Absolute Instability near the Band Edge of Traveling-Wave Amplifiers.

Applying the Briggs-Bers "pole-pinch" criterion to the exact transcendental dispersion relation of a dielectric traveling wave tube (TWT), we find that there is no absolute instability regardless of the beam current. We extend this analysis to the circuit band edges of a linear beam TWT by approximating the circuit mode as a hyperbola in the frequency-wave-number (ω-k) plane and consider the weak coupling limit. For an operating mode whose group velocity is in the same direction as the beam mode, we find that the lower band edge is not subjected to absolute instability. At the upper band edge, we find a threshold beam current beyond which absolute instability is excited. The nonexistence of absolute instability in a linear beam TWT and the existence in a gyrotron TWT, both at the lower band edge, is contrasted. The general study given here is applicable to some contemporary TWTs such as metamaterial-based and advanced Smith-Purcell TWTs.

Pooled analysis of prospective European studies assessing the impact of using the 21-gene Recurrence Score assay on clinical decision making in women with oestrogen receptor-positive, human epidermal growth factor receptor 2-negative early-stage breast cancer.

PURPOSE: The 21-gene Recurrence Score assay (Oncotype DX) provides prognostic/predictive information in oestrogen receptor positive (ER+) early breast cancer, but access/reimbursement has been limited in most European countries in the absence of prospective outcome data. Recently, two large prospective studies and a real-life 5-year outcome study have been reported. We performed a pooled analysis of prospective European impact studies to generate robust data on impact of use in different clinical subgroups. METHODS: The analysis included four studies (French, German, Spanish, and British) in ER+ human epidermal growth factor receptor 2-negative breast cancer patients (n = 527). Node-positive patients were excluded. RESULTS: The analysis demonstrated that treatment recommendations changed in 32% of patients post-testing; chemotherapy recommendation rate decreased from 55% to 34%. Change rates in the individual studies ranged from 30% to 37%. The highest change rates were in patients originally recommended chemotherapy and in grade II tumours; there was no subgroup without a treatment recommendation change. Notably, 31% of patients with an intermediate Recurrence Score result had a treatment recommendation change suggesting that testing provides actionable information in this group. With the exception of the German study (where chemotherapy rates remained high [41%] post-testing), between-study variability in treatment recommendations decreased post-testing (chemotherapy: from 36-52% to 26-29%; hormonal therapy: from 48-64% to 71-74%). Physicians' confidence regarding treatment recommendations improved in all the studies after testing. CONCLUSION: Recurrence Score testing led to changes in adjuvant chemotherapy use in approximately a third of patients, to an overall reduced chemotherapy use, and to more homogeneous decision making.