Cornelia Walter

Frameless stereotactic radiosurgery of a solitary liver metastasis using active breathing control and stereotactic ultrasound.

Background and Purpose:Radiosurgery of liver metastases is effective but a technical challenge due to respiration-induced movement. The authors report on the initial experience of the combination of active breathing control (ABC®) with stereotactic ultrasound (B-mode acquisition and targeting [BAT®]) for frameless radiosurgery.Patients and Methods:A patient with a solitary, inoperable liver metastasis from cholangiocellular carcinoma is presented (Figure 4). ABC® (Figure 3) was used for tumor/liver immobilization. Tumor/liver position was controlled and corrected using ultrasound (BAT®; Figure 1). The tumor was irradiated with a single dose of 24 Gy.Results:Using ABC®, the motion of the tumor was significantly reduced and the overall positioning error was < 5 mm (Figure 2). BAT® allowed a rapid localization of the lesion during breath hold which could be performed without difficulties for 20 s. Overall treatment time was acceptable (30 min).Conclusion:Frameless stereotactic radiotherapy with the combination of ABC® and BAT® allows the delivery of high single doses to targets accessible to ultrasound with high precision comparable to a frame-based approach.Hintergrund und Ziel:Die Radiochirurgie solitärer Lebermetastasen ist effektiv, stellt jedoch aufgrund der Atembewegung des Targets eine technische Herausforderung dar. Die Autoren berichten über die initiale Erfahrung mit der rahmenlosen Radiochirurgie durch die Kombination einer aktiven Atmungskontrolle („active breathing control“ [ABC®]) mit dem stereotaktischen Ultraschall („B-mode acquisition and targeting“ [BAT®]).Patient und Methodik:Präsentiert wird ein Patient mit einer solitären Lebermetastase bei cholangiozellulärem Karzinom (Abbildung 4). ABC® (Abbildung 3) wurde zur Immobilisation des Tumors bzw. der Leber verwendet. Die Position des Tumors bzw. der Leber wurde mit Ultraschall (BAT®) kontrolliert und ggf. korrigiert (Abbildung 1). Der Tumor wurde mit einer Einzeldosis von 24 Gy konformal bestrahlt.Ergebnisse:Durch ABC® konnte die Leber-/Tumorbewegung minimiert werden, die gesamte Positionierungsunsicherheit betrug < 5 mm (Abbildung 2). BAT® erlaubte eine schnelle Lokalisierung des Zielvolumens unter Atemanhalt, was wiederholt über 20 s vom Patienten problemlos ausgeführt wurde. Die Gesamtbehandlungszeit war gegenüber einer ungetriggerten Behandlung kaum verlängert (30 min).Schlussfolgerung:Die rahmenlose Stereotaxie durch Kombination von ABC® und BAT® erlaubt, bei sonographisch zugänglichen Zielvolumina hohe Dosen zu applizieren. Die erreichte Präzision liegt im Bereich jener von rahmenbasierten Verfahren.

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.

Fast kilovoltage/megavoltage (kVMV) breathhold cone-beam CT for image-guided radiotherapy of lung cancer

Long image acquisition times of 60-120 s for cone-beam CT (CBCT) limit the number of patients with lung cancer who can undergo volume image guidance under breathhold. We developed a low-dose dual-energy kilovoltage-megavoltage-cone-beam CT (kVMV-CBCT) based on a clinical treatment unit reducing imaging time to < or =15 s. Simultaneous kVMV-imaging was achieved by dedicated synchronization hardware controlling the output of the linear accelerator (linac) based on detector panel readout signals, preventing imaging artifacts from interference of the linacs MV-irradiation and panel readouts. Optimization was performed to minimize the imaging dose. Single MV-projections, reconstructed MV-CBCT images and images of simultaneous 90 degrees kV- and 90 degrees MV-CBCT (180 degrees kVMV-CBCT) were acquired with different parameters. Image quality and imaging dose were evaluated and compared to kV-imaging. Hardware-based kVMV synchronization resulted in artifact-free projections. A combined 180 degrees kVMV-CBCT scan with a total MV-dose of 5 monitor units was acquired in 15 s and with sufficient image quality. The resolution was 5-6 line pairs cm(-1) (Catphan phantom). The combined kVMV-scan dose was equivalent to a kV-radiation scan dose of approximately 33 mGy. kVMV-CBCT based on a standard linac is promising and can provide ultra-fast online volume image guidance with low imaging dose and sufficient image quality for fast and accurate patient positioning for patients with lung cancer under breathhold.