Kai Schubert

Intensity-Modulated Whole Abdominal Radiotherapy After Surgery and Carboplatin/Taxane Chemotherapy for Advanced Ovarian Cancer: Phase I Study

PURPOSE To assess the feasibility and toxicity of consolidative intensity-modulated whole abdominal radiotherapy (WAR) after surgery and chemotherapy in high-risk patients with advanced ovarian cancer. METHODS AND MATERIALS Ten patients with optimally debulked ovarian cancer International Federation of Gynecology and Obstetrics Stage IIIc were treated in a Phase I study with intensity-modulated WAR up to a total dose of 30 Gy in 1.5-Gy fractions as consolidation therapy after adjuvant carboplatin/taxane chemotherapy. Treatment was delivered using intensity-modulated radiotherapy in a step-and-shoot technique (n = 3) or a helical tomotherapy technique (n = 7). The planning target volume included the entire peritoneal cavity and the pelvic and para-aortal node regions. Organs at risk were kidneys, liver, heart, vertebral bodies, and pelvic bones. RESULTS Intensity-modulated WAR resulted in an excellent coverage of the planning target volume and an effective sparing of the organs at risk. The treatment was well tolerated, and no severe Grade 4 acute side effects occurred. Common Toxicity Criteria Grade III toxicities were as follows: diarrhea (n = 1), thrombocytopenia (n = 1), and leukopenia (n = 3). Radiotherapy could be completed by all the patients without any toxicity-related interruption. Median follow-up was 23 months, and 4 patients had tumor recurrence (intraperitoneal progression, n = 3; hepatic metastasis, n = 1). Small bowel obstruction caused by adhesions occurred in 3 patients. CONCLUSIONS The results of this Phase I study showed for the first time, to our knowledge, the clinical feasibility of intensity-modulated whole abdominal radiotherapy, which could offer a new therapeutic option for consolidation treatment of advanced ovarian carcinoma after adjuvant chemotherapy in selected subgroups of patients. We initiated a Phase II study to further evaluate the toxicity of this intensive multimodal treatment.

Megavoltage CT in Helical Tomotherapy — Clinical Advantages and Limitations of Special Physical Characteristics:

Helical tomotherapy is a form of image-guided intensity-modulated radiotherapy that introduces the ring gantry concept into radiation oncology. The system is a combination of a therapeutic linear accelerator and a megavoltage CT-scanner. This work describes the clinical experience with megavoltage CT with 456 patients in more than 11000 fractions. It also provides a review of the current literature of the possibilities and limitations of megavoltage CT. Between July 2006 and October 2008 456 patients were treated with helical tomotherapy and a pretreatment megavoltage CT was performed in 98.1% of the 11821 fractions to perform position control and correction. CT image acquisition was done with 3.5 MV x-rays in the helical tomotherapy machine. MVCT was used for dose recalculations to quantify doses distributions in cases of changing geometry, tumor shrinkage or presence of metal implants. Inverse treatment planning for prostate cancer patients with bilateral hip replacements was performed based upon an MVCT. A mean 3D-correction vector of 7.1mm with a considerable variation was detected and immediately corrected. Mean shifts were lateral 0.9mm (sd 5.0mm), mean longitudinal shift 1.0mm (sd 5.1mm) and mean vertical shift 3.2mm (sd 5.2mm). The MVCT enables imaging of anatomical structures in the presence of dental metal or orthopedic implants. Especially in these cases, dose recomputations can increase the precision of dose calculations. Due to a mean 3d correction vector of more than 7mm and a variation of corrections of more than 5mm daily image-guidance is recommended to achieve a precise dose application. The MVCT shows evident advantages in cases with metal implants but has limitations due to a reduced soft tissue contrast. Compared with megavoltage cone-beam-CT the tomotherapy fan beam CT adds less extra dose fore the patient and has a better soft tissue contrast.

