Heinz Czempiel

Telekom Germany GmbH, Bonn, North Rhine-Westphalia, Germany

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Publications (12)20.63 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The new DIN ('Deutsche Industrie-Norm') 6875-1, which is currently being finalised, deals with quality assurance (QA) criteria and tests methods for linear accelerator and Gamma Knife stereotactic radiosurgery/radiotherapy including treatment planning, stereotactic frame and stereotactic imaging and a system test to check the whole chain of uncertainties. Our existing QA program, based on dedicated phantoms and test procedures, has been refined to fulfill the demands of this new DIN. The radiological and mechanical isocentre corresponded within 0.2 mm and the measured 50% isodose lines were in agreement with the calculated ones within less than 0.5 mm. The measured absorbed dose was within 3%. The resultant output factors measured for the 14-, 8- and 4-mm collimator helmet were 0.9870 +/- 0.0086, 0.9578 +/- 0.0057 and 0.8741 +/- 0.0202, respectively. For 170 consecutive tests, the mean geometrical accuracy was 0.48 +/- 0.23 mm. Besides QA phantoms and analysis software developed in-house, the use of commercially available tools facilitated the QA according to the DIN 6875-1 with which our results complied.
    Stereotactic and Functional Neurosurgery 02/2004; 82(5-6):235-43. · 1.46 Impact Factor
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    ABSTRACT: Single dose irradiation techniques require methods of quality assurance of high precision. The complete operational sequence of a treatment from imaging over irradiation planning up to the patient irradiation has to be controlled and verified in a phantom (Figure 2). These demands receive special topicality by the E-DIN 6875-1 [38], which will appear soon. A quality assurance package was developed to meet the requirements of the E-DIN 6875-1 [38]. It consists of versatile usable precision phantom (Figure 1), a dose measuring system for the tissue equivalent radiochromic film GAFCHROMIC trade mark type MD 55 II using a high-quality scanner, and a software for standardized test routines (Figures 2 to 4). Correction routines for film fog, darkening, temperature effect as well as for film inhomogeneities (double exposure technology) are implemented. The measuring system permits routine dosimetry with inaccuracies typically < 5%, for the double exposure procedure typically < 3% with local dissolutions of approx. 1/100 mm in film plane, perpendicularly to it the film stack density and the film thickness (0.3 mm) are determining. The measuring system is designed to simulate the complete three-dimensional treatment of a patient (Figure 4). The procedure achieves a high quality standard for all steps in radiosurgery. The simple handling permits the employment for the daily routine (according to E-DIN 6875-1 [38]), in addition, for the modelling of complicated 3-d of scattering conditions, e. g. close to risk structures.
    Strahlentherapie und Onkologie 11/2003; 179(11):760-6. · 4.16 Impact Factor
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    ABSTRACT: Hintergrund: Ein-Zeit-Bestrahlungen in der Stereotaxie erfordern Methoden der Qualittssicherung von hoher Przision. Der komplette Ablauf einer Behandlung von der Bildgebung ber die Bestrahlungsplanung bis zur Patientenbestrahlung muss kontrollierbar sein und im Phantom nachgebildet werden knnen. Diese Forderungen erhalten besondere Aktualitt durch die E-DIN 6875-1 [38], die in Krze erscheinen wird. Material und Methoden: Ein Qualittssicherungspaket wurde entwickelt, das den Anforderungen der E-DIN 6875-1 [38] gengt. Es besteht aus einem vielseitig verwendbaren Przisionsphantom, einem Dosismesssystem fr den gewebequivalenten Radiochrom- Film GAFCHROMIC Typ MD 55 mit hochwertigem Scanner und vielseitiger, nutzerfreundlicher Software fr standardisierte Testroutinen. Korrekturroutinen fr