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Biomedical subjects

Uwe Schneider

Publications and source records attributed to Uwe Schneider.

At least 19 recordsLinked to original sources
PubMed2006

Intensity modulated photon and proton therapy for the treatment of head and neck tumors.

PURPOSE: A comparative treatment planning study has been performed between intensity modulated photon and proton therapy to investigate the ability of both modalities to spare organs at risk in the head and neck region while keeping target dose homogeneous. Additional advantage of reducing the spot size for IMPT was also investigated. The treatment planning comparison was extended by varying the number of fields to study its effect on the performance of each modality. Risks of secondary cancer induction were also calculated for all modalities. MATERIALS AND METHODS: Five planning CTs were selected for the study. Four different constraints were set to the organs at risk in order to measure the resulting dose homogeneity in the target volume. Five and nine field plans were made for IMXT and 3, 5 and 9 field plans were made for IMPT, for both spot sizes. Dose homogeneity as a function of the mean parotid dose was visualized using a 'pseudo' Pareto-optimal front approach. Risks of secondary cancer were estimated using the organ equivalent dose model. RESULTS: Critical organs were best spared using 3-field IMPT and, at least for IMPT, little advantage was seen with increasing field numbers. Reducing the spot size does give an advantage. In contrast, there was a significant advantage in going from 5 to 9 fields for IMXT. Secondary cancer risk was lowest for the IMPT plans with reduced spot size, for which normal tissue received the lowest integral dose. Interestingly, although integral dose remained the same, increasing the number of IMPT fields increased the secondary cancer risk, due to the increased volume of tissue irradiated to low dose. CONCLUSIONS: IMPT has a better ability to spare organs at risk than IMXT for the same dose homogeneity. It also significantly reduced the estimated risk of secondary cancer induction and the use of small numbers of fields further increased this advantage. Given that target homogeneity and normal tissue sparing were equally good with the 3 field IMPT, there appears to be a clear rationale to deliver small numbers of fields for IMPT.

Carcinoma, Squamous Cell↗
PubMed2006

Is the risk for secondary cancers after proton therapy enhanced distal to the Planning Target Volume? A two-case report with possible explanations.

It is often assumed that radiation-induced secondary cancer after proton therapy forms preferentially close to the distal fall-off of the spread-out Bragg peak because of an increased relative biological effectiveness (RBE) with regard to cancer induction of low-energy protons. In this study we analyze to what extent dose gradients distal to the Planning Target Volume (PTV) may, independently from the RBE, contribute to enhanced radiation carcinogenesis. The study is based on two dogs which, out of 30 dogs treated with proton therapy at the Paul Scherrer Institute (PSI), developed a secondary cancer. Both dogs were originally diagnosed and treated for a fibrosarcoma and developed an osteosarcoma 48 and almost 60 months, respectively, after radiotherapy. From the dose distributions of the initial radiotherapy for both dogs three-dimensional maps of secondary cancer complication probability (SCCP) were computed. The SCCP maps were analyzed in the regions where the dogs developed a secondary cancer. The SCCP maps showed an enhanced risk in the regions of the femur where the secondary cancers were detected, as compared to the SCCP of the total femur. Excess risk of radiation-induced cancer at the distal part of proton radiation fields can thus be explained using SCCP calculations on the basis of the physical dose distributions. Therefore, the occurrence of secondary cancer close to the distal dose gradients of proton therapy is not necessarily due to an increased RBE of low-energy protons. More extensive studies based on more patients will be necessary to further elucidate the factors influencing the development of secondary tumors.

Animals↗
PubMed2005

Radiation risk estimates after radiotherapy: application of the organ equivalent dose concept to plateau dose-response relationships.

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. Modern treatment planning systems provide accurate three-dimensional (3D) dose distributions for each individual patient. The dose distributions can be converted into organ equivalent doses to describe radiation-induced cancer after radiotherapy (OED(rad-ther)) in the irradiated organs. The OED(rad-ther) concept assumes that any two dose distributions in an organ are equivalent if they cause the same radiation-induced cancer risk. In this work, this concept is applied to dose-response relationships, which are leveling off at high dose. The organ-dependent operational parameter of this dose-response relationship was estimated by analyzing secondary cancer incidence data of patients with Hodgkin's disease. The dose distributions of a typical radiotherapy treatment plan for treating Hodgkin's disease was reconstructed. Dose distributions were calculated in individual organs from which cancer incidence data were available. The model parameter was obtained by comparing dose and cancer incidence rates for the individual organs.

Body Burden↗
PubMed2005

Quantification of the response of circulating epithelial cells to neodadjuvant treatment for breast cancer: a new tool for therapy monitoring.