The Influence of Different IMRT Techniques on the Peripheral Dose A Comparison between sMLM-IMRT and Helical Tomotherapy

Purpose:To investigate how segmented multileaf modulation-(sMLM-)based intensity-modulated radiotherapy (IMRT) and dynamic helical tomotherapy (ToTh) affect the peripheral dose (PD) outside the treated region.Material and Methods:A cuboid Perspex phantom was scanned in a computed tomograph. Different artificial cases were contoured consisting of OARs surrounded by cylindrically shaped planning target volumes (PTVs) with different dimensions. Radiotherapy plans were generated with the sMLM system Konrad (Siemens) and with the ToTh planning system. The plans were optimized in such a way that the dose-volume histograms showed comparable results. The sMLM plans were applied with a linac Primus (Siemens OCS), the ToTh plans with the HiArt system (TomoTherapy); both with 6 MV. Measurements of PDs were performed along the longitudinal axis of the phantom outside the primary beam at different distances from the edge of the PTV (horizontal PD) and also at different depths at a fixed distance from the isocenter (vertical PD). Additional experiments to separate the scatter dose caused by the phantom were performed. This was realized by removing the part of the phantom lying in the primary beam, then applying the same plans like before.Results:All PD values were normalized to the median dose of the PTV. The PD values for the different PTVs decrease with decreasing PTV size. They also decrease with increasing distance from the isocenter. The horizontal values are in a range of 7% for the largest PTV (diameter = 15 cm) near the primary dose region to 0.2% for the smallest PTV (diameter = 5 cm) far from the primary dose region. The ToTh values are higher than the sMLM values by a maximal factor of 2 near the primary dose region. They become more similar with increasing distance from the edge of the PTV in longitudinal direction. The PD values are nearly equal at a distance of 25 cm from the edge of the PTV. The vertical PDs are higher for the ToTh at depths of > 1 cm but higher for sMLM close to the surface. By removing the scatter cube, the horizontal PD values at middle distances are reduced to one third of the PD values with scatter cube for ToTh (0.5%) and to one half for sMLM (0.8%). This means that without scatter cube the PD for ToTh is lower than that for sMLM. The measured PD values without scatter cube are in the same dimension as published data.Conclusion:The increasing PDs and their trend with increasing PTV size can be explained by Compton scattering of photons from the irradiated volume toward the off-axis measuring points. The further increase of the PD in case of ToTh relative to sMLM is not easy to explain. Different presumptions are possible. The larger field length (in longitudinal direction) of the ToTh plans (consisting of the “real” field length and the overlap) relative to the sMLM plans could be one reason for the higher PD values. The softer energy spectrum of the HiArt machine with more