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Pencil beam scanning (PBS) proton therapy enables better dose conformality for complex anatomical geometries than passive proton scattering techniques, but is more susceptible to organ motion. This becomes an issue when treating moving tumours in the thorax or abdomen. Novel four-dimensional treatment planning approaches have been developed to increase the robustness of PBS plans against motion. However, their efficacy still needs to be examined by means of 4D dynamically accumulated dose (4DDD) analyses. This study investigates the potential use of 4D robust optimisation to maintain sufficient target coverage in the presence of organ motion, while sparing surrounding healthy tissue, for hepatocellular carcinoma (HCC). The liver is particularly suited to study motion interplay effects since the treatment region exhibits smaller density gradients and more homogeneous tissue than targets in the thorax, making it less prone to range errors. A facility-specific beam time model, developed and experimentally validated previously, was used for the clinical evaluation. 4DDD analyses of eleven target volumes did not show a significant improvement of the target coverage using 4D robust optimisation, but a reduction of the dose to close-by organs at risk. Interplay effects were averaged out for the applied fractionation scheme of 15 fractions. Contrary to PBS, passive double scattering (DS) plans yielded homogeneous 4DDD dose distributions in a single fraction. But, in some cases, they exceeded organ at risk dose limits, which were only satisfied in PBS. The average normal liver dose could be decreased by almost 6% compared to non-robustly optimised PBS plans and by 16% compared to DS plans when implementing 4D robust optimisation. Except for some very small tumours with large motion amplitudes, 4D robustly optimised PBS plans were found to be clinically acceptable even without supplementary motion mitigation techniques. [ABSTRACT FROM AUTHOR]

Background. The level of participation in research by GPs is low internationally. Previous reports of the reasons why practitioners decline opportunities for research participation have tended to recount the barriers that they describe as if they are objective accounts. Objective. By theoretical sampling of practitioners who had declined to participate in a research trial, we sought to interpret the functional significance and interrelationship of the barriers that they reported. Methods. Twenty-three GPs who had declined to participate in a trial of training to manage medically unexplained symptoms were interviewed and their accounts analysed interpretatively. Results. The practitioners described general practice and research as alien fields. Research lacked intrinsic, clinical or professional value and was linked to evidence-based medicine which they rejected as incompatible with person-centered care. Every doctor described a lack of time for research, but time was an elastic resource that payment could release from the reservoir of their ‘own time. Conclusion. The findings should inform the design and interpretation of future quantitative surveys to identify how common the attitudes that we report are. Doctors with the attitudes of those whom we interviewed will not be drawn into research by measures predicated on the assumption that it is intrinsically, clinically or professionally valuable. If they cannot be convinced of its utility, value could be conferred by payment for participation. [ABSTRACT FROM AUTHOR]