Biomedical subjects

R Krempien

Publications and source records attributed to R Krempien.

31 records · Page 2Linked to original sources

PubMed2002

Daily patient set-up control in radiation therapy by coded light projection.

Advances in conformal radiation therapy to control disease via dose escalation are challenged by set-up uncertainties. Recently, techniques have been developed to use surface features to evaluate the patient's position and correct it where necessary. The aim of this study was to use the patient's surface as a tool for daily set-up control and monitoring. We use a surface scanner based on the projection of coded light to receive--in a daily routine--a large amount of surface points which enables us to register the CT-based planning data with the patients current position. By superimposing current and planned volumes, a volume of congruency was obtained. An error below 1 mm was considered acceptable. In cases where set-up was not satisfactory a map of the surface comparison was evaluated showing the areas of missing alignment. According to this information a manual repositioning was performed. This procedure was repeated until the error was acceptable. No more then 3 repetitions where necessary to obtain an acceptable result. The whole procedure including registration, calculation and visualization took about 20 sec for one repetition. The use of structured light projection in the daily set-up control and monitoring proved to be a noninvasive, easy, quick, inexpensive and reliable solution.

Data Collection↗

PubMed2002

Integration of intraoperative radiotherapy (IORT) dose distribution into the postoperative CT-based external beam radiotherapy (EBRT) treatment planing.

In the treatment of malignant disease external beam radiation therapy (EBRT) is often combined with surgery. Intraoperative radiotherapy (IORT) improves the local control by dose escalation. For reasons of recording, improvement and security of the intervention, it would be necessary to merge the IORT-dose distribution with the postoperative CT-based EBRT-planing. The aim of this work was to develop a method to reconstruct the IORT field and register it with the postoperative planing CT. This enables the reconstruction of the IORT dose distribution and merge it with the CT-based EBRT planing data. We use a surface scanner to receive a large amount of surface points which enables us reconstruct the IORT-field and to register it with the CT-based EBRT planning data. Scanning and calculation time is not over 2 seconds, depending mainly on the CPU power. The error of a single point is below 1 mm. The density of the point cloud is approx. 4 per mm2. In this paper we give an overview of our experimental setup and the accuracy of the method.

Brachytherapy↗

PubMed2001

Correlation of intraoperatively irradiated volume and fibrosis in patients with soft-tissue sarcoma of the extremities.

PURPOSE: To investigate the influence of intraoperatively irradiated volume on soft-tissue fibrosis. METHODS AND MATERIALS: Fifty-three patients with soft-tissue sarcoma of the extremities were treated with intraoperative radiotherapy (IORT) (median dose 15 Gy) and postoperative fractionated therapy (median dose 46 Gy). The median follow-up was 41.5 months (range 18-94). Late toxicity was classified according to the LENT-SOMA criteria. A Cox regression model was calculated to identify the parameters that could influence soft-tissue fibrosis Grade 3 or 4. Five parameters were observed: extent of surgical procedure, IORT in case of recurrence, extent of IORT volume, extent of IORT dose, and extent of postoperative volume. In addition, a logistic regression model was calculated to demonstrate the relationship between the IORT volume and fibrosis development. RESULTS: The overall survival rate after 5 years was 84%. The actuarial tumor control rate was 90% after 5 years. Eleven patients developed soft-tissue fibrosis. Five patients developed Grade 3 fibrosis and 1 patient developed Grade 4 fibrosis. Only the IORT volume had a significant influence on Grade 3 or 4 fibrosis development. An IORT volume of 210 cm(3) conveyed a 5% risk (confidence interval 1-20%) of the development of severe fibrosis. The risk of severe Grade 3 or 4 fibrosis increased to 50% (confidence interval 15-80%) if a volume of 420 cm(3) was irradiated. CONCLUSION: The effect of volume in patients treated with IORT was remarkable. The ratio of side effects was relatively low. The risk of soft-tissue Grade 3 or 4 fibrosis increased with the extent of the IORT volume. Compared with the literature, IORT provides excellent local control in these patients.

Adolescent↗

PubMed2001

Results of chest wall reirradiation using pulsed-dose-rate (PDR) brachytherapy molds for breast cancer local recurrences.