sideward Compton scattering contributions could be another reason.Ziel:Im Rahmen eines Vergleichs sollte der Einfluss von intensitätsmodulierter Radiotherapie (IMRT) mit „step-and-shoot“-Technik (sMLM) und von helikaler Tomotherapie (ToTh) auf die periphere Dosis (PD) außerhalb der primären Bestrahlungsregion untersucht werden.Material und Methodik:Ein Quaderphantom aus Plexiglas wurde im CT gescannt. Bestrahlungspläne für drei verschieden große, konstruierte Fälle (Risikoorgane umgeben von Hohlzylinder-Planungszielvolumina [PTVs]) erzeugt. Die Pläne wurden für sMLM mit Konrad (Siemens) und für ToTh mit dem HiArt-Planungssystem berechnet. Alle Pläne wurden so optimiert und normalisiert, dass die Dosis-Volumen-Histogramme vergleichbare Ergebnisse zeigten. Die sMLM-Pläne wurden mit einem Beschleuniger Primus (Siemens), die ToTh-Pläne mit einem HiArt-System appliziert, beide mit 6 MV. Dabei wurden PD-Messungen außerhalb des primären Strahlenfelds in verschiedenen Abständen vom PTV (horizontale PD) und in verschiedenen Tiefen bei festem Abstand vom PTV (vertikale PD) durchgeführt. Zur Separierung der Dosisanteile aus dem Phantom und aus dem Beschleunigerkopf bzw. der Strahlkollimiereinheit wurde ein Teil der Experimente ohne Phantom im Primärstrahl wiederholt.Ergebnisse:Alle PD-Werte wurden auf die mediane Dosis im PTV normalisiert. Die PD-Werte steigen mit abnehmender PTV-Größe. Sie sinken ebenfalls mit zunehmender Entfernung vom Isozentrum. Die horizontalen PD-Werte liegen im Bereich von 7% in Nähe der Primärregion für das größte PTV (Durchmesser = 15 cm) bis zu 0,2% für das kleinste PTV (Durchmesser = 5 cm) fern der Primärregion. Die PD-Werte sind bei ToTh nahe der Primärregion maximal um den Faktor 2 höher als die sMLM-Werte. Die PD-Werte bei sMLM und ToTh nähern sich mit wachsender longitudinaler Entfernung vom PTV an. Sie sind in 25 cm Entfernung vom PTV nahezu identisch. Die vertikalen PD-Werte sind in Tiefen > 1 cm für ToTh, nahe der Oberfläche jedoch für sMLM höher. Durch Entfernung des Streuquaders wurden die horizontalen PD-Werte in mittlerer Entfernung vom PTV verringert, beim ToTh-Plan auf ein Drittel (0,5%) und beim sMLM-Plan auf die Hälfte (0,8%). Damit sind die aus dem Kollimiersystem stammenden Dosisbeiträge vom HiArt-System geringer als vom „herkömmlichen“ Primus-Beschleunigerkopf mit Multileafkollimatoren. Die gemessenen PDs ohne Streuphantom liegen in der gleichen Größenordnung wie bereits publizierte Daten.Schlussfolgerung:Der Anstieg der PD-Werte und deren Zunahme mit der Größe des PTVs können mit der Compton-Streuung der Photonen vom primären Bestrahlungsvolumen in Richtung der Messpunkte erklärt werden. Die weitere Zunahme der PD bei ToTh im Verhältnis zu sMLM ist nicht einfach zu erklären. Die größere Feldlänge bei ToTh (in longitudinaler Richtung), bestehend aus „realer“ Feldlänge und Überlappung (bedingt durch Spiralapplikation), im Vergleich zu herkömmlicher IMRT kann ein Grund sein, das weichere Spektrum des HiArt-Systems mit daraus resultierender stärkerer Compton-Streuung zur Seite ein anderer.

