Dirk Wolff

Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer

INTRODUCTION Volumetric modulated arc therapy (VMAT), a complex treatment strategy for intensity-modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares VMAT against established IMRT and 3D-conformal radiation therapy (3D-CRT) delivery techniques. METHODS Based on CT datasets of 9 patients treated for prostate cancer step-and-shoot IMRT, serial tomotherapy (MIMiC), 3D-CRT and VMAT were compared with regard to plan quality and treatment efficiency. Two VMAT approaches (one rotation (VMAT1x) and one rotation plus a second 200 degrees rotation (VMAT2x)) were calculated for the plan comparison. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D(95%) (dose encompassing 95% of the target volume). For plan efficiency evaluation, treatment time and number of monitor units (MU) were considered. RESULTS For MIMiC/IMRT(MLC)/VMAT2x/VMAT1x/3D-CRT, mean CI was 1.5/1.23/1.45/1.51/1.46 and HI was 1.19/1.1/1.09/1.11/1.04. For a prescribed dose of 76 Gy, mean doses to organs-at-risk (OAR) were 50.69 Gy/53.99 Gy/60.29 Gy/61.59 Gy/66.33 Gy for the anterior half of the rectum and 31.85 Gy/34.89 Gy/38.75 Gy/38.57 Gy/55.43 Gy for the posterior rectum. Volumes of non-target normal tissue receiving > or =70% of prescribed dose (53 Gy) were 337 ml/284 ml/482 ml/505 ml/414 ml, for > or =50% (38 Gy) 869 ml/933 ml/1155 ml/1231 ml/1993 ml and for > or =30% (23 Gy) 2819 ml/3414 ml/3340 ml/3438 ml /3061 ml. D(95%) was 69.79 Gy/70.51 Gy/71,7 Gy/71.59 Gy/73.42 Gy. Mean treatment time was 12 min/6 min/3.7 min/1.8 min/2.5 min. CONCLUSION All approaches yield treatment plans of improved quality when compared to 3D-conformal treatments, with serial tomotherapy providing best OAR sparing and VMAT being the most efficient treatment option in our comparison. Plans which were calculated with 3D-CRT provided good target coverage but resulted in higher dose to the rectum.

Evaluation of Possible Prostate Displacement Induced by Pressure Applied during Transabdominal Ultrasound Image Acquisition

Background and Purpose:For accurate positioning of the prostate in external radiotherapy, transabdominal ultrasound localization and positioning systems are available. Reports have stated that probe pressure applied during image acquisition causes clinically relevant prostate displacement. The aim of this study was to investigate the prostate displacement due to the pressure applied during transabdominal ultrasound image acquisition with the BAT® ultrasound system.Material and Methods:For ten patients who had undergone iodine-125 seed implantation for brachytherapy of prostate cancer, X-ray simulations were performed before and during ultrasound image acquisition. The iodine seeds are visible on the X-ray images, representing the position of the prostate. The simulator’s crosshair, indicating the isocenter, was used as reference coordinate system. For each patient the change in prostate position was calculated based on the seed positions during and after ultrasound examination.Results:A maximum displacement of the prostate of 2.3 mm in anteroposterior and 1.9 mm in craniocaudal direction and a rotational change of up to 2.5° were observed. If the system was not handled correctly and too much pressure was applied, a shift of the prostate of up to 10 mm could be induced.Conclusion:Compared to the prostate displacement due to changes in rectal filling, which according to Crook et al. can be as much as 1.7 cm, the maximum displacement of less than 0.3 cm caused by the probe pressure is negligible. However, proper education of the staff and preparation of the patient are essential for the safe use of the system.Hintergrund und Ziel:Zur genauen Positionierung der Prostata in der Teletherapie stehen Ultraschall-Lokalisationssysteme zur Verfügung. Ziel der Studie war zu untersuchen, ob der Druck, der während der BAT®-Ultraschallaufnahme ausgeübt wird, eine klinisch relevante Verschiebung der Prostata bewirkt, die den Nutzen eines solchen Systems für die Patientenpositionierung in Frage stellt.Material und Methodik:Von zehn Patienten mit Iod-125-Seed-Implantaten wurden während und nach der Ultraschallaufnahme Röntgensimulationsaufnahmen angefertigt. Die in den Röntgenaufnahmen sichtbaren Seeds repräsentieren die Lage der Prostata. Das Fadenkreuz des Simulators wurde als Referenzkoordinatensystem verwendet. Für jeden Patienten wurde die Lageänderung der Prostata aus der Änderung der Seedpositionen bestimmt.Ergebnisse:Bei korrekter Anwendung des Ultraschallsystems wurde die Prostata maximal bis zu 2,3 mm in anteroposteriorer und 1,9 mm in kraniokaudaler Richtung verschoben und um maximal 2.5° rotiert. Durch falsche Handhabung des Systems mit zu hohem Druck konnte eine Verschiebung der Prostata um bis zu 10 mm bewirkt werden.Schlussfolgerung:Im Vergleich zu der natürlichen Lagevariation der Prostata durch unterschiedlich starke Rektumfüllung, die nach Crook et al. bis zu 1,7 cm betragen kann, ist eine maximale Verschiebung von weniger als 0,3 cm durch den Schallkopfdruck vernachlässigbar. Um das Potential des Systems voll zu nutzen, müssen eine korrekte Handhabung und Patientenvorbereitung gewährleistet sein.

