Gabriele Sroka-Perez

Estimation of pneumonitis risk in three-dimensional treatment planning using dose-volume histogram analysis

PURPOSE Investigations to study correlations between the estimations of biophysical models in three dimensional (3D) treatment planning and clinical observations are scarce. The development of clinically symptomatic pneumonitis in the radiotherapy of thoracic malignomas was chosen to test the predictive power of Lymans normal tissue complication probability (NTCP) model for the assessment of side effects for nonuniform irradiation. METHODS AND MATERIALS In a retrospective analysis individual computed-tomography-based 3D dose distributions of a random sample of 46/20 patients with lung/esophageal cancer were reconstructed. All patients received tumor doses between 50 and 60 Gy in a conventional treatment schedule. Biological isoeffective dose-volume histograms (DVHs) were used for the calculation of complication probabilities after applying Lymans and Kutchers DVH-reduction algorithm. Lung dose statistics were performed for single lung (involved ipsilateral and contralateral) and for the lung as a paired organ. RESULTS In the lung cancer group, about 20% of the patients (9 out of 46) developed pneumonitis 3-12 (median 7.5) weeks after completion of radiotherapy. For the majority of these lung cancer patients, the involved ipsilateral lung received a much higher dose than the contralateral lung, and the pneumonitis patients had on average a higher lung exposure with a doubling of the predicted complication risk (38% vs. 20%). The lower lung exposure for the esophagus patients resulted in a mean lung dose of 13.2 Gy (lung cancer: 20.5 Gy) averaged over all patients in correlation with an almost zero complication risk and only one observed case of pneumonitis (1 out of 20). To compare the pneumonitis risk estimations with observed complication rates, the patients were ranked into bins of mean ipsilateral lung dose. Particularly, in the bins with the highest patient numbers, a good correlation was achieved. Agreement was not reached for the lung functioning as a paired organ. CONCLUSIONS Realistic assessments for the prediction of radiation-induced pneumonitis seem to be possible. In this respect, the implementation of DVH-analysis in 3D planning could be a helpful tool for the evaluation of treatment plans.

Helical tomotherapy. Experiences of the first 150 patients in Heidelberg.