Surface dose in the treatment of breast cancer with helical tomotherapy.

Purpose:Investigation of the effects of breathing motion- and misregistration-induced errors on the superficial dose in the treatment of breast cancer using helical tomotherapy (HT).Material and Methods:Surface dose measurements were performed with thermoluminescence dosimetry (TLD). Two treatment plans with different planning target volume (PTV) definitions of the left breast were used: PTVskin had its ventral border exactly on skin level, while PTVair included also a 10-mm extension ventral to the PTVskin. With a thoracic static phantom, misregistration errors in an HT were simulated. A dynamic phantom was used to simulate a breathing patient during HT. Surface doses of breast cancer patients were measured both for an HT (179 points) and a conventional three-dimensional conformal treatment (70 points).Results:In the static phantom misregistration setup, dose deviations of –31.9% for PTVskin to +35.4% for PTVair could be observed. The dynamic phantom measurements resulted in surface dose deviations from those in a static position between 0.8% and 3.8% without a significant difference for the PTV definitions. The measured surface doses on patients averaged (mean ± standard deviation) 1.65 ± 0.13 Gy for the HT and 1.42 ± 0.11 Gy for the three-dimensional conformal treatment.Conclusion:HT enables a homogeneous and reproducible surface dose with small dose deviations in the treatment of breast cancer. HT is a feasible method to treat breast cancer under free shallow breathing of the patient using a treatment plan with a ventral PTV border on the skin level.Ziel:Untersuchung der Effekte von atembewegungs- und fehlpositionierungsbedingten Störungen auf die Oberflächendosis in der Behandlung des Mammakarzinoms mit helikaler Tomotherapie (HT).Material und Methodik:Die Oberflächendosismessungen wurden mit Thermolumineszenzdosimetrie (TLD) durchgeführt. Zwei Bestrahlungspläne mit verschiedenen Planungszielvolumen-(PTV-)Definitionen der linken Brust wurden verwendet: PTVskin hatte seine ventrale Begrenzung exakt auf Hautniveau, während PTVair zusätzlich eine 10-mm-Erweiterung ventral von PTVskin enthielt. Mit einem statischen Thoraxphantom wurden verschiedene Fehlpositionierungen während einer HT simuliert. Ein dynamisches Phantom wurde verwendet, um eine atmende Patientin während einer HT zu simulieren. Die Oberflächendosen von Mammakarzinompatientinnen wurden sowohl bei HT (179 Messpunkte) als auch bei der dreidimensionalen konformalen Radiotherapie (70 Messpunkte) gemessen.Ergebnisse:Im Versuch des statischen Phantoms konnten Dosisunterschiede von –31,9% bei PTVskin bis +35,4% bei PTVair beobachtet werden. Die Messungen mit dem dynamischen Phantom ergaben Dosisunterschiede von den Dosen in statischer Position zwischen 0,8% und 3,8% ohne einen signifikanten Unterschied zwischen den PTV-Definitionen. Die gemessenen Oberflächendosen von Patientinnen lagen durchschnittlich bei (Mittelwert ± Standardabweichung) 1,65 ± 0,13 Gy bei HT und 1,42 ± 0,11 Gy bei der dreidimensionalen konformalen Behandlung.Schlussfolgerung:HT ermöglicht eine homogene und reproduzierbare Oberflächendosis mit geringen Abweichungen in der Behandlung des Mammakarzinoms. Die HT eignet sich zur Behandlung des Mammakarzinoms unter freier flacher Atmung der Patientin, wenn ein Bestrahlungsplan mit ventraler PTV-Begrenzung auf Hautniveau verwendet wird.

Clinical evaluation of a laser surface scanning system in 120 patients for improving daily setup accuracy in fractionated radiation therapy.

PURPOSE To evaluate the clinical suitability of a specific optical surface imaging system to detect setup errors in fractionated radiation therapy. METHODS AND MATERIALS The setup correction accuracy of a 3-dimensional laser imaging system was analyzed for 6 different tumor locations with 20 patients each. For each patient, the setup corrections of the megavoltage computed tomography (MVCT) images of a TomoTherapy unit (TomoTherapy, Madison, WI) were compared with those of the laser system for the first 10 fractions. For the laser system, the reference surface either was obtained from the DICOM (Digital Imaging and Communications in Medicine) surface structure delineated on the planning computed tomography images or was acquired with the system itself at the first fraction after the MVCT-based setup correction. Data analysis was performed for both reference types. RESULTS By use of the DICOM reference image, systematic shifts between 3 and 9 mm were found, depending on the tumor location. For the optical reference, no clinically relevant systematic shifts were found. MVCT-based setup corrections were detected with high accuracy, and only small movements were observed during treatment. CONCLUSIONS Using a reference image acquired with the laser system itself after MVCT-based setup correction appears more reliable than importing the DICOM reference surface. After generation of the optical reference, the laser system may be used to derive setup corrections over a certain number of fractions, but additional radiologic imaging may still be necessary on a regular basis (eg, weekly) or if the corrections of the optical system appear implausibly large. Nevertheless, such a combined application may help to reduce the imaging dose for the patient.

Dosimetric Comparison of Image Guidance by Megavoltage Computed Tomography versus Bone Alignment for Prostate Cancer Radiotherapy

