properties of tungsten and ab initio formation energies of defects, as well as ab initio interatomic forces computed for random liquid configurations. The availability of data on atomic force fields proves critical for the development of the new potentials. Several point and extended defect configurations were used to test the transferability of the potentials. The trends predicted for the Peierls barrier of the [Formula: see text] screw dislocation are in qualitative agreement with ab initio calculations, enabling quantitative comparison of the predicted kink-pair formation energies with experimental data.

Free energy generalization of the Peierls potential in iron

In body-centered-cubic (bcc) crystals, 1/2<111> screw dislocations exhibit high intrinsic lattice friction as a consequence of their nonplanar core structure, which results in a periodic energy landscape known as the Peierls potential U(P). The main features determining plastic flow, including its stress and temperature dependences, can be derived directly from this potential, hence its importance. In this Letter, we use thermodynamic integration to provide a full thermodynamic extension of U(P) for bcc Fe. We compute the Peierls free energy path as a function of stress and temperature and show that the critical stress vanishes at 700 K, supplying the qualitative elements that explain plastic behavior in the athermal limit.

Assessment of interatomic potentials for atomistic analysis of static and dynamic properties of screw dislocations in W

Screw dislocations in bcc metals display non-planar cores at zero temperature which result in high lattice friction and thermally-activated strain rate behavior. In bcc W, electronic structure molecular statics calculations reveal a compact, non-degenerate core with an associated Peierls stress between 1.7 and 2.8 GPa. However, a full picture of the dynamic behavior of dislocations can only be gained by using more efficient atomistic simulations based on semiempirical interatomic potentials. In this paper we assess the suitability of five different potentials in terms of static properties relevant to screw dislocations in pure W. Moreover, we perform molecular dynamics simulations of stress-assisted glide using all five potentials to study the dynamic behavior of screw dislocations under shear stress. Dislocations are seen to display thermally-activated motion in most of the applied stress range, with a gradual transition to a viscous damping regime at high stresses. We find that one potential predicts a core transformation from compact to dissociated at finite temperature that affects the energetics of kink-pair production and impacts the mechanism of motion. We conclude that a modified embedded-atom potential achieves the best compromise in terms of static and dynamic screw dislocation properties, although at an expense of about ten-fold compared to central potentials.

RTOG 0525: Molecular correlates from a randomized phase III trial of newly diagnosed glioblastoma

LBA2000

Background: Formalin-fixed, paraffin embedded GBM tumor tissue, adequate for conventional MGMT methylation analyses, was required for entry onto the RTOG 0525 clinical trial. Methods: Four prognostic biomarkers were evaluated on a training set of 220 retrospectively obtained GBM samples, consisting of IDH1 mutation, the glioma-CpG island methylator phenotype (G-CIMP), a microarray-based mRNA panel and a novel MGMT promoter methylation assay. For each biomarker, 2 (IDH1 and mRNA) or 3 subgroups (G-CIMP and MGMT) were defined based on associations with overall survival. All combinations (36 possible) of each of the 4 biomarker-derived subgroups were then defined and compared with survival data and then consolidated into 4 risk groups. Once created in the training set, this model was applied to the RTOG 0525 samples (n=763) for external validation. Results: Application of the molecular risk classification to RTOG 0525 samples (left table) showed a highly significant survival association (p<0.001). When compared to the recursive partitioning analysis (RPA, table on right), this composite molecular classifier better identified patients with long term survival and appears to improve resolution by revealing an additional distinct risk group. The molecular classifier was prognostic in each of the treatment arms individually. Conclusions: Four distinct biomarkers or biomarker panels were tested in GBM. These biomarkers were compared with clinical outcome in a training set to optimize a method to combine them into a classifier. This classifier was then validated on a large sample set from a large phase III clinical trial. This composite panel may represent an improvement over the existing RPA with respect to risk stratification of patients for GBM. Additionally, it has the potential to impact future clinical trial designs and provide enhanced opportunities for personalization of therapy for GBM. Support: NCI U10 CA2121661, U10 CA37422, P50 CA127001.

