Search

Offenbart wird die Kontaktierung eines quaderförmigen CZT-Kristalls zur Detektierung von Gammastrahlung in einer Compton-Kamera, wobei der CZT-Kristall eine der einfallenden Strahlung zugewandte, vollflächige Vorderseitenelektrode und auf der der Vorderseite gegenüberliegenden Rückseite mehrere, voneinander beabstandete rechteckige und als Elektroden ausgeführte Pixelflächen aufweist, wobei die zu den Pixelflächen komplementären Anschlussflächen eines oder mehrerer Flachbandkabel mit diesen Pixelflächen elektrisch leitfähig mittels eines leitfähigen Klebstoffs verbunden sind.

The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potential of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine. Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment under development in several research centers, the prompt gamma ray timing method has been recently proposed. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies. From the resulting distributions, particle range differences of around 5 millimeters in heterogeneous phantoms were observed. In conclusion, we proved the feasibility of the prompt gamma ray timing method for range verification in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.

Characterization of Scintillators with respect to their Application in Prompt Gamma Imaging Systems.

The proton therapy in oncology requires instantaneous and reliable particle range verification, which can be done using prompt gamma emissions. The characteristic requirements of prompt gamma detection include the energy range of up to several MeV, increased background due to secondary emissions and high counting rates. Different concepts make use of these prompt gammas for dose verification like collimated systems or Compton cameras. Additionally to prompt gamma imaging, the prompt gamma timing method has been proposed, utilizing the proton time-of-flight inside the body. Those approaches imply different needs on energy-, spatial- or timing-resolution of the detection system. Various scintillator materials with multiple shapes have been characterized with respect to those requirements using classical photomultiplier tubes (PMT) and different experimental setups and locations. The light output, non-linearity and energy resolution were measured using gamma sources. The timing was characterized at the ELBE facility at Helmholtz-Zentrum Dresden-Rossendorf (HZDR), using the bremsstrahlung beam with photons up to 12.5 MeV. Planned measurements at the 3 MV Tandetron accelerator at HZDR will provide information at the energy resolution at therapy relevant energies of 4.4 MeV.

The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potentialities of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine. Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment, the prompt gamma ray timing method has been recently proposed and tested at a research accelerator. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies. From the resulting distributions, particle range differences of around 5 millimetres in heterogeneous phantoms were observed by simple qualitative inspection. In conclusion, our preliminary analysis points out that the prompt gamma ray timing method for range verification is feasible in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.

In the context of ion beam therapy, particle range verification is a major challenge for the quality assurance of the treatment. One approach is the measurement of the prompt gamma rays resulting from the tissue irradiation. A Compton camera based on several position sensitive gamma ray detectors, together with an imaging algorithm, is expected to reconstruct the prompt gamma ray emission density map, which is correlated with the dose distribution. At OncoRay and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a Compton camera setup is being developed consisting of two scatter planes: two CdZnTe (CZT) cross strip detectors, and an absorber consisting of one Lu2SiO5 (LSO) block detector. The data acquisition is based on VME electronics and handled by software developed on the ROOT framework. The setup has been tested at the linear electron accelerator ELBE at HZDR, which is used in this experiment to produce bunched bremsstrahlung photons with up to 12.5 MeV energy and a repetition rate of 13 MHz. Their spectrum has similarities with the shape expected from prompt gamma rays in the clinical environment, and the flux is also bunched with the accelerator frequency. The charge sharing effect of the CZT detector is studied qualitatively for different energy ranges. The LSO detector pixel discrimination resolution is analyzed and it shows a trend to improve for high energy depositions. The time correlation between the pulsed prompt photons and the measured detector signals, to be used for background suppression, exhibits a time resolution of 3 ns FWHM for the CZT detector and of 2 ns for the LSO detector. A time walk correction and pixel-wise calibration is applied for the LSO detector, whose resolution improves up to 630 ps. In conclusion, the detector setup is suitable for time-resolved background suppression in pulsed clinical particle accelerators. Ongoing tasks are the quantitative comparison with simulations and the test of imaging algorithms. Experiments at proton accelerators have also been performed and are currently under analysis.

