Explicit optimization of plan quality measures in intensity-modulated radiation therapy treatment planning

Conventional planning objectives in optimization of intensity-modulated radiotherapy treatment (IMRT) plans are designed to minimize the violation of dose-volume histogram (DVH) thresholds using penalty functions. Although successful in guiding the DVH curve towards these thresholds, conventional planning objectives offer limited control of the individual points on the DVH curve (doses-at-volume) used to evaluate plan quality. In this study, we abandon the usual penalty-function framework and propose planning objectives that more explicitly relate to DVH statistics. The proposed planning objectives are based on mean-tail-dose, resulting in convex optimization. We also demonstrate how to adapt a standard optimization method to the proposed formulation in order to obtain a substantial reduction in computational cost. We investigate the potential of the proposed planning objectives as tools for optimizing DVH statistics through juxtaposition with the conventional planning objectives on two patient cases. Sets of treatment plans with differently balanced planning objectives are generated using either the proposed or the conventional approach. Dominance in the sense of better distributed doses-at-volume is observed in plans optimized within the proposed framework, indicating that the DVH statistics are better optimized and more efficiently balanced using the proposed planning objectives

QuizzEuropa - et brætspil om et andet Europa

Bliv udfordret på din sammenhængsforståelse for Europas historie, kulturelle mangfoldighed og politiske geografi gennem fokus på regioner frem for nationalstater. Et lærerigt og underholdende bidrag til undervisningen

The Twisted String Vertex Algorithm Applied to the Z2Z_2-Twisted Scalar String Four Vertex

Recently an algorithm was found by means of which one can calculate terms at arbitrary oscillator level in the four-Ramond vertex obtained by sewing. Here we show that this algorithm is applicable also to the case of ${\bf Z}_2$-twisted scalars and derive the full propagator for scalars on the Riemann sphere with two branch cuts. The relation to similar results previously derived in the literature by other means is discussed briefly.Comment: 18 pages (LaTeX), G\"oteborg ITP 94-

Kreditorekstinksjon ved rettsstiftelser uten rettsvern i bakenforliggende ledd

MasteroppgaveJUS399MAJUR-2MAJU

Ny forskning i grammatik

Many Danish cognition verbs take both indicative and infinitive complements. We examine what the contrast between the two complement types codes. The literature offers two answers. One is that the contrast has to do with coreferentiality: if the cognition verb’s primary argument is coreferential with the primary argument of the complement, the complement tends to be infinitive; if not, the complement must be indicative. The other answer concerns the contrast between propositions and states-of-affairs: the indicative complement designates a proposition, the infinitive complement a state-of-affairs. Corpus studies support both answers. They also support an analysis of indicatives as proposition markers. But infinitives cannot – straightforwardly – be analysed as state-of-affairs markers

Kognitionsverber og kontrasten mellem indikativ- og infinitivkomplement

Many Danish cognition verbs take both indicative and infinitive complements. We examine what the contrast between the two complement types codes. The literature offers two answers. One is that the contrast has to do with coreferentiality: if the cognition verb’s primary argument is coreferential with the primary argument of the complement, the complement tends to be infinitive; if not, the complement must be indicative. The other answer concerns the contrast between propositions and states-of-affairs: the indicative complement designates a proposition, the infinitive complement a state-of-affairs. Corpus studies support both answers. They also support an analysis of indicatives as proposition markers. But infinitives cannot – straightforwardly – be analysed as state-of-affairs markers