Background and Purpose:Daily image guidance in irradiation of prostate cancer can be based on simple portal images or on soft-tissue imaging. This study compares daily bone alignment with daily pretreatment megavoltage computed tomography (MVCT).Patients and Methods:Ten patients with a total of 356 fractions were analyzed. Before each fraction, the patient was positioned to match the prostate on pretreatment MVCT and planning CT. In seven fractions, rectum distension prevented a satisfactory match and the fraction was restarted after the patient went to the restroom. After treatment, organs were manually contoured on each daily MVCT and doses recalculated. Bone alignment was simulated by a software that matches the bones on MVCT and planning CT.Results:In the seven interrupted fractions, median improvement of rectum volume receiving full fraction dose was 14 cm3 between simulated treatment before and actual treatment after the patient went to the restroom. In the 349 noninterrupted fractions, the average difference of the isodose that covers 95% of the prostate between actual treatment position and simulated bone match position was < 1% and there was no significant change in the rectum volume with a fraction dose ≥ 2 Gy.Conclusion:Full fraction dose rectum irradiation can be avoided with daily MVCT by interruption of single fractions. There was no relevant benefit of daily MVCT in the noninterrupted fractions with the margins used in this study.Hintergrund und Ziel:Die tägliche bildgestützte Lagerung von Patienten mit Prostatakarzinom kann auf der Grundlage von „portal imaging“ oder Weichteilbildgebung erfolgen. In dieser Arbeit wird die tägliche Lagerung nach knöchernen Strukturen mit der täglichen Lagerung nach Megavolt-Computertomographie (MVCT) verglichen.Patienten und Methodik:Zehn Patienten mit insgesamt 356 Fraktionen wurden analysiert. Vor jeder Fraktion wurde die Prostata auf dem vor Bestrahlung erstellten MVCT in Deckung mit dem Planungs-CT gebracht. In sieben Fraktionen war dies bei vergrößertem Rektumdurchmesser nicht zufriedenstellend möglich. Diese Fraktionen wurden nach einem Toilettengang des Patienten erneut gestartet. Nach der Behandlung wurden die Organe auf jedem der täglichen MVCTs konturiert und die applizierte Dosis berechnet. Die knochenbasierte Lagerung wurde durch eine Software simuliert, die die Knochen auf MVCT und Planungs-CT in Deckung bringt.Ergebnisse:In den sieben unterbrochenen Fraktionen wurde durch Toilettengang und MVCT-Lagerung ein im Median 14 cm3 geringeres Rektumvolumen mit voller Fraktionsdosis bestrahlt (Tabellen 2 und 3). In den 349 nicht unterbrochenen Fraktionen war die durchschnittliche Differenz der Isodose mit 95%-Prostataabdeckung in der MVCT-Lagerung um < 1% besser (Abbildung 4), und es ergab sich kein signifikanter Unterschied für das Rektumvolumen, das der Fraktionsdosis ≥ 2 Gy ausgesetzt war (Abbildung 3a).Schlussfolgerung:Bestrahlung des Rektums mit der vollen Fraktionsdosis kann mit täglichem MVCT durch Unterbrechung einzelner Fraktionen vermieden werden. In nicht unterbrochenen Fraktionen ergibt sich durch die täglichen MVCTs kein relevanter Vorteil mit den hier verwendeten Sicherheitsabständen.

CT-myelography for high-dose irradiation of spinal and paraspinal tumors with helical tomotherapy: revival of an old tool.

