Statistical Modeling of the Eye for Multimodal Treatment Planning for External Beam Radiation Therapy of Intraocular Tumors.

PURPOSE: Ocular anatomy and radiation-associated toxicities provide unique challenges for external beam radiation therapy. For treatment planning, precise modeling of organs at risk and tumor volume are crucial. Development of a precise eye model and automatic adaptation of this model to patients' anatomy remain problematic because of organ shape variability. This work introduces the application of a 3-dimensional (3D) statistical shape model as a novel method for precise eye modeling for external beam radiation therapy of intraocular tumors. METHODS AND MATERIALS: Manual and automatic segmentations were compared for 17 patients, based on head computed tomography (CT) volume scans. A 3D statistical shape model of the cornea, lens, and sclera as well as of the optic disc position was developed. Furthermore, an active shape model was built to enable automatic fitting of the eye model to CT slice stacks. Cross-validation was performed based on leave-one-out tests for all training shapes by measuring dice coefficients and mean segmentation errors between automatic segmentation and manual segmentation by an expert. RESULTS: Cross-validation revealed a dice similarity of 95% ± 2% for the sclera and cornea and 91% ± 2% for the lens. Overall, mean segmentation error was found to be 0.3 ± 0.1 mm. Average segmentation time was 14 ± 2 s on a standard personal computer. CONCLUSIONS: Our results show that the solution presented outperforms state-of-the-art methods in terms of accuracy, reliability, and robustness. Moreover, the eye model shape as well as its variability is learned from a training set rather than by making shape assumptions (eg, as with the spherical or elliptical model). Therefore, the model appears to be capable of modeling nonspherically and nonelliptically shaped eyes.

Nation-wide survey on radiation doses in diagnostic and interventional radiology in Switzerland in 1998.

A nation-wide survey on radiation doses in diagnostic and interventional radiology was conducted in Switzerland in 1998 aiming at establishing their collective radiological impact on the Swiss population. The study consisted on the one hand of surveying the frequency of more than 250 types of examinations, covering conventional radiology, mammography, fluoroscopy, angiography, interventional radiology, CT, bone densitometry, conventional tomography and dental radiology. On the other hand, for each type of examination the associated patient dose was established by modeling. The results of this study show that about 9.5 million diagnostic and interventional examinations are performed annually in Switzerland (1.34 per caput) and that the associated annual collective dose is of the order of 7100 person.Sv (1.0 mSv per caput). Switzerland is similar to other European countries in terms of the frequency of examinations and the collective dose.

Ionizing radiation enhances immunogenicity of cells expressing a tumor-specific T-cell epitope.

BACKGROUND: p53 point mutations represent potential tumor-specific cytolytic T lymphocyte (CTL) epitopes. Whether ionizing radiation (IR) alters the immunological properties of cells expressing mutant p53 in respect of the CTL epitope generated by a defined point mutation has not been evaluated. METHODS: Mutant p53-expressing syngeneic, nontumor forming BALB/c 3T3 fibroblasts, tumor forming ras-transfected BALB/c 3T3 sarcomas, and DBA/2-derived P815 mastocytoma cells, which differ at the level of minor histocompatibility antigens, were used as cellular vaccines. Cells were either injected with or without prior IR into naive BALB/c mice. Cellular cytotoxicity was assessed after secondary restimulation of effector spleen cells in vitro. RESULTS: Injection of P815 mastocytoma cells expressing the mutant p53 induced mutation-specific CTL in BALB/c mice irrespective of prior irradiation. However, syngeneic fibroblasts or fibrosarcomas endogenously expressing mutant p53 were able to induce significant mutation-specific CTL only when irradiated prior to injection into BALB/c mice. IR of fibroblasts did not detectably alter the expression of cell surface molecules involved in immune response induction, nor did it alter the short-term in vitro viability of the fibroblasts. Interestingly, radioactively-labeled fibroblasts injected into mice after irradiation showed altered organ distribution, suggesting that the in vivo fate of these cells may play a crucial role in their immunogenicity. CONCLUSIONS: These findings indicate that IR can alter the immunogenicity of syngeneic normal as well as tumor forming fibroblasts in vivo, and support the view that ionizing radiation enhances immunogenicity of cellular tumor vaccines.

IMRT credentialing for prospective trials using institutional virtual phantoms: results of a joint European Organization for the Research and Treatment of Cancer and Radiological Physics Center project.

