The optimum parameters for the generation of synchrotron radiation in ultraintense laser pulse interactions with planar foils are investigated with the application of Bayesian optimization, via Gaussian process regression, to 2D particle-in-cell simulations. Individual properties of the synchrotron emission, such as the yield, are maximized, and simultaneous mitigation of bremsstrahlung emission is achieved with multi-variate objective functions. The angle-of-incidence of the laser pulse onto the target is shown to strongly influence the synchrotron yield and angular profile, with oblique incidence producing the optimal results. This is further explored in 3D simulations, in which additional control of the spatial profile of synchrotron emission is demonstrated by varying the polarization of the laser light. The results demonstrate the utility of applying a machine learning-based optimization approach and provide new insights into the physics of radiation generation in laser–foil interactions, which will inform the design of experiments in the quantum electrodynamics (QED)-plasma regime.

We prove that the radiation damping force and the rate of change of the damping energy, in the Landau-Lifshitz forms, in interactions between very intense laser beams and relativistic electron beams, are periodic functions of only one variable, that is the phase of the electromagnetic field. The property is proved without using any approximation, in the most general case, when the degree of polarization of the electromagnetic field, the initial phase of the incident field and the initial energy of the electron have arbitrary values. This property leads to a strong simplification of the calculation of the radiation reaction parameters and of their dependence on the initial electron energy and angular frequency of the laser beam. Our analysis is performed in the proper inertial system of the electron. The radiation reaction is significant for laser beam intensities of the order 1022 W/cm2, and for electron energy greater than 1 GeV. The calculations reveal limitations of the method of generating hard radiations by interactions between laser beams and relativistic electron beams.

The effects of coherently enhanced radiation reaction on the motion of subwavelength electron bunches in interaction with intense laser pulses are analyzed. The radiation reaction force behaves as a radiation pressure in the laser beam direction, combined with a viscous force in the perpendicular direction. Due to Coulomb expansion of the electron bunch, coherent radiation reaction takes effect only in the initial stage of the laser-bunch interaction while the bunch is still smaller than the wavelength. It is shown that this initial stage can have observable effects on the trajectory of the bunch. By scaling the system to larger bunch charges, the radiation reaction effects are strongly increased. On the basis of the usual equation of motion, this increase is shown to be such that radiation reaction may suppress the radial instability normally found in ponderomotive acceleration schemes, thereby enabling the full potential of laser-vacuum electron bunch acceleration to GeV energies. However, the applicability of the used equation of motion still needs to be validated experimentally, which becomes possible using the presented experimental scheme.

Purpose: A questionnaire was developed to explore variations among radiation oncologists in managing early-stage breast cancer, specifically radiation-induced skin reaction (RISK).

Materials and methods: A survey was designed to target a database of 962 radiation oncologists, self-identified as ‘interested in treatment of breast cancer’. This database was obtained from the American Society of Therapeutic Radiology & Oncology (ASTRO). Participants submitted the survey online or by mail. Overall response to the survey was 282 out of 962 (29.3%). Data were handled as rates.

Results: Out of 282 respondents, 275 (97.5%) agreed on delivering 4500–5040 cGy. The most frequently employed dose was 5040/180 cGy. Three-dimensional-conformal (3DCRT) treatment was used by 55.4%, intensity-modulated radiotherapy (IMRT) by 24.5%, and conventional by 20.1%. Almost all (92.5%) agreed on using boost in ductal carcinoma in situ (DCIS). Image-guided boost placement (IGBP) was used by 87.3%. Boost dose included variations: 50.2, 7.3, and 18% used 1000, 1200, and 1400 cGy, respectively; the remaining used higher doses. In management of RISK, Aquaphor was the most popular agent (72.1%). Other agents were utilized either alone or in combination. Almost all (99%) agreed that large breast size increases RISK.

Conclusion: This survey offers a glimpse of management practices in early-stage breast cancer amongst a cross-section of radiation oncologists in the United States. Although there appears to be an overall congruence on the doses and techniques of radiation delivery, the management of RISK is varied. Additional efforts are warranted to standardize practices in order to practice evidence based medicine in a cost-effective manner.