PURPOSE: We report in a retrospective study on the effect and toxicity of chest wall reirradiation using pulsed-dose-rate (PDR) afterloading molds. METHODS AND MATERIALS: Between 1993 and 1999, a total of 58 patients were treated. All patients presented with locally recurrent breast cancer (31 patients had concomitant distant metastases) after mastectomy and a previously completed course of radiation therapy (median, 54 Gy; range, 36-70). Indication for reirradiation was a progressive macroscopic skin recurrence in 30 cases and an incomplete surgical resection in 28 patients. Standard treatment consisted of a split course with two fractions of 20 Gy (interval, 31 days). The reference dose was prescribed to the skin surface at 5 mm distance from the source. PDR brachytherapy (37 GBq, (192)Ir) was carried out after geometric distance optimization with 0.5-1 Gy/pulse/h. The irradiated median area was 423 cm(2) (range, 100-919). The median follow-up was 18 months (range, 7-84). RESULTS: The actuarial 1-, 2- and 3-year local recurrence-free survival rates in patients treated for macroscopic disease (microscopic disease in parenthesis) were 89% (96%), 81% (85%), and 75% (71%). Local control was obtained in 24/30 (22/28) patients. Twenty-nine of the 34 patients (85%) who deceased during follow-up were locally controlled. 9/58 patients experienced Grade III acute toxicity, 35/58 patients Grade III (29/58 telangiectasia, 6/58 contracture), and 4/58 Grade IV late toxicity (RTOG/EORTC). CONCLUSION: Reirradiation of the chest wall using PDR brachytherapy molds is effective and provides a high local control rate with acceptable toxicity.

Adult↗

PubMed2000

3D norm data: the first step towards semiautomatic virtual craniofacial surgery.

When planning craniofacial surgical interventions, the ideal appearance of the patient is very important. The final appearance should be as close as possible to that which the patient would have if he/she were without defects. Our first step towards achieving this is to build a database containing sets of three-dimensional CT images that allows for comparison of the shape of a patient with defects to the typical shape of an age- and sex-matched "average" person without defects. We started to collect CT data from patients without pathologies and, in co-operation with two radiology institutes (in Mannheim and Heidelberg), over 100 CT data sets have now been collected and classified according to age and sex. It is necessary to choose an appropriate statistical method to calculate the norm data from the different data sets. Based on the statistical method, an age- and sex-matched "average" model of the anatomy will be created.

Adolescent↗

PubMed2000

[Computer-assisted oral, maxillary and facial surgery].

BACKGROUND: Methods from the area of virtual reality are used in oral and maxillofacial surgery for the planning and three-dimensional individual simulation of surgeries. SIMULATION: In order to simulate complex surgeries with the aid of a computer, the diagnostic image data and especially various imaging modalities (CT, MRT, US) must be arranged in relation to each other, thus enabling rapid switching between the various modalities as well as the viewing of mixed images. Segmenting techniques for the reconstruction of three-dimensional representations of soft-tissue and osseous areas are required. We must develop ergonomic and intuitively useable interaction methods for the surgeon, thus allowing for precise and fast entry of the planned surgical intervention in the planning and simulation phase. SURGERY: During the surgical phase, instrument navigation tools offer the surgeon interactive support through operation guidance and control of potential dangers. This feature is already available today. Future intraoperative assistance will take the form of such passive tools for the support of intraoperative orientation as well as so-called tracking systems (semi-active systems) which accompany and support the surgeons' work. The final form are robots which execute specific steps completely autonomously. DISCUSSION: The techniques of virtual reality keep gaining in importance for medical applications. Many applications are still being developed or are still in the form of a prototype. However, it is already clear that developments in this area will have a considerable effect on the surgeon's routine work.

Computer Simulation↗

PubMed1999

[Possibilities of an open magnetic resonance scanner integration in therapy simulation and three-dimensional radiotherapy planning].

PURPOSE: A system for digital integration of an open MR scanner (0.23 T, Figure 1) in therapy simulation and 3D radiation treatment planning is described. METHOD: MR images were acquired using the body coil and various positioning and immobilization aids. A gradient echo sequence (TR/TE 320 ms/24 ms) was used to create axial and coronal data sets. Image distortions were measured and corrected using phantom measurements (Figure 2) and specially developed software. RESULTS: Maximal and mean distortions of the MR images could be reduced from 19 mm to 8.2 mm and from 2.7 mm to 0.7 mm, respectively (Figure 3 to 5, Table 1). Coronal MR images were recalculated in fan beam projection for use at the therapy simulator. Tumor and organ contours were transferred from the MR image to the digitally acquired and corrected simulator image using a landmark matching algorithm (Figure 6 and 7). For 3D treatment planning, image fusion of axial MR images with standard CT planning images was performed using a landmark matching algorithm, as well (Figure 8). Representative cases are shown to demonstrate potential applications of the system. CONCLUSION: The described system enables the integration of the imaging information from an open MR system in therapy simulation and 3D treatment planning. The low-field MR scanner is an attractive adjunct for the radio-oncologist because of the open design and the low costs.