Filmschleier, Nachdunkelung, Temperatureffekt sowie fr Filminhomogenitten (Doppelbelichtungstechnik) sind integriert. Ergebnisse: Das Messsystem erlaubt routinemige Dosimetrie mit Ungenauigkeiten typisch < 5%, im Doppelbelichtungsverfahren typisch < 3% mit Ortsauflsungen von ca. 1/100 mm in der Filmebene, senkrecht dazu sind die Filmstapeldichte und die Filmdicke (0,3 mm) bestimmend. Das Messsystem ermglicht die komplette dreidimensionale Simulation einer Patientenbehandlung. Schlussfolgerungen: Das Verfahren erreicht einen hohen Qualittsstandard fr smtliche Schritte der Radiochirurgie. Die einfache Handhabung erlaubt den Einsatz fr die tgliche Routine (nach E-DIN 6875-1 [38]), aber auch fr die Modellierung komplizierter dreidimsionaler Streuverhltnisse, z. B. nahe an Risikostrukturen. Background: Single dose irradiation techniques require methods of quality assurance of high precision. The complete operational sequence of a treatment from imaging over irradiation planning up to the patient irradiation has to be controlled and verified in a phantom (Figure 2). These demands receive special topicality by the E-DIN 6875-1 [38], which will appear soon. Material and Methods: A quality assurance package was developed to meet the requirements of the E-DIN 6875-1 [38]. It consists of versatile usable precision phantom (Figure 1), a dose measuring system for the tissue equivalent radiochromic film GAFCHROMIC type MD 55 II using a high-quality scanner, and a software for standardized test routines (Figures 2 to 4). Correction routines for film fog, darkening, temperature effect as well as for film inhomogeneities (double exposure technology) are implemented. Results: The measuring system permits routine dosimetry with inaccuracies typically < 5%, for the double exposure procedure typically < 3% with local dissolutions of approx. 1/100 mm in film plane, perpendicularly to it the film stack density and the film thickness (0.3 mm) are determining. The measuring system is designed to simulate the complete three-dimensional treatment of a patient (Figure 4). Conclusions: The procedure achieves a high quality standard for all steps in radiosurgery. The simple handling permits the employment for the daily routine (according to E-DIN 6875-1 [38]), in addition, for the modelling of complicated 3-d of scattering conditions, e. g. close to risk structures.
    Strahlentherapie und Onkologie 01/2003; 179(11):760-766. · 4.16 Impact Factor
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    ABSTRACT: The purpose of the paper is to describe a workable three-dimensional dosimetry system for use in quality assurance programs of departments in which radiosurgery is performed. A system was developed on the basis of radiochromatic films. The experimental findings of the measured dose distributions for small complex-shaped targets, within a specially designed phantom, are described and compared with the same parameters calculated from the corresponding dose plan. The following parameters were determined for 83 patients with irregularly shaped targets who underwent gamma knife radiosurgery (GKS): target volume; dose-volume histograms of the target; 12-Gy, 15-Gy, and 18-Gy volumes; dose plan conformity; dose fall profiles in all dimensions to 50% of the prescription dose; and a quality factor (QF) to evaluate the adequacy of a GKS plan or treatment. The precise function and accuracy of the developed measuring device is shown and it demonstrated the expected steep dose falloff outside the irregularly shaped targets in all directions. The dose falloff was of the order of > 3 Gy/mm and the values of the QF were in the range between 0.5 and 0.9. A comparison with data from the literature shows that at least for small targets (< 2 cm3 and < 2.5 cm3) simulated within a head phantom, the dose gradient is significantly steeper in all directions than when using alternative treatment devices in radiosurgery and the overall QF is superior in most of the cases.
