All-Optical GeV Electron Bunch Generation in a Laser-Plasma Accelerator via Truncated-Channel Injection

We describe a simple scheme, truncated-channel injection, to inject electrons directly into the wakefield driven by a high-intensity laser pulse guided in an all-optical plasma channel. We use this approach to generate dark-current-free 1.2 GeV, 4.5% relative energy spread electron bunches with 120 TW laser pulses guided in a 110 mm-long hydrodynamic optical-field-ionized plasma channel. Our experiments and particle-in-cell simulations show that high-quality electron bunches were only obtained when the drive pulse was closely aligned with the channel axis, and was focused close to the density down ramp formed at the channel entrance. Start-to-end simulations of the channel formation, and electron injection and acceleration show that increasing the channel length to 410 mm would yield 3.65 GeV bunches, with a slice energy spread ∼5×10^{-4}.

Computed tomography-based radiomic markers are independent prognosticators of survival in advanced laryngeal cancer: a pilot study

OBJECTIVE

Advanced laryngeal cancers are clinically complex; there is a paucity of modern decision-making models to guide tumour-specific management. This pilot study aims to identify computed tomography-based radiomic features that may predict survival and enhance prognostication.

METHODS

Pre-biopsy, contrast-enhanced computed tomography scans were assembled from a retrospective cohort (n = 72) with advanced laryngeal cancers (T3 and T4). The LIFEx software was used for radiomic feature extraction. Two features: shape compacity (irregularity of tumour volume) and grey-level zone length matrix - grey-level non-uniformity (tumour heterogeneity) were selected via least absolute shrinkage and selection operator-based Cox regression and explored for prognostic potential.

RESULTS

A greater shape compacity (hazard ratio 2.89) and grey-level zone length matrix - grey-level non-uniformity (hazard ratio 1.64) were significantly associated with worse 5-year disease-specific survival (p < 0.05). Cox regression models yielded a superior C-index when incorporating radiomic features (0.759) versus clinicopathological variables alone (0.655).

CONCLUSIONS

Two radiomic features were identified as independent prognostic biomarkers. A multi-centre prospective study is necessary for further exploration. Integrated radiomic models may refine the treatment of advanced laryngeal cancers.

Excitation and Control of Plasma Wakefields by Multiple Laser Pulses

We demonstrate experimentally the resonant excitation of plasma waves by trains of laser pulses. We also take an important first step to achieving an energy recovery plasma accelerator by showing that a plasma wave can be damped by an out-of-resonance trailing laser pulse. The measured laser wakefields are found to be in excellent agreement with analytical and numerical models of wakefield excitation in the linear regime. Our results indicate a promising direction for achieving highly controlled, GeV-scale laser-plasma accelerators operating at multikilohertz repetition rates.

Two-pulse ionization injection into quasilinear laser wakefields

We describe a scheme for controlling electron injection into the quasilinear wakefield driven by a guided drive pulse via ionization of a dopant species by a collinear injection laser pulse with a short Rayleigh range. The scheme is analyzed by particle-in-cell simulations which show controlled injection and acceleration of electrons to an energy of 370 MeV, a relative energy spread of 2%, and a normalized transverse emittance of 2.0 μm.

Magnetic resonance imaging accuracy in assessing tumour down-staging following chemoradiation in rectal cancer

OBJECTIVE

Magnetic resonance imaging (MRI) is increasingly accepted as the radiological modality of choice staging rectal cancer but is subject to error. Neoadjuvant therapy is increasingly used in rectal cancer and MRI is used to stage response and occasionally plan surgery. We aim to assess the staging accuracy of MRI following chemoradiotherapy in rectal cancer.

METHOD

Retrospective analysis of 86 patients with MRI stage pre- and postlong-course chemoradiotherapy and comparison with pathological assessment.

RESULTS

Fourty-nine patients (34 men, 15 women) with median age 68 years (60-74) were analysed. The median time from completion of CRT to MRI was 32 days (16-37). Chemoradiotherapy led to significant down-staging (P < 0.001). MRI-staging accuracy was 43% (21/49) with over- and under-staging in 43% (21/49) and 14% (7/49) respectively. T-stage accuracy was 45% (22/49) with over-staging in 33% (16/49) and under-staging in 22% (11/49). MRI stage correlated poorly with pathological assessment for International Union Against Cancer (kappa = 0.255) and T stages (kappa = 0.112). MRI nodal assessment was 71% (35/49) accurate, with 82% (9/11) sensitivity, 68% (26/38) specificity and positive predictive value (PPV) of 43% (9/21) and negative predictive value of 93% (26/28). There was a significant difference in node positivity between MRI and pathological staging (P = 0.005, Fisher's exact). Complete radiological response was observed in 4% (2/49). Complete pathological response was observed in 10% (5/49), which were staged 0(1), I(1), II(2) and III(1) postchemoradiotherapy by MRI.

CONCLUSION

MRI staging following chemoradiation is poor. Over-staging occurs three times more commonly than under-staging. Over-staging is due to poor PPV of nodal assessment.

Training birth attendants in the Sahel

A small-scale training programme for birth attendants in a remote area of Burkina Faso was evaluated two years after it had been started. The evaluation methods included interviews with trained birth attendants and the analysis of health service statistics and survey data. The findings showed that the programme had been moderately successful in imparting knowledge and overcoming cultural inhibitions about assisted deliveries. However, the effectiveness of the programme was severely curtailed by structural deficits in the health system, especially lack of skilled staff, supervision and transport. In deprived areas such as the Sahel, it is probably the health centre, the hospital and the referral system that should be the first priority for improvement, rather than grass-roots practices.

Analysis of the roles of bluetongue virus outer capsid proteins VP2 and VP5 in determination of virus serotype

Analyses of reassortant and parental strains of BTV serotypes 3 and 10, in serum neutralization tests, confirmed the major role of outer capsid protein VP2 in determination of virus serotype and its involvement in serum neutralization. However, a reassortant BTV strain (R70), containing protein VP5 derived from BTV 3 and VP2 derived from BTV 10, cross-neutralized with both parental virus strains (BTV 3 and BTV 10). It is concluded that VP5 also plays some part in serotype determination of these virus isolates, as analyzed by serum-neutralization, but its role may be less significant than that of VP2.

A comparison of six different bluetongue virus isolates by cross-hybridization of the dsRNA genome segments

The relationship between six different isolates of BTV was analyzed by cross-hybridization of genomic dsRNA using blotting and probe techniques (using an alkali fragmented probe made from BTV dsRNA). The viruses compared in this way included BTV serotype 1 from South Africa, serotypes 3 and 4 from Cyprus, serotype 10 from North America, and serotypes 1 and 20 from Australia. Under the hybridization and washing conditions used, which were calculated to allow stable duplex formation between RNA molecules containing greater than 90% sequence homology, two of the genome segments (segments 2 and either 5 or 6, which encode the two major outer capsid proteins VP2 and VP5) appeared to contain serotype-specific RNA sequences. Significant cross-hybridization between these segments from different serotypes was detected only with serotypes 4 and 20, which are known to have a particularly close antigenic relationship. The amounts of homologous sequence that were detected in segments other than 2 and 5 between different viruses indicated some correlation between their geographical origins and a degree of relatedness, which is independent of the virus serotype. High levels of sequence homology were detected between the isolates from Cyprus and Africa and to a slightly lesser extent from North America, suggesting a common ancestry. These results also indicated that within the limited number of viruses studied, the Australian isolates form a separate interrelated group of bluetongue viruses.