Optimisation of radiotherapy for carcinoma of the parotid gland: a comparison of conventional, three-dimensional conformal, and intensity-modulated techniques

Background and purpose: To compare external beam radiotherapy techniques for parotid gland tumours using conventional radiotherapy (RT), three-dimensional conformal radiotherapy (3DCRT), and intensity-modulated radiotherapy (IMRT). To optimise the IMRT techniques, and to produce an IMRT class solution.Materials and methods: The planning target volume (PTV), contra-lateral parotid gland, oral cavity, brain-stem, brain and cochlea were outlined on CT planning scans of six patients with parotid gland tumours. Optimised conventional RT and 3DCRT plans were created and compared with inverse-planned IMRT dose distributions using dose-volume histograms. The aim was to reduce the radiation dose to organs at risk and improve the PTV dose distribution. A beam-direction optimisation algorithm was used to improve the dose distribution of the IMRT plans, and a class solution for parotid gland IMRT was investigated.Results: 3DCRT plans produced an equivalent PTV irradiation and reduced the dose to the cochlea, oral cavity, brain, and other normal tissues compared with conventional RT. IMRT further reduced the radiation dose to the cochlea and oral cavity compared with 3DCRT. For nine- and seven-field IMRT techniques, there was an increase in low-dose radiation to non-target tissue and the contra-lateral parotid gland. IMRT plans produced using three to five optimised intensity-modulated beam directions maintained the advantages of the more complex IMRT plans, and reduced the contra-lateral parotid gland dose to acceptable levels. Three- and four-field non-coplanar beam arrangements increased the volume of brain irradiated, and increased PTV dose inhomogeneity. A four-field class solution consisting of paired ipsilateral coplanar anterior and posterior oblique beams (15, 45, 145 and 170o from the anterior plane) was developed which maintained the benefits without the complexity of individual patient optimisation.Conclusions: For patients with parotid gland tumours, reduction in the radiation dose to critical normal tissues was demonstrated with 3DCRT compared with conventional RT. IMRT produced a further reduction in the dose to the cochlea and oral cavity. With nine and seven fields, the dose to the contra-lateral parotid gland was increased, but this was avoided by optimisation of the beam directions. The benefits of IMRT were maintained with three or four fields when the beam angles were optimised, but were also achieved using a four-field class solution. Clinical trials are required to confirm the clinical benefits of these improved dose distributions.

Conformal oxide coating of carbon nanotubes

The International Roadmap for Ferroelectric Memories requires three-dimensional integration of high-dielectric materials onto metal interconnects or bottom electrodes by 2010. Here, we demonstrate the possibility of conformally coating carbon nanotubes with high-dielectric oxide as a first step toward ultrahigh integration density of three-dimensional ferroelectric random access memories.

Temporal characterization and in vitro comparison of cell survival following the delivery of 3D-conformal, intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT)

A phantom was designed and implemented for the delivery of treatment plans to cells in vitro. Single beam, 3D-conformal radiotherapy (3D-CRT) plans, inverse planned five-field intensity-modulated radiation therapy (IMRT), nine-field IMRT, single-arc volumetric modulated arc therapy (VMAT) and dual-arc VMAT plans were created on a CT scan of the phantom to deliver 3 Gy to the cell layer and verified using a Farmer chamber, 2D ionization chamber array and gafchromic film. Each plan was delivered to a 2D ionization chamber array to assess the temporal characteristics of the plan including delivery time and 'cell's eye view' for the central ionization chamber. The effective fraction time, defined as the percentage of the fraction time where any dose is delivered to each point examined, was also assessed across 120 ionization chambers. Each plan was delivered to human prostate cancer DU-145 cells and normal primary AGO-1522b fibroblast cells. Uniform beams were delivered to each cell line with the delivery time varying from 0.5 to 20.54 min. Effective fraction time was found to increase with a decreasing number of beams or arcs. For a uniform beam delivery, AGO-1552b cells exhibited a statistically significant trend towards increased survival with increased delivery time. This trend was not repeated when the different modulated clinical delivery methods were used. Less sensitive DU-145 cells did not exhibit a significant trend towards increased survival with increased delivery time for either the uniform or clinical deliveries. These results confirm that dose rate effects are most prevalent in more radiosensitive cells. Cell survival data generated from uniform beam deliveries over a range of dose rates and delivery times may not always be accurate in predicting response to more complex delivery techniques, such as IMRT and VMAT.