Background and Purpose:Helical tomotherapy was introduced into clinical routine at the Department of Radiation Oncology, University Hospital of Heidelberg, Germany, in July 2006. This report is intended to describe the experience with the first 150 patients treated with helical tomotherapy. Patient selection, time effort, handling of daily image guidance with megavoltage (MV) CT, and quality of radiation plans shall be assessed.Patients and Methods:Between July 2006 and May 2007, 150 patients were treated with helical tomotherapy in the University Hospital of Heidelberg. Mean age was 60 years with a minimum of 30 years and a maximum of 85 years. 79 of these patients received radiotherapy as a part of multimodal treatment pre- or postoperatively, 17 patients received treatment as a combined radiochemotherapy. 76% were treated with curative intent. Radiotherapy sites were central nervous system (n = 7), head and neck (n = 28), thoracic (n = 37), abdominal (n = 58) and skeletal system (n = 20). Most common tumor entities were prostate cancer (n = 28), breast cancer (n = 17), gastrointestinal tumors (n = 19), pharyngeal carcinoma (n = 14), lymphoma (n = 13), metastatic disease (bone n = 14, liver n = 6, lung n = 4, lymph node n = 2), sarcoma (n = 8), malignant pleural mesothelioma (n = 5), ovarian cancer treated with whole abdominal irradiation (n = 4), lung cancer (n = 3), skin malignancies (n = 3), chordoma (n = 2), meningioma (n = 2), one ependymoma and one medulloblastoma treated with craniospinal axis irradiation (n = 2), and others (n = 4). Nine patients were treated with single-fraction radiosurgery, nine with image-guided spinal reirradiation, and twelve patients were treated at multiple targets simultaneously. A pretreatment MV-CT scan was performed in 98.2% of the 3,026 fractions applied. After matching with the kilovoltage planning CT, corrections for translations and rotation around longitudinal axis (roll) were done.Results:Mean time on table was 24.8 min for the mentioned tumor entities with fractionated radiation, mean treatment time 10.7 min. Mean correction vector after MV-CT registration was 6.9 mm. With helical tomotherapy it was possible to achieve highly conformal dose distributions for targets of all sizes and multiple targets within one procedure. Image guidance with MV-CT allowed daily position correction and safe and precise treatment application. This was feasible even if the desired immobilization was not possible due to obesity, claustrophobia, pain, or neurologic or orthopedic impairment.Conclusion:Helical tomotherapy and daily image guidance with MV-CT could fast be introduced into daily clinical routine. This technique allows precise intensity-modulated radiotherapy (IMRT) in standard cases and offers new treatment options in a huge variety of difficult cases.Hintergrund und Ziel:Die helikale Tomotherapie wurde im Juli 2006 in der radioonkologischen Abteilung der Universitätsklinik Heidelberg in die klinische Routine eingeführt. Diese Arbeit soll die Erfahrungen der ersten 150 mit helikaler Tomotherapie behandelten Patienten beschreiben. Die Selektion der Patienten, Zeitaufwand, täglicher Gebrauch der Bildführung mittels Megavolt-(MV-)CT sowie die Qualität der Bestrahlungspläne sollen untersucht werden.Patienten und Methodik:Zwischen Juli 2006 und Mai 2007 wurden 150 Patienten mittels helikaler Tomotherapie im Universitätsklinikum Heidelberg behandelt. Das mittlere Alter betrug 60 Jahre mit einem Minimum von 30 Jahren und einem Maximum von 85 Jahren. 79 der Patienten erhielten eine Radiotherapie als Teil einer multimodalen Behandlung prä- oder postoperativ, 17 Patienten wurden einer kombinierten Radiochemotherapie unterzogen. 76% wurden in kurativer Absicht therapiert. Orte der Radiotherapieapplikation waren zentrales Nervensystem (n = 7), Kopf/Hals (n = 28), Thorax (n = 37), Abdomen (n = 58) und Skelettsystem (n = 20). Die häufigsten Tumorentitäten waren Prostatakarzinome (n = 28), Mammakarzinome (n = 17), gastrointestinale Tumoren (n = 19), Pharynxkarzinome (n = 14), Lymphome (n = 13), Metastasen (ossär n = 14, hepatisch n = 6, pulmonal n = 4, Lymphknoten n = 2), Sarkome (n = 8), maligne Pleuramesotheliome (n = 5), Ovarialkarzinome, die mittels Ganzabdomenbestrahlung behandelt wurden (n = 4), Bronchialkarzinome (n = 3), Hautmalignome (n = 3), Chordome (n = 2), Meningeome (n = 2), ein Ependymom und ein Medulloblastom, welche mittels Neuroachsenbestrahlung behandelt wurden, sowie andere Histologien (n = 4). Neun Patienten erhielten eine radiochirurgische Therapie in einer einzelnen Fraktion, neun Patienten eine bildgeführte spinale Rebestrahlung, und zwölf Patienten wurden an multiplen Targets gleichzeitig behandelt. Ein prätherapeutisches MV-CT wurde in 98,2% der 3 026 applizierten Fraktionen durchgeführt, und nach dem Matching wurden hierauf basierend Korrekturen für Translationen und Rotation um die Longitudinalachse („roll“) durchgeführt.Ergebnisse:Für die beschriebenen Tumorentitäten betrug die durchschnittliche Zeit auf dem Bestrahlungstisch bei fraktionierter Bestrahlung 24,8 min, die durchschnittliche Nettobehandlungszeit 10,7 min. Der mittlere Korrekturvektor nach MV-CT-Matching lag bei 6,9 mm. Mittels helikaler Tomotherapie war es möglich, hochkonformale Dosisverteilungen für Zielvolumina aller Größen oder multiple Zielvolumina in einer einzelnen Bestrahlungsprozedur zu erzielen. Dabei erlaubte die tägliche Bildführung mittels MV-CT eine sichere Positionskorrektur und präzise Durchführung der Therapie. Dies war auch möglich, wenn eine gewünschte Immobilisation aufgrund von Platzangst, Adipositas, Schmerzen oder neurologischer oder orthopädischer Begleiterkrankungen nicht vorgenommen werden konnte.Schlussfolgerung:Helikale Tomotherapie und tägliche Bildführung mittels MV-CT konnten schnell und erfolgreich in die klinische Routine eingeführt werden. Diese Technik ermöglicht die präzise und schonende Behandlung von Standardfällen mittels intensitätsmodulierter Strahlentherapie (IMRT) und eröffnet neue Behandlungsoptionen für schwierige Fälle.

