Martin Polednik

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.

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.

Optimization of extracranial stereotactic radiation therapy of small lung lesions using accurate dose calculation algorithms

BackgroundThe aim of this study was to compare and to validate different dose calculation algorithms for the use in radiation therapy of small lung lesions and to optimize the treatment planning using accurate dose calculation algorithms.MethodsA 9-field conformal treatment plan was generated on an inhomogeneous phantom with lung mimics and a soft tissue equivalent insert, mimicking a lung tumor. The dose distribution was calculated with the Pencil Beam and Collapsed Cone algorithms implemented in Masterplan (Nucletron) and the Monte Carlo system XVMC and validated using Gafchromic EBT films. Differences in dose distribution were evaluated. The plans were then optimized by adding segments to the outer shell of the target in order to increase the dose near the interface to the lung.ResultsThe Pencil Beam algorithm overestimated the dose by up to 15% compared to the measurements. Collapsed Cone and Monte Carlo predicted the dose more accurately with a maximum difference of -8% and -3% respectively compared to the film. Plan optimization by adding small segments to the peripheral parts of the target, creating a 2-step fluence modulation, allowed to increase target coverage and homogeneity as compared to the uncorrected 9 field plan.ConclusionThe use of forward 2-step fluence modulation in radiotherapy of small lung lesions allows the improvement of tumor coverage and dose homogeneity as compared to non-modulated treatment plans and may thus help to increase the local tumor control probability. While the Collapsed Cone algorithm is closer to measurements than the Pencil Beam algorithm, both algorithms are limited at tissue/lung interfaces, leaving Monte-Carlo the most accurate algorithm for dose prediction.

Improving dose homogeneity in large breasts by IMRT: efficacy and dosimetric accuracy of different techniques.

Purpose:Evaluation of a simplified intensity-modulated irradiation (IMRT), a three-field (MFT), and a conventional two-tangential-field technique regarding dose homogeneity, target coverage, feasibility and, for the first time, dosimetric reliability in patients with large breasts treated postoperatively for breast cancer on a low-energy linac.Material and Methods:CT datasets of ten patients with relatively large breast volumes treated for breast cancer were selected. For each patient, four treatment plans were created: low-energy conventional (C-LE), high-energy conventional (C-HE), three-field (MFT), and a two-field aperture-based IMRT technique. Apertures for the IMRT and MFT were created with the aid of a three-dimensional dose display. Dosimetric accuracy of each technique was evaluated in an anthropomorphic thorax/breast phantom.Results:The mean of planning target volumes receiving < 95% or > 105% of the prescribed total dose was reduced from 16.0% to 13.9% to 10.4% to 8.9% in the C-LE, C-HE, MFT, and IMRT plans, respectively. Phantom dose measurements agreed well with the calculated dose within the breast tissue.Conclusion:Aperture-based IMRT using two tangential incident beam directions, as well as a three-field technique with inverse optimization, provide a better alternative to the standard wedged tangential beams for patients with large breasts treated on low-energy linacs while maintaining the efficiency of the treatment-planning and delivery process.Ziel:Evaluation einer einfachen tangentialen intensitätsmodulierten Bestrahlungs-(IMRT-)Technik, einer Drei-Felder-Technik (MFT) und der konventionellen tangentialen Technik im Hinblick auf Dosishomogenität, Erfassung des Zielvolumens, Durchführbarkeit und – erstmalig – dosimetrische Reproduzierbarkeit bei der postoperativen Mammabestrahlung von Patientinnen mit großem Mammavolumen an einem Linac mit niedriger Energie.Material und Methodik:CT-Datensätze von zehn Patientinnen mit relativ großem Mammavolumen, bei denen eine postoperative Radiotherapie wegen Mammakarzinoms durchgeführt worden war, wurden für diese Untersuchung verwendet. Für jede Patientin wurden vier Bestrahlungspläne generiert: Niedrigenergie konventionell (C-LE), Hochenergie konventionell (C-HE), Drei-Felder-Plan (MFT) und eine aperturbasierte Zwei-Felder-IMRT-Technik. Aperturen (Segmente) für die IMRT und MFT wurden mit Hilfe eines dreidimensionalen Dosisdisplays generiert. Die dosimetrische Reproduzierbarkeit der generierten Pläne wurde in einem anthropomorphen Thorax/Mamma-Phantom evaluiert.Ergebnisse:Das mittlere Volumen des Planungszielvolumens, das < 95% oder > 105% der Verschreibungsdosis erhielt, wurde von 16,0% (C-LE) auf 13,9% (C-HE) auf 10,4% (MFT) bzw. 8,9% (IMRT) reduziert. Die gemessene Dosis stimmte für alle Pläne im Bereich der Mamma gut mit der berechneten Dosis überein.Schlussfolgerung:Die aperturbasierte IMRT mit zwei tangentialen Primäreinstrahlrichtungen und die Drei-Felder-Technik mit inverser Optimierung verbessern die Planqualität bei der postoperativen Bestrahlung voluminöser Mammae an Linacs mit niedriger Energie bei hervorragender Behandlungsökonomie.

