Biomedical subjects

V Rudat

Publications and source records attributed to V Rudat.

42 records · Page 3Linked to original sources

PubMed1994

Influence of the positioning error on 3D conformal dose distributions during fractionated radiotherapy.

The influence of patient immobilization error on 3D planned conformal radiation therapy in tumors of the thorax and pelvis was studied. The mean positioning error in 43 patients with carcinomas of the thorax and pelvis undergoing 3D conformal radiotherapy (laser supported alignment, no immobilization device) was measured. A total of 194 portal films were superposed with the corresponding simulator radiographs according to anatomic landmarks and using a subtrascope. x-, y- and z-axis deviation was determined within a coordinate system. Using specialized software including Fourier transformation the mean positioning error was employed to recalculate the dose distributions of all cases under the influence of random (Gaussian) immobilization uncertainty. The mean two-dimensional positioning error using the data from all patients was 5.5 (+/- 3.7) mm. The distribution was Gaussian. Dose volume histograms (DVHs) of each patient with and without consideration of positioning uncertainty were compared on the base of tumor control probability estimations (TCP) using published DVH reduction and TCP algorithms. Inclusion of the positioning error resulted in a mean decrease in TCP (given as the difference between the TCP assuming no positioning error and the TCP modified by the positioning error) of 2% in a series of esophagus carcinomas and of 5% in the prostate carcinomas when looking at gross tumor volume (GTV), only. Planning target volume (PTV) exhibited a relative decrease in TCP of 5% and 11%, respectively.

Algorithms↗

PubMed1993

Ultrasound image properties influenced by abdominal wall thickness and composition.

The influence of different examination conditions on the ultrasound B-scan was investigated using a tissue-mimicking phantom and a computerized ultrasound system. Several fat-muscle combinations simulated differences in abdominal wall thickness and composition. The analysis of the ultrasound images was performed by use of statistical parameters applied in ultrasound tissue characterization, thereby the influence of the abdominal wall thickness and composition on the ultrasound image brightness, microtexture, and macrotexture (image sharpness) was studied. An increasing fat path caused a decrease in ultrasound image brightness and microtexture. The macrotexture was largely unaffected. Muscle tissue alone had a weak influence on the microtexture parameters. Our results show that an increase in the fat layer of the abdominal wall causes a darker, unsharp image and may lead to false diagnoses, especially in adiposity. Furthermore, fat-muscle combinations caused a decrease in image brightness and contrast. The decrease in these image properties was dependent on the thickness of the combination as well as on the frequency of the transducer. The effects were stronger for high-frequency transducers.

Abdominal Muscles↗

PubMed1992

Adeno-associated virus sensitizes HeLa cell tumors to gamma rays.

Infection with the helper virus-dependent human parvovirus adeno-associated virus (AAV) is known to interfere with cellular transformation in vitro and oncogenesis in vivo. Here we report on sensitization to gamma irradiation by AAV infection of cells in culture and of tumors established from HeLa cells grafted into immunodeficient (nude) mice: infection of HeLa cells with AAV type 2 enhanced cell killing and reduced plating efficiency after irradiation compared with uninfected cells. Similarly, HeLa cell tumors in nude mice displayed a reduced growth rate and were more sensitive to gamma irradiation when the animals were infected with AAV type 2 prior to or after tumor cell inoculation. Since no pathogenicity is known for AAV, the ability of this virus to render radiotherapy of human tumor cells more efficient may up open novel approaches in cancer treatment.

Animals↗

PubMed1991

[Influence of abdominal wall composition and thickness on ultrasound B scan].

Using a tissue-mimicking phantom and a computerised sonography system an ultrasound b scan analysis was performed. The images were acquired with different fat-muscle combinations as ultrasound wave path. These are simulations of a different composition or thickness of the abdominal wall. The analysis of the ultrasound images was performed using mathematical statistical parameters for ultrasound tissue characterisation. We examined the influence of the thickness or composition of the abdominal wall on ultrasound image brightness, microtexture and macrotexture. A dependence of ultrasound image brightness and microtexture on the thickness of the fat path was observed. Muscle tissue shows only a weak influence on the microtexture of the ultrasound image. These data demonstrate that a thick fat layer leads to a darker and diffuse image. This disturbs the evaluation e.g. of the liver parenchyma by analysis of the echo structure and may lead to false diagnoses especially in adiposity.

Abdominal Muscles↗

PubMed1991

Glucose uptake, perfusion, and cell proliferation in head and neck tumors: relation of positron emission tomography to flow cytometry.

The uptake of 18F-Deoxyglucose (FDG) was studied in vivo in relation to the proliferation rate of human head and neck tumors. Forty-two patients with histologically proven squamous-cell carcinoma of the head and neck and four patients with metastases of head and neck tumors were examined with PET and FDG prior to surgery. In 35 of these patients, a flow cytometric analysis of the DNA content and the proliferation rate was done using one-dimensional flow cytometry rate was done using one-dimensional flow cytometry (DAPI staining). In 17 cases, perfusion studies with 15O-labeled water were performed. Twenty-seven specimens were evaluable by flow cytometry. The analysis of the distribution of the FDG uptake revealed two groups, showing a high and a lower uptake pattern. In both groups the FDG uptake and the proliferation rate were correlated with an r-value of 0.64 and 0.8 respectively. However, the slope of the regression function was flat. No correlation was found between the perfusion and the proliferation rate. It is suggested that these differences in uptake in histologically identical tumor populations may correspond to differences at the molecular level, e.g., differences in the amount of the glucose carrier, perhaps caused by oncogenic transformation.

Carcinoma, Squamous Cell↗

PubMedDate not supplied

Role of multimodal treatment in oropharynx, larynx, and hypopharynx cancer.

Due to recent advances in radiation fractionation, radiochemotherapy, and conservative surgical techniques, the concept of multimodal therapy in head and neck cancer is currently changing. The recently published RTOG Phase III trial 9003, with 1,113 patients accrued, showed that hyperfractionation and accelerated fractionation with concomitant boost are more efficacious than standard fractionation for locally-advanced head and neck cancer. Acute, but not late, toxicity was also increased. Three meta-analyses have suggested that the impact of chemotherapy in head and neck cancer is small but is highly associated with the timing of therapy. Concomitant administration of radiation therapy and chemotherapy led to an absolute benefit in 5-year survival of about 10%. This finding has been further supported by recently published randomized prospective trials comparing concomitant radiochemotherapy with radiotherapy alone in advanced head and neck cancer. There is now clear evidence that radiochemotherapy provides a substantial and statistically significant improvement in survival and local-regional control, as compared to radiotherapy alone. Radiochemotherapy should be considered an accepted standard of care in cancers of the oropharynx, particularly for patients with locally-advanced disease who have a good performance status. Two randomized studies conducted by the Department of Veterans' Affairs and the EORTC, with a total of 534 patients accrued, showed that induction chemotherapy followed by radiotherapy of responders yields survival rates equal to those of total laryngectomy with postoperative radiotherapy. After 4 years, one-half to two-thirds of survivors of the chemotherapy arm retained a functional larynx. Larynx preservation using induction chemotherapy can now be regarded as feasible but still investigational. Current phase II studies show excellent larynx preservation rates using a primary concomitant radiochemotherapy with an altered fractionation regimen. More clinical and laboratory research is required to further evaluate the different treatment options of the multimodality concept, and to develop prognostic models that will allow individualization of the therapy.

Combined Modality Therapy↗