Accuracy of a commercial optical 3D surface imaging system for realignment of patients for radiotherapy of the thorax

Accurate and reproducible patient setup is a prerequisite to fractionated radiotherapy. To evaluate the applicability and technical performance of a commercial 3D surface imaging system for repositioning of breast cancer patients, measurements were performed in a rigid anthropomorphic phantom as well as in healthy volunteers. The camera system records a respiration-gated surface model of the imaged object, which may be registered to a previously recorded reference model. A transformation is provided, which may be applied to the treatment couch to correct the setup of the patient. The system showed a high stability and detected pre-defined shifts of phantoms and healthy volunteers with an accuracy of 0.40 +/- 0.26 mm and 1.02 +/- 0.51 mm, respectively (spatial deviation between pre-defined shift and suggested correction). The accuracy of the suggested rotational correction around the vertical axis was always better than 0.3 degrees in phantom measurements and 0.8 degrees in volunteers, respectively. Comparison of the suggested setup correction with that detected by a second and independently operated marker-based optical system provided consistent results. The results demonstrate that the camera system provides highly accurate setup corrections in a phantom and healthy volunteers. The most efficient use of the system for improving the setup accuracy in breast cancer patients has to be investigated in routine patient treatments.

Evaluating target coverage and normal tissue sparing in the adjuvant radiotherapy of malignant pleural mesothelioma: Helical tomotherapy compared with step-and-shoot IMRT

PURPOSE To evaluate the potential of helical tomotherapy in the adjuvant treatment of malignant pleural mesothelioma and compare target homogeneity, conformity and normal tissue dose with step-and-shoot intensity-modulated radiotherapy. METHODS AND MATERIALS Ten patients with malignant pleural mesothelioma who had undergone neoadjuvant chemotherapy with cisplatin and permetrexed followed by extrapleural pneumonectomy (EPP) were treated in our department with 54 Gy to the hemithorax delivered by step-and-shoot IMRT. A planning comparison was performed by creating radiation plans for helical tomotherapy. The different plans were compared by analysing target homogeneity using the homogeneity indices HI(max) and HI(min) and target conformity by using the conformity index CI(95). To assess target coverage and normal tissue sparing TV(90), TV(95) and mean and maximum doses were compared. RESULTS Both modalities achieved excellent dose distributions while sparing organs at risk. Target coverage and homogeneity could be increased significantly with helical tomotherapy compared with step-and-shoot IMRT. Mean dose to the contralateral lung could be lowered beyond 5 Gy. CONCLUSIONS Our planning study showed that helical tomotherapy is an excellent option for the adjuvant intensity-modulated radiotherapy of MPM. It is capable of improving target coverage and homogeneity.

