Publications by authors named "Wolfgang W Baus"

11 Publications

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Radiomics for prediction of radiation-induced lung injury and oncologic outcome after robotic stereotactic body radiotherapy of lung cancer: results from two independent institutions.

Radiat Oncol 2021 Apr 16;16(1):74. Epub 2021 Apr 16.

Department of Stereotactic and Functional Neurosurgery, University Hospital of Cologne, Kerpener Str. 62, 50937, Cologne, Germany.

Objectives: To generate and validate state-of-the-art radiomics models for prediction of radiation-induced lung injury and oncologic outcome in non-small cell lung cancer (NSCLC) patients treated with robotic stereotactic body radiation therapy (SBRT).

Methods: Radiomics models were generated from the planning CT images of 110 patients with primary, inoperable stage I/IIa NSCLC who were treated with robotic SBRT using a risk-adapted fractionation scheme at the University Hospital Cologne (training cohort). In total, 199 uncorrelated radiomic features fulfilling the standards of the Image Biomarker Standardization Initiative (IBSI) were extracted from the outlined gross tumor volume (GTV). Regularized models (Coxnet and Gradient Boost) for the development of local lung fibrosis (LF), local tumor control (LC), disease-free survival (DFS) and overall survival (OS) were built from either clinical/ dosimetric variables, radiomics features or a combination thereof and validated in a comparable cohort of 71 patients treated by robotic SBRT at the Radiosurgery Center in Northern Germany (test cohort).

Results: Oncologic outcome did not differ significantly between the two cohorts (OS at 36 months 56% vs. 43%, p = 0.065; median DFS 25 months vs. 23 months, p = 0.43; LC at 36 months 90% vs. 93%, p = 0.197). Local lung fibrosis developed in 33% vs. 35% of the patients (p = 0.75), all events were observed within 36 months. In the training cohort, radiomics models were able to predict OS, DFS and LC (concordance index 0.77-0.99, p < 0.005), but failed to generalize to the test cohort. In opposite, models for the development of lung fibrosis could be generated from both clinical/dosimetric factors and radiomic features or combinations thereof, which were both predictive in the training set (concordance index 0.71- 0.79, p < 0.005) and in the test set (concordance index 0.59-0.66, p < 0.05). The best performing model included 4 clinical/dosimetric variables (GTV-D, PTV-D, Lung-D, age) and 7 radiomic features (concordance index 0.66, p < 0.03).

Conclusion: Despite the obvious difficulties in generalizing predictive models for oncologic outcome and toxicity, this analysis shows that carefully designed radiomics models for prediction of local lung fibrosis after SBRT of early stage lung cancer perform well across different institutions.
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http://dx.doi.org/10.1186/s13014-021-01805-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8052812PMC
April 2021

Interdisciplinary Clinical Target Volume Generation for Cardiac Radioablation: Multicenter Benchmarking for the RAdiosurgery for VENtricular TAchycardia (RAVENTA) Trial.

Int J Radiat Oncol Biol Phys 2021 Jan 27. Epub 2021 Jan 27.

I. Medizinische Klinik, Universitätsklinikum Mannheim and German Center for Cardiovascular Research (DZHK), Partner Site Heidelberg/Mannheim, Mannheim, Germany.

Purpose: Cardiac radioablation is a novel treatment option for therapy-refractory ventricular tachycardia (VT) ineligible for catheter ablation. Three-dimensional clinical target volume (CTV) definition is a key step, and this complex interdisciplinary procedure includes VT-substrate identification based on electroanatomical mapping (EAM) and its transfer to the planning computed tomography (PCT). Benchmarking of this process is necessary for multicenter clinical studies such as the RAVENTA trial.

Methods And Materials: For benchmarking of the RAVENTA trial, patient data (epicrisis, electrocardiogram, high-resolution EAM, contrast-enhanced cardiac computed tomography, PCT) of 3 cases were sent to 5 university centers for independent CTV generation, subsequent structure analysis, and consensus finding. VT substrates were first defined on multiple EAM screenshots/videos and manually transferred to the PCT. The generated structure characteristics were then independently analyzed (volume, localization, surface distance and conformity). After subsequent discussion, consensus structures were defined.

