Probing Magnetic Exchange Interactions with Helium.

Controlling and sensing spin polarization of electrons forms the basis of spintronics. Here, we report a study of the effect of helium on the spin polarization of the tunneling current and magnetic contrast in spin-polarized scanning tunneling microscopy (SP STM). We show that the magnetic contrast in SP STM images recorded in the presence of helium depends sensitively on the tunneling conditions. From tunneling spectra and their variation across the atomic lattice we establish that the helium can be reversibly ejected from the tunneling junction by the tunneling electrons. The energy of the tunneling electrons required to eject the helium depends on the relative spin polarization of the tip and sample, making the microscope sensitive to the magnetic exchange interactions. We show that the time-averaged spin polarization of the tunneling current is suppressed in the presence of helium and thereby demonstrate voltage control of the spin polarization of the tunneling current across the tip-sample junction.

Tomographic mapping of the hidden dimension in quasi-particle interference.

Quasiparticle interference (QPI) imaging is well established to study the low-energy electronic structure in strongly correlated electron materials with unrivalled energy resolution. Yet, being a surface-sensitive technique, the interpretation of QPI only works well for anisotropic materials, where the dispersion in the direction perpendicular to the surface can be neglected and the quasiparticle interference is dominated by a quasi-2D electronic structure. Here, we explore QPI imaging of galena, a material with an electronic structure that does not exhibit pronounced anisotropy. We find that the quasiparticle interference signal is dominated by scattering vectors which are parallel to the surface plane however originate from bias-dependent cuts of the 3D electronic structure. We develop a formalism for the theoretical description of the QPI signal and demonstrate how this quasiparticle tomography can be used to obtain information about the 3D electronic structure and orbital character of the bands.

Cryogenic STM in 3D vector magnetic fields realized through a rotatable insert.

Spin-polarized scanning tunneling microscopy (SP-STM) performed in vector magnetic fields promises atomic scale imaging of magnetic structure, providing complete information on the local spin texture of a sample in three dimensions. Here, we have designed and constructed a turntable system for a low temperature STM which in combination with a 2D vector magnet provides magnetic fields of up to 5 T in any direction relative to the tip-sample geometry. This enables STM imaging and spectroscopy to be performed at the same atomic-scale location and field-of-view on the sample, and most importantly, without experiencing any change on the tip apex before and after field switching. Combined with a ferromagnetic tip, this enables us to study the magnetization of complex magnetic orders in all three spatial directions.

An in vitro study of the radiobiological effects of flattening filter free radiotherapy treatments.

Flattening filter free (FFF) linear accelerators allow for an increase in instantaneous dose-rate of the x-ray pulses by a factor of 2-6 over the conventional flattened output. As a result, radiobiological investigations are being carried out to determine the effect of these higher dose-rates on cell response. The studies reported thus far have presented conflicting results, highlighting the need for further investigation. To determine the radiobiological impact of the increased dose-rates from FFF exposures a Varian Truebeam medical linear accelerator was used to irradiate two human cancer cell lines in vitro, DU-145 prostate and H460 non-small cell lung, with both flattened and FFF 6 MV beams. The fluence profile of the FFF beam was modified using a custom-designed Nylon compensator to produce a similar dose profile to the flattened beam (6X) at the cell surface but at a higher instantaneous dose-rate. For both cell lines there appeared to be no significant change in cell survival. Curve fitting coefficients for DU145 cells irradiated with constant average dose-rates were 6X: α = 0.09 ± 0.03, ß = 0.03 ± 0.01 and 6FFF: α = 0.14 ± 0.13, ß = 0.03 ± 0.02 with a significance of p = 0.75. For H460 cells irradiated with the same instantaneous dose-rate but different average dose-rate the fit coefficients were 6FFF (low dose-rate): α = 0.21 ± 0.11, 0.07 ± 0.02 and 6FFF (high dose-rate): α = 0.21 ± 0.16, 0.07 ± 0.03, with p = 0.79. The results indicate that collective damage behaviour does not occur at the instantaneous dose-rates investigated here and that the use of either modality should result in the same clinical outcome, however this will require further validation in vivo.

[Mesothelioma of the pleura and peritoneum. Diagnostic and therapeutic sequelae]. / Mesotheliom der Pleura und des Peritoneums. Diagnostische und therapeutische Folgerungen.

In patients with pleural or peritoneal mesothelioma, surgery is a technically difficult procedure. Whereas those rare forms of localized pleural mesotheliomy are being detected incidentally and can be cured by complete resection, most patients with diffuse malignant mesothelioma present with an advanced stage of disease. Most of these patients survive less than 12 months irrespective of the treatment modality. For diffuse pleural mesothelioma, some favorable prognostic factors were identified: IMIG (International Mesothelioma Interest Group), stages I and II, epithelial type, age under 50, female gender. In IMIG stages I and II, extended pleuropneumonectomy followed by chemo- and/or radiotherapy is recommended. For this subset of patients, a median survival time of between 20 and 30 months is reported. Pleurectomy and decortication are recommended as palliative surgical strategies against pleural effusion. In patients with technically inoperable infiltration of the thoracic wall, irradiation is helpful; sometimes partial remission and relief of pain can be achieved by chemotherapy.

