Optimization of spatiotemporally fractionated radiotherapy treatments with bounds on the achievable benefit

Spatiotemporal fractionation schemes, that is, treatments delivering different dose distributions in different fractions, may lower treatment side effects without compromising tumor control. This is achieved by hypofractionating parts of the tumor while delivering approximately uniformly fractionated doses to the healthy tissue. Optimization of such treatments is based on biologically effective dose (BED), which leads to computationally challenging nonconvex optimization problems. Current optimization methods yield only locally optimal plans, and it has been unclear whether these are close to the global optimum. We present an optimization model to compute rigorous bounds on the normal tissue BED reduction achievable by such plans. The approach is demonstrated on liver tumors, where the primary goal is to reduce mean liver BED without compromising other treatment objectives. First a uniformly fractionated reference plan is computed using convex optimization. Then a nonconvex quadratically constrained quadratic programming model is solved to local optimality to compute a spatiotemporally fractionated plan that minimizes mean liver BED subject to the constraints that the plan is no worse than the reference plan with respect to all other planning goals. Finally, we derive a convex relaxation of the second model in the form of a semidefinite programming problem, which provides a lower bound on the lowest achievable mean liver BED. The method is presented on 5 cases with distinct geometries. The computed spatiotemporal plans achieve 12-35% mean liver BED reduction over the reference plans, which corresponds to 79-97% of the gap between the reference mean liver BEDs and our lower bounds. This indicates that spatiotemporal treatments can achieve substantial reduction in normal tissue BED, and that local optimization provides plans that are close to realizing the maximum potential benefit

Mikrokurse

In den Lehrplänen einiger Bundesländer gibt es noch keinen eigenständigen Themenbereich Teilchenphysik. Für diesen Fall sind die hier vorgestellten Mikrokurse zusammengestellt worden. Alle Kurse schlagen auf originelle Weise eine Brücke von klassischen Lehrplanthemen zu aktuellen Forschungsgegenständen. Denn viele der im Physikunterricht behandelten Themen lassen sich leicht um einen Bezug zur modernen Physik und insbesondere der Teilchenphysik ergänzen. Der zeitliche Bedarf für die Behandlung eines Kurses beträgt ca. ein bis zwei Unterrichtsstunden. Vorkenntnisse zur Teilchenphysik sind kaum notwendig. Die Mikrokurse können und sollen deshalb auch gerade dort eingesetzt werden, wo nur wenig Zeit zur Verfügung steht oder das Thema Teilchenphysik nicht im Lehrplan verankert ist. Zu jedem Kurs werden Einsatzmöglichkeiten und wünschenswerte Vorkenntnisse der Schüler:innen angegeben. Auf mögliche Erweiterungen und Vertiefungen wird hingewiesen

Comment on ``Large-space shell-model calculations for light nuclei''

In a recent publication Zheng, Vary, and Barrett reproduced the negative quadrupole moment of Li-6 and the low-lying positive-parity states of He-5 by using a no-core shell model. In this Comment we question the meaning of these results by pointing out that the model used is inadequate for the reproduction of these properties.Comment: Latex with Revtex, 1 postscript figure in separate fil

Spin Flip Probabilities in 208-Pb Measured with 200 MeV Protons

This research was sponsored by the National Science Foundation Grant NSF PHY-931478

Is there a Pronounced Giant Dipole Resonance in ^4He?