Results: VT substrate on the EAM showed visible variability in extent and localization for cases 1 and 2 and only minor variability for case 3. CTVs ranged from 6.7 to 22.9 cm, 5.9 to 79.9 cm, and 9.4 to 34.3 cm; surface area varied from 1087 to 3285 mm, 1077 to 9500 mm, and 1620 to 4179 mm, with a Hausdorff-distance of 15.7 to 39.5 mm, 23.1 to 43.5 mm, and 15.9 to 43.9 mm for cases 1 to 3, respectively. The absolute 3-dimensional center-of-mass difference was 5.8 to 28.0 mm, 8.4 to 26 mm, and 3.8 to 35.1 mm for cases 1 to 3, respectively. The entire process resulted in CTV structures with a conformity index of 0.2 to 0.83, 0.02 to 0.85, and 0.02 to 0.88 (ideal 1) with the consensus CTV as reference.

Conclusions: Multicenter efficacy endpoint assessment of cardiac radioablation for therapy-refractory VT requires consistent CTV transfer methods from the EAM to the PCT. VT substrate definition and CTVs were comparable with current clinical practice. Remarkable differences regarding the degree of agreement of the CTV definition on the EAM and the PCT were noted, indicating a loss of agreement during the transfer process between EAM and PCT. Cardiac radioablation should be performed under well-defined protocols and in clinical trials with benchmarking and consensus forming.
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http://dx.doi.org/10.1016/j.ijrobp.2021.01.028DOI Listing
January 2021

Definition and quality requirements for stereotactic radiotherapy: consensus statement from the DEGRO/DGMP Working Group Stereotactic Radiotherapy and Radiosurgery.

Strahlenther Onkol 2020 May;196(5):417-420

Klinik für Strahlentherapie, Universitätsklinikum Münster, Munster, Germany.

Stereotactic radiotherapy with its forms of intracranial stereotactic radiosurgery (SRS), intracranial fractionated stereotactic radiotherapy (FSRT) and stereotactic body radiotherapy (SBRT) is today a guideline-recommended treatment for malignant or benign tumors as well as neurological or vascular functional disorders. The working groups for radiosurgery and stereotactic radiotherapy of the German Society for Radiation Oncology (DEGRO) and for physics and technology in stereotactic radiotherapy of the German Society for Medical Physics (DGMP) have established a consensus statement about the definition and minimal quality requirements for stereotactic radiotherapy to achieve best clinical outcome and treatment quality in the implementation into routine clinical practice.
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http://dx.doi.org/10.1007/s00066-020-01603-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7182610PMC
May 2020

Technological quality requirements for stereotactic radiotherapy : Expert review group consensus from the DGMP Working Group for Physics and Technology in Stereotactic Radiotherapy.

Strahlenther Onkol 2020 May 24;196(5):421-443. Epub 2020 Mar 24.

Klinik für Strahlentherapie-Radioonkologie, Universitätsklinikum Münster, Münster, Germany.

This review details and discusses the technological quality requirements to ensure the desired quality for stereotactic radiotherapy using photon external beam radiotherapy as defined by the DEGRO Working Group Radiosurgery and Stereotactic Radiotherapy and the DGMP Working Group for Physics and Technology in Stereotactic Radiotherapy. The covered aspects of this review are 1) imaging for target volume definition, 2) patient positioning and target volume localization, 3) motion management, 4) collimation of the irradiation and beam directions, 5) dose calculation, 6) treatment unit accuracy, and 7) dedicated quality assurance measures. For each part, an expert review for current state-of-the-art techniques and their particular technological quality requirement to reach the necessary accuracy for stereotactic radiotherapy divided into intracranial stereotactic radiosurgery in one single fraction (SRS), intracranial fractionated stereotactic radiotherapy (FSRT), and extracranial stereotactic body radiotherapy (SBRT) is presented. All recommendations and suggestions for all mentioned aspects of stereotactic radiotherapy are formulated and related uncertainties and potential sources of error discussed. Additionally, further research and development needs in terms of insufficient data and unsolved problems for stereotactic radiotherapy are identified, which will serve as a basis for the future assignments of the DGMP Working Group for Physics and Technology in Stereotactic Radiotherapy. The review was group peer-reviewed, and consensus was obtained through multiple working group meetings.
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http://dx.doi.org/10.1007/s00066-020-01583-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7182540PMC
May 2020

