Interface superconductor with gap behaviour like a high-temperature superconductor.

The physics of the superconducting state in two-dimensional (2D) electron systems is relevant to understanding the high-transition-temperature copper oxide superconductors and for the development of future superconductors based on interface electron systems. But it is not yet understood how fundamental superconducting parameters, such as the spectral density of states, change when these superconducting electron systems are depleted of charge carriers. Here we use tunnel spectroscopy with planar junctions to measure the behaviour of the electronic spectral density of states as a function of carrier density, clarifying this issue experimentally. We chose the conducting LaAlO3-SrTiO3 interface as the 2D superconductor, because this electron system can be tuned continuously with an electric gate field. We observed an energy gap of the order of 40 microelectronvolts in the density of states, whose shape is well described by the Bardeen-Cooper-Schrieffer superconducting gap function. In contrast to the dome-shaped dependence of the critical temperature, the gap increases with charge carrier depletion in both the underdoped region and the overdoped region. These results are analogous to the pseudogap behaviour of the high-transition-temperature copper oxide superconductors and imply that the smooth continuation of the superconducting gap into pseudogap-like behaviour could be a general property of 2D superconductivity.

Electric-field-induced polar order and localization of the confined electrons in LaAlO3/SrTiO3 heterostructures.

With ellipsometry, x-ray diffraction, and resistance measurements we investigated the electric-field effect on the confined electrons at the LaAlO3/SrTiO3 interface. We obtained evidence that the localization of the electrons at negative gate voltage is induced, or at least enhanced, by a polar phase transition in SrTiO3 which strongly reduces the lattice polarizability and the subsequent screening. In particular, we show that the charge localization and the polar order of SrTiO3 both develop below ∼50 K and exhibit similar, unipolar hysteresis loops as a function of the gate voltage.

[Unusual infection complication of total hip arthroplasty]. / Neobvyklá infekcná komplikácia totálnej náhrady bedrového klbu.

Authors present the case history of a 66-year old patient after repeated reimplantations of the THA with a deep infect caused by a rare aetiological agent (Serratia marcescens) associated with a pyogenic sinus. They describe the disease history, therapeutic procedure, complications associated with the surgery as well as postoperative course after the reimplantation of a customized total hip replacement. In the conclusion they state that in case of an infected total hip arthroplasty the treatment is focused on the salvage of the infection process and preservation of the function of the affected limb. Of essential importance is surgical revision with a radical removal of necrotic tissues and hardware in combination with an intensive parenteral antibiotic administration.

Is the standardized helmet technique adequate for irradiation of the brain and the cranial meninges?

PURPOSE: To evaluate whether the standardized helmet technique is adequate to reliably cover the clinical target volume (whole brain including cranial meninges) during treatment planning and treatment delivery. METHODS AND MATERIALS: In 21 patients undergoing irradiation of the brain in acute lymphoblastic leukemia or primary cerebral lymphoma, the coverage of the clinical target volume was checked with a repeat computed tomography (CT) in the treatment position (head fixation with face mask). The accuracy of field alignment was quantitatively assessed with sequential verification films. For each patient, linear and rotational discrepancies were measured between the simulation and first check film, and between five consecutive verification films. RESULTS: Coverage of clinical target volume. In 11 cases (52%), the CT examinations showed that parts of the subfrontal region and midcranial fossa were not included by the field assigned under simulation. Accuracy of field alignment. For the total group of patients, all deviations were normally distributed with mean values between -1.2 mm and 1.5 mm and standard deviations of 2.9 mm to 3.7 mm for linear discrepancies, and 0.3 degrees +/- 3.2 degrees for rotational discrepancies. For all patients, deviations were similar for the transition from simulation to the treatment machine and for subsequent treatment delivery, with 50% and 95% of absolute differences being less than 2.0 mm and 6.5 mm, respectively. Maximum linear deviations were less than 9.5 mm. CONCLUSIONS: The currently used helmet technique is inadequate to cover the clinical target volume. Repeat CT examinations are a useful method to delineate the clinical target volume on an individual patient basis. In addition, statistical fluctuations of field displacements up to 1.0 cm have to be considered when prescribing safety margins for reliable coverage of the clinical target volume during treatment planning and delivery.