    Journal of Neurosurgery 12/2002; 97(5 Suppl):551-5. · 3.15 Impact Factor
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    ABSTRACT: Treatment units for radiosurgery, like Leksell Gamma Knife and adapted, or dedicated, linear accelerators use small circular beams of ionizing radiation down to 4 mm in diameter at the isocenter. By cross-firing, these beams generate a high dose region at the isocenter together with steep dose gradients of up to 30% per mm. These units are used to treat small complex shaped lesions, often located close to critical structures within the brain, by superimposing several single high dose regions. In order to commission such treatment units for stereotactic irradiations, to carry out quality assurance and to simulate treatment conditions, as well as to collect input data for treatment planning, a precise dosimetric system is necessary. Commercially available radiation dosimeters only partially meet the requirements for narrow photon beams and small field sizes as used in stereotactic treatment modalities. The aim of this study was the experimental determination of the output factors for the field defining collimators used in Gamma Knife radiosurgery, in particular for the smallest, the 4 mm collimator helmet. For output factor measurements a pin point air ionization chamber, a liquid ionization chamber, a diode detector, a diamond detector, TLD microcubes and microrods, alanine pellets, and radiochromic films were used. In total, more than 1000 measurements were performed with these different detection systems, at the sites in Munich and Zurich. Our results show a resultant output factor for the 4 mm collimator helmet of 0.8741 +/- 0.0202, which is in good agreement with recently published results and demonstrates the feasibility of such measurements. The measured output factors for the 8 mm and 14 mm collimator helmets are 0.9578 +/- 0.0057 and 0.9870 +/- 0.0086, respectively.
    Medical Physics 10/2002; 29(9):2080-9. · 2.91 Impact Factor
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    ABSTRACT: A detailed quality assurance (QA) program is essential for high precision single dose irradiations. The accuracy of stereotactic radiosurgery is limited by the errors of each step in the chain for optimal treatment beginning with the diagnostic imaging and target localization leading to the dose planning and ending up with the treatment of the patient. Two main goals were followed on the way to finding a concept for a suitable and sufficient quality assurance routine. First, the chain of items in terms of a complete patient simulation should be followed and second, the stereotactic MR image data should be verified against a reference in our case stereotactic radiographic projection images. Target point verifications were performed using the so-called, unknown target method based on MRI, CT, and stereotactic projection images. A marked radiochromic film, embedded between inserts of the phantom is fixed parallel to either the xy or the xz plane of the stereotactic coordinate system. After imaging and planning, the phantom is adjusted and irradiated. At the end, the film, dyed by the radiation field around the premarked cross, is evaluated. The measured distance between the unit center point (shadow) and the localization of the marked film leads to the deviation to be minimized. This is referred to as the displacement vector. The results, evaluating 170 system tests within 5 years. show that the mean displacement vector of the complete system is 0.48 mm +/-0.23 mm (mean+/- sd). Factors having a significant influence on the overall accuracy are associated with MRI parameters. Test results based on axial images (xy plane; 0.42 mm +/- 0.24 mm) are significantly superior to coronal images (xz plane; x = 0.60 mm +/- 0.02 mm). Further on, the 3D-mpr sequence (0.40 mm +/- 0.19 mm) is significantly superior to the T1 weighted SE sequences (0.66 mm +/- 0.24 mm). Given the high mechanical accuracy of the Leksell gamma knife, the most sensitive technical factor having an influence on the overall precision of radiosurgery is the MRI study. However, using the appropriate imaging sequences and parameters the dislocation error inferred by MRI can be kept very low and restricted to the rare patient inherent distortion factors. With these precautions in mind, MRI is recommended as the imaging method of choice in radiosurgery.