Radiomic analysis of planning computed tomograms for predicting radiation-induced lung injury and outcome in lung cancer patients treated with robotic stereotactic body radiation therapy.

Strahlenther Onkol 2019 Sep 15;195(9):830-842. Epub 2019 Mar 15.

Department of Stereotactic and Functional Neurosurgery, University Hospital of Cologne, Kerpener Str. 62, 50937, Cologne, Germany.

Objectives: To predict radiation-induced lung injury and outcome in non-small cell lung cancer (NSCLC) patients treated with robotic stereotactic body radiation therapy (SBRT) from radiomic features of the primary tumor.

Methods: In all, 110 patients with primary stage I/IIa NSCLC were analyzed for local control (LC), disease-free survival (DFS), overall survival (OS) and development of local lung injury up to fibrosis (LF). First-order (histogram), second-order (GLCM, Gray Level Co-occurrence Matrix) and shape-related radiomic features were determined from the unprocessed or filtered planning CT images of the gross tumor volume (GTV), subjected to LASSO (Least Absolute Shrinkage and Selection Operator) regularization and used to construct continuous and dichotomous risk scores for each endpoint.

Results: Continuous scores comprising 1-5 histogram or GLCM features had a significant (p = 0.0001-0.032) impact on all endpoints that was preserved in a multifactorial Cox regression analysis comprising additional clinical and dosimetric factors. At 36 months, LC did not differ between the dichotomous risk groups (93% vs. 85%, HR 0.892, 95%CI 0.222-3.590), while DFS (45% vs. 17%, p < 0.05, HR 0.457, 95%CI 0.240-0.868) and OS (80% vs. 37%, p < 0.001, HR 0.190, 95%CI 0.065-0.556) were significantly lower in the high-risk groups. Also, the frequency of LF differed significantly between the two risk groups (63% vs. 20% at 24 months, p < 0.001, HR 0.158, 95%CI 0.054-0.458).

Conclusion: Radiomic analysis of the gross tumor volume may help to predict DFS and OS and the development of local lung fibrosis in early stage NSCLC patients treated with stereotactic radiotherapy.
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http://dx.doi.org/10.1007/s00066-019-01452-7DOI Listing
September 2019

ICRU report 91 on prescribing, recording, and reporting of stereotactic treatments with small photon beams : Statement from the DEGRO/DGMP working group stereotactic radiotherapy and radiosurgery.

Strahlenther Onkol 2019 Mar 16;195(3):193-198. Epub 2019 Jan 16.

Klinik für Strahlentherapie, Universitätsspital Zürich, Zürich, Switzerland.

The International Commission on Radiation Units and Measurements (ICRU) report 91 with the title "prescribing, recording, and reporting of stereotactic treatments with small photon beams" was published in 2017. This extensive publication covers different relevant aspects of stereotactic radiotherapy such as small field dosimetry, accuracy requirements for volume definition and planning algorithms, and the precise application of treatment by means of image guidance. Finally, recommendations for prescribing, recording and reporting are given.
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http://dx.doi.org/10.1007/s00066-018-1416-xDOI Listing
March 2019

Radiotoxicity in robotic radiosurgery: proposing a new quality index for optimizing the treatment planning of brain metastases.

Radiat Oncol 2017 Aug 17;12(1):136. Epub 2017 Aug 17.

Department of Stereotaxy and Functional Neurosurgery, University Hospital Cologne, Cologne, Germany.

Background: As irradiated brain volume at 12 Gy (V12) is a predictor for radionecrosis, the purpose of the study was to develop a model for Cyberknife (CK) plans that is able to predict the lowest achievable V12 at a given tumor size and prescription dose (PD), and to suggest a new quality index regarding V12 for optimizing the treatment planning of brain metastases.

