A novel concept for CT with fixed anodes (FACT): Medical imaging based on the feasibility of thermal load capacity.

Focussing primarily on thermal load capacity, we describe the performance of a novel fixed anode CT (FACT) compared with a 100 kW reference CT. Being a fixed system, FACT has no focal spot blurring of the X-ray source during projection. Monte Carlo and finite element methods were used to determine the fluence proportional to thermal capacity. Studies of repeated short-time exposures showed that FACT could operate in pulsed mode for an unlimited period. A virtual model for FACT was constructed to analyse various temporal sequences for the X-ray source ring, representing a circular array of 1160 fixed anodes in the gantry. Assuming similar detector properties at a very small integration time, image quality was investigated using an image reconstruction library. Our model showed that approximately 60 gantry rounds per second, i.e. 60 sequential targetings of the 1160 anodes per second, were required to achieve a performance level equivalent to that of the reference CT (relative performance, RP = 1) at equivalent image quality. The optimal projection duration in each direction was about 10 µs. With a beam pause of 1 µs between projections, 78.4 gantry rounds per second with consecutive source activity were thermally possible at a given thermal focal spot. The settings allowed for a 1.3-fold (RP = 1.3) shorter scan time than conventional CT while maintaining radiation exposure and image quality. Based on the high number of rounds, FACT supports a high image frame rate at low doses, which would be beneficial in a wide range of diagnostic and technical applications.

TOPOS: a new topometric patient positioning and tracking system for radiation therapy based on structured white light.

PURPOSE: A patient positioning system for radiation therapy based on structured white light and using off-the-shelf hardware components for flexibility and cost-effectiveness has been developed in house. Increased accuracy, patient comfort, abandonment of any skin marks, accelerated workflow, objective reading/recording, better usability and robust sensor design, compared to other positioning approaches, were the main goals of this work. Another aim was the application of a 6 degrees of freedom tracking system working without dose deposition. METHODS: Two optical sensors are the main parts of the TOPOS® system (Topometrical Positioning, cyberTECHNOLOGIES, Germany). The components: cameras, projectors, and computers are commercial off-the-shelf products, allowing for low production costs. The black/white cameras of the prototype are capable of taking up to 240 frames per second (resolution: 640 × 488 pixels). The projector has a resolution of 1024 × 768 and a refresh rate of 120 Hz. The patient's body surface is measured continuously and registered to a reference surface, providing a transformation to superimpose the patient's surface to the reference (planning CT) surface as best as possible. The execution of the calculated transformation provides the correct patient position before the treatment starts. Due to the high-speed acquisition of the surfaces, a surveillance of the patient's (respiration) motion during treatment is also accomplished. The accuracy of the system was determined using a male mannequin. Two treatment sites were evaluated: one simulating a head and neck treatment and the other simulating a thoracic wall treatment. The mannequin was moved to predefined positions, and shift vectors given by the surface registration were evaluated. Additionally manual positioning using a color-coding system was evaluated. RESULTS: Two prototypes have been developed, each allowing a continuous high density scan of a 500 × 500 × 400 mm(3) (L × W × D) large volume with a refresh rate of 10 Hz (extendible to 20 Hz for a single sensor system). Surface and position correction display, as well as respiratory motion, is shown in real-time (delay < 200 ms) using present graphical hardware acceleration. For an intuitive view of the patient's misalignment, a fast surface registration algorithm has been developed and tested and a real-time color-coding technique is proposed and verified that allows the user to easily verify the position of the patient. Using first the surface registration and then the color coding the best results were obtained: for the head and neck case, the mean difference between the actual zero position and the final match was 0.1 ± 0.4, -0.2 ± 0.7, and -0.1 ± 0.3 mm in vertical, longitudinal, and lateral direction. For the thoracic case, the mean differences were 0.3 ± 0.5, -0.6 ± 1.9, 0.0 ± 0.4 mm. CONCLUSIONS: The presented system copes with the increasing demand for more accurate patient positioning due to more precise irradiation technologies and minimizes the preparation times for correct patient alignment, therefore optimizing the treatment workflow. Moreover, TOPOS is a versatile and cost effective image guided radiation therapy device. It allows an objective rating of the patient's position before and during the irradiation and could also be used for respiratory gating or tracking.

Multibeam tomotherapy: a new treatment unit devised for multileaf collimation, intensity-modulated radiation therapy.