    Medical Physics 05/2002; 29(4):561-8. · 2.91 Impact Factor
  • B Wowra, G A Horstmann, R Cibis, H Czempiel
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    ABSTRACT: Gamma Knife radiosurgery (GKRS) was applied in 500 consecutive treatments for 445 patients within 2 years. Indications were arterio-venous malformations (93 patients), schwannomas of cranial nerves (75 patients), meningiomas (79 patients; 73 of the tumors involving the skull base), pituitary adenomas (40 patients), craniopharyngiomas (13 cases), gliomas (13 cases), rare indications (12 cases), and brain metastases (126 patients). In arterio-venous malformations two complications were observed whereas two other patients underwent surgery due to intracranial hemorrhage in the latent period after GKRS. In all cases follow-up with MRI showed evidence of an active obliteration process. Out of 24 patients with a follow-up over 1 year, angiography revealed complete obliteration in 9 patients so far. A partial obliteration was evidenced by MRI in 15 cases. In benign tumors (meningiomas and vestibular schwannomas) tumor control rates of 88% and 89% were achieved, respectively. Treatment related side effects were mild and rare; no facial palsy occured after primary Gamma Knife treatment. GKRS was particularly effective in inoperable skull base meningiomas. Cerebral metastases were controlled in 89.5% by a single Gamma Knife treatment. The mean survival period was 11.8 months. In patients receiving a single Gamma Knife treatment the mean survival time was 9.1 months. For patients undergoing multiple (up to 5) sessions of GKRS (because of new tumors) the mean survival period was 17.2 months. MRI showed evidence of adverse radiation reactions in 10/124 patients (8.1%) which were symptomatic in 3 patients (0.8%). The results obtained in patients with cerebral metastases emphasize that GKRS alone is as effective as the combined treatment of these lesions by surgery and fractionated radiotherapy. Our results demonstrated an attractively high therapeutic gain factor of Gamma Knife treatment in key indications of radiosurgery.
    Der Radiologe 01/1998; 37(12):1003-15. · 0.47 Impact Factor
  • B Wowra, H Czempiel, R Cibis, G A Horstmann
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    ABSTRACT: Radiosurgery represents a minimally invasive radiologic method for the treatment of intracranial tumours and arteriovenous malformations. In 1994 the radiosurgical device 'Leksell Gamma Knife' (LGK) was installed in a dedicated logistic environment for outpatient treatments. High quality requirements have to be met for radiosurgery. The target point accuracy taking into account the whole system was shown to be reliably below 0.5 mm whereas the spatial therapeutic resolution was 0.035 cm3. Quality parameters of the dose plan were evaluated for the first 500 consecutive treatments. These values and examples of dose plans were used to emphasize the advantages of the treatment principle with multiple isocenters. An analysis of data in the literature revealed that there is no uniform standard of treatment available in radiosurgery. A highly significant correlation between a risk prediction model for the stereotactic linear accelerator on the one hand and a different model for the LGK on the other could be shown. This result could be helpful in order to proceed towards a more uniform treatment standard in radiosurgery and to improve overall treatment results.
    Der Radiologe 01/1998; 37(12):995-1002. · 0.47 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Gamma Knife radiosurgery (GKRS) was applied in 500 consecutive treatments for 445 patients within 2 years. Indications were arterio-venous malformations (93 patients), schwannomas of cranial nerves (75 patients), meningiomas (79 patients; 73 of the tumors involving the skull base), pituitary adenomas (40 patients), craniopharyngiomas (13 cases), gliomas (13 cases), rare indications (12 cases), and brain metastases (126 patients). In arterio-venous malformations two complications were observed whereas two other patients underwent surgery due to intracranial hemorrhage in the latent period after GKRS. In all cases follow-up with MRI showed evidence of an active obliteration process. Out of 24 patients with a follow-up over 1 year, angiography revealed complete obliteration in 9 patients so far. A partial obliteration