Background and Purpose:High-dose irradiation or reirradiation of spinal and paraspinal tumors is a challenge particularly in the presence of metal artifacts after surgery. Image-guided advanced intensity-modulated radiotherapy delivers high-dose radiation to the tumor sparing the spinal cord. Precise delineation of the spinal cord is necessary treating para- and intraspinal tumors with a sufficient dose.Patients and Methods:The use of myelo-CT was evaluated in 23 patients with spinal and paraspinal tumors. All patients had had previous surgery with metal implants in the radiation area. All patients had an indication for high-dose irradiation. Treatment planning was performed using nonenhanced and contrast-enhanced myelo-CT in the same position and immobilization and both CT scans were matched. Treatment was performed by using a tomotherapy treatment unit.Results:Contouring of the myelon in all slices of the myelo-CT was possible in 20 of 23 patients. All these patients were treated with doses of median 69.4 Gy in 2 Gy/1.8 Gy single doses using daily image guidance. One patient received an integrated boost with a TD/SD of 70/2.3 Gy. No side effects have been observed so far during a median follow-up of 15.5 months. No separation between tumor and myelon could be observed in 3 patients.Conclusion:Myelo-CT offers a distinct delineation of the myelon and the paraspinal tumor in case of artifacts due to metal implants after surgery. Using this tool in combination with advanced image guidance and IMRT techniques, patients with relatively radioresistent paraspinal tumors might have the chance of improved local control using higher target doses.Hintergrund:Hochdosisbestrahlung oder Rebestrahlung von spinalen und paraspinalen Tumoren ist eine Herausforderung, besonders in Gegenwart von Metallartefakten nach Operation. Bildgeführte intensitätsmodulierte Radiotherapie liefert eine hohe Strahlendosis auf den Tumor unter Schonung des Rückenmarks. Daher ist eine genaue Abgrenzung des Rückenmarks notwendig, um die Behandlung para- und intraspinaler Tumoren mit einer ausreichenden Dosis durchführen zu können.Patienten und Methoden:Die Verwendung eines Myelo-CT wurde bei 23 Patienten mit spinalen und paraspinalen Tumoren untersucht. Alle Patienten hatten Voroperationen mit Metallimplantaten im Bestrahlungsbereich. Alle Patienten hatten eine Indikation zur Hochdosisbestrahlung. Die Bestrahlungsplanung erfolgte mit einem nativen CT und einem Myelo-CT in gleicher Lagerung und Immobilisation. Die beiden CT-Scans wurden fusioniert. Die Bestrahlung erfolgte mittels einer Tomotherapieeinheit.Ergebnisse:Die Konturierung des Myelon in allen Schichten des Myelo-CT war bei 20/23 Patienten möglich. Alle diese Patienten wurden erfolgreich mit einer medianen Dosis von 69.4 Gy in 2-Gy-/1,8-Gy-Einzeldosen behandelt. Ein Patient erhielt einen integrierten Boost mit einer GD/ED von 70/2,3 Gy. Bei einem medianen Follow-up von 15,5 Monaten wurden keine Nebenwirkungen der Behandlung festgestellt. Eine Abgrenzung des Myelon vom Tumorgewebe war bei 3 Patienten nicht möglich.Schlussfolgerung:Das Myelo-CT führt zu einer deutlichen Abgrenzbarkeit des Myelons von paraspinalen und spinalen Tumoren bei Metallartefakten nach Operation. Mit diesem Werkzeug in Kombination mit modernen IMRT-Techniken, könnte eine Verbesserung der Lokalrezidivrate bei Patienten mit relativ radioresistenten paraspinalen Tumoren erreicht werden.