Method: In our model V12 was approximated as a spherical shell around the tumor volume. The radial distance between tumor surface and the 12 Gy isodose line was calculated using an approximation of the mean dose gradient in that area. Assuming a radially symmetrical irradiation from the upper half space, the dose distribution is given by the superposition of single fields. The dose profiles of a single field were derived by the measured off-center ratios (OCR) of the CK system. Using the calculated gradients of the sum dose profiles, minimal-V12 was estimated for different tumor sizes. The model calculation was tested using a phantom dataset and retrospectively applied on clinical cases.

Results: Our model allows the prediction of a best-case scenario for V12 at a given tumor size and PD which was confirmed by the results of the isocentric phantom plans. The results of the non-isocentric phantom plans showed that an optimization of coverage caused an increase in V12. This was in accordance with the results of the retrospective analysis. V12 s of the clinical cases were on average twice that of the predicted model calculation. A good agreement was achieved for plans with an optimal conformity index (nCI). Re-planning of cases with high V12 showed that lower values could be reached by selecting smaller collimators and by allowing a larger number of total MU and more MU per beam.

Conclusions: V12 is a main parameter for assessing plan quality in terms of radiotoxicity. The index f12 defined as the ratio of V12 from the actual plan with the evaluated V12 from our model describes the conformity of an optimally possible V12 and thus can be used as a new quality index for optimizing treatment plans.
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http://dx.doi.org/10.1186/s13014-017-0867-zDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5561581PMC
August 2017

Risk-adapted robotic stereotactic body radiation therapy for inoperable early-stage non-small-cell lung cancer.

Strahlenther Onkol 2018 02 15;194(2):91-97. Epub 2017 Aug 15.

Department of Radiation Oncology, Center for Integrated Oncology, University of Cologne, Kerpener Str. 62, 50937, Cologne, Germany.

Purpose: To evaluate efficacy and toxicity of stereotactic body radiation therapy (SBRT) with CyberKnife® (Accuray, Sunnyvale, CA, USA) in a selected cohort of primary, medically inoperable early-stage non-small cell lung cancer (NSCLC) patients.

Methods: From 2012 to 2016, 106 patients (median age 74 years, range 50-94 years) with primary NSCLC were treated with SBRT using CyberKnife®. Histologic confirmation was available in 87 patients (82%). For mediastinal staging, 92 patients (87%) underwent F-fluorodeoxyglucose positron-emission tomography (18-FDG-PET) and/or endobronchial ultrasound (EBUS)-guided lymph node biopsy or mediastinoscopy. Tumor stage (UICC8, 2017) was IA/B (T1a-c, 1-3 cm) in 86 patients (81%) and IIA (T2a/b, 3-5 cm) in 20 patients (19%). Depending on tumor localization, three different fractionation schedules were used: 3 fractions of 17Gy, 5 fractions of 11Gy, or 8 fractions of 7.5 Gy. Tracking was based on fiducial implants in 13 patients (12%) and on image guidance without markers in 88%.

Results: Median follow-up was 15 months (range 0.5-46 months). Acute side effects were mild (fatigue grade 1-2 in 20% and dyspnea grade 1-2 in 17%). Late effects were observed in 4 patients (4%): 3 patients developed pneumonitis requiring therapy (grade 2) and 1 patient suffered a rib fracture (grade 3). In total, 9/106 patients (8%) experienced a local recurrence, actuarial local control rates were 88% (95% confidence interval, CI, 80-96%) at 2 years and 77% (95%CI 56-98%) at 3 years. The median disease-free survival time was 27 months (95%CI 23-31 months). Overall survival was 77% (95%CI 65-85%) at 2 years and 56% (95%CI 39-73%) at 3 years.