A four-nucleon calculation of the total ^4He photodisintegration cross section is performed. The full final-state interaction is taken into account for the first time. This is achieved via the method of the Lorentz integral transform. Semi-realistic NN interactions are employed. Different from the known partial two-body ^4He(\gamma,n)^3He and ^4He(\gamma,p)^3H cross sections our total cross section exhibits a pronounced giant resonance. Thus, in contrast to older $(\gamma,np)$ data, we predict quite a strong contribution of the $(\gamma,np)$ channel at the giant resonance peak energy.Comment: 10 pages, Latex (REVTEX), 4 Postscript figures, to appear in Phys. Rev. Let

Neural parameters estimation for brain tumor growth modeling

Understanding the dynamics of brain tumor progression is essential for optimal treatment planning. Cast in a mathematical formulation, it is typically viewed as evaluation of a system of partial differential equations, wherein the physiological processes that govern the growth of the tumor are considered. To personalize the model, i.e. find a relevant set of parameters, with respect to the tumor dynamics of a particular patient, the model is informed from empirical data, e.g., medical images obtained from diagnostic modalities, such as magnetic-resonance imaging. Existing model-observation coupling schemes require a large number of forward integrations of the biophysical model and rely on simplifying assumption on the functional form, linking the output of the model with the image information. In this work, we propose a learning-based technique for the estimation of tumor growth model parameters from medical scans. The technique allows for explicit evaluation of the posterior distribution of the parameters by sequentially training a mixture-density network, relaxing the constraint on the functional form and reducing the number of samples necessary to propagate through the forward model for the estimation. We test the method on synthetic and real scans of rats injected with brain tumors to calibrate the model and to predict tumor progression

Metacognition as Evidence for Evidentialism

Metacognition is the monitoring and controlling of cognitive processes. I examine the role of metacognition in ‘ordinary retrieval cases’, cases in which it is intuitive that via recollection the subject has a justified belief. Drawing on psychological research on metacognition, I argue that evidentialism has a unique, accurate prediction in each ordinary retrieval case: the subject has evidence for the proposition she justifiedly believes. But, I argue, process reliabilism has no unique, accurate predictions in these cases. I conclude that ordinary retrieval cases better support evidentialism than process reliabilism. This conclusion challenges several common assumptions. One is that non-evidentialism alone allows for a naturalized epistemology, i.e., an epistemology that is fully in accordance with scientific research and methodology. Another is that process reliabilism fares much better than evidentialism in the epistemology of memory

The Epistemic Status of Processing Fluency as Source for Judgments of Truth

This article combines findings from cognitive psychology on the role of processing fluency in truth judgments with epistemological theory on justification of belief. We first review evidence that repeated exposure to a statement increases the subjective ease with which that statement is processed. This increased processing fluency, in turn, increases the probability that the statement is judged to be true. The basic question discussed here is whether the use of processing fluency as a cue to truth is epistemically justified. In the present analysis, based on Bayes’ Theorem, we adopt the reliable-process account of justification presented by Goldman (1986) and show that fluency is a reliable cue to truth, under the assumption that the majority of statements one has been exposed to are true. In the final section, we broaden the scope of this analysis and discuss how processing fluency as a potentially universal cue to judged truth may contribute to cultural differences in commonsense beliefs

The home advantage over the first 20 seasons of the English Premier League: Effects of shirt colour, team ability and time trends

This study explored the relationship between teams' home shirt colour and the magnitude of the home advantage in English professional soccer. Secondary aims were to explore the consistency of the home advantage over time and the relationship between the home advantage and team ability. Archival data from 7720 matches contested over the first 20 seasons of the English Premier League were analysed. The data show that teams wearing red are more successful than teams wearing other colours, and that teams are more successful in home games than in away games (home advantage index = 0.608). The home advantage has also remained consistent over time (1992/1993-2011/2012) and is greater in low-ability teams (teams with lower league positions) than in high-ability teams. After controlling for team ability, it was found that teams opting for red shirts in their home games did not show a greater home advantage than teams opting for other colour shirts. Two possibilities for this finding are offered: (1) shirt colour is not a contributing factor to team success, or (2) changes in psychological functioning associated with viewing or wearing red stay with team members after the shirt colour has been changed. It is recommended that researchers continue to explore the effect of shirt colour on athlete and team behaviour and further explore how team ability can affect the magnitude of the home-field advantage. © 2012 International Society of Sport Psychology