Methoden und Anwendungen für bildgebende Verfahren mit hohen Neutronenflüssen

Die vorliegende Dissertation entwickelt neue Methoden für die Neutronenradiographie und Neutronentomographie bei hohen Flüssen und beschreibt deren Anwendung in konkreten Experimenten. Anstelle einzelner Aufnahmen können dank der hohen Intensität mit kurzen Belichtungszeiten Serien von Bildern aufgenommen werden. Um die gestiegene Informationsmenge bestmöglich ausnutzen zu können, werden Schätzmethoden eingeführt, die aus den gemessenen Ensembles auch bei starkem Rauschen der einzelnen Messwerte und in Anwesenheit systematischer Einflüsse wie etwa störender Gammastrahlung sehr exakte Erwartungswerte der Messgrößen liefern. Die Ortsauflösung von Radiographien, die gewöhnlich durch Strahldivergenz und das inhärente Auflösungsvermögen von Szintillatoren begrenzt ist, kann durch Abrastern der Probe mit einem Nadelloch-Mikrokollimator wesentlich erhöht werden. Diese Technik umgeht alle Limitierungen konventioneller Detektorsysteme und konnte dank des hohen Flusses erfolgreich erprobt werden. Die Abbildung gestreuter Neutronen erlaubt im Gegensatz zur konventionellen, auf der gesamten Attenuation basierenden Radiographie, die getrennte Bestimmung der Absorptions- und Streuquerschnitte innerhalb der Probe. Erstmals konnte sogar kohärente winkelabhängige Streuung räumlich aufgelöst werden. Als neue Anwendungen der Hochflussneutronenbildgebung werden unter anderem materialwissenschaftliche Untersuchungen an innovativen Metallverbindungen, zeitaufgelöste Tomographien an mehrlagigen Brennstoffzellen im Betrieb und andere Experimente präsentiert. Eine neue Implementierung eines algebraischen Rekonstruktionsverfahrens für Tomographiedaten ermöglicht es, auch bei fehlender Information, wie etwa einem eingeschränkten Winkelbereich, quantitative Rekonstruktionen zu erzeugen. Der Aufbau der weltweit führenden Hochfluss-Radiographie- und Tomographiestation am Institut Laue-Langevin wird vorgestellt. Ein umfassender Anhang präsentiert die physikalischen und technischen Grundlagen der Bildgebung mit Neutronen

Intra-fraction motion of the prostate is not increased by patient couch shifts

Background: During a fraction of external beam radiotherapy for prostate cancer, a mismatch between target volume and dose coverage may accumulate over time due to intra-fraction motion. One way to remove the residual error is to perform a couch shift in opposite direction. In principle, such couch shifts could cause secondary displacements of the patient and prostate. Hence it is interesting to investigate if couch shifts might amplify intra-fraction motion. Findings: Intra-fraction motion of the prostate and patient couch position were simultaneously recorded during 359 fractions in 15 patients. During this time, a total of 22 couch shifts of up to 31.5 mm along different axes were recorded. Prostate position and couch position were plotted before, during and after each couch shift. There was no visible impact of couch shifts on prostate motion. The standard deviation of prostate position was calculated before, during and after each couch shift. The standard deviation did not significantly increase during couch shifts (by 3 % on average, p = 0.88) and even slightly decreased after a couch shift (by 37 % on average;p = 0.02). Conclusions: Shifts of the patient couch did not adversely affect the motion of the prostate relative to the patient couch. Hence, shifts of the patient couch may be a viable way to correct the position of the prostate relative to the dose distribution

Surface refraction of sound waves affects calibration of three-dimensional ultrasound