Accuracy of Ultrasound-Based (BAT) Prostate-Repositioning: A Three-Dimensional On-Line Fiducial-Based Assessment With Cone-Beam Computed Tomography

PURPOSE To assess the accuracy of ultrasound-based repositioning (BAT) before prostate radiation with fiducial-based three-dimensional matching with cone-beam computed tomography (CBCT). PATIENTS AND METHODS Fifty-four positionings in 8 patients with 125I seeds/intraprostatic calcifications as fiducials were evaluated. Patients were initially positioned according to skin marks and after this according to bony structures based on CBCT. Prostate position correction was then performed with BAT. Residual error after repositioning based on skin marks, bony anatomy, and BAT was estimated by a second CBCT based on user-independent automatic fiducial registration. RESULTS Overall mean value (MV+/-SD) residual error after BAT based on fiducial registration by CBCT was 0.7+/-1.7 mm in x (group systematic error [M]=0.5 mm; SD of systematic error [Sigma]=0.8 mm; SD of random error [sigma]=1.4 mm), 0.9+/-3.3 mm in y (M=0.5 mm, Sigma=2.2 mm, sigma=2.8 mm), and -1.7+/-3.4 mm in z (M=-1.7 mm, Sigma=2.3 mm, sigma=3.0 mm) directions, whereas residual error relative to positioning based on skin marks was 2.1+/-4.6 mm in x (M=2.6 mm, Sigma=3.3 mm, sigma=3.9 mm), -4.8+/-8.5 mm in y (M=-4.4 mm, Sigma=3.7 mm, sigma=6.7 mm), and -5.2+/-3.6 mm in z (M=-4.8 mm, Sigma=1.7 mm, sigma=3.5 mm) directions and relative to positioning based on bony anatomy was 0+/-1.8 mm in x (M=0.2 mm, Sigma=0.9 mm, sigma=1.1 mm), -3.5+/-6.8 mm in y (M=-3.0 mm, Sigma=1.8 mm, sigma=3.7 mm), and -1.9+/-5.2 mm in z (M=-2.0 mm, Sigma=1.3 mm, sigma=4.0 mm) directions. CONCLUSIONS BAT improved the daily repositioning accuracy over skin marks or even bony anatomy. The results obtained with BAT are within the precision of extracranial stereotactic procedures and represent values that can be achieved with several users with different education levels. If sonographic visibility is insufficient, CBCT or kV/MV portal imaging with implanted fiducials are recommended.

Clinical Implementation of Volumetric Intensity-Modulated Arc Therapy (VMAT) with ERGO++