DYNAMIC JAWS AND DYNAMIC COUCH IN HELICAL TOMOTHERAPY

PURPOSE To investigate the next generation of helical tomotherapy delivery with dynamic jaw and dynamic couch movements. METHODS AND MATERIALS The new technique of dynamic jaw and dynamic couch movements is described, and a comparative planning study is performed. Ten nasopharyngeal cancer patients with skull base infiltration were chosen for this comparison of longitudinal dose profiles using regular tomotherapy delivery, running-start-stop treatment, and dynamic jaw and dynamic couch delivery. A multifocal simultaneous integrated boost concept was used (70.4Gy to the primary tumor and involved lymph nodes; 57.4Gy to the bilateral cervical lymphatic drainage pathways, 32 fractions). Target coverage, conformity, homogeneity, sparing of organs at risk, integral dose, and radiation delivery time were evaluated. RESULTS Mean parotid dose for all different deliveries was between 24.8 and 26.1Gy, without significant differences. The mean integral dose was lowered by 6.3% by using the dynamic technique, in comparison with a 2.5-cm-field width for regular delivery and 16.7% with 5-cm-field width for regular delivery. Dynamic jaw and couch movements reduced the calculated radiation time by 66% of the time required with regular 2.5-cm-field width delivery (199 sec vs. 595 sec, p < 0.001). CONCLUSIONS The current delivery mode of helical tomotherapy produces dose distributions with conformal avoidance of parotid glands, brain stem, and spinal cord. The new technology with dynamic jaw and couch movements improves the plan quality by reducing the dose penumbra and thereby reducing the integral dose. In addition, radiation time is reduced by 66% of the regular delivery time.

Inversely Planned Intensity Modulated Radiotherapy of the Breast Including the Internal Mammary Chain: A Plan Comparison Study

The aim of this paper is to evaluate the benefit of inversely planned intensity modulated radiotherapy (IMRT) in the adjuvant irradiation of breast cancer when internal mammary lymph nodes are included in the treatment volume. 20 patients treated with 3D-planned conventional radiotherapy (CRT) following breast conserving surgery were included in the study. We chose 10 patients with left-sided and 10 patients with right-sided tumors. All treatment volumes included the internal mammary chain. For plan comparison to the applied CRT plan an inverse IMRT-plan in ‘step-and-shoot’-technique was calculated. For all patients IMRT resulted in an improved conformity of dose distribution to the target volume compared to CRT (mean COIN95: 0.798 vs. 0.514 with COIN95 = C1* C2 (C1= fraction of CTV that is covered by > 95% of the prescribed dose and C2 = volume of CTV that is covered by > 95% of the prescribed dose/total volume that is covered by > 95% of the prescribed dose). In all cases with matching adjacent beams, the homogeneity in the target volume was improved. The volume of the ipsilateral lung irradiated with a dose higher than 20 Gy was reduced with IMRT from 24.6% to 13.1% compared to CRT. For left-sided target volume the heart volume with a dose higher than 30 Gy was reduced from 6.2% to 0.2%. The presented plan comparison study for irradiation of the breast and the parasternal lymph nodes showed a substantial improvement of the dose distribution by inversely planned IMRT compared to CRT. This is visible for the target volume, the ipsilateral lung and, in case of left-sided target volume, the heart. Despite an increase in integral dose to the entire normal tissue, the application of IMRT might be clinically advantageous in cases where no satisfying dose distribution can be obtained by CRT.