Background: Three-dimensional ultrasound (3D-US) is used in planning and treatment during external beam radiotherapy. The accuracy of the technique depends not only on the achievable image quality in clinical routine, but also on technical limitations of achievable precision during calibration. Refraction of ultrasound waves is a known source for geometric distortion, but such an effect was not expected in homogenous calibration phantoms. However, in this paper we demonstrate that the discontinuity of the refraction index at the phantom surface may affect the calibration unless the ultrasound probe is perfectly perpendicular to the phantom. Methods: A calibration phantom was repeatedly scanned with a 3D-US system (Elekta Clarity) by three independent observers. The ultrasound probe was moved horizontally at a fixed angle in the sagittal plane. The resulting wedge shaped volume between probe and phantom was filled with water to couple in the ultrasound waves. Because the speed of sound in water was smaller than the speed of sound in Zerdine, the main component of the phantom, the angle of the ultrasound waves inside the phantom increased. This caused an apparent shift in the calibration features which was recorded as a function of the impeding angle. To confirm the magnitude and temperature dependence, the experiment was repeated by two of the observers with a mixture of ice and water at 0 degrees C and with thermalized tap water at 21 degrees C room temperature. Results: During the first series of measurements, a linear dependency of the displacements dx of the calibration features on the angle a of the ultrasound probe was observed. The three observers recorded significantly nonzero (p < 0.0001) and very consistent slopes of dx/da of 0.12, 0.12, and 0.13 mm/degrees, respectively. At 0 degrees C water temperature, the slope increased to 0.18 +/- 0.04 mm/degrees. This matched the prediction of Snell's law of 0.185 mm/degrees for a speed of sound of 1, 402 m/s at the melting point of ice. At 21 degrees C, slopes of 0.11 and 0.12 mm/degrees were recorded in agreement with the first experiment at about room temperature. The difference to the theoretical expectation of 0.07 mm/degrees was not significant (p = 0.09). Conclusions: The surface refraction of sound waves my affect the calibration of three-dimensional ultrasound. The temperature dependence of the effect rules out alternative explanations for the observed shifts in calibration. At room temperature and for a structure that is 10 cm below the water-phantom interface, a tilt of the ultrasound probe of 10 degrees may result in a position reading that is off by more than half a millimeter. Such errors are of the order of other relevant errors typically encountered during the calibration of a 3D-US system. Hence, care must be taken not to tilt the ultrasound probe during calibration

Post-processing sets of tilted CT volumes as a method for metal artifact reduction

Background: Metal implants, surgical clips and other foreign bodies may cause `streaking' or `star' artifacts in computed tomography (CT) reconstructions, for example in the vicinity of dental restorations or hip implants. The deteriorated image quality complicates contouring and has an adverse effect on quantitative planning in external beam therapy. Methods: The potential to reduce artifacts by acquisition of tilted CT reconstructions from different angles of the same object was investigated. While each of those reconstructions still contained artifacts, they were not necessarily in the same place in each CT. By combining such CTs with complementary information, a reconstructed volume with less or even without artifacts was obtained. The most straightforward way to combine the co-registered volumes was to calculate the mean or median per voxel. The method was tested with a calibration phantom featuring a titanium insert, and with a human skull featuring multiple dental restorations made from gold and steel. The performance of the method was compared to established metal artifact reduction (MAR) algorithms. Dose reduction was tested. Results: In a visual comparison, streaking artifacts were strongly reduced and details in the vicinity of metal foreign bodies became much more visible. In case of the calibration phantom, average bias in Hounsfield units was reduced by 94% and per-voxel-errors and noise were reduced by 83%. In case of the human skull, bias was reduced by 95% and noise was reduced by 94%. The performance of the method was visually superior and quantitatively compareable to established MAR algorithms. Dose reduction was viable. Conclusions: A simple post-processing method for MAR was described which required one or more complementary scans but did not rely on any a priori information. The method was computationally inexpensive. Performance of the method was quantitatively comparable to established algorithms and visually superior in a direct comparison. Dose reduction was demonstrated, artifacts could be reduced without compromising total dose to the patient

Excellent local control and survival after postoperative or definitive radiation therapy for sarcomas of the head and neck

