Biomedical subjects

Juergen Wilbert

Publications and source records attributed to Juergen Wilbert.

3 recordsLinked to original sources

PubMed2006

Magnitude and clinical relevance of translational and rotational patient setup errors: a cone-beam CT study.

PURPOSE: To establish volume imaging using an on-board cone-beam CT (CB-CT) scanner for evaluation of three-dimensional patient setup errors. METHODS AND MATERIALS: The data from 24 patients were included in this study, and the setup errors using 209 CB-CT studies and 148 electronic portal images were analyzed and compared. The effect of rotational errors alone, translational errors alone, and combined rotational and translational errors on target coverage and sparing of organs at risk was investigated. RESULTS: Translational setup errors using the CB-CT scanner and an electronic portal imaging device differed <1 mm in 70.7% and <2 mm in 93.2% of the measurements. Rotational errors >2 degrees were recorded in 3.7% of pelvic tumors, 26.4% of thoracic tumors, and 12.4% of head-and-neck tumors; the corresponding maximal rotational errors were 5 degrees , 8 degrees , and 6 degrees . No correlation between the magnitude of translational and rotational setup errors was observed. For patients with elongated target volumes and sharp dose gradients to adjacent organs at risk, both translational and rotational errors resulted in considerably decreased target coverage and highly increased doses to the organs at risk compared with the initial treatment plan. CONCLUSIONS: The CB-CT scanner has been successfully established for the evaluation of patient setup errors, and its feasibility in day-to-day clinical practice has been demonstrated. Our results have indicated that rotational errors are of clinical significance for selected patients receiving high-precision radiotherapy.

Head and Neck Neoplasms↗

PubMed2006

Cone-beam CT based image-guidance for extracranial stereotactic radiotherapy of intrapulmonary tumors.

Cone-beam CT (CB-CT) based image-guidance was evaluated for extracranial stereotactic radiotherapy of intrapulmonary tumors. A total of 21 patients (25 lesions: prim. NSCLC n = 6; pulmonary metastases n = 19) were treated with stereotactic radiotherapy (1 to 8 fractions). Prior to every fraction a CB-CT was acquired in treatment position, errors between planned and actual tumor position were measured and corrected. Intra- and inter-observer variability of manual evaluation of tumor position error was investigated and this manual method was compared with automatic image registration. Based on CB-CTs from 66 fractions the discrepancy (3-D vector) between planned and actual tumor position was 7.7 mm +/-1.3 mm. Tumor position error relative to the bony anatomy was 5.3 mm +/-1.2 mm, the correlation between bony anatomy and tumor position was poor. Intra-observer and inter-observer variability of manual evaluation of tumor position error was 0.9 mm +/-0.8 mm and 2.3 mm +/-1.1 mm, respectively. Automatic image registration showed highly reproducible results (<1 mm). However, compared with manual registration a systematic error was found in direction of predominant tumor breathing motion (2.5 mm vs 1.4 mm). Image-guidance using CB-CT was validated for high precision radiotherapy of intrapulmonary tumors. It was shown that both the planning reference and the verification image study have to consider tumor breathing motion.

Aged↗

PubMed2006

Tracking moving objects with megavoltage portal imaging: a feasibility study.

Four different algorithms were investigated with the aim to determine their suitability to track an object in conventional megavoltage portal images. The algorithms considered were the mean of the sum of squared differences (MSSD), mutual information (MI), the correlation ratio (CR), and the correlation coefficient (CC). Simulation studies were carried out with various image series containing a rigid object of interest that was moved along a predefined trajectory. For each of the series the signal-to-noise ratio (SNR) was varied to compare the performance of the algorithms under noisy conditions. For a poor SNR of -6 dB the mean tracking error was 2.4, 6.5, 39.0, and 17.2 pixels for MSSD, CC, CR and MI, respectively, with a standard deviation of 1.9, 12.9, 19.5, and 7.5 pixels, respectively. The size of a pixel was 0.5 mm. These results improved to 1.1, 1.3, 1.3, and 2.0 pixels, respectively, with a standard deviation of 0.6, 0.8, 0.8, and 2.1 pixels, respectively, when a mean filter was applied to the images prior to tracking. The implementation of MSSD into existing in-house software demonstrated that, depending on the search range, it was possible to process between 2 and 15 images/s, making this approach capable of real-time applications. In conclusion, the best geometric tracking accuracy overall was obtained with MSSD, followed by CC, CR, and MI. The simplest and best algorithm, both in terms of geometric accuracy as well as computational cost, was the MSSD algorithm and was therefore the method of choice.

Algorithms↗