Background and Purpose:Volumetric modulated arc therapy (VMAT) has the potential to deliver dose distributions comparable to the established intensity-modulated radiotherapy techniques for a multitude of target paradigms. Prior to implementing VMAT into their clinical routine in December 2008, the authors evaluated the dose calculation/delivery accuracy of 24 sample VMAT plans (prostate and anal cancer target paradigms) with film and ionization dosimetry. After the start of the clinical program, in vivo measurements with a rectal probe were performed.Material and Methods:The VMAT plans were generated by the treatment-planning system (TPS) ERGO++ (Elekta, Crawley, UK) and transferred to a phantom. Film dosimetry was performed with Kodak EDR2 films, and evaluated with dose profiles and γ-index analysis. Appropriate ionization chambers were used for absolute dose measurements in the phantom and for in vivo measurements. The ionization chamber was used with localization of the measurement volume based on positioning cone-beam computed tomography.Results:Plans were transferred from ERGO++ to the record and verify (R&V) system/linear accelerator (linac). The absolute dose deviations recorded with the ionization chamber were 1.74% ± 1.62% across both indications. The γ-index analysis of the film dosimetry showed no deviation > 3%/3 mm in the high-dose region. On in vivo measurements, a deviation between calculation and measurement of 2.09% ± 2.4% was recorded, when the chamber was successfully positioned in the high-dose region.Conclusion:VMAT plans can be planned and treated reproducibly in high quality after the commissioning of the complete delivery chain consisting of TPS, R&V system and linac. The results of the individual plan verification meet the commonly accepted requirements. The first in vivo measurements confirm the reproducible precision of the delivered dose during clinical treatments.ZusammenfassungHintergrund und Ziel:Die volumetrisch modulierte Arc-Therapie (VMAT) bietet die Möglichkeit, für einige Planparadigmata zur bisher etablierten intensitätsmodulierten Strahlentherapie vergleichbare Dosisverteilungen zu generieren. Vor der im Dezember 2008 erfolgten Einführung von VMAT in die eigene klinische Routine überprüften die Autoren Dosisberechnung und Bestrahlungsgenauigkeit anhand von 24 VMAT-Plänen (Anal- und Prostatakarzinomplanungsparadigmata) mittels Film- und Ionisationsdosimetrie. Erste Patientenbestrahlungen wurden mittels rektaler In-vivo-Dosimetrie verifiziert.Material und Methodik:Die VMAT-Pläne wurden mit dem Planungssystem ERGO++ (Elekta, Crawley, UK) generiert und in einem Phantom verifiziert. Filmdosimetrie wurde mittels Kodak-EDR2-Film, Dosisprofilen und der γ-Analyse realisiert. Geeignete Ionisationskammern wurden für absolute Dosismessungen im Phantom und für die In-vivo-Dosimetrie verwendet. Ein Cone-Beam-Computertomogramm wurde für die Lokalisation des Messvolumens der Ionisationskammer im Rektum verwendet.Ergebnisse:Die Pläne wurden durchgängig fehlerfrei von ERGO++ an das „record and verify“-(R&V-)System und an den Beschleuniger übertragen. Die mittlere Abweichung der Absolutdosimetrie betrug 1,74% ± 1,62%. Die γ-Index-Analyse der Filmdosimetrie zeigte keine Abweichung > 3%/3 mm im Hochdosisbereich. Die In-vivo-Messungen ergaben nach erfolgreicher Positionierung im Hochdosisbereich eine mittlere Abweichung zwischen berechneter und applizierter Dosis von 2,09% ± 2,4%.Schlussfolgerung:VMAT-Pläne können auf Basis der klinisch zugelassenen Kette aus Planungs-, R&V- und Bestrahlungssystem nach adäquater Kommissionierung reproduzierbar erzeugt und zuverlässig bestrahlt werden. Die Ergebnisse der Individualplanverifikation erfüllen die allgemein akzeptierten Bedingungen. Erste in vivo ermittelte Dosen bestätigen die Präzision der Dosisapplikation im klinischen Einsatz.

A comparison of several modulated radiotherapy techniques for head and neck cancer and dosimetric validation of VMAT