Reirradiation of multiple brain metastases with helical tomotherapy

Background and Purpose:Recurrent brain metastases or new brain lesions after whole-brain radiotherapy represent a therapeutic challenge. While several treatment methods for single or few lesions have been described, options for multiple lesions are limited. This case report is intended to show an approach of whole-brain reirradiation with a simultaneous multifocal integrated boost using helical tomotherapy. Technique, feasibility, and acute side effects are presented.Patients and Methods:Two patients with multiple relapsed brain metastases (eight and eleven lesions) were reirradiated after previous whole-brain radiotherapy (total dose of 40 Gy 18 months before). Whole-brain reirradiation was performed using helical tomotherapy with a total dose of 15 Gy (single dose 1.5 Gy) and a multifocal simultaneous integrated boost with a total dose of 30 Gy (single dose 3 Gy) to the brain lesions. The boost planning target volume was delineated around the lesions visible on MRI plus a 2-mm margin. Follow-up of these patients was 6 and 12 months.Results:Radiation plans with excellent conformity and homogeneity were obtained. High dose exposure to normal brain tissue was kept minimal. Mean radiation time was 13 min. The only acute side effect observed was a mild headache over 2 days at the end of treatment. So far, no further side effects and no signs of recurrence have been observed.Conclusion:Helical tomotherapy offers new treatment options for the reirradiation of multiple brain metastases. The number of cases treated with the described protocol is very limited but it is considered a promising option for patients that have responded well to the initial radiotherapy and are in a good performance status.Hintergrund und Ziel:Rezidive von Hirnmetastasen oder neue Herde nach vorangegangener Ganzhirnbestrahlung stellen eine therapeutische Herausforderung dar. Während mehrere Techniken zur Behandlung singulärer oder weniger Läsionen beschrieben wurden, sind die Optionen bei multiplen Metastasen limitiert. Dieser Fallbericht beschreibt einen Ansatz der Ganzhirnrebestrahlung mit simultanem multifokalem integriertem Boost mittels helikaler Tomotherapie. Technik, Machbarkeit und akute Nebenwirkungen werden berichtet.Patienten und Methodik:Zwei Patienten mit multiplen Rezidiven von Hirnmetastasen (acht bzw. elf Herde) wurden nach vorangegangener Ganzhirnradiotherapie rebestrahlt (40 Gy 18 Monate zuvor). Mittels helikaler Tomotherapie wurden das Neurokranium mit einer Dosis von 15 Gy (Einzeldosis 1,5 Gy) und die Metastasen selbst mit einem multifokalen simultanen integrierten Boost mit einer Dosis von 30 Gy (Einzeldosis 3 Gy) rebestrahlt. Das Planungszielvolumen des Boosts wurde mit einem 2-mm-Sicherheitssaum um die Kontrastmittelaufnahme im MRT definiert. Der Nachbeobachtungszeitraum dieser Patienten betrug 6 bzw. 12 Monate.Ergebnisse:Es konnten Bestrahlungspläne mit hervorragender Konformität und Homogenität erreicht werden. Die Hochdosisbelastung des Hirnparenchyms konnte gering gehalten werden. Die mittlere Bestrahlungszeit betrug 13 min. Einzige Akutnebenwirkung war ein geringer Kopfschmerz zum Ende der Behandlung. Es wurden keine weiteren Toxizitäten oder Zeichen eines Rezidivs beobachtet.Schlussfolgerung:Die helikale Tomotherapie eröffnet neue Optionen in der Rebestrahlung multipler Hirnmetastasen. Die Anzahl der so behandelten Patienten ist sehr limitiert, dennoch erscheint diese Behandlungsmöglichkeit sehr vielversprechend für Patienten, die auf die initiale Therapie gut angesprochen haben.

Reirradiation of Multiple Brain Metastases with Helical Tomotherapy A Multifocal Simultaneous Integrated Boost for Eight or More Lesions