was evidenced by MRI in 15 cases. In benign tumors (meningiomas and vestibular schwannomas) tumor control rates of 88 % and 89 % were achieved, respectively. Treatment related side effects were mild and rare; no facial palsy occured after primary Gamma Knife treatment. GKRS was particularly effective in inoperable skull base meningiomas. Cerebral metastases were controlled in 89.5 % by a single Gamma Knife treatment. The mean survival period was 11.8 months. In patients receiving a single Gamma Knife treatment the mean survival time was 9.1 months. For patients undergoing multiple (up to 5) sessions of GKRS (because of new tumors) the mean survival period was 17.2 months. MRI showed evidence of adverse radiation reactions in 10/124 patients (8.1 %) which were symptomatic in 3 patients (0.8 %). The results obtained in patients with cerebral metastases emphasize that GKRS alone is as effective as the combined treatment of these lesions by surgery and fractionated radiotherapy. Our results demonstrated an attractively high therapeutic gain factor of Gamma Knife treatment in key indications of radiosurgery. In dieser Zwischenbilanz der klinischen Ergebnisse wird über die fortlaufende Serie der ersten 500 Behandlungen mit dem Gamma-Knife(GK)-System in Deutschland berichtet. In einem Zeitraum von 2 Jahren wurden 93 Patienten mit AV-Malformationen, 67 mit Akustikusneurinomen, 73 mit Meningeomen und 126 mit Hirnmetastasen behandelt. Der Anteil der kostenfreien Wiederholungsbehandlungen betrug bei Hirnmetastasen 33 %. Bei AV-Malformationen wurde regelmäßig ein Obliterationsprozeß induziert, welcher bereits vor der vollständigen Obliteration der AV-Malformationen zu einem relativen Blutungsschutz führt; der dieser Beobachtung zugrundeliegende Mechanismus wird erörtert; mit dem Risikomodell von Lax und Karlsson war eine prospektive Abschätzung des Behandlungsrisikos und eine individuelle Optimierung des Dosisplans möglich. Die GK-Behandlungen der AV-Malformationen erfolgten bei einem mittleren Nebenwirkungsrisiko von 4,2 %, wobei bisher bei 2 von 93 behandelten Patienten symptomatische Nebenwirkungen beobachtet wurden. Bei Akustikusneurinomen wurde eine Wachstumskontrolle bei 40 von 45 (89 %) Tumoren erzielt, bei benignen Meningeomen (über 90 % im Bereich der Schädelbasis) in 88 % der Fälle (44/50 Tumore). Bei 20 % der Akustikusneurinome ist bisher eine Hörverschlechterung eingetreten, davon sind 2 Patienten ertaubt. Nach primärer GK-Behandlung sind bisher bei beiden Indikationen keine Fazialisparesen aufgetreten. Irritationen des Trigeminus waren selten (7 % bei Akustikusneurinomen, 18 % bei Meningeomen), passager und traten nur bei direktem Kontakt des Tumors mit dem Trigeminushauptstamm oder dem Cavum Meckeli auf. Die ungünstigste Komplikation war eine symptomatische Brückenvenenthrombose bei einem 2. Rezidiv eines parasagittalen Falxmeningeoms. Diese vorläufigen Ergebnisse belegen die Wirksamkeit der Methode bei benignen Schädelbasistumoren, wobei inoperable Schädelbasismeningeome besonders gut auf die GK-Behandlung ansprechen. Das günstige Nebenwirkungsprofil ist auf die hohen Präzisionsanforderungen zurückzuführen. Die lokale Tumorkontrollrate für die einmalige GK-Behandlung bei Patienten mit multiplen Hirnmetastasen betrug 89,5 % (111/124 Patienten). Die mittlere Überlebenszeit des Kollektivs lag bei 11,8 Monaten. Bei Patienten mit Hirnmetastasen, die nur einmal radiochirurgisch behandelt wurden, betrug sie 9,1 Monate, bei mehrfach (wegen neuer Hirnmetastasen) radiochirurgisch behandelten Patienten 17,2 Monate. Bei 10 (8,1 %) Patienten mit Hirnmetastasen wurden in der Bildgebung lokale Strahlenreaktionen beobachtet, die bei 3 Patienten (0,8 %) deutliche klinische Symptome verursachten und einer symptomatischen Strahlennekrose entsprachen. Die Ergebnisse der alleinigen GK-Behandlung bei Hirnmetastasen sind damit sehr günstig und vergleichbar mit den besten publizierten Ergebnissen für die kombinierte chirurgische und strahlentherapeutische Behandlung bei teilweise wesentlich stärker selektierten Patientenkollektiven. Zusammenfassend belegen die Ergebnisse bei Schlüsselindikationen der Radiochirurgie die große therapeutische Breite dieses ambulanten und hochpräzisen Verfahrens; sie unterstreichen ihre Eigenständigkeit und den Bedarf an dieser Spezialmethode. Die Erfüllung hoher Qualitätsstandards ist dabei essentiell.