PURPOSE Volumetric modulated arc therapy (VMAT) has the potential to shorten treatment times for fluence modulated radiotherapy. We compared dose distributions of VMAT, step-and-shoot IMRT and serial tomotherapy for typical head and neck (H&N) planning target volumes (PTV) with sparing of one parotid, a complex paradigm and a situation often encountered in H&N radiotherapy. Finally, we validated the dosimetric accuracy of VMAT delivery. MATERIAL AND METHODS Based on CT datasets of 10 patients treated for H&N cancer (PTV1:60 Gy/PTV2:56 Gy) with IMRT (7/9 fields), serial tomotherapy (MIMiC) and VMAT were compared with regard to plan quality and treatment efficiency. Plan quality was assessed by calculating homogeneity/conformity index (HI/CI), mean dose to parotid and brain stem and the maximum dose to the spinal cord. For plan efficiency evaluation, total treatment time (TTT) and number of monitor units (MU) were considered. A dosimetric evaluation of VMAT was performed using radiosensitive film, ion chamber and 2D-array. RESULTS For MIMiC/IMRT(7F)/IMRT(9F)/VMAT, mean CI was 1.98/2.23/2.23/1.82, HI(PTV1) was 1.12/1.20/1.20/1.11 and HI(PTV2) was 1.11/1.15/1.13/1.12. Mean doses to the shielded parotid were 19.5 Gy/14.1 Gy/13.9 Gy/14.9 Gy and the spinal cord received maximum doses of 43.6 Gy/40.8 Gy/41.6 Gy/42.6 Gy. The mean MUs were 2551/945/925/521 and the mean TTT was 12.8 min/7.6 min/8.5 min/4.32 min. The ion chamber measurements showed an absolute deviation of 0.08 ± 1.10% and 98.45 ± 3.25% pixels passed γ-analyses for 3%/3mm and 99.95 ± 0.09% for 5%/5mm for films. 2D-array measurements reported an agreement for 3%/3mm of 95.65 ± 2.47%-98.33 ± 0.65% and for 5%/5mm 99.79 ± 0.24%-99.92 ± 0.09% depending on the measurement protocol. CONCLUSION All treatment paradigms produced plans of excellent quality and dosimetric accuracy with IMRT providing best OAR sparing and VMAT being the most efficient treatment option in our comparison of treatment plans with high complexity.

A fast radiotherapy paradigm for anal cancer with volumetric modulated arc therapy (VMAT)

Background/PurposeRadiotherapy (RT) volumes for anal cancer are large and of moderate complexity when organs at risk (OAR) such as testis, small bowel and bladder are at least partially to be shielded. Volumetric intensity modulated arc therapy (VMAT) might provide OAR-shielding comparable to step-and-shoot intensity modulated radiotherapy (IMRT) for this tumor entity with better treatment efficiency.Materials and methodsBased on treatment planning CTs of 8 patients, we compared dose distributions, comformality index (CI), homogeneity index (HI), number of monitor units (MU) and treatment time (TTT) for plans generated for VMAT, 3D-CRT and step-and-shoot-IMRT (optimized based on Pencil Beam (PB) or Monte Carlo (MC) dose calculation) for typical anal cancer planning target volumes (PTV) including inguinal lymph nodes as usually treated during the first phase (0-36 Gy) of a shrinking field regimen.ResultsWith values of 1.33 ± 0.21/1.26 ± 0.05/1.3 ± 0.02 and 1.39 ± 0.09, the CIs for IMRT (PB-Corvus/PB-Hyperion/MC-Hyperion) and VMAT are better than for 3D-CRT with 2.00 ± 0.16. The HIs for the prescribed dose (HI36) for 3D-CRT were 1.06 ± 0.01 and 1.11 ± 0.02 for VMAT, respectively and 1.15 ± 0.02/1.10 ± 0.02/1.11 ± 0.08 for IMRT (PB-Corvus/PB-Hyperion/MC-Hyperion). Mean TTT and MUs for 3D-CRT is 220s/225 ± 11MU and for IMRT (PB-Corvus/PB-Hyperion/MC-Hyperion) is 575s/1260 ± 172MU, 570s/477 ± 84MU and 610s748 ± 193MU while TTT and MU for two-arc-VMAT is 290s/268 ± 19MU.ConclusionVMAT provides treatment plans with high conformity and homogeneity equivalent to step-and-shoot-IMRT for this mono-concave treatment volume. Short treatment delivery time and low primary MU are the most important advantages.

Evaluation of calculation algorithms implemented in different commercial planning systems on an anthropomorphic breast phantom using film dosimetry.