Background and Purpose:Recurrent brain metastases or new brain lesions after whole-brain radiotherapy represent a therapeutic challenge. While several treatment methods for single or few lesions have been described, options for multiple lesions are limited. This case report is intended to show an approach of whole-brain reirradiation with a simultaneous multifocal integrated boost using helical tomotherapy. Technique, feasibility, and acute side effects are presented.Patients and Methods:Two patients with multiple relapsed brain metastases (eight and eleven lesions) were reirradiated after previous whole-brain radiotherapy (total dose of 40 Gy 18 months before). Whole-brain reirradiation was performed using helical tomotherapy with a total dose of 15 Gy (single dose 1.5 Gy) and a multifocal simultaneous integrated boost with a total dose of 30 Gy (single dose 3 Gy) to the brain lesions. The boost planning target volume was delineated around the lesions visible on MRI plus a 2-mm margin. Follow-up of these patients was 6 and 12 months.Results:Radiation plans with excellent conformity and homogeneity were obtained. High dose exposure to normal brain tissue was kept minimal. Mean radiation time was 13 min. The only acute side effect observed was a mild headache over 2 days at the end of treatment. So far, no further side effects and no signs of recurrence have been observed.Conclusion:Helical tomotherapy offers new treatment options for the reirradiation of multiple brain metastases. The number of cases treated with the described protocol is very limited but it is considered a promising option for patients that have responded well to the initial radiotherapy and are in a good performance status.Hintergrund und Ziel:Rezidive von Hirnmetastasen oder neue Herde nach vorangegangener Ganzhirnbestrahlung stellen eine therapeutische Herausforderung dar. Während mehrere Techniken zur Behandlung singulärer oder weniger Läsionen beschrieben wurden, sind die Optionen bei multiplen Metastasen limitiert. Dieser Fallbericht beschreibt einen Ansatz der Ganzhirnrebestrahlung mit simultanem multifokalem integriertem Boost mittels helikaler Tomotherapie. Technik, Machbarkeit und akute Nebenwirkungen werden berichtet.Patienten und Methodik:Zwei Patienten mit multiplen Rezidiven von Hirnmetastasen (acht bzw. elf Herde) wurden nach vorangegangener Ganzhirnradiotherapie rebestrahlt (40 Gy 18 Monate zuvor). Mittels helikaler Tomotherapie wurden das Neurokranium mit einer Dosis von 15 Gy (Einzeldosis 1,5 Gy) und die Metastasen selbst mit einem multifokalen simultanen integrierten Boost mit einer Dosis von 30 Gy (Einzeldosis 3 Gy) rebestrahlt. Das Planungszielvolumen des Boosts wurde mit einem 2-mm-Sicherheitssaum um die Kontrastmittelaufnahme im MRT definiert. Der Nachbeobachtungszeitraum dieser Patienten betrug 6 bzw. 12 Monate.Ergebnisse:Es konnten Bestrahlungspläne mit hervorragender Konformität und Homogenität erreicht werden. Die Hochdosisbelastung des Hirnparenchyms konnte gering gehalten werden. Die mittlere Bestrahlungszeit betrug 13 min. Einzige Akutnebenwirkung war ein geringer Kopfschmerz zum Ende der Behandlung. Es wurden keine weiteren Toxizitäten oder Zeichen eines Rezidivs beobachtet.Schlussfolgerung:Die helikale Tomotherapie eröffnet neue Optionen in der Rebestrahlung multipler Hirnmetastasen. Die Anzahl der so behandelten Patienten ist sehr limitiert, dennoch erscheint diese Behandlungsmöglichkeit sehr vielversprechend für Patienten, die auf die initiale Therapie gut angesprochen haben.

Einsatzmöglichkeiten eines offenen magnetresonanztomographen in der therapiesimulation und dreidimensionalen bestrahlungsplanung