Improving Dose Homogeneity in Large Breasts by IMRT

Purpose:Evaluation of a simplified intensity-modulated irradiation (IMRT), a three-field (MFT), and a conventional two-tangential-field technique regarding dose homogeneity, target coverage, feasibility and, for the first time, dosimetric reliability in patients with large breasts treated postoperatively for breast cancer on a low-energy linac.Material and Methods:CT datasets of ten patients with relatively large breast volumes treated for breast cancer were selected. For each patient, four treatment plans were created: low-energy conventional (C-LE), high-energy conventional (C-HE), three-field (MFT), and a two-field aperture-based IMRT technique. Apertures for the IMRT and MFT were created with the aid of a three-dimensional dose display. Dosimetric accuracy of each technique was evaluated in an anthropomorphic thorax/breast phantom.Results:The mean of planning target volumes receiving < 95% or > 105% of the prescribed total dose was reduced from 16.0% to 13.9% to 10.4% to 8.9% in the C-LE, C-HE, MFT, and IMRT plans, respectively. Phantom dose measurements agreed well with the calculated dose within the breast tissue.Conclusion:Aperture-based IMRT using two tangential incident beam directions, as well as a three-field technique with inverse optimization, provide a better alternative to the standard wedged tangential beams for patients with large breasts treated on low-energy linacs while maintaining the efficiency of the treatment-planning and delivery process.Ziel:Evaluation einer einfachen tangentialen intensitätsmodulierten Bestrahlungs-(IMRT-)Technik, einer Drei-Felder-Technik (MFT) und der konventionellen tangentialen Technik im Hinblick auf Dosishomogenität, Erfassung des Zielvolumens, Durchführbarkeit und – erstmalig – dosimetrische Reproduzierbarkeit bei der postoperativen Mammabestrahlung von Patientinnen mit großem Mammavolumen an einem Linac mit niedriger Energie.Material und Methodik:CT-Datensätze von zehn Patientinnen mit relativ großem Mammavolumen, bei denen eine postoperative Radiotherapie wegen Mammakarzinoms durchgeführt worden war, wurden für diese Untersuchung verwendet. Für jede Patientin wurden vier Bestrahlungspläne generiert: Niedrigenergie konventionell (C-LE), Hochenergie konventionell (C-HE), Drei-Felder-Plan (MFT) und eine aperturbasierte Zwei-Felder-IMRT-Technik. Aperturen (Segmente) für die IMRT und MFT wurden mit Hilfe eines dreidimensionalen Dosisdisplays generiert. Die dosimetrische Reproduzierbarkeit der generierten Pläne wurde in einem anthropomorphen Thorax/Mamma-Phantom evaluiert.Ergebnisse:Das mittlere Volumen des Planungszielvolumens, das < 95% oder > 105% der Verschreibungsdosis erhielt, wurde von 16,0% (C-LE) auf 13,9% (C-HE) auf 10,4% (MFT) bzw. 8,9% (IMRT) reduziert. Die gemessene Dosis stimmte für alle Pläne im Bereich der Mamma gut mit der berechneten Dosis überein.Schlussfolgerung:Die aperturbasierte IMRT mit zwei tangentialen Primäreinstrahlrichtungen und die Drei-Felder-Technik mit inverser Optimierung verbessern die Planqualität bei der postoperativen Bestrahlung voluminöser Mammae an Linacs mit niedriger Energie bei hervorragender Behandlungsökonomie.