Algorithms↗

PubMed1999

[MRI simulation of bronchogenic carcinomas using an open low-field MRI].

AIM: The initial target volume for primary radiation therapy of lung cancer is usually determined with the aid of computed tomography. Due to the axial CT-scans the simulation of the RT-field is often difficult. MRI in its superior ability to demonstrate and characterize soft tissue and its possibilities of multiplanar imaging can be beneficial. As MRI is less available and more expensive the use of MRI in radiotherapy planning is still restricted. With the introduction of open low-field MRI-systems there is now a cost-saving alternative. The aim of this study was the clinical evaluation of the use of a new open low-field MRI in radiotherapy planning of bronchogenic cancer. PATIENTS AND METHODS: Fifteen patients undergoing primary radiotherapy for lung cancer were studied using an open low-field MRI-system (Picker Outlook 0.23 Tesla). Conventional CT-assisted treatment planning was compared to a MRI-assisted procedure. Contours from coronary T1-weighted MRI-sections were superimposed onto the simulator radiograph using a subtrascope (MR-simulation). RESULTS: Open low-field MR-imaging using T1-weighted sequences resulted in excellent delineation of tumor masses from mediastinal fat, the airways and the vascular structures as well as the radial tumor infiltration into the vicinity of the lung (Figures 1a to 1c). This allowed an exact and reproducible transfer of tumor contours onto the simulator radiograph. The MR-simulation led to optimization in the field configuration in 5/15 patients (Figure 2). CONCLUSIONS: Open low-field MRI-systems can be very useful in treatment planning. They are less expensive and need less extensive rebuilding compared to high-field MRI-systems. In the radiotherapy planning of bronchogenic carcinoma the MR-simulation is reasonable and clinically practicable. One of the main advantages of open MRI-systems in comparison to CT and standard MRI-systems in radiotherapy planning is that there is a much greater variety of treatment positions.

Aged↗

PubMed1999

HDR-brachytherapy boost for residual tumour after external beam radiotherapy in patients with tracheal malignancies.

Seven inoperable patients with tracheal neoplasms received a high dose rate (HDR) brachytherapy boost (median 15 Gy, single dose 3-5 Gy) for residual tumour after external beam radiotherapy (median 50 Gy, 5 x 2 Gy/week). The median actuarial survival was 34.3 months. The 1-, 2- and 3-year actuarial survival rates were 85.7%, 85.7% and 32%. Local control was obtained in 5/7 patients. Late toxicity occurred in three patients (stenosis n = 2, hemorrhage n = 1). Our data indicate, that a HDR brachytherapy boost is effective and feasible.

Actuarial Analysis↗

PubMed1999

Age-related changes in insulin-like growth factor I and II in human femoral cortical bone: lack of correlation with bone mass.

The concentration of insulin-like growth factor-I (IGF-I) in human cortical bone declines with age, but the relevance of this decline for cortical bone turnover and bone mass is unknown. In the present study, we simultaneously assessed the concentration of IGF-I and -II in cortical bone matrix and histomorphometric parameters of bone mass and bone turnover in 125 samples from the proximal human femur shaft. Bone width decreased by 27% and porosity increased by 100% in female cortical bone between the fourth and the ninth decade. Similar, but weaker, changes tended to occur in male cortical bone. The concentrations of both IGF species were correlated with the percentage of osteons undergoing bone remodeling. However, despite age-related decreases in both IGF species in men and in IGF-I in women, neither of the IGFs accounted for age-related or age-independent variability in cortical porosity or bone width. In conclusion, these data suggest that the local concentrations of IGF-I and -II are related to cortical bone turnover. In contrast, our study provides no evidence for a major role of bone matrix IGF-I and -II as determinants of cortical bone mass in elderly individuals. Whether other components of the IGF system may be stronger determinants of cortical bone loss remains to be determined.