Purpose:To evaluate the accuracy of dose calculation algorithms of different planning systems for postoperative tangential radiotherapy in breast cancer.Material and Methods:On a CT dataset of an anthropomorphic phantom, a structure set of the left lung, clinical target volume (CTV), planning target volume, heart, and external contour were delineated. The dataset was processed by six radiation oncology centers participating in this multicenter dosimetry project. Conventional plans with two tangential wedged fields were generated in MasterPlan®, Pinnacle®, Eclipse®, TMS®, and PrecisePLAN®. Plan calculations were done using the beam data of local linacs. The dose distributions were verified under local conditions with Gafchromic®-EBT films.Results:In all planning systems, deviations between calculation and measurement were around ±3% in the CTV in the measured plane. Only small areas with deviations of ±5% were detected. Pencil-beam (PB) calculations overestimated the dose inside the lung by up to 23%. Collapsed cone (CC) underestimated the lung dose by up to 6%.Conclusion:CC calculates the dose distribution more accurately than PB. Inside regions with electron disequilibrium, however, the dose is slightly underestimated.Ziel:Evaluation der Dosisberechnungsgenauigkeit von Algorithmen, implementiert in verschiedene Planungssysteme für die konventionelle tangentiale Bestrahlungstechnik des Mammakarzinoms.Material und Methodik:CT-Daten eines anthropomorphen Phantoms mit eingezeichneten Konturen von linker Lunge, Herz, Planungszielvolumen, klinischem Zielvolumen (CTV) und Außenkontur wurden von sechs an dieser Studie teilnehmenden Kliniken verwendet. Bestrahlungspläne mit zwei tangentialen Keilfilterfeldern wurden in MasterPlan®, Pinnacle®, Eclipse®, TMS® und PrecisePLAN® generiert. Die Berechnungen der Pläne wurden mit den lokalen Maschinenbasisdaten durchgeführt. Die berechneten Dosisverteilungen wurden vor Ort in den teilnehmenden Kliniken mit Gafchromic®-EBT-Filmen verifiziert.Ergebnisse:Alle untersuchten Dosisberechnungsalgorithmen zeigten eine vergleichbare Genauigkeit im CTV. Die Differenz zwischen der Berechnung und Messung betrug ±3%, in kleinen Bereichen bis ±5% in der gemessenen Schicht. Im Lungenbereich wurde die Dosis durch Pencil Beam (PB) bis zu 23% überschätzt. Collapsed Cone (CC) unterschätzte die Lungendosis in bis zu 6%.Schlussfolgerung:In Volumina ohne Sekundärelektronengleichgewicht ist die Dosisberechnung mit CC genauer, liefert allerdings für die absorbierte Dosis zu niedrige Werte, im Gegensatz zu deutlich überhöhten Werten bei PB.

Intensity-Modulated Radiation Therapy (IMRT)with Different Combinations ofTreatment-Planning Systems and Linacs

Purpose:Purpose: To compare different combinations of intensity-modulated radiation therapy (IMRT) system components with regard to quality assurance (QA), especially robustness against malfunctions and dosimetry.Material and Methods:Three different treatment-planning systems (TPS), two types of linacs and three multileaf collimator (MLC) types were compared: commissioning procedures were performed for the combination of the TPS Corvus® 5.0 (Nomos) and KonRad® v2.1.3 (Siemens OCS) with the linacs KD2® (Siemens) and Synergy® (Elekta). For PrecisePLAN® 2.03 (Elekta) measurements were performed for Elekta Synergy only. As record and verify (R&V) system Multi-Access v7® (IMPAC) was used. The use of the serial tomotherapy system Peacock® (Nomos) was investigated in combination with the Siemens KD2 linac.Results:In the comparison of calculated to measured dose, problems were encountered for the combination of KonRad and Elekta MLC as well as for the Peacock system. Multi-Access failed to assign the collimator angle correctly for plans with multiple collimator angles per beam. Communication problems of Multi-Access with both linacs were observed, resulting in incorrect recording of the treatment. All reported issues were addressed by the manufacturers.Conclusion:For the commissioning of IMRT systems, the whole chain from the TPS to the linac has to be investigated. Components that passed the commissioning in another clinical environment can have severe malfunctions when used in a new environment. Therefore, not only single components but the whole chain from planning to delivery has to be evaluated in commissioning and checked regularly for QA.Ziel:Ziel: Vergleich verschiedener Kombinationen von IMRT-Systemkomponenten (intensitätsmodulierte Strahlentherapie) hinsichtlich Qualitätssicherung (QA), insbesondere Dosimetrie und Anfälligkeit für Fehlfunktion.Material und Methodik:Es wurden die Kombinationen der Planungssysteme Corvus® 5.0 (Nomos) und KonRad® v2.1.3 (Siemens OCS) mit den Linacs KD2® (Siemens) und Synergy® (Elekta) sowie des TPS PrecisePLAN® 2.03 (Elekta) mit dem Synergy-Linac (Elekta) anhand von Standardmethoden der IMRT-QA verglichen. Als R&V-System („record and verify“) wurde Multi-Access v7® (IMPAC) verwendet. Zusätzlich wurde das Tomotherapiesystem Peacock® (Nomos) für den Einsatz am KD2-Linac (Siemens) überprüft.Ergebnisse:Beim Vergleich von berechneter zu gemessener Dosis zeigte KonRad Probleme in Kombination mit dem Elekta MLC (Multileaf-Kollimator). Pläne mit mehreren Kollimatorwinkeln pro Feld wurden von Multi-Access mit nur einem Kollimatorwinkel importiert. Kommunikationsprobleme zwischen dem R&V-System und den beiden Linacs führten zu einer fehlerhaften Protokollierung der Bestrahlung. Alle Probleme wurden sofort an die Hersteller gemeldet.Schlussfolgerung:Komponenten, die sich bereits in einer anderen Umgebung bewährt haben, können schwere Mängel aufweisen, wenn sie in einer neuen Kombination verwendet werden. Daher sollten nicht nur einzelne Komponenten, sondern immer die gesamte Bestrahlungskette kommissioniert und regelmäßig überprüft werden.