Reproducibility of field alignment in difficult patient positioning.

PURPOSE: Quantitative assessment of the accuracy of field alignment in a homogeneous group of patients with difficult positioning (postoperative irradiation after total hip replacement). METHODS AND MATERIALS: In 95 patients linear and rotational discrepancies were measured between the simulation and first check film and between five consecutive verification films. RESULTS: For the total group of patients, all deviations were normally distributed with mean values of approximately zero and standard deviations of 4.0-8.0 mm (linear discrepancies) and 3.5-5 degrees (rotational discrepancies). Deviations were similar for the transition from simulator to the treatment machine and for subsequent treatment delivery, with 50% and 95% of absolute differences being less than 5 mm and 15 mm, respectively. CONCLUSIONS: Our analysis indicates that statistical fluctuations are considerably more important than errors introduced at start of treatment. Therefore, a first check film seems to be inadequate to predict the expected inaccuracies for the whole course of treatment. In addition, our results should help to prescribe appropriate safety margins for patients with difficult positioning.

Repeated CT examinations in limited volume irradiation of brain tumors: quantitative analysis of individualized (CT-based) treatment plans.

Deviations of the position of the isocenter were quantitatively assessed for CT-based limited volume irradiation of brain tumors. Of the linear deviations, 95% were within 10 mm and 3 mm during treatment planning and delivery, respectively. The application of face masks before CT planning improved the accuracy of field alignment. Repeated CT examinations seemed to be more important after simulation than during treatment delivery.

Accuracy of field alignment in radiotherapy of head and neck cancer utilizing individualized face mask immobilization: a retrospective analysis of clinical practice.

Deviations between simulation and first check films were quantitatively assessed for 95 unselected head and neck cancer patients. All measured deviations--calculated on the basis of a total of 190 simulation and 380 verification films--were normally distributed, with mean values of 0-3 mm and standard deviations of 3-5 mm. Of the absolute deviations, 50% and 95% were within 3 mm and 9 mm, respectively. These results should be considered in clinical practice when prescribing safety margins and adequate cut off doses for sparing critical organs in head and neck cancer.

Superior efficacy in suppression of heterotopic bone formation using fractionated irradiation of 5 x 2 Gy compared to a single dose of 7 Gy. An experimental study in rats.

Postoperative irradiation of the operative field is an established method to prevent heterotopic ossification in total hip arthroplasty. In this study two theoretical dose-equivalent regimens of radiation therapy were compared. Allogenic bone matrix was implanted in both thighs of 50 adult male Wistar rats to induce heterotopic ossification. Immediately after operation the implants of 40 animals were irradiated using a single-dose of 7 Gy or 5 fractions of 2 Gy each. Ten rats served as a controlgroup and did not undergo irradiation. Radiation therapy with 5 x 2 Gy led to a highly significantly better suppression of heterotopic ossification than irradiation with 1 x 7 Gy (p < 0.001; paired-t-test). Single-dose irradiation reduced the mean calcium contents to 138.87 +/- 22.84 micrograms Ca2+/mg implanted bone matrix; fractionated irradiation obtained a reduction to 63.35 +/- 21.16 micrograms Ca2+/mg implanted bone matrix. In thigh implants not exposed to irradiation the mean calcium content was 191.50 +/- 11.46 micrograms Ca2+/mg implanted bone matrix. Radiographically better suppression of bone formation could be documented after irradiation with 5 x 2 Gy compared to 1 x 7 Gy and non-irradiated implants. The histological aspect of the explanted specimens showed quantitatively more new bone formation in the non-irradiated controls than in both irradiation groups. In view of experimentally demonstrated better effects, as well as the reduced side effects, fractionated irradiation appears preferable.