MRT-simulation von bronchialkarzinomen mittels eines offenen niederfeld-MRT

AIM The initial target volume for primary radiation therapy of lung cancer is usually determined with the aid of computed tomography. Due to the axial CT-scans the simulation of the RT-field is often difficult. MRI in its superior ability to demonstrate and characterize soft tissue and its possibilities of multiplanar imaging can be beneficial. As MRI is less available and more expensive the use of MRI in radiotherapy planning is still restricted. With the introduction of open low-field MRI-systems there is now a cost-saving alternative. The aim of this study was the clinical evaluation of the use of a new open low-field MRI in radiotherapy planning of bronchogenic cancer. PATIENTS AND METHODS Fifteen patients undergoing primary radiotherapy for lung cancer were studied using an open low-field MRI-system (Picker Outlook 0.23 Tesla). Conventional CT-assisted treatment planning was compared to a MRI-assisted procedure. Contours from coronary T1-weighted MRI-sections were superimposed onto the simulator radiograph using a subtrascope (MR-simulation). RESULTS Open low-field MR-imaging using T1-weighted sequences resulted in excellent delineation of tumor masses from mediastinal fat, the airways and the vascular structures as well as the radial tumor infiltration into the vicinity of the lung (Figures 1a to 1c). This allowed an exact and reproducible transfer of tumor contours onto the simulator radiograph. The MR-simulation led to optimization in the field configuration in 5/15 patients (Figure 2). CONCLUSIONS Open low-field MRI-systems can be very useful in treatment planning. They are less expensive and need less extensive rebuilding compared to high-field MRI-systems. In the radiotherapy planning of bronchogenic carcinoma the MR-simulation is reasonable and clinically practicable. One of the main advantages of open MRI-systems in comparison to CT and standard MRI-systems in radiotherapy planning is that there is a much greater variety of treatment positions.HintergrundDas initiate Zielvolumen zur primären Strahlentherapie von Bronchialkarzinomen wird meist anhand der Tumorausdehnung im CT bestimmt. Die transversale Schnittführung erschwert hierbei die Umsetzung in die Simulation der Bestrahlungsfelder. Die MRT bietet durch den besseren Weichteilkontrast und die freie Wahl der Schnittebenen Vorteile. Mit der Entwicklung der Niederfeld-MRT-Systeme steht jetzt eine kostengünstige Alternative zur Verfügung. Ziel dieser Studie war die klinische Evaluierung eines offenen Niederfeld-MRT-Gerätes in der Therapiesimulation von nichtkleinzelligen Bronchialkarzinomen.Patienten und Methode15 Patienten mit primärer Strahlentherapie bei Bronchialkarzinom wurden mittels eines offenen Niederfeld-MRT (Picker Outlook, 0,23 T) untersucht. Die Fremd-CT-gestützte Simulatortechnik wurde mit einem MRT-gestützten Vorgehen verglichen. In Bestrahlungsposition angefertigte koronare native T1-gewichtete MRT-Schnitte wurden dazu subtraskopisch mit den Simulatoraufnahmen überlagert.ErgebnisseDie Niederfeld-MRT unter Verwendung von nativen T1-Sequenzen zeigte eine gute Abgrenzbarkeit des Tumorgewebes vom mediastinalen Fettgewebe und vom Gefäß- und Bronchialbaum sowie eine gute Darstellung der feinen Tumorausläufer ins Lungenparenchym. Die Wahl der Schnittführung in der Simulationsebene erlaubte eine topographisch exakte und gut reproduzierbare Übertragung des Tumors auf die Simulatoraufnahme. Insgesamt mußte bei 5/15 Patienten aufgrund der MRT-Simulation eine Optimierung der Bestrahlungsfelder durchgeführt werden.SchlußfolgerungOffene Niederfeld-MRT-Systeme können eine wertvolle Ergänzung für die Therapieplanung sein. Sie sind vergleichsweise kostengünstig. Bei der Bestrahlungsplanung von Bronchialkarzinomen erscheint die MRT-Simulation in speziellen Fällen sinnvoll, und sie ist klinisch anwendbar. Ein entscheidender Vorteil der offenen MRT gegenüber der CT und auch der geschlossenen MRT liegt in den freier wählbaren Lagerungsmöglichkeiten des Patienten.AbstractAimThe initial target volume for primary radiation therapy of lung cancer is usually determined with the aid of computed tomography. Due to the axial CT-scans the simulaton of the RT-field is often difficult. MRI in its superior ability to demonstrate and characterize soft tissue and its possibilities of multiplanar imaging can be beneficial. As MRI is less available and more expensive the use of MRI in radiotherapy planning is still restricted. With the introduction of open low-field MRI-systems there is now a cost-saving alternative. The aim of this study was the clinical evaluation of the use of a new open low-field MRI in radiotherapy planning of bronchogenic cancer.Patients and MethodsFifteen patients undergoing primary radiotherapy for lung cancer were studied using an open low-field MRI-system (Picker Outlook 0.23 Tesla). Conventional CT-assisted treatment planning was compared to a MRI-assisted procedure. Contours from coronary T1-weighted MRI-sections were superimposed onto the simulator radiograph using a subtrascope (MR-simulation).ResultsOpen low-field MR-imaging using T1-weighted sequences resulted in excellent delineation of tumor masses from mediastinal fat, the airways and the vascular structures as well as the radial tumor infiltration into the vicinity of the lung (Figures la to 1c). This allowed an exact and reproducible transfer of tumor contours onto the simulator radiograph. The MR-simulation led to optimization in the field configuration in 5/15 patients (Figure 2).ConclusionsOpen low-field MRI-systems can be very useful in treatment planning. They are less expensive and need less extensive rebuilding compared to high-field MRI-systems. In the radiotherapy planning of bronchogenic carcinoma the MR-simulation is reasonable and clinically practicable. One of the main advantages of open MRI-systems in comparison to CT and standard MRI-systems in radiotherapy planning is that there is a much greater variety of treatment positions.