BACKGROUND AND PURPOSE: Intensity-modulated radiotherapy (IMRT) credentialing for a EORTC study was performed using an anthropomorphic head phantom from the Radiological Physics Center (RPC; RPCPH). Institutions were retrospectively requested to irradiate their institutional phantom (INSTPH) using the same treatment plan in the framework of a Virtual Phantom Project (VPP) for IMRT credentialing. MATERIALS AND METHODS: CT data set of the institutional phantom and measured 2D dose matrices were requested from centers and sent to a dedicated secure EORTC uploader. Data from the RPCPH and INSTPH were thereafter centrally analyzed and inter-compared by the QA team using commercially available software (RIT; ver.5.2; Colorado Springs, USA). RESULTS: Eighteen institutions participated to the VPP. The measurements of 6 (33%) institutions could not be analyzed centrally. All other centers passed both the VPP and the RPC ±7%/4 mm credentialing criteria. At the 5%/5 mm gamma criteria (90% of pixels passing), 11(92%) as compared to 12 (100%) centers pass the credentialing process with RPCPH and INSTPH (p = 0.29), respectively. The corresponding pass rate for the 3%/3 mm gamma criteria (90% of pixels passing) was 2 (17%) and 9 (75%; p = 0.01), respectively. CONCLUSIONS: IMRT dosimetry gamma evaluations in a single plane for a H&N prospective trial using the INSTPH measurements showed agreement at the gamma index criteria of ±5%/5 mm (90% of pixels passing) for a small number of VPP measurements. Using more stringent, criteria, the RPCPH and INSTPH comparison showed disagreement. More data is warranted and urgently required within the framework of prospective studies.

Swiss population exposure to radiation by interventional radiology in 2008.

The aim of this study was to investigate the radiation exposure of the Swiss population to interventional procedures. A nationwide survey was conducted in Switzerland. The annual effective dose per capita due to interventional procedures was found to be 0.14 mSv, corresponding to 12% of the total dose. Coronary angiography and percutaneous coronary interventions were found to be the most frequent and the most irradiating interventional procedures, accounting for 52% of the total examination frequency and 64% of the dose delivered to the population. Switzerland stands at the same level as other countries in terms of effective dose per capita due to interventional radiology.

A critical evaluation of secondary cancer risk models applied to Monte Carlo dose distributions of 2-dimensional, 3-dimensional conformal and hybrid intensity-modulated radiation therapy for breast cancer.

The comparison of radiotherapy techniques regarding secondary cancer risk has yielded contradictory results possibly stemming from the many different approaches used to estimate risk. The purpose of this study was to make a comprehensive evaluation of different available risk models applied to detailed whole-body dose distributions computed by Monte Carlo for various breast radiotherapy techniques including conventional open tangents, 3D conformal wedged tangents and hybrid intensity modulated radiation therapy (IMRT). First, organ-specific linear risk models developed by the International Commission on Radiological Protection (ICRP) and the Biological Effects of Ionizing Radiation (BEIR) VII committee were applied to mean doses for remote organs only and all solid organs. Then, different general non-linear risk models were applied to the whole body dose distribution. Finally, organ-specific non-linear risk models for the lung and breast were used to assess the secondary cancer risk for these two specific organs. A total of 32 different calculated absolute risks resulted in a broad range of values (between 0.1% and 48.5%) underlying the large uncertainties in absolute risk calculation. The ratio of risk between two techniques has often been proposed as a more robust assessment of risk than the absolute risk. We found that the ratio of risk between two techniques could also vary substantially considering the different approaches to risk estimation. Sometimes the ratio of risk between two techniques would range between values smaller and larger than one, which then translates into inconsistent results on the potential higher risk of one technique compared to another. We found however that the hybrid IMRT technique resulted in a systematic reduction of risk compared to the other techniques investigated even though the magnitude of this reduction varied substantially with the different approaches investigated. Based on the epidemiological data available, a reasonable approach to risk estimation would be to use organ-specific non-linear risk models applied to the dose distributions of organs within or near the treatment fields (lungs and contralateral breast in the case of breast radiotherapy) as the majority of radiation-induced secondary cancers are found in the beam-bordering regions.

A treatment planning method for sequentially combining radiopharmaceutical therapy and external radiation therapy.