INTRODUCTION: In adjuvant treatment for breast cancer there is no tool available with which to measure the efficacy of the therapy. In contrast, in neoadjuvant therapy reduction in tumour size is used as an indicator of the sensitivity of tumour cells to the agents applied. If circulating epithelial (tumour) cells can be shown to react to therapy in the same way as the primary tumour, then this response may be exploited to monitor the effect of therapy in the adjuvant setting. METHOD: We used MAINTRAC analysis to monitor the reduction in circulating epithelial cells during the first three to four cycles of neoadjuvant therapy in 30 breast cancer patients. RESULTS: MAINTRAC analysis revealed a patient-specific response. Comparison of this response with the decline in size of the primary tumour showed that the reduction in number of circulating epithelial cells accurately predicted final tumour reduction at surgery if the entire neoadjuvant regimen consisted of chemotherapy. However, the response of the circulating tumour cells was unable to predict the response to additional antibody therapy. CONCLUSION: The response of circulating epithelial cells faithfully reflects the response of the whole tumour to adjuvant therapy, indicating that these cells may be considered part of the tumour and can be used for therapy monitoring.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed2005

Alkylchlorotins grafted to cross-linked polystyrene beads by a -(CH2)n- spacer (n=4, 6, 11): selective, clean and recyclable catalysts for transesterification reactions.

Insoluble polystyrene grafted compounds of the type (P-H)(1-t){P-(CH2)n SnBu(p)Cl(3-p)}(t), (P-H)(1-t){P-(CH2)n SnBuO}(t) and (P-H)(1-t)[{P-(CH2)n SnBuCl}2O](t/2), in which (P-H) is a cross-linked polystyrene; n=4, 6, and 11; p=0 and 1; and t the degree of functionalisation, were synthesised from Amberlite XE-305, a polystyrene cross-linked with divinylbenzene. The compounds were characterised by using elemental analysis, and IR, Raman, solid-state 117Sn NMR, and 1H and 119Sn high-resolution MAS NMR spectroscopy. The influence of the spacer length and the tin functionality on the catalytic activity of these compounds, as well as their recycling ability, was assessed in the transesterification reaction of ethyl acetate with various alcohols. These studies showed significant differences in the activity of the catalysts interpreted in terms of changes in the mobility of the catalytic centres. Some of the supported catalysts could be recycled at least seven times without noticeable loss of activity. The residual tin content in the reaction products was found to be as low as 3 ppm.

Journal Article↗
PubMed2005

Estimation of radiation-induced cancer from three-dimensional dose distributions: Concept of organ equivalent dose.

PURPOSE: Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. Modern treatment planning systems provide accurate three-dimensional dose distributions for each individual patient. These data open up new possibilities for more precise estimates of secondary cancer incidence rates in the irradiated organs. We report a new method to estimate organ-specific radiation-induced cancer incidence rates. The concept of an organ equivalent dose (OED) for radiation-induced cancer assumes that any two dose distributions in an organ are equivalent if they cause the same radiation-induced cancer incidence. METHODS AND MATERIALS: The two operational parameters of the OED concept are the organ-specific cancer incidence rate at low doses, which is taken from the data of the atomic bomb survivors, and cell sterilization at higher doses. The effect of cell sterilization in various organs was estimated by analyzing the secondary cancer incidence data of patients with Hodgkin's disease who were treated with radiotherapy in between 1962 and 1993. The radiotherapy plans used at the time the patients had been treated were reconstructed on a fully segmented whole body CT scan. The dose distributions were calculated in individual organs for which cancer incidence data were available. The model parameter that described cell sterilization was obtained by analyzing the dose and cancer incidence rates for the individual organs. RESULTS: We found organ-specific cell radiosensitivities that varied from 0.017 for the mouth and pharynx up to 1.592 for the bladder. Using the two model parameters (organ-specific cancer incidence rate and the parameter characterizing cell sterilization), the OED concept can be applied to any three-dimensional dose distribution to analyze cancer incidence. CONCLUSION: We believe that the concept of OED presented in this investigation represents a first step in assessing the potential risk of secondary cancer induction after the clinical application of radiotherapy.

Dose-Response Relationship, Radiation↗
PubMed2005

Prenatal diagnosis of a long QT syndrome by fetal magnetocardiography in an unshielded bedside environment.