Intensity-modulated radiation therapy (IMRT) with different combinations of treatment-planning systems and linacs: issues and how to detect them.

Purpose:Purpose: To compare different combinations of intensity-modulated radiation therapy (IMRT) system components with regard to quality assurance (QA), especially robustness against malfunctions and dosimetry.Material and Methods:Three different treatment-planning systems (TPS), two types of linacs and three multileaf collimator (MLC) types were compared: commissioning procedures were performed for the combination of the TPS Corvus® 5.0 (Nomos) and KonRad® v2.1.3 (Siemens OCS) with the linacs KD2® (Siemens) and Synergy® (Elekta). For PrecisePLAN® 2.03 (Elekta) measurements were performed for Elekta Synergy only. As record and verify (R&V) system Multi-Access v7® (IMPAC) was used. The use of the serial tomotherapy system Peacock® (Nomos) was investigated in combination with the Siemens KD2 linac.Results:In the comparison of calculated to measured dose, problems were encountered for the combination of KonRad and Elekta MLC as well as for the Peacock system. Multi-Access failed to assign the collimator angle correctly for plans with multiple collimator angles per beam. Communication problems of Multi-Access with both linacs were observed, resulting in incorrect recording of the treatment. All reported issues were addressed by the manufacturers.Conclusion:For the commissioning of IMRT systems, the whole chain from the TPS to the linac has to be investigated. Components that passed the commissioning in another clinical environment can have severe malfunctions when used in a new environment. Therefore, not only single components but the whole chain from planning to delivery has to be evaluated in commissioning and checked regularly for QA.Ziel:Ziel: Vergleich verschiedener Kombinationen von IMRT-Systemkomponenten (intensitätsmodulierte Strahlentherapie) hinsichtlich Qualitätssicherung (QA), insbesondere Dosimetrie und Anfälligkeit für Fehlfunktion.Material und Methodik:Es wurden die Kombinationen der Planungssysteme Corvus® 5.0 (Nomos) und KonRad® v2.1.3 (Siemens OCS) mit den Linacs KD2® (Siemens) und Synergy® (Elekta) sowie des TPS PrecisePLAN® 2.03 (Elekta) mit dem Synergy-Linac (Elekta) anhand von Standardmethoden der IMRT-QA verglichen. Als R&V-System („record and verify“) wurde Multi-Access v7® (IMPAC) verwendet. Zusätzlich wurde das Tomotherapiesystem Peacock® (Nomos) für den Einsatz am KD2-Linac (Siemens) überprüft.Ergebnisse:Beim Vergleich von berechneter zu gemessener Dosis zeigte KonRad Probleme in Kombination mit dem Elekta MLC (Multileaf-Kollimator). Pläne mit mehreren Kollimatorwinkeln pro Feld wurden von Multi-Access mit nur einem Kollimatorwinkel importiert. Kommunikationsprobleme zwischen dem R&V-System und den beiden Linacs führten zu einer fehlerhaften Protokollierung der Bestrahlung. Alle Probleme wurden sofort an die Hersteller gemeldet.Schlussfolgerung:Komponenten, die sich bereits in einer anderen Umgebung bewährt haben, können schwere Mängel aufweisen, wenn sie in einer neuen Kombination verwendet werden. Daher sollten nicht nur einzelne Komponenten, sondern immer die gesamte Bestrahlungskette kommissioniert und regelmäßig überprüft werden.

Reirradiation of spinal column metastases: comparison of several treatment techniques and dosimetric validation for the use of VMAT.