Background: To report our results with postoperative or definitive radiation therapy in head and neck sarcomas. Methods: We performed a retrospective analysis of 26 patients suffering from head and neck sarcomas, who received postoperative or definitive radiation therapy between 2003 and 2012. Median age was 64 years (19-88) and 69 % were male. Tumor locations were skull (including skin) in 31 %,paranasal sinus/orbita in 27 % and neck (including pharynx/larynx) in 42 %. Median tumor size was 4.6 cm (1-12 cm). 22 patients (85 %) presented in primary situation. Stage at presentation (UICC 7th for soft tissue sarcomas) was as follows: Ia: 4 %,IIa:50 %,IIb:15 %,III:31 %. All except one patient suffered from high grade lesions (G2/3 FNCLCC),predominantly angiosarcoma (35 %),MFH (19 %) and synovial sarcoma (15 %). Surgery was performed in 21 pts (81 %),resulting in free margins in 10 (38 %),microscopically positive margins in 6 (23 %) and gross residual disease in 5 (19 %). Median dose to the primary tumor region was 66Gy (45-72Gy) in conventional fractionation, using 3D-CRT in 65 %,IMRT in 27 % and electrons in 8 %. 50 % of the patients also received sequential chemotherapy. Results: Median follow up was 39 months (8-136). We observed three local recurrences, transferring into estimated 3-and 5-year local control rates of 86 %. One additional patient failed distantly, resulting in 3-and 5-year freedom from treatment failure rates of 82 %. Four patients have deceased, transferring into 3-and 5-year overall survival rates of 88 % and 82 %,respectively. Only two of the four deaths were sarcoma related. Maximum acute toxicity (CTCAE 3.0) was grade 1 in 27 % of the patients, grade 2 in 50 % and grade 3 in 23 %. Severe acute toxicity was mainly represented by mucositis and dysphagia. Maximum late toxicity was grade 1 in 31 %,grade 2 in 15 % and grade 3 in 19 % of the patients. Severe late toxicity included skin ulceration (n = 1),dysphagia with persistent tube dependency (n = 1),persistent sinusitis (n = 1) and hearing loss (n = 2). Conclusion: Excellent local control and overall survival rates can be achieved with postoperative or definitive radiation therapy with acceptable acute and late toxicities in patients suffering from sarcomas of the head and neck region

Excellent local control and survival after postoperative or definitive radiation therapy for sarcomas of the head and neck

Background: To report our results with postoperative or definitive radiation therapy in head and neck sarcomas. Methods: We performed a retrospective analysis of 26 patients suffering from head and neck sarcomas, who received postoperative or definitive radiation therapy between 2003 and 2012. Median age was 64 years (19-88) and 69 % were male. Tumor locations were skull (including skin) in 31 %,paranasal sinus/orbita in 27 % and neck (including pharynx/larynx) in 42 %. Median tumor size was 4.6 cm (1-12 cm). 22 patients (85 %) presented in primary situation. Stage at presentation (UICC 7th for soft tissue sarcomas) was as follows: Ia: 4 %,IIa:50 %,IIb:15 %,III:31 %. All except one patient suffered from high grade lesions (G2/3 FNCLCC),predominantly angiosarcoma (35 %),MFH (19 %) and synovial sarcoma (15 %). Surgery was performed in 21 pts (81 %),resulting in free margins in 10 (38 %),microscopically positive margins in 6 (23 %) and gross residual disease in 5 (19 %). Median dose to the primary tumor region was 66Gy (45-72Gy) in conventional fractionation, using 3D-CRT in 65 %,IMRT in 27 % and electrons in 8 %. 50 % of the patients also received sequential chemotherapy. Results: Median follow up was 39 months (8-136). We observed three local recurrences, transferring into estimated 3-and 5-year local control rates of 86 %. One additional patient failed distantly, resulting in 3-and 5-year freedom from treatment failure rates of 82 %. Four patients have deceased, transferring into 3-and 5-year overall survival rates of 88 % and 82 %,respectively. Only two of the four deaths were sarcoma related. Maximum acute toxicity (CTCAE 3.0) was grade 1 in 27 % of the patients, grade 2 in 50 % and grade 3 in 23 %. Severe acute toxicity was mainly represented by mucositis and dysphagia. Maximum late toxicity was grade 1 in 31 %,grade 2 in 15 % and grade 3 in 19 % of the patients. Severe late toxicity included skin ulceration (n = 1),dysphagia with persistent tube dependency (n = 1),persistent sinusitis (n = 1) and hearing loss (n = 2). Conclusion: Excellent local control and overall survival rates can be achieved with postoperative or definitive radiation therapy with acceptable acute and late toxicities in patients suffering from sarcomas of the head and neck region