[Table: see text]

RTOG 0625: A phase II study of bevacizumab with irinotecan in recurrent glioblastoma (GBM)

2011

Background: Angiogenesis is a hallmark of GBM, making the tumor vasculature an attractive therapeutic target. In gliomas, vascular endothelial growth factor (VEGF) promotes both angiogenesis and invasion of tumor cells. Bevacizumab is a humanized monoclonal antibody against VEGF-A that rapidly reduces the concentration of VEGF in the circulation. Irinotecan may enhance efficacy by synergistic tumor endothelial cell death or improved tumor delivery of the chemotherapy via “normalized” tumor vasculature. Prior studies of this combination demonstrated high radiographic response and 6-month progression free (6-mPFS) rates. This study was designed to determine the efficacy and safety of this regimen in the cooperative group setting. Methods: Eligibility included age ≥ 18, centrally confirmed GBM or gliosarcoma, progressive or recurrent disease. Enzyme-inducing anticonvulsants were not allowed. Treatment was intravenous bevacizumab 10 mg/kg and irinotecan 200 mg/m2 every 2 weeks. Accrual goal was 57 eligible patients. Primary endpoint was 6-mPFS rate where an estimate of ≥ 35% would define efficacy (15% improvement over historical data). Results: Full enrollment (57) was achieved, median age was 57, median KPS was 80; all had prior radiation and temozolomide treatment. The 6m-PFS rate was 37% (95% CI: 24–50%), with 21 of 57 patients progression-free at 6 months. Moderate toxicity was noted with 21(37%) grade 3, seven (12%) grade 4, and one (<2%) treatment-related death (intracranial hemorrhage). There were six episodes of venous thrombosis, 14 episodes of grade 3 or 4 hematologic toxicity, predominantly lymphopenia (7), and neutropenia (4), no opportunistic infections or febrile neutropenia were noted. Other toxicities included fatigue (9), diarrhea (2), and hypertension (2). Conclusions: These results, in the cooperative group context, corroborate the efficacy of the bevacizumab and irinotecan combination for recurrent GBM with the 6m-PFS surpassing the predetermined efficacy threshold. Previously described toxicities were confirmed with a moderately high rate of venous thrombosis, one intracranial hemorrhage, and moderate hypertension. Studies to determine the contribution of the cytotoxic agent to efficacy and the role of bevacizumab in newly diagnosed GBM are planned.

[Table: see text]

MGMT methylation testing in RTOG 0525: A phase III trial of newly diagnosed glioblastoma

2051

Background: MGMT promoter methylation has been described as a prognostic marker in glioblastoma (GBM) and may be associated with chemosensitivity to alkylating agents. This study determined the feasibility of real-time determination of MGMT promoter methylation testing in a large international phase III clinical trial. Methods: Paraffin tumor blocks were obtained from patients registered onto RTOG 0525 then distributed to one of two central pathology labs: MD Anderson (Houston TX, K. Aldape) or CHUV (Lausanne, CH, R. Janzer). After histologic confirmation of GBM, unstained slides (40 microns of tumor tissue) were sent to the testing laboratories. Results were used for randomization into a treatment arm. MGMT methylation was assessed using methylation specific real-time PCR (MSP). The assay determined the number of copies of both methylated MGMT and of beta-actin (ACTB) in the sample. The ACTB copy number was used to assess the quality and quantity of the sample DNA. Results: Results were available for 995 samples. Following MSP samples were categorized into one of five possible results: failed (2, 0.2%), methylated (302, 30.2%), non-methylated (602, 60.2%), indeterminate (62, 6.2%), and invalid (27, 2.7%). Among cases that were evaluable as either methylated or unmethylated (n = 904) the MGMT promoter methylation rate in newly diagnosed GBM was approximately 1/3 (33.4%), a rate that is somewhat lower than prior reports. The average time from receipt of sample at the central pathology laboratory to reporting of results was 9.3 days. The time required decreased over the course of the clinical trial. This was due, in part, to training of the sites to deliver samples just before the start of runs. Conclusions: The results demonstrate the feasibility of performing real-time MGMT methylation testing, a tumor based assay, as a stratification factor in a multinational clinical trial. This study confirms that treatment decisions based on the molecular characteristics of the tumor are feasible, thereby providing opportunities to develop more molecularly-based tumor stratification or selection, a major advance in developing personalized treatment regimens.

No significant financial relationships to disclose.