Background:For reirradiation of spinal column metastases, intensity-modulated radiation therapy (IMRT) reduces the dose to the spinal cord, while allowing longer treatment times. We analyzed the potential of volumetric modulated arc therapy (VMAT) to reduce treatment time and number of monitor units (MU).Patients and Methods:In CT datasets of 9 patients with spinal column metastases, the planned target volume (PTV) encompassed the macroscopic tumor including the spinal cord or medullary cone, respectively. The prescribed dose for the target was 40 Gy, but median spinal cord dose was intended to be < 26 Gy. We compared a posterior (3D-PA) static field technique, a two-field wedge technique (3D-wedge) and 5-/7-beam IMRT with VMAT. Conformity index (CI), homogeneity index (HI40), dose volume histogram (DVH) parameters, treatments delivery time (T), and MU were analyzed. Dosimetry was validated with EDR2-film/ionization chambers.Results:PTV coverage was insufficient for 3D-conformal radiotherapy (3D-CRT) when spinal cord tolerance was respected. The IMRT approach provided excellent results but has the longest treatment time. VMAT produced dose distributions similar to IMRT with shorter treatment times (VMAT: mean 4:49 min; IMRT: mean 6:50 min) and fewer MU (VMAT: 785; IMRT: 860). Reduced conformity and increased homogeneity for VMAT when compared to IMRT were observed. An absolute deviation between measured and calculated dose of +0.70 ± 3.69% was recorded. γ-Index analysis showed an agreement of 91.33 ± 3.53% for the 5%/5 mm criteria.Conclusion:For this paradigm, VMAT produces high quality treatment plans with homogeneity/conformity similar to static IMRT, shorter treatment times, and fewer MU. Verification measurements showed good agreement between calculation and delivered dose, leading to clinical implementation.Ziel:Die Intensitätsmodulierte Radiotherapie (IMRT) ermöglicht bei der Rebestrahlung von Wirbelsäulenmetastasen eine Reduktion der Dosis im Spinalkanal bei gleichzeitig längerer Bestrahlungszeit im Vergleich zur konventionellen 3D-Technik. Wir analysierten das Potential der volumetrisch modulierten Rotationstherapie (VMAT), um die Bestrahlungszeit und die Anzahl der Monitor-Einheiten (MU) zu reduzieren.Patienten und Methoden:9 CT-Datensätze von Patienten mit Wirbelsäulenmetastasen wurden untersucht, bei denen das Zielvolumen (ZV) den makroskopischen Tumor inklusive Spinalkanal umfasste. Verschreibungsdosis für das ZV waren 40 Gy unter Berücksichtigung der medianen Spinalkanaldosis von < 26 Gy. Wir verglichen eine posteriore 3D-Technik (3D-PA), eine 2-Felder-Technik mit Keilen (3D-Wedge) und 5/7-Felder-IMRT mit VMAT. Konformitätsindex (CI), Homogenitätsindex (HI40), Dosis-Volumen-Histogramme (DVH), Bestrahlungszeit (T) und MU wurden verglichen. Die Dosimetrie wurde mit EDR2 Filmen und Ionistationskammer überprüft.Ergebnisse:Die ZV-Abdeckung für die 3D-Techniken war insuffizient, wenn die Toleranzdosis des Spinalmarks berücksichtigt wurde. Der IMRT-Ansatz ergab exzellente Resultate, allerdings mit der längsten Bestrahlungszeit. Mit VMAT ließen sich ähnliche Dosisverteilungen wie mit IMRT mit kürzeren Bestrahlungszeiten (VMAT Mittel 4:49 Min., IMRT Mittel 6:50 Min.) und weniger MU (VMAT:785, IMRT:860) realisieren. Eine geringere Konformität und höhere Homogenität von VMAT wurde im Vergleich zu IMRT beobachtet. Die absolute Abweichung zwischen gemessener und berechneter Dosis betrug +0.70±3.69%. Die γ-Analyse zeigte eine Übereinstimmung von 91.33 ± 3.53% für 5%/5 mm.Schlussfolgerung:Für dieses Paradigma erzeugt VMAT qualitativ hochwertige Bestrahlungspläne mit zu IMRT vergleichbarer Homogenität/Konformität, kürzeren Bestrahlungszeiten und weniger MU. Verifikationsmessungen zeigten gute Übereinstimmungen zwischen errechneten und gemessenen Dosen und erlaubten die klinische Implementierung.