PURPOSE: Effective cancer treatment generally requires combination therapy. The combination of external beam therapy (XRT) with radiopharmaceutical therapy (RPT) requires accurate three-dimensional dose calculations to avoid toxicity and evaluate efficacy. We have developed and tested a treatment planning method, using the patient-specific three-dimensional dosimetry package 3D-RD, for sequentially combined RPT/XRT therapy designed to limit toxicity to organs at risk. METHODS AND MATERIALS: The biologic effective dose (BED) was used to translate voxelized RPT absorbed dose (D(RPT)) values into a normalized total dose (or equivalent 2-Gy-fraction XRT absorbed dose), NTD(RPT) map. The BED was calculated numerically using an algorithmic approach, which enabled a more accurate calculation of BED and NTD(RPT). A treatment plan from the combined Samarium-153 and external beam was designed that would deliver a tumoricidal dose while delivering no more than 50 Gy of NTD(sum) to the spinal cord of a patient with a paraspinal tumor. RESULTS: The average voxel NTD(RPT) to tumor from RPT was 22.6 Gy (range, 1-85 Gy); the maximum spinal cord voxel NTD(RPT) from RPT was 6.8 Gy. The combined therapy NTD(sum) to tumor was 71.5 Gy (range, 40-135 Gy) for a maximum voxel spinal cord NTD(sum) equal to the maximum tolerated dose of 50 Gy. CONCLUSIONS: A method that enables real-time treatment planning of combined RPT-XRT has been developed. By implementing a more generalized conversion between the dose values from the two modalities and an activity-based treatment of partial volume effects, the reliability of combination therapy treatment planning has been expanded.

Development of advanced silicon radiation detectors for harsh radiation environment

This thesis describes the development of advanced silicon radiation detectors and their characterization by simulations, used in the work for searching elementary particles in the European Organization for Nuclear Research, CERN. Silicon particle detectors will face extremely harsh radiation in the proposed upgrade of the Large Hadron Collider, the future high-energy physics experiment Super-LHC. The increase in the maximal fluence and the beam luminosity up to 1016 neq / cm2 and 1035 cm-2s-1 will require detectors with a dramatic improvement in radiation hardness, when such a fluence will be far beyond the operational limits of the present silicon detectors. The main goals of detector development concentrate on minimizing the radiation degradation. This study contributes mainly to the device engineering technology for developing more radiation hard particle detectors with better characteristics. Also the defect engineering technology is discussed. In the nearest region of the beam in Super-LHC, the only detector choice is 3D detectors, or alternatively replacing other types of detectors every two years. The interest in the 3D silicon detectors is continuously growing because of their many advantages as compared to conventional planar detectors: the devices can be fully depleted at low bias voltages, the speed of the charge collection is high, and the collection distances are about one order of magnitude less than those of planar technology strip and pixel detectors with electrodes limited to the detector surface. Also the 3D detectors exhibit high radiation tolerance, and thus the ability of the silicon detectors to operate after irradiation is increased. Two parameters, full depletion voltage and electric field distribution, is discussed in more detail in this study. The full depletion of the detector is important because the only depleted area in the detector is active for the particle tracking. Similarly, the high electric field in the detector makes the detector volume sensitive, while low-field areas are non-sensitive to particles. This study shows the simulation results of full depletion voltage and the electric field distribution for the various types of 3D detectors. First, the 3D detector with the n-type substrate and partial-penetrating p-type electrodes are researched. A detector of this type has a low electric field on the pixel side and it suffers from type inversion. Next, the substrate is changed to p-type and the detectors having electrodes with one doping type and the dual doping type are examined. The electric field profile in a dual-column 3D Si detector is more uniform than that in the single-type column 3D detector. The dual-column detectors are the best in radiation hardness because of their low depletion voltages and short drift distances.

End point of Hawking radiation

The formation and semiclassical evaporation of two-dimensional black holes is studied in an exactly solvable model. Above a certain threshold energy flux, collapsing matter forms a singularity inside an apparent horizon. As the black hole evaporates the apparent horizon recedes and meets the singularity in a finite proper time. The singularity emerges naked, and future evolution of the geometry requires boundary conditions to be imposed there. There is a natural choice of boundary conditions which matches the evaporated black hole solution onto the linear dilaton vacuum. Below the threshold energy flux no horizon forms and boundary conditions can be imposed where infalling matter is reflected from a timelike boundary. All information is recovered at spatial infinity in this case.

Design and characterization of large area position sensitive radiation detectors

Planar, large area, position sensitive silicon detectors are widely utilized in high energy physics research and in medical, computed tomography (CT). This thesis describes author's research work relating to development of such detector components. The key motivation and objective for the research work has been the development of novel, position sensitive detectors improving the performance of the instruments they are intended for. Silicon strip detectors are the key components of barrel-shaped tracking instruments which are typically the innermost structures of high energy physics experimental stations. Particle colliders such as the former LEP collider or present LHC produce particle collisions and the silicon strip detector based trackers locate the trajectories of particles emanating from such collisions. Medical CT has become a regular part of everyday medical care in all developed countries. CT scanning enables x-ray imaging of all parts of the human body with an outstanding structural resolution and contrast. Brain, chest and abdomen slice images with a resolution of 0.5 mm are possible and latest CT machines are able to image whole human heart between heart beats. The two application areas are presented shortly and the radiation detection properties of planar silicon detectors are discussed. Fabrication methods and preamplifier electronics of the planar detectors are presented. Designs of the developed, large area silicon detectors are presented and measurement results of the key operating parameters are discussed. Static and dynamic performance of the developed silicon strip detectors are shown to be very satisfactory for experimental physics applications. Results relating to the developed, novel CT detector chips are found to be very promising for further development and all key performance goals are met.