[Lung metastases: tumor reduction as an oncologic concept]. / Lungenmetastasen: Tumorreduktion als onkologisches Konzept.

The principle of surgery for lung metastases is the removal of all lesions in the lung that are either visible or detectable by palpation. This may be combined with complete dissection of all ipsilateral lymph nodes. Therefore, "tumor reduction" rather than "complete" or "radical resection" may be an adequate description of this surgical approach. Since the dissemination of--macroscopically not detectable--tumor cells represents the major mannerism of every metastatic disease, any local therapy appears to be a discrepancy. However, in most cases the rationale of surgery for lung metastases is the lack of effective systemic therapy and the low morbidity of surgery, along with up to 60% 5-year survival rates.

[Treatment strategy in pleural mesothelioma]. / Behandlungsstrategie beim Pleuramesotheliom.

The development of diffuse malignant pleural mesothelioma is associated with exposure to asbestos. The surgical treatment comprises a radical pleuropneumonectomy with resection of the pericardium and diaphragm (P3D) or palliative pleurectomy/decortication of the tumor. The prognosis in general is poor. P3D is most effective in patients with epithelial mesothelioma at an early stage. Complete resection has the best prognosis. Palliative tumor decortication is restricted to symptomatic patients with acceptable performance status. The prognosis of patients after radical resection is not significantly different from patients with pleurectomy/decortication. Preliminary results of multimodal therapy concepts, including additional chemo- and/or radiotherapy, suggest an improvement in survival. Nevertheless, so far treatment has been focused on the palliation of clinical symptoms like pain and dyspnee.

[Incomplete resections in bronchial carcinoma: morbidity and prognosis]. / Inkomplette Resektionen bei Bronchialcarcinom: Morbidität und Prognose.

Residual tumor (R1) was proven at the proximal bronchial resection margin in 88 (3.6%) of 2464 cases of lung cancer following lung resection and standard lymph node dissection. Postoperative complications (8%) were: fistula of the bronchial suture line (n = 7), bleeding (n = 2) and heart luxation (n = 1). The in-hospital mortality was 16.6%. Causes of death were: bronchial fistula (n = 7), erosion of the pulmonary artery (n = 4), respiratory failure (n = 1), and empyema (n = 1). Forty-three patients received postoperative radiation therapy. Median survival of all patients following incomplete resection was 16 months, compared to 37 months following complete resection (P < 0.001). Length of survival was independent of tumor stage, histology, site of infiltration and postoperative radiation. In conclusion, in resection for lung cancer clear margins should be verified by intraoperative frozen section. In the case of residual tumor at the bronchial resection margin, wider resection is mandatory in stage I and II if the patient meets the functional criteria. Even in stage III a and III b prognosis is significantly better after complete resection than R1-resection; the difference, however, is smaller than in lower stages.

[Radical surgery and lymph node dissection in bronchial carcinoma]. / Radikalität und Lymphknotendissektion beim Bronchialkarzinom.

Lymphatic spread of bronchial carcinoma can involve each position in the mediastinum. Localisation of the primary tumor has no influence. Metastatic skipping of topographical lymph node positions is not calculable. Therefore, systematic mediastinal lymph node dissection includes all ipsilateral compartments of the mediastinum. It is also possible to reach contralateral sides. In right-sided thoracotomies, the lymph node dissection is standardised. Mobilising the aortic arch and the large vessels also allows from a left-sided approach a complete mediastinal dissection. The surgical technique is described. Perioperative morbidity does not increase. Systematic mediastinal lymph node dissection is the golden standard for the evaluation of an exact pN stage. The stage-related survival rate is significantly improved. Therefore, the systematic mediastinal lymph node dissection should be a standard in the surgical therapy of bronchial carcinoma.

[Results of surgical therapy of bronchial carcinoma in advanced age]. / Ergebnisse der chirurgischen Therapie des Bronchialkarzinoms im höheren Lebensalter.

Surgery is the treatment of choice in patients with non-small cell lung cancer stages I-IIIA. This is not restricted to younger patients, it may also be true for elderly ones. 6907 patients suffering bronchial carcinoma were analysed at the Thoraxklinik Heidelberg-Rohrbach (10/1984-12/1994). 2464 patients underwent resection of bronchial carcinoma. The age distribution was as follows: 0-64 years (n = 1734), 65-74 years (n = 662), 75-85 years (n = 67), older than 85 years (n = 1). Lobectomy was the most common type of resection for all patients. The frequency of pneumonectomy was lower in older patients, while the relative proportion of segmental resections was higher. The 30-day mortality was 6% for patients younger than 64 years and 10% for patients older than 65 years. For the latter group, the 5-year-survival probability was 44% for the combined p-stages I and II, and 19% for p-stage IIIA. In conclusion, the results indicate that, under the condition of a precise preoperative risk-to-benefit evaluation, surgical treatment of bronchial carcinoma is also indicated for elderly patients.