[Incorporation of bone allografts with the use of Octopus revision system in total hip arthroplasty]. / Inkorporácia kostných alostepov pri pouzití revízneho systému Octopus.

PURPOSE OF THE STUDY: The study describes the revision arthroplasty of hip joints with grade III acetabular defects, as rated according to Paprosky, employing morsellized bone allografts and the Octopus revision acetabular system. MATERIAL: In the period from 1998 to 2002, a total of 8297 operations were performed in our Department; of these 1527 (18.4%) were total hip replacements. In this group, 267 (15.5%) revision arthroplasties were carried out, with the the Octopus revision system being used in 32 patients (age range, 30 to 79 years; average age, 60.3 years). The average period between the initial surgery and reimplantation was 6.5 (range, 2-14) years. METHODS: Acetabular defects were filled with morsellized cancellous bone allografts (one to three femoral heads per patient) obtained from the tissue bank. In nine patients, allografts were combined with hydroxypatite (Biovan). Osteointegration of the bone allografts and, if it occurred, loosening of the implant were checked by X-ray examination. RESULTS: The patients were examined at intervals of two months. The average Harris hip score was 76 points at 1 to 3 years. None of the patients had deep post-operative wound infection; in one patient, the distal hook of the Octopus system broke off. The complete incorporation of allografts was seen on X-ray images in 28 patients; at follow-up, a radiolucent zone between the acetabular bed and the allograft was still visible in four patients. No implant loosening was recorded. DISCUSSION: The Octopus system has an advantage of using morsellized allografts instead of solid ones that are associated with poorer incorporation and a higher risk of loosening. The remodeling of an allograft below the ring leads to the production of bone tissue, which is useful if revision arthroplasty were to be performed. CONCLUSION: Based on their experience, the authors regard the Octopus revision system with the use of morsellized bone allografts from the tissue bank as an effective surgical procedure for the treatment of Paprosky grade III acetabular defects. The allografts below the ring are fully incorporated and remodeled; as a result the initial defect is gradual filling with the patient's own tissue, which has very good clinical outcomes.

Long-term follow-up of Syme amputations for peripheral vascular disease associated with diabetes mellitus.

Ten patients underwent Syme amputation for diabetic peripheral vascular disease between 1980 and 1986 and were observed postoperatively for an average of 5 years. Surgical wounds healed in only five of the 10 patients; they were then fitted for a permanent Syme's prosthesis. All failures resulted from the inability to heal the surgical incisions primarily. The clinical records of these patients were retrospectively analyzed for predictors of successful clinical outcome. The ischemic index, grade of the lesion, initial wound treatment, and presence of the infection at the time of amputation were not found to be reliable predictors of a successful level of amputation. Clinical assessment of both the vascular and nutritional status of the patient was necessary to predict a successful result at this level of amputation.

[Dosage specification at the ICRU reference point: the consequences for clinical practice. International Commission on Radiation Units and Measurements]. / Dosisspezifikation im "ICRU-Referenzpunkt": Auswirkungen auf die klinische Praxis.

In the Department of Radiotherapy, University of Tübingen, dose specification is performed according to the new ICRU recommendations since June, 1991. The purpose was to prescribe, record and report photon beam therapy in a consistent way applicable to most clinical situations and to provide uniform criteria for a comparison of treatment results from different radiotherapy centers. For "level 2" plans (including CT planning), the concept of dose specification has been changed to the "ICRU reference point" instead of to form the isodose encompassing the target volume as we did previously. A total of 24 representative treatment plans have been analyzed to assess the consequences of this change on dose prescription, treatment technique, and the size of the irradiated volume. Our results revealed that the prescription of single and total doses have to be individually adjusted according to the specific treatment plans. ICRU recommendations on dose homogeneity may significantly affect treatment technique and field sizes. Small deviations in dose prescription may be of particular influence on late responding normal tissues ("double trouble" due to simultaneous adjustment of single and total doses). Detailed comparisons of individual treatment plans with respect to physical, biological, and clinical data are obviously necessary in order to make sure that the outcome of a radiation treatment is not deviating too much from the clinical experience based on the former dose specification concept.