Mesure des champs de radiation dans le détecteur ATLAS et sa caverne avec les détecteurs au silicium à pixels ATLAS-MPX

Les collisions proton-proton produites par le LHC imposent un environnement radiatif hostile au détecteur ATLAS. Afin de quantifier les effets de cet environnement sur la performance du détecteur et la sécurité du personnel, plusieurs simulations Monte Carlo ont été réalisées. Toutefois, la mesure directe est indispensable pour suivre les taux de radiation dans ATLAS et aussi pour vérifier les prédictions des simulations. À cette fin, seize détecteurs ATLAS-MPX ont été installés à différents endroits dans les zones expérimentale et technique d'ATLAS. Ils sont composés d'un détecteur au silicium à pixels appelé MPX dont la surface active est partiellement recouverte de convertisseurs de neutrons thermiques, lents et rapides. Les détecteurs ATLAS-MPX mesurent en temps réel les champs de radiation en enregistrant les traces des particules détectées sous forme d'images matricielles. L'analyse des images acquises permet d'identifier les types des particules détectées à partir des formes de leurs traces. Dans ce but, un logiciel de reconnaissance de formes appelé MAFalda a été conçu. Étant donné que les traces des particules fortement ionisantes sont influencées par le partage de charge entre pixels adjacents, un modèle semi-empirique décrivant cet effet a été développé. Grâce à ce modèle, l'énergie des particules fortement ionisantes peut être estimée à partir de la taille de leurs traces. Les convertisseurs de neutrons qui couvrent chaque détecteur ATLAS-MPX forment six régions différentes. L'efficacité de chaque région à détecter les neutrons thermiques, lents et rapides a été déterminée par des mesures d'étalonnage avec des sources connues. L'étude de la réponse des détecteurs ATLAS-MPX à la radiation produite par les collisions frontales de protons à 7TeV dans le centre de masse a montré que le nombre de traces enregistrées est proportionnel à la luminosité du LHC. Ce résultat permet d'utiliser les détecteurs ATLAS-MPX comme moniteurs de luminosité. La méthode proposée pour mesurer et étalonner la luminosité absolue avec ces détecteurs est celle de van der Meer qui est basée sur les paramètres des faisceaux du LHC. Vu la corrélation entre la réponse des détecteurs ATLAS-MPX et la luminosité, les taux de radiation mesurés sont exprimés en termes de fluences de différents types de particules par unité de luminosité intégrée. Un écart significatif a été obtenu en comparant ces fluences avec celles prédites par GCALOR qui est l'une des simulations Monte Carlo du détecteur ATLAS. Par ailleurs, les mesures effectuées après l'arrêt des collisions proton-proton ont montré que les détecteurs ATLAS-MPX permettent d'observer la désintégration des isotopes radioactifs générés au cours des collisions. L'activation résiduelle des matériaux d'ATLAS peut être mesurée avec ces détecteurs grâce à un étalonnage en équivalent de dose ambiant.

Axially Symmetric Radiation Patterns from Flanged E-Plane Sectoral Horn

A simple technique for obtaining identical E- and H-plane patterns from E-plane sectoral feed horn is presented. Halfpower beam width and gain of the antenna are also improved considerably. Experimental results for a number of horns with flanges of various parameters are also presented. This system may find practical application in radar and space communication systems

Axially Symmetric Radiation Patterns from Corrugated

A modified H-plane sectoral horn antenna with identical E- and'H- plane.patterns over the X-band frequency is discussed. This system has significantly reduced side lobes and hack lobes. Half=power beam width and gain of the antenna are also improved with enhanced matching , Experimental results for a number of horns with various flanges are presented . These find practical application for illuminating symmetric antennas like paraboloids and polarization measurements in radio astronomy, etc. Compared to the fixed pyramidal horns. the present system offers great convenience in trimming the antenna characteristics

An Experimental Investigation of the Effect of Flange Angle on Radiation Patterns of V-Slot Waveguide Antenna

Results of exhaustive study of the effect of metallic flanges on H-plane radiation characteristics of V-slot waveguide antenna are presented . It has been established that the beam can be sharpened or broadened by varying the flange angle . The adjustment of the flange angle and flange width would further improve the radiation pattern , yielding optimum efficiency from the flanged system