OBJECTIVE: The potentially life threatening long QT syndrome should be diagnosed during pregnancy to improve perinatal care. METHODS: A patient with a family history for a hereditary long QT syndrome presented at 30 weeks of her first pregnancy with fetal bradycardia and a narrow oscillation bandwidth on cardiotocography without structural abnormalities of the fetal heart. Fetal magnetocardiography was performed with a prototype biomagnetometer/gradiometer device in a magnetically unshielded environment. The cardiac time intervals were determined in the averaged PQRST complex. RESULTS: The QT time and the frequency-corrected QTc showed a marked prolongation to 380 ms and 0.52 s, respectively. The findings were confirmed in the postnatal electrocardiogram after spontaneous term delivery in a perinatal center. The causative mutation on chromosome 11 had been passed on to the newborn from his mother. CONCLUSION: Bedside fetal magnetocardiography revealed the exact diagnosis of the long QT syndrome in a period of the gestation when the fetus was electrically isolated by the vernix caseosa that hinders electrocardiography. To patients at risk of fetal cardiac abnormalities, magnetocardiography can be offered as a non-invasive diagnostic bedside procedure. The diagnosis should trigger closer surveillance and delivery in a perinatal center.

Adult↗
PubMed2005

A simple dose-response relationship for modeling secondary cancer incidence after radiotherapy.

Estimates of secondary cancer risk after radiotherapy are becoming more important for comparative treatment planning. There is great uncertainty concerning the dose-response relationship for radiation-induced carcinogenesis at doses higher than 4 Gy. The purpose of this report is to determine a simple dose-response relationship for secondary cancer incidence after radiotherapy treatment which can be used for comparative treatment planning. In this report a simple one-parameter model to estimate the complication probability of secondary cancer was fitted to literature data on secondary cancer incidence after radiotherapy. The results showed a linear dose-response relationship in the low-dose part and an exponentially decreasing one after a maximum at around 10 Gy. The observed dose-response relationship and the literature data used to fit the dose-response indicate that cell death effects are important for the explanation of secondary cancer incidence. Even using a dose and dose-rate effectiveness factor (DDREF) of two (instead of one), a cancer incidence maximum is observed at around 10 Gy, with decreasing incidence at higher doses.

Dose-Response Relationship, Radiation↗
PubMed2005

Patient specific optimization of the relation between CT-hounsfield units and proton stopping power with proton radiography.

The purpose of this work is to show the feasibility of using in vivo proton radiography of a radiotherapy patient for the patient individual optimization of the calibration from CT-Hounsfield units to relative proton stopping power. Water equivalent tissue (WET) calibrated proton radiographs of a dog patient treated for a nasal tumor were used as baseline in comparison with integrated proton stopping power through the calibrated CT of the dog. In an optimization procedure starting with a stoichiometric calibration curve, the calibration was modified randomly. The result of this iteration is an optimized calibration curve which was used to recalculate the dose distribution of the patient. One result of this experiment was that the mean value of the deviations between WET calculations based on the stoichiometric calibration curve and the measurements was shifted systematically away from zero. The calibration produced by the optimization procedure reduced this shift to around 0.4 mm. Another result was that the precision of the calibration, reflected as the standard deviation of the normally distributed deviations between WET calculation and measurement, could be reduced from 7.9 to 6.7 mm with the optimized calibration. The dose distributions based on the two calibration curves showed major deviations at the distal end of the target volume.

Animals↗
PubMed2005

Laparoscopic and vaginal repair of uterine scar dehiscence following cesarean section as detected by ultrasound.

INTRODUCTION AND OBJECTIVE: Cesarean section (CS) is the most common operation in obstetrics, with rising incidence in most countries. As a result of this operation late scar dehiscence may occur, which may lead to uterine rupture in a subsequent pregnancy. In this case series we have described sonographic detection of scar dehiscence after CS and feasibility of vaginal or combined laparoscopic and vaginal scar excision and uterine repair. METHODS: Five consecutive patients underwent vaginal or laparoscopic assisted vaginal approach for repair of suspected scar dehiscence following CS, during a 5 year period. In all cases, transvaginal sonography detected suspicious features of scar dehiscence over the anterior uterine wall. Except of one, all patients had reported recurrent pelvic pain and/or irregular menstrual bleedings. Furthermore all patients planned for a further pregnancy. RESULTS: Resection of the uterine defect and re-constitution of the uterine wall was successfully achieved in all five patients. There were no intra-operative complications and none of the patients required blood transfusion. The mean operation time was 117 min (27-192). Presence of scar tissue was confirmed on histology in all specimens. Four patients remained free of symptoms with no evidence of recurrent scar dehiscence on sonography over a median follow up of 30 months (3-46). One patient had an uneventful pregnancy 24 months after scar removal and was delivered by repeat CS at 39 weeks' gestation. CONCLUSION: Patients with a history of CS should undergo transvaginal sonography of the scar region in order to detect latent scar dehiscence in combination with uterine wall thinning prior to planning further pregnancy. In suspected cases, a combined laparoscopic - vaginal or vaginal approach can be employed to repair the defect.

Adult↗
PubMed2004

Neutron dose from prostheses material during radiotherapy with protons and photons.