    Der Radiologe 37(12):1003-1015. · 0.47 Impact Factor
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    ABSTRACT: Radiosurgery represents a minimally invasive radiologic method for the treatment of intracranial tumours and arteriovenous malformations. In 1994 the radiosurgical device ’Leksell Gamma Knife' (LGK) was installed in a dedicated logistic environment for outpatient treatments. High quality requirements have to be met for radiosurgery. The target point accuracy taking into account the whole system was shown to be reliably below 0.5 mm whereas the spatial therapeutic resolution was 0.035 cm3. Quality parameters of the dose plan were evaluated for the first 500 consecutive treatments. These values and examples of dose plans were used to emphasize the advantages of the treatment principle with multiple isocenters. An analysis of data in the literature revealed that there is no uniform standard of treatment available in radiosurgery. A highly significant correlation between a risk prediction model for the stereotactic linear accelerator on the one hand and a different model for the LGK on the other could be shown. This result could be helpful in order to proceed towards a more uniform treatment standard in radiosurgery and to improve overall treatment results. Die Radiochirurgie ist eine wenig invasive, radiologische Spezialmethode zur Behandlung bestimmter intrakranieller Krankheitsprozesse. Seit 1994 steht erstmals in Deutschland ein „Gamma-knife-System“ für die Radiochirurgie zur Verfügung. Es umfaßt neben der Bestrahlungseinheit (dem „Gamma-Knife“ (GK) im engeren Sinn) auch den stereotaktischen Rahmen, die Bildgebung und die Planungssoftware. In diesem System sind besonders hohe Präzisions- und Qualitätsanforderungen zu erfüllen; sie werden dargestellt, begründet und durch Meßwerte belegt: es wird eine Zielpunktsgenauigkeit im Gesamtsystem von mindestens 0,5 mm bei einer therapeutischen Volumenauflösung von 0,035 cm3 vorgegeben. Spezielle Qualitätsparameter des Dosisplans beschreiben die Formgebung des Strahlenfelds und die Dosiskonzentration im Zielvolumen. Durch Beispiele und Meßwerte aus einer fortlaufenden Serie der ersten 500 Behandlungen werden die Vorteile des multizentrischen Bestrahlungskonzepts in der Radiochirurgie aufgezeigt. Am Beispiel von Literaturdaten wird belegt, daß die Radiochirurgie international kein standardisiertes Verfahren ist, so daß ein Vergleich klinischer Behandlungsergebnisse kaum möglich ist. Um einen Beitrag zu einer Qualitätsverbesserung und Standardisierung in der Radiochirurgie zu leisten, wurde am Beispiel der zerebralen AV-Malformationen untersucht, welche Parameter des Dosisplans sich für eine systemübergreifende Qualitätsanalyse radiochirurgischer Behandlungskonzepte eignen. Darüber hinaus wird in der Diskussion auf die wichtige Frage der Gewebetoleranzen eingegangen. Nach den bisherigen Erfahrungen läßt sich das GK-System als sehr zuverlässiges und genaues Spezialgerät für die Radiochirurgie charakterisieren, mit dem eine adäquate Umsetzung des multizentrischen Bestrahlungskonzepts möglich ist. Die Notwendigkeit der manuellen Einstellung der Zielpunkte ist der wesentliche, unzeitgemäße Mangel des Geräts, durch den die Behandlungsqualität aber nicht kompromittiert wird; er limitiert jedoch die mittelfristige Perspektive des Systems im Wettbewerb der unterschiedlichen Geräte für die Radiochirurgie.
    Der Radiologe 37(12):995-1002. · 0.47 Impact Factor