Segmented Cadmium Zinc Telluride (CdZnTe) detectors are promising candidates for a high resolution radiation detection system due to their good energy and spatial resolution. They are also well suited for medical imaging in a Compton camera application. This first Compton camera prototype is set up with a double sided strip detector in the scatter layer. Such an electrode layout enables a fast timing at the expense of efficiency losses. As a Compton camera needs an adequate number of valid scattering events with precise timing, a pixelated electrode layout performs best. The analog readout electronics for a 8 x 8 pixeldetector (20 x 20 x 5mm3) has been replaced by a digital FPGA-based system. All detector signals are sampled by charge sensitive preamplifiers with 100MS/s and 14 bit resolution. The pulse heights are extracted with an adjustable Moving Window Deconvolution in combination with a slow shaping IIR filter (Recursive Moving Average). To generate a trigger, we implemented a digital constant fraction discriminator (DCFD) on the fast shaped signal. This signal is derived by applying a FIR filter to the deconvoluted cathode signal. The algorithm uses a symmetric [−1, 1] coefficient structure for fast computation. Our results show that the accuracy of the DCFD can be improved by optimizing the filter length. Both algorithms for energy and timestamp calculation have been evaluated with measurements of a 22Na source and at the ELBE accelerator with a pulsed beam. The initial implementation results in an energy resolution of about 5% (FWHM at 511 keV) for a randomly selected pixel and a timing resolution better than 12 ns FWHM for all events up to 10MeV.

The aim of this trial was to demonstrate the efficacy of one month of oral cobalamin (vitamin B12) therapy in elderly patients with cobalamin deficiency related to food-cobalamin malabsorption (FCM).Twenty elderly patients (mean age: 78+/-17 years) with established cobalamin deficiency related to FCM were included in an open-label, non-randomized, non-placebo trial. They were treated with a maximum of 1,000 microgram per day of oral crystalline cyanocobalamin for at least 1 month. Serum cobalamin levels (primary endpoint), blood count abnormalities and reticulocytes count (secondary endpoints) were determined at baseline and during the first month of treatment.85% of the patients normalized their serum cobalamin levels with a mean increase of+167 pg/ml (p0.001 compared with baseline). 100% of the patients corrected their initial macrocytosis and 25% their anemia; 100% of the patients had medullar regeneration with a mean increase of reticulocytes count of 32+/-11.3 x 106/l (p=0.03 compared with baseline).Our findings support the view that one month of oral crystalline cyanocobalamin is effective to correct serum vitamin B12 levels and to obtain hematological responses in elderly patients with cobalamin deficiency related to FCM.

Non-dissociation of vitamin B12 from its carrying proteins is the most frequent cause of vitamin B12 deficiency in the elderly. The aim of this study was to determine the initial dose of oral cyanocobalamin that would correct the B12 vitamin deficiency within one week.This was an open, prospective, study on 30 elderly patients suffering from vitamin deficiency (B120.20 microg/L) induced by food-cobalamin malabsorption. Ten patients (group I) were treated with a daily dose of 1000 microg of oral cyanocobalamin (from D1 to D8), 10 (group II) with 1000 microg every other day (D1, D3, D5 and D7), 5 (group III) with 1000 microg every 4 days (D1 and D5) and 5 (group IV) with 1000 microg only on D1. The biological response was assessed by control measurement of vitamin B12 serum levels on the 8th day.Mean vitamin B12 serum levels had significantly increased (p0.01) in groups I, II and III, but not in group IV. The dose-effect, assessed by the mean increase in vitamin B12 serum levels, was significantly greater (p0.05) in groups I (0.25 microg/L) and II (0.18 microg/L), than in groups III and IV (0.09 microg/L).This prospective study shows that an oral dose of 1000 microg of cyanocobalamin every 4 days, which corresponds to 250 microg per day, was sufficient to correct B12 vitamin deficiency induced by food-cobalamin malabsorption within one week. However, initial doses of 1000 microg per day or every other day would be preferable because of the greater dose-effect with daily doses higher than 500 microg. A randomised study is warranted to validate these preliminary results.