The purpose of this investigation is to measure the impact of Ti-alloy-prostheses on the neutron dose during proton and photon radiotherapy. Such unwanted neutron dose to the patient should be kept as low as possible (ALARA principle), as such additional dose can create secondary malignancies. For this purpose we performed neutron dose measurements using etch track detectors under the same conditions on a proton and a photon beam line used for radiotherapy. We found no influence of the prostheses material on the neutron dose both for proton and photon treatment.

Alloys↗
PubMed2004

Developmental changes of auditory-evoked fields in fetuses.

Fetal magnetoencephalography (fMEG) could be a viable noninvasive tool to investigate the development of neuronal functioning in the unborn by means of the maturation of cortical auditory-evoked fields (CAEF). The earliest successful recording of a CAEF component was performed at the gestational age of 27 completed weeks with an observed peak latency of 294 ms. Several different components could be differentiated in the CAEF complex. They were classified in accordance with a nomenclature introduced for cortical auditory-evoked potential (AEP) components in preterm neonates. During the third trimester of pregnancy, the detection of any component was successful in 77% of the cases. The detection rates for the different components observed were P1pm 31%; N1pm 21%; P2pm 27%; N2pm 39%; and P3pm 27%. The development of fetal CAEF is described both intraindividually in longitudinal observations and interindividually by grouped comparison throughout the second half of the pregnancy in the largest series of subjects in the literature. The components P2pm and N2pm show a significant negative correlation of their peak latencies with increasing gestational age (P < 0.05). fMEG allows to observe the development of a parameter of prenatal cortical function that can be interpreted as maturation. The results are in good accordance with those obtained in newborn EEG studies in preterm neonates.

Acoustic Stimulation↗
PubMed2004

First proton radiography of an animal patient.

The purpose of this work is to show the feasibility of proton radiography in terms of radiation dose, imaging speed, image quality (density and spatial resolution), and image content under clinical conditions. Protons with 214 MeV energy can penetrate through most patients and were used for imaging. The measured residual range (or energy) of the protons behind the patient was subtracted from the range without an object in the beam path and used to create a projected image. The image content is therefore proportional to the range that protons have lost in the patient. We took proton images of the head of a dog after it received proton radiotherapy treatment of a nasal tumor. The spatial resolution by measuring for each proton separately its coordinate in front of and behind the patient was approximately 1 mm. The acquisition time was on the order of several seconds and was limited by the patient table movement. The range sensitivity of the images was approximately 0.6 mm, which is good enough to use the images for therapy range verification. The dose that the dog received during exposure was 0.03 mGy, which is approximately a factor 50-100 smaller than for a comparable x-ray image. The potential to obtain quantitative images of proton ranges with satisfying spatial and range resolution and low dose to the patient suggests that proton radiography should be applied to patients who are under proton radiotherapy treatment.

Animals↗
PubMed2003

Influence of intrauterine growth restriction on cardiac time intervals evaluated by fetal magnetocardiography.

OBJECTIVE: Differences in the cardiac excitation cycle between normotrophic and intrauterine growth-restricted fetuses were to be investigated by fetal magnetocardiography (fMCG). STUDY DESIGN: In this study, the time intervals of the fMCG signal in dependence on gestational age were compared between a group of 30 growth-restricted fetuses and 60 normotrophic fetuses by using Spearman's correlation coefficient and two-way analyses of variance. RESULTS: A significantly increasing duration of the P wave and the QRS complex could be observed with advancing gestational age in the normotrophic collective. This prolongation was not evident in the group of growth-restricted fetuses. The QRS complex showed a significant difference between both groups. In regard to the duration of the PR and the QT intervals, neither a distinct increase nor a clear difference between both groups was observable. CONCLUSION: In contrast to the observations in the normally grown fetuses, none of the cardiac time intervals in the group of the growth-restricted fetuses were significantly correlated with gestational age. More especially, the results of the QRS complex could be an indicator of the altered conditions when intrauterine life is complicated by intrauterine growth restriction (IUGR).

Adult↗
PubMed2003

Recommended standards for fetal magnetocardiography.

Fetal magnetocardiography (FMCG) is increasingly being used in research and diagnostics of fetal heart function. Currently, FMCG is the only noninvasive procedure available, comparable to postnatal ECG, which can be used to assess cardiac electrophysiology during the second and third trimester of pregnancy. For a reliable evaluation and full clinical acceptance of this new technique, large numbers of patient investigations are required which can only be obtained in multicenter studies. An international standard protocol is needed to allow pooling of sufficient data and to permit the comparison of studies performed in different centers. This article provides recommended standards for FMCG in the fields of data acquisition and data analysis.

Arrhythmias, Cardiac↗