HintergrundEs wird ein Verfahren zur rein digitalen Einbindung der diagnostischen Information aus einem offenen Niederfeld-MR-Tomographen (0,23 T) in die Therapiesimulation und die CT-gestützte dreidimensionale Bestrahlungsplanung vorgestellt.MethodikDie Bilder der Magnetresonanztomographie (MRT) wurden unter Verwendung spezieller Lagerungs- und Positionierungshilfen mit der Körperspule akquiriert. Standardmäßig wurde eine Gradientenechosequenz mit einer Repetitionszeit von 320 ms und einer Echozeit von 24 ms verwendet, um transversale und koronare Datensätze aufzunehmen. Eventuell auftretende Verzeichnungen der Bilder wurden bestimmt und mittels Phantommessungen und spezieller Software korrigiert.ErgebnisseDie Bildverzeichnungen konnten durch die Verzeichnungskorrektur von maximal 19 mm auf maximal 8,2 mm und durchschnittlich von 2,7 mm auf 0,7 mm korrigiert werden. Für den Einsatz am Therapiesimulator wurden koronare Aufnahmen verwendet und gemäß Strahlensatz in die Fächerstrahlprojektion umgerechnet. Ein Landmark-Matching-Algorithmus ermöglichte es, die aus der MRT erhaltene Tumorausdehnung in das zuvor digital eingelesene und korrigierte Simulatorbild zu übertragen. An einem Bestrahlungsplanungssystem (TMS, Helax) wurde, ebenfalls mittels Landmark-Matching mit CT-Schichten, die diagnostische MRT-Information aus den transversalen Schichten zur Kontrolle des Zielvolumens eingesetzt. Verschiedene Einsatzmöglichkeiten werden an repräsentativen Patientenbeispielen aufgezeigt.SchlußfolgerungMit dem vorgestellten System kann die Bildinformation aus einem offenen MR-System in die Therapiesimulation und die dreidimensionale Bestrahlungsplanung eingebunden werden. Das Niederfeld-MRT stellt für die Radioonkologie aufgrund der offenen Bauweise und der geringen Kosten eine attraktive Erweiterung der Planungsmöglichkeiten dar.AbstractPurposeA system for digital integration of an open MR scanner (0.23 T, Figure 1) in therapy simulation and 3D radiation treatment planning is described.MethodMR images were acquired using the body coil and various positioning and immobilization aids. A gradient echo sequence (TRITE 320 ms/24 ms) was used to create axial and coronal data sets. Image distortions were measured and corrected using phantom measurements (Figure 2) and specially developed software.ResultsMaximal and mean distortions of the MR images could be reduced from 19 mm to 8.2 mm and from 2.7 mm to 0.7 mm, respectively (Figure 3 to 5, Table 1). Coronal MR images were recalculated in fan beam projection for use at the therapy simulator. Tumor and organ conturs were transferred from the MR image to the digitally acquired and corrected simulator image using a landmark matching algorithm (Figure 6 and 7). For 3D treatment planning, image fusion of axial MR images with standard CT planning images was performed using a landmark matching algorithm, as well (Figure 8). Representative cases are shown to demonstrate potential applications of the system.ConclusionThe described system enables the integration of the imaging information from an open MR system in therapy simulation and 3D treatment planning. The low-field MR scanner is an attractive adjunct for the radiooncologist because of the open design and the low costs.PURPOSE A system for digital integration of an open MR scanner (0.23 T, Figure 1) in therapy simulation and 3D radiation treatment planning is described. METHOD MR images were acquired using the body coil and various positioning and immobilization aids. A gradient echo sequence (TR/TE 320 ms/24 ms) was used to create axial and coronal data sets. Image distortions were measured and corrected using phantom measurements (Figure 2) and specially developed software. RESULTS Maximal and mean distortions of the MR images could be reduced from 19 mm to 8.2 mm and from 2.7 mm to 0.7 mm, respectively (Figure 3 to 5, Table 1). Coronal MR images were recalculated in fan beam projection for use at the therapy simulator. Tumor and organ contours were transferred from the MR image to the digitally acquired and corrected simulator image using a landmark matching algorithm (Figure 6 and 7). For 3D treatment planning, image fusion of axial MR images with standard CT planning images was performed using a landmark matching algorithm, as well (Figure 8). Representative cases are shown to demonstrate potential applications of the system. CONCLUSION The described system enables the integration of the imaging information from an open MR system in therapy simulation and 3D treatment planning. The low-field MR scanner is an attractive adjunct for the radio-oncologist because of the open design and the low costs.

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.