Assessing the daily consistency of bladder filling using an ultrasonic Bladderscan device in men receiving radical conformal radiotherapy for prostate cancer

Consistency in target organ and organ at risk position from planning to treatment is an important basic principle of radiotherapy. This study evaluates the effectiveness of bladder-filling instructions in achieving a consistent and reproducible bladder volume at the time of planning CT and daily during the course of radical radiotherapy for prostate cancer. It also assessed the rate of bladder filling before and at the end of radiotherapy.

In-vitro investigation of out-of-field cell survival following the delivery of conformal, intensity-modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans

The aim of this work is to determine the out-of-field survival of cells irradiated with either the primary field or scattered radiation in the presence and absence of intercellular communication following delivery of conformal, IMRT and VMAT treatment plans. Single beam, conformal, IMRT and VMAT plans were created to deliver 3 Gy to half the area of a T80 flask containing either DU-145 or AGO-1522 cells allowing intercellular communication between the in-and out-of-field cell populations. The same plans were delivered to a similar custom made phantom used to hold two T25 culture flasks, one flask in-field and one out-of-field to allow comparison of cell survival responses when intercellular communication is physically inhibited. Plans were created for the delivery of 8 Gy to the more radio-resistant DU-145 cells only in the presence and absence of intercellular communication. Cell survival was determined by clonogenic assay. In both cell lines, the out-of-field survival was not statistically different between delivery techniques for either cell line or dose. There was however, a statistically significant difference between survival out-of-field when intercellular communication was intact (single T80 culture flask) or inhibited (multiple T25 culture flasks) to in-field for all plans. No statistically significant difference was observed in-field with or without cellular communication to out-of-field for all plans. These data demonstrate out-of-field effects as important determinants of cell survival following exposure to modulated irradiation fields when cellular communication between differentially irradiated cell populations is present. This data is further evidence that refinement of existing radiobiological models to include indirect cell killing effects is required.

Design of a wideband conformal array antenna system with beamforming and null steering, for application in a DVB-T based passive radar

The use of radars in detecting low flying, small targets is being explored for several decades now. However radar with counter-stealth abilities namely the passive, multistatic, low frequency radars are in the focus recently. Passive radar that uses Digital Video Broadcast Terrestrial (DVB-T) signals as illuminator of opportunity is a major contender in this area. A DVB-T based passive radar requires the development of an antenna array that performs satisfactorily over the entire DVB-T band. At Fraunhofer FHR, there is currently a need for an array antenna to be designed for operation over the 450-900 MHz range with wideband beamforming and null steering capabilities. This would add to the ability of the passive radar in detecting covert targets and would improve the performance of the system. The array should require no mechanical adjustments to inter-element spacing to correspond to the DVB-T carrier frequency used for any particular measurement. Such an array would have an increased flexibility of operation in different environment or locations.

The design of such an array antenna and the applied techniques for wideband beamforming and null steering are presented in the thesis. The interaction between the inter-element spacing, the grating lobes and the mutual couplings had to be carefully studied and an optimal solution was to be reached at that meets all the specifications of the antenna array for wideband applications. Directional beams, nulls along interference directions, low sidelobe levels, polarization aspects and operation along a wide bandwidth of 450-900 MHz were some of the key considerations.

Solutions de rang k et invariants de Riemann pour les systèmes de type hydrodynamique multidimensionnels

Dans ce travail, nous adaptons la méthode des symétries conditionnelles afin de construire des solutions exprimées en termes des invariants de Riemann. Dans ce contexte, nous considérons des systèmes non elliptiques quasilinéaires homogènes (de type hydrodynamique) du premier ordre d'équations aux dérivées partielles multidimensionnelles. Nous décrivons en détail les conditions nécessaires et suffisantes pour garantir l'existence locale de ce type de solution. Nous étudions les relations entre la structure des éléments intégraux et la possibilité de construire certaines classes de solutions de rang k. Ces classes de solutions incluent les superpositions non linéaires d'ondes de Riemann ainsi que les solutions multisolitoniques. Nous généralisons cette méthode aux systèmes non homogènes quasilinéaires et non elliptiques du premier ordre. Ces méthodes sont appliquées aux équations de la dynamique des fluides en (3+1) dimensions modélisant le flot d'un fluide isentropique. De nouvelles classes de solutions de rang 2 et 3 sont construites et elles incluent des solutions double- et triple-solitoniques. De nouveaux phénomènes non linéaires et linéaires sont établis pour la superposition des ondes de Riemann. Finalement, nous discutons de certains aspects concernant la construction de solutions de rang 2 pour l'équation de Kadomtsev-Petviashvili sans dispersion.