Stereoscopic X-ray imaging, cone beam CT, and couch positioning in stereotactic radiotherapy of intracranial tumors: preliminary results from a cross-modality pilot installation

Background: To assess the accuracy and precision of a fully integrated pilot installation of stereoscopic X-ray imaging and kV-CBCT for automatic couch positioning in stereotactic radiotherapy of intracranial tumors. Positioning errors as detected by stereoscopic X-ray imaging are compared to those by kV-CBCT (i.e. the accuracy of the new method is verified by the established method), and repeated X-ray images are compared (i.e. the precision of new method is determined intra-modally). Methods: Preliminary results are reported from a study with 32 patients with intracranial tumors. Patients were treated with stereotactic radiotherapy guided by stereoscopic X-ray imaging and kV-CBCT. Patient positioning was automatically corrected by a robotic couch. Cross-modal discrepancies in position detection were measured (N = 42). Intra-modal improvements after correction and re-verification by stereoscopic X-ray imaging were measured (N = 70). The accuracy and precision of stereoscopic X-ray imaging and the accuracy and precision of CBCT were confirmed in phantom measurements (N = 12 shifts of a ball bearing phantom, N = 24 shifts of a head phantom). Results: After correction based on stereoscopic X-ray imaging 95% of residual mean errors were below 0.4, 0.4, 0.5, and 0.7 mm (lateral, longitudinal, vertical, radial, respectively). Stereoscopic X-ray imaging and CBCT were in close agreement with an average discrepancy of 0.1, 0.5, 0.3 and 0.8 mm, respectively. 95% of discrepancies were below 0.8, 1.2, 1.0, and 1.4 mm, respectively. After correction and re-verification by stereoscopic X-ray imaging, the remaining intra-modal residual error was consistent with zero (p = 0.31, p = 0.48, p = 0.81 in lateral, longitudinal, and vertical direction;p-values from two-tailed t-test). The inherent technical accuracy and precision of stereoscopic X-ray imaging and the accuracy and precision of CBCT were found to be of the order of 0.1 mm in controlled phantom settings. Conclusions: In a routine clinical setting, both stereoscopic X-ray imaging and CBCT were able to reduce positioning errors by an order of magnitude. The end-to-end precision of the system, measured from the discrepancy (mean) between ExacTrac and CBCT, in a clinical setting seems to be about 0.8 mm radially, including couch positioning. The precision (measured from repeatability of ExacTrac, intra-modal) was found to be about 0.7 mm radially in a clinical setting

A comparative assessment of prostate positioning guided by three-dimensional ultrasound and cone beam CT

Background: The accuracy of the Elekta Clarity (TM) three-dimensional ultrasound system (3DUS) was assessed for prostate positioning and compared to seed-and bone-based positioning in kilo-voltage cone-beam computed tomography (CBCT) during a definitive radiotherapy. Methods: The prostate positioning of 6 patients, with fiducial markers implanted into the prostate, was controlled by 3DUS and CBCT. In total, 78 ultrasound scans were performed trans-abdominally and compared to bone-matches and seed-matches in CBCT scans. Setup errors detected by the different modalities were compared. Systematic and random errors were analysed, and optimal setup margins were calculated. Results: The discrepancy between 3DUS and seed-match in CBCT was -0.2 +/- 2.7 mm laterally,-1.9 +/- 2.3 mm longitudinally and 0.0 +/- 3.0 mm vertically and significant only in longitudinal direction. Using seed-match as reference, systematic errors of 3DUS were 1.3 mm laterally, 0.8 mm longitudinally and 1.4 mm vertically, and random errors were 2.5 mm laterally, 2.3 mm longitudinally, and 2.7 mm vertically. No significant difference could be detected for 3DUS in comparison to bone-match in CBCT. Conclusions: 3DUS is feasible for image guidance for patients with prostate cancer and appears comparable to CBCT based image guidance in the retrospective study. While 3DUS offers some distinct advantages such as no need of invasive fiducial implantation and avoidance of extra radiation, its disadvantages include the operator dependence of the technique and dependence on sufficient bladder filling. Further study of 3DUS for image guidance in a large patient cohort is warranted