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.

On the performances of different IMRT treatment planning systems for selected paediatric cases

BackgroundTo evaluate the performance of seven different TPS (Treatment Planning Systems: Corvus, Eclipse, Hyperion, KonRad, Oncentra Masterplan, Pinnacle and PrecisePLAN) when intensity modulated (IMRT) plans are designed for paediatric tumours.MethodsDatasets (CT images and volumes of interest) of four patients were used to design IMRT plans. The tumour types were: one extraosseous, intrathoracic Ewing Sarcoma; one mediastinal Rhabdomyosarcoma; one metastatic Rhabdomyosarcoma of the anus; one Wilms tumour of the left kidney with multiple liver metastases. Prescribed doses ranged from 18 to 54.4 Gy. To minimise variability, the same beam geometry and clinical goals were imposed on all systems for every patient. Results were analysed in terms of dose distributions and dose volume histograms.ResultsFor all patients, IMRT plans lead to acceptable treatments in terms of conformal avoidance since most of the dose objectives for Organs At Risk (OARs) were met, and the Conformity Index (averaged over all TPS and patients) ranged from 1.14 to 1.58 on primary target volumes and from 1.07 to 1.37 on boost volumes. The healthy tissue involvement was measured in terms of several parameters, and the average mean dose ranged from 4.6 to 13.7 Gy. A global scoring method was developed to evaluate plans according to their degree of success in meeting dose objectives (lower scores are better than higher ones). For OARs the range of scores was between 0.75 ± 0.15 (Eclipse) to 0.92 ± 0.18 (Pinnacle3 with physical optimisation). For target volumes, the score ranged from 0.05 ± 0.05 (Pinnacle3 with physical optimisation) to 0.16 ± 0.07 (Corvus).ConclusionA set of complex paediatric cases presented a variety of individual treatment planning challenges. Despite the large spread of results, inverse planning systems offer promising results for IMRT delivery, hence widening the treatment strategies for this very sensitive class of patients.

Arc therapy for total body irradiation--a robust novel treatment technique for standard treatment rooms.

BACKGROUND AND PURPOSE We developed a simple and robust total body irradiation (TBI) method for standard treatment rooms that obviates the need for patient translation devices. METHODS AND MATERIALS Two generic arcs with rectangular segments for a patient thickness of 16 and 20 cm (arc16/arc20) were generated. An analytical fit was performed to determine the weights of the arc segments depending on patient thickness and gantry angle. Stability and absolute dose for both arcs were measured using EBT3 films in a range of solid water slab phantom thicknesses. Additionally ionization chamber measurements were performed every 10 cm at a source surface distance (SSD) of ∼ 200 cm. RESULTS The measured standard deviation for arc16 is ± 3% with a flatness ⩽ 9.0%. Arc20 had a standard deviation of ± 3% with a flatness ⩽ 7.3% for all measured thicknesses. The theoretical curves proved to be accurate for the prediction of the segment weightings for the two arcs. In vivo measurements for the first 22 clinical patients showed a dose deviation of less than 3%. CONCLUSIONS Arc therapy is a convenient and stable method for TBI. This cost-effective approach has been introduced clinically, obviating the need for field patches and to physically move the patient.