RESUMO
The manipulation of the antiferromagnetic interlayer coupling in epitaxial Fe/Cr/Fe(001) trilayers by 5 keV He ion beam irradiation has been investigated. It is shown that even for irradiation with low fluences a drastic change in strength of the coupling appears. For thin Cr spacers (below 0.6-0.7 nm) it decreases with fluence, becoming ferromagnetic for fluences above 2x10(14) ions/cm(2). The effect is connected with the creation of magnetic bridges in the layered system due to atomic exchange events caused by the bombardment. For thicker Cr spacers an enhancement of the antiferromagnetic coupling strength is found. A possible explanation of the enhancement effect is given.
RESUMO
BACKGROUND: Hepatic metastases of neuroendocrine tumors demand differentiated therapeutic management due to the unique natural course and hormone secretion of the tumors. AIM: The purpose of the prospective nonrandomized study was to review the institutional experience with surgical treatment of hepatic neuroendocrine metastases. PATIENTS AND METHODS: From September 1992 until March 1996 29 consecutive patients with neuroendocrine tumors have been evaluated for surgical treatment of liver metastases. Of them, 11 (37.9%) fulfilled criteria for surgical treatment of hepatic secondary tumors. Extensive preoperative workup was carried out. Patients were divided in groups for curative or palliative resection. Liver transplantation was carried out in selected patients with disseminated liver metastases. RESULTS: Of 29 patients 4 (13.7%) underwent curative resection and in 3 patients (10.3%) palliative resection was performed. The patients who underwent curative resection are all biochemically and clinically tumor free at a mean postoperative follow-up of 22.3 months. Two patients who underwent palliative resection are alive at 40 and 29 months, respectively. From 12 patients evaluated for liver transplantation 4 were considered as suitable candidates. CONCLUSIONS: Liver resection can be recommended in patients with hepatic metastases of neuroendocrine tumors in terms of potential survival prolongation and palliation. Liver transplantation is generally acceptable treatment in highly selected group of these patients. Long-term results have to be awaited before definitive proof of the beneficial effect of surgical treatment.