Accelerated large volume irradiation with dynamic Jaw/Dynamic Couch Helical Tomotherapy

BackgroundHelical Tomotherapy (HT) has unique capacities for the radiotherapy of large and complicated target volumes. Next generation Dynamic Jaw/Dynamic Couch HT delivery promises faster treatments and reduced exposure of organs at risk due to a reduced dose penumbra.MethodsThree challenging clinical situations were chosen for comparison between Regular HT delivery with a field width of 2.5 cm (Reg 2.5) and 5.0 cm (Reg 5.0) and DJDC delivery with a maximum field width of 5.0 cm (DJDC 5.0): Hemithoracic Irradiation, Whole Abdominal Irradiation (WAI) and Total Marrow Irradiation (TMI). For each setting, five CT data sets were chosen, and target coverage, conformity, integral dose, dose exposure of organs at risk (OAR) and treatment time were calculated.ResultsBoth Reg 5.0 and DJDC 5.0 achieved a substantial reduction in treatment time while maintaining similar dose coverage. Treatment time could be reduced from 10:57 min to 3:42 min / 5:10 min (Reg 5.0 / DJDC 5.0) for Hemithoracic Irradiation, from 18:03 min to 8:02 min / 8:03 min for WAI and to 18:25 min / 18:03 min for TMI. In Hemithoracic Irradiation, OAR exposure was identical in all modalities. For WAI, Reg 2.5 resulted in lower exposure of liver and bone. DJDC plans showed a small but significant increase of ∼ 1 Gy to the kidneys, the parotid glans and the thyroid gland. While Reg 5.0 and DJDC were identical in terms of OAR exposure, integral dose was substantially lower with DJDC, caused by a smaller dose penumbra.ConclusionsAlthough not clinically available yet, next generation DJDC HT technique is efficient in improving the treatment time while maintaining comparable plan quality.

Technical performance of a commercial laser surface scanning system for patient setup correction in radiotherapy

In conformal radiotherapy, careful setup of the patient and setup verification prior to irradiation is essential. The technical performance of a commercial 3D-surface imaging system (Galaxy, LAP Laser, Lüneburg, Germany) for patient setup correction was evaluated. The system reconstructs a 3D-surface model by scanning the patient with a laser line while a camera records its reflections. This surface model is then compared with a reference model and a setup correction with 6 degrees of freedom is derived. The calibration stability of the system was investigated using the daily check phantom of the manufacturer. The accuracy and reproducibility of the system were investigated with an anthropomorphic phantom by performing 1D- and 3D-shifts with and without breathing of the phantom, respectively. In addition, measurements in a healthy volunteer were performed. With a few exceptions, the day-by-day variations of the calibration were <0.5mm in LAT and LNG direction and <1.5mm in VRT direction, respectively. Besides day-by-day variations, also baseline-shifts of up to 3mm were observed. The lowest observed accuracy of the system in detecting pre-defined shifts of the rigid phantom was found in lateral direction. Here, mean deviations of -0.15 ± 0.46 mm for 1D-shifts and -0.12 ± 0.26 mm for 3D-shifts were found. For the ventilated phantom, the lowest observed accuracy was found in vertical direction with mean deviations of 1.16 ± 0.6mm for 1D-shifts and -0.45 ± 0.57 mm for 3D-shifts. In a healthy volunteer, the accuracy was lowest in longitudinal direction with 1.7 ± 1.5mm. The overall technical accuracy of the surface imaging system can be considered to be acceptable for application in fractionated radiotherapy. For special radiotherapy techniques such as SBRT, an increased accuracy might be necessary. To define the clinical role of the system, patient studies for different target locations are required.