[Suppression of heterotopic ossification: single-dose versus fractionated irradiation--animal study]. / Suppression heterotoper Ossifikationen: Single dose versus fraktionierte Radiatio--eine tierexperimentelle Studie.

Periarticular ossification is one of the main problems of total hip replacement. Irradiation with megavolt photons is known to be a well recognized means of prevention of heterotopic ossification. So far only little scientific basis exists about the most favourable way of radiotherapy for prevention of ectopic ossification. In this study two theoretically equivalent doses are compared. Allogeneic bone matrix was implanted into both thighs of 50 adult male Wistar rats for experimental induction of heterotopic ossification. Immediately after operation the thigh implants were irradiated with a single dose of 7 Gy or a total dose of 10 Gy given in 5 fractions of 2 Gy each. In the model of matrix-induced osteogenesis in rats fractionated irradiation by 5 x 2 Gy leaded to a highly-significant (p = 0.001) better suppression of ectopic ossification compared to irradiation by 1 x 7 Gy. Once-only irradiation with 1 x 7 Gy leads to a reduction of the calcium contents by 27.5%, split irradiation by 5 x 2 Gy obtained a reduction by 66.9% compared to the calcium contents of thigh implants not exposed to radiation. In view of experimentally proven better effects, fractionated irradiation has to be preferred to single dose radiation also considering less side effects in split radiation.

[Prevention of heterotopic ossification following cementless hip replacement using 5 x 2 Gy fractionated irradiation. A prospective study]. / Prävention heterotoper Ossifikationen nach zementfreiem Hüftgelenksersatz durch fraktionierte Radiatio mit 5 x 2 Gy. Eine prospektive Studie.

97 patients were treated with cementless custom-made total hip replacement of the Aldinger type for osteoarthritis of the hip. All were prophylactically treated by radiotherapy with 5 x 2 Gy. 10.3% showed heterotopic ossification. 8 patients showed ossification grade I by the Arcq scale and 2 of grade II. Clinical results according to the Merle d'Aubigné score were good or very good in over 90% at one year postoperatively. One patient showed loosening of the femoral stem caused by sinking-in of the custom-made implant. During the revision procedure there were no signs of radiation induced damage to the implant bed. Negative sequelae to the bony implant bed by prophylactic radiotherapy cannot be detected on radiological assessment. Side effects like delayed wound healing or alteration of local immune status with subsequent infection which are commonly discussed, were not seen. Fractionated irradiation is an effective means of prophylaxis of heterotopic ossification.

The suppression of heterotopic ossifications: radiation versus NSAID therapy--a prospective study.

This prospective, randomized study compares the effect of postoperative irradiation and nonsteroidal anti-inflammatory drug (NSAID) therapy on the prevention of heterotopic ossifications after the implantation of a total hip endoprosthesis. A total of 154 operations were performed; one group of patients underwent radiation treatment of 3 x 3.3 Gy, and the other group took 3 x 50 mg of diclofenac per day over a period of 3 weeks. Average age, sex, preoperative diagnosis, and risk factors were similar in both groups. Postoperative radiation began on average 2.9 days after operation, and the radiation therapy was finished on average within 3.8 days. NSAID prophylaxis was begun on the first postoperative day. Heterotopic ossifications occurred in two of the patients who had undergone postoperative prophylaxis by radiation. In both cases, the ossification was Brooker I, and there was no functional impairment. There were no ossifications of Brooker II-IV in this group. One patient had a Staphylococcus epidermidis infection, and fistula revision had to be carried out; the prosthesis could be left in place. In the group treated with NSAID, 16 heterotopic ossifications stage Brooker I and 2 stage Brooker II could be detected. Eleven patients stopped the treatment because of gastrointestinal problems. Both postoperative radiation and NSAID therapy have proved to be effective prophylactic methods. In direct comparison, radiation prophylaxis by 3 x 3.3 Gy proved to be slightly more successful than NSAID prophylaxis.