Conclusion: CyberKnife® lung SBRT which allows for real-time tumor tracking and risk-adapted fractionation achieves satisfactory local control and low toxicity rates in inoperable early-stage primary lung cancer patients.
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http://dx.doi.org/10.1007/s00066-017-1194-xDOI Listing
February 2018

Stereotactic body radiotherapy for liver tumors: principles and practical guidelines of the DEGRO Working Group on Stereotactic Radiotherapy.

Strahlenther Onkol 2014 Oct 5;190(10):872-81. Epub 2014 Aug 5.

Klinische Kooperationseinheit Strahlentherapie, Deutsches Krebsforschungszentrum (dkfz), INF 280, 69120, Heidelberg, Germany,

Purpose: This report of the Working Group on Stereotactic Radiotherapy of the German Society of Radiation Oncology (DEGRO) aims to provide a practical guideline for safe and effective stereotactic body radiotherapy (SBRT) of liver tumors.

Methods: The literature on the clinical evidence of SBRT for both primary liver tumors and liver metastases was reviewed and analyzed focusing on both physical requirements and special biological characteristics.

Results: Recommendations were developed for patient selection, imaging, planning, treatment delivery, motion management, dose reporting, and follow-up. Radiation dose constraints to critical organs at risk are provided.

Conclusion: SBRT is a well-established treatment option for primary and secondary liver tumors associated with low morbidity.
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http://dx.doi.org/10.1007/s00066-014-0714-1DOI Listing
October 2014

Portal verification of high-energy electron beams using their photon contamination by film-cassette systems.

Strahlenther Onkol 2006 Jan;182(1):37-44

Department of Radiotherapy and Radiooncology, University Hospital Carl Gustav Carus, University of Technology, Dresden, Germany.

Background And Purpose: Though electron beams are widely used in radiotherapy, their verification is not well established in clinical practice. The present study compares the suitability of several sensitive film-cassette systems for electron-portal verification by contaminating photons.

Material And Methods: The characteristics of the optical density curves of film-cassette combinations were determined by exposing them to the bremsstrahlung contamination of a variety of electron beams. Using a Las-Vegas Phantom the spatial low-contrast resolution of the combinations was investigated. The absorbed dose rates due to the contaminant photons were measured for different geometric conditions.

Results: Suitable film-cassette combinations were found for portal verification of all usual electron energies. The best image quality was obtained using the EC film and the EC-L cassettes. For electron energies higher than 6 MeV some film-cassette combinations are suitable to verify abutted electron and photon portals using the same film sheet.

Conclusion: The verification of electron portals and of abutted electron-photon portals can be performed by sensitive film-cassette systems with an image quality comparable to photon-beam verification.
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http://dx.doi.org/10.1007/s00066-006-1456-5DOI Listing
January 2006

In vivo verification of electron beam energy by patient exit dose and optical density of portal films.

Strahlenther Onkol 2004 Jan;180(1):62-5

Department of Radiotherapy and Radiooncology, University Hospital Carl Gustav Carus, Technical University Dresden, Germany.

Background And Purpose: The depth-dose curve of electron beams is mainly determined by their energy. For accelerators with scatter foils, the electron energy can, in principle, be verified by measuring the amount of the contaminating photons. This paper investigates whether exit dose measurements and evaluations of the optical density of portal films can be used to verify the energy of the electron beam in a clinically relevant setting.

Material And Methods: During irradiation of the head and neck region of an Alderson-Rando phantom with 6- to 21-MeV electron beams, the exit dose rates behind the phantom and the dose rates at the position of a film cassette were measured. The optical density of films (EC film/EC-L Regular and EC-L Fast cassettes, Eastman Kodak Comp., Rochester, NY, USA) exposed to beams of different energies was evaluated.

Results: The exit and the cassette dose rates showed a steep increase with increasing electron energy. Due to its density behavior, the film with both types of cassettes failed to generate images for lower electron energies (6 and 9 MeV) but presented a strong ascent of the optical density-until reaching the saturation-with increasing electron energy.

Conclusion: Measurements of the exit dose and evaluations of the optical density of portal films can be used to verify and document the energy of electron beams during radiotherapy.
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http://dx.doi.org/10.1007/s00066-004-1172-yDOI Listing
January 2004