A fully integrated system for treatment planning, application, and verification for automated multileaf collimator (MLC) based, intensity-modulated, image-guided, and adaptive radiation therapy (IMRT, IGRT and ART, respectively) is proposed. Patient comfort, which was the major development goal, will be achieved through a new unit design and short treatment times. Our device for photon beam therapy will consist of a new dual energy linac with five fixed treatment heads positioned evenly along one plane but one electron beam generator only. A minimum of moving parts increases technical reliability and reduces motion times to a minimum. Motion is allowed solely for the MLCs, the robotic patient table, and the small angle gantry rotation of +/- 36 degrees. Besides sophisticated electron beam guidance, this compact setup can be built using existing modules. The flattening-filter-free treatment heads are characterized by reduced beam-on time and contain apertures restricted in one dimension to the area of maximum primary fluence output. In the case of longer targets, this leads to a topographic intensity modulation, thanks to the combination of "step and shoot" MLC delivery and discrete patient couch motion. Owing to the limited number of beam directions, this multislice cone beam serial tomotherapy is referred to as "multibeam tomotherapy." Every patient slice is irradiated by one treatment head at any given moment but for one subfield only. The electron beam is then guided to the next head ready for delivery, while the other heads are preparing their leaves for the next segment. The "Multifocal MLC-positioning" algorithm was programmed to enable treatment planning and optimize treatment time. We developed an overlap strategy for the longitudinally adjacent fields of every beam direction, in doing so minimizing the field match problem and the effects of possible table step errors. Clinical case studies show for the same or better planning target volume coverage, better organ-at-risk sparing, and comparable mean integral dose to the normal tissue a reduction in treatment time by more than 50% to only a few minutes in comparison to high-quality 3-D conformal and IMRT treatments. As a result, it will be possible to incorporate features for better patient positioning and image guidance, while sustaining reasonable overall treatment times at the same time. The virtual multibeam tomotherapy design study TOM'5-CT contains a dedicated electron beam CT (TOM'AGE) and an objective optical topometric patient positioning system (TOPOS). Thanks to the wide gantry bore of 120 cm and slim gantry depths of 70 cm, patients can be treated very comfortably, in all cases tumor-isocentrically, as well as with noncoplanar beam arrangements as in stereotactic radiosurgery with a couch rotation of up to +/- 54 degrees. The TOM'5 treatment unit on which this theoretical concept is based has a stand-alone depth of 40 cm and an outer diameter of 245 cm; the focus-isocenter distance of the heads is 100 cm with a field size of 40 cm x 7 cm and 0.5 cm leaves, which operate perpendicular to the axis of table motion.

High-dose intracoronary irradiation after de novo stent implantation results of the EVEREST (Evaluation of Endoluminal Radiation in Elective Stenting) trial.

PURPOSE: This randomized study was designed to compare the efficacy of high-dose coronary beta-radiation after intravascular ultrasound-(IVUS-)guided direct stenting with sham treatment in patients with de novo lesions. PATIENTS AND METHODS: 32 patients were enrolled in the study protocol. Following angioplasty procedure, intracoronary brachytherapy was performed with the Novoste Beta-Cath System. The prescribed dose was 24 Gy referred to the lamina elastica externa. Quantitative coronary angiography and IVUS were performed to analyze the treated coronary vessel. RESULTS: Angiographic results revealed a significantly smaller minimal lumen diameter compared with the pos-tprocedural minimal lumen diameter within the stented segment (p = 0.004) in the nonirradiated group. The same significant result was observed in the injured segment of the nonirradiated patients (p = 0.011). The IVUS data revealed a significant increase of the plaque volume after 8 months in the nonirradiated group compared to the post-procedural value (irradiated 5.41 +/- 8.83 mm(3) vs. nonirradiated 21.11 +/- 16.08 mm(3); p = 0.001). Late luminal loss was significantly greater in the nonirradiated group (p = 0.004). The primary clinical endpoint (death, myocardial infarction, repeat target lesion revascularization, percutaneous revascularization, coronary artery bypass surgery) was reached by seven irradiated (33.3%) and four (18.2%) nonirradiated patients (p = 0.623). Late stent thrombosis was observed in one irradiated patient. CONCLUSION: The EVEREST trial has demonstrated the feasibility of high-dose intracoronary brachytherapy in de novo coronary lesions. There is a significant reduction of neointimal proliferation within the stented segment. Nevertheless, this benefit is vitiated by an increase of restenotic lesions outside the stent segment.