Adult↗

PubMed1998

Concentration of transforming growth factor beta in human bone tissue: relationship to age, menopause, bone turnover, and bone volume.

Transforming growth factor beta (TGF-beta) is thought to play an important role in bone metabolism, but its relationship to human bone turnover and bone mass has not been examined yet. In this study, we measured the concentration of TGF-beta in 811 samples of male and female bone from four representative sites of the human skeleton and in the supernatants of 72 short-term human bone marrow cultures from the iliac crest. The concentrations of TGF-beta1 and TGF-beta2 in the bone matrix were positively correlated with histomorphometric indices of bone resorption and bone formation and with serum levels of osteocalcin and bone-specific alkaline phosphatase. We also observed a positive association between the release of TGF-beta in the bone marrow cultures and serum osteocalcin. Changes in the rate of cancellous or cortical bone remodeling with age or menopause were accompanied by corresponding changes in skeletal TGF-beta. In contrast, there was no significant relationship between the concentration of TGF-beta and bone volume at any skeletal site. In conclusion, our study supports the hypothesis that TGF-beta plays an important role in human bone remodeling, but fails to demonstrate an association between the skeletal concentration of TGF-beta and human bone mass.

Aging↗

PubMed1992

Differential effects of platelet-derived growth factor isoforms on plasminogen activator activity in fetal rat osteoblasts due to isoform-specific receptor functions.

We examined receptor binding and metabolic effects of the platelet-derived growth factor (PDGF) isoforms AA, AB, and BB in cultures of osteoblastic cells from fetal rat calvaria. Saturation binding experiments demonstrated the presence of 6,000 binding sites for PDGF-AA, 42,000 for PDGF-AB, and 60,000 for PDGF-BB. Binding competition experiments were compatible with the recently postulated model of three PDGF receptor subtypes with differential affinity for the PDGF isoforms. The effects of the PDGF isoforms on DNA synthesis, collagen synthesis, and alkaline phosphatase activity in osteoblasts strictly correlated with the number of available binding sites. Accordingly, PDGF-BB was the most potent isoform, PDGF-AB was slightly less potent, and PDGF-AA was the least potent. In contrast, we found that PDGF-BB was less potent than PDGF-AB in increasing plasminogen activator activity in the osteoblast-conditioned medium. Our data strongly suggest that the PDGF receptor subtypes in fetal rat osteoblasts not only selectively bind one or more PDGF isoforms, but are also capable of responding differently to these isoforms.

Alkaline Phosphatase↗

PubMedDate not supplied

Contemporary role of modern brachytherapy techniques in the management of malignant thoracic tumors.

Sole brachytherapy for carcinoma of the lung is most often performed using high-dose-rate (HDR) remote afterloading equipment, which delivers the treatment within the tracheobronchial tree in an outpatient setting. It provides excellent, rapid palliation in advanced stages, and can also be used selectively for curative intent in early stages. In better-performance patients, fractionated external beam radiation therapy (EBRT) is preferred to brachytherapy as an initial treatment because it appears to provide a modest gain in survival, and more sustained palliation. In patients with centrally located tumors and limited extent of disease, the combination of external and endoluminal irradiation enables curative treatment options. Intraoperative brachytherapy may complement standard adjuvant treatment in incompletely resected, unresectable, or medically inoperable patients, and has the potential to improve local control in selected cases. Due to the rarity of the disease, the role of endoluminal brachytherapy in the treatment regimen of tracheal neoplasms is not yet clearly defined. The risk of fatal bleeding after endoluminal brachytherapy appears to be correlated with tumor localization and fraction size, but in the majority of cases fatal bleeds are caused by progression of local disease. The use of a distanceable applicator provides a central positioning of the source, prevents the delivery of high-contact doses to the mucosa, and may reduce toxicity. The standard technique for interstitial brachytherapy after breast-conserving surgery and adjuvant EBRT is the use of low-dose-rate (LDR) brachytherapy, but it may also be applied by means of pulsed-dose-rate (PDR) or HDR techniques. Prospective trials comparing different boost techniques and indications are needed to define more precisely the subgroup of patients who are most suitable for interstitial brachytherapy. Reirradiation of chest wall local recurrences using brachytherapy molds is effective and provides a high local control rate with acceptable toxicity.

Brachytherapy↗