Feasibility of postoperative spine stereotactic body radiation therapy in proximity of carbon and titanium hybrid implants using a robotic radiotherapy device.

BACKGROUND AND PURPOSE To assess the feasibility of postoperative stereotactic body radiation therapy (SBRT) for patients with hybrid implants consisting of carbon fiber reinforced polyetheretherketone and titanium (CFP-T) using CyberKnife. MATERIALS AND METHODS All essential steps within a radiation therapy (RT) workflow were evaluated. First, the contouring process of target volumes and organs at risk (OAR) was done for patients with CFP-T implants. Second, after RT-planning, the accuracy of the calculated dose distributions was tested in a slab phantom and an anthropomorphic phantom using film dosimetry. As a third step, the accuracy of the mandatory image guided radiation therapy (IGRT) including automatic matching was assessed using the anthropomorphic phantom. For this goal, a standard quality assurance (QA) test was modified to carry out its IGRT part in presence of CFP-T implants. RESULTS Using CFP-T implants, target volumes could precisely delineated. There was no need for compromising the contours to overcome artifact obstacles. Differences between measured and calculated dose values were below 11% for the slab phantom, and at least 95% of the voxels were within 5% dose difference. The comparisons for the anthropomorphic phantom showed a gamma-passing rate (5%, 1 mm) of at least 97%. Additionally the test results with and without CFP-T implants were comparable. No issues concerning the IGRT were detected. The modified machine QA test resulted in a targeting error of 0.71 mm, which corresponds to the results of the unmodified standard tests. CONCLUSION Dose calculation and delivery of postoperative spine SBRT is feasible in proximity of CFP-T implants using a CyberKnife system

Skin surface markers for stereotactic body radiation therapy of sternal metastasis.

Stereotactic body radiation therapy is an effective and safe treatment modality for bone metastasis which allows clinicians to accurately target lesions to high doses while minimizing dose to organs at risk. The commercially available CyberKnife Xsight™ Spine Tracking System (Accuray, Inc., Sunnyvale, CA) tracks static skeletal structures and eliminates the need for implanted fiducial markers (FMs). However, the Xsight™ Spine Tracking system is not appropriate for bone metastases outside the spine, which are moving due to respiration and typically, FMs have to be implanted close to the lesion. These FMs will be used to track the dynamic target. For targets close to the surface, non-invasive fixation of the FMs to the patient's skin could be an option

SU-F-T-586: Pre-Treatment QA of InCise2 MLC Plans On a Cyberknife-M6 Using the Delta4 System in SBRT.

PURPOSE Performing pre-treatment quality assurance (QA) with the Delta4 system (ScandiDos Inc., Madison, WI) is well established for linac-based radiotherapy. This is not true when using a Cyberknife (Accuray Inc., Sunnyvale, CA) where, typically film-based QA is applied. The goal of this work was to test the feasibility to use the Delta4 system for pre-treatment QA for stereotactic body radiation therapy (SBRT) using a Cyberknife-M6 equipped with the InCise2 multileaf collimator (MLC). METHODS In order to perform measurements without accelerator pulse signal, the Tomotherapy option within the Delta4 software was used. Absolute calibration of the Delta4 phantom was performed using a 10×10 cm(2) field shaped by the InCise2 MLC of the Cyberknife-M6. Five fiducials were attached to the Delta4 phantom in order to be able to track the phantom before and during measurements. For eight SBRT treatment plans (two liver, two prostate, one lung, three bone metastases) additional verification plans were recalculated on the Delta4 phantom using MultiPlan. Dicom data was exported from MultiPlan and was adapted in order to be compatible with the Delta4 software. The measured and calculated dose distributions were compared using the gamma analysis of the Delta4 system. RESULTS All eight SBRT plans were successfully measured with the aid of the Delta4 system. In the mean, 98.0±1.9%, 95.8±4.1% and 88.40±11.4% of measured dose points passed the gamma analysis using a global dose deviation criterion of 3% (100% corresponds to the dose maximum) and a distance-to-agreement criterion of 3 mm, 2 mm and 1 mm, respectively, and a threshold of 20%. CONCLUSION Pre-treatment QA of SBRT plans using the Delta4 system on a Cyberknife-M6 is feasible. Measured dose distributions of SBRT plans showed clinically acceptable agreement with the corresponding calculated dose distributions

Validation of the Swiss Monte Carlo Plan for a static and dynamic 6 MV photon beam

Monte Carlo (MC) based dose calculations can compute dose distributions with an accuracy surpassing that of conventional algorithms used in radiotherapy, especially in regions of tissue inhomogeneities and surface discontinuities. The Swiss Monte Carlo Plan (SMCP) is a GUI-based framework for photon MC treatment planning (MCTP) interfaced to the Eclipse treatment planning system (TPS). As for any dose calculation algorithm, also the MCTP needs to be commissioned and validated before using the algorithm for clinical cases. Aim of this study is the investigation of a 6 MV beam for clinical situations within the framework of the SMCP. In this respect, all parts i.e. open fields and all the clinically available beam modifiers have to be configured so that the calculated dose distributions match the corresponding measurements. Dose distributions for the 6 MV beam were simulated in a water phantom using a phase space source above the beam modifiers. The VMC++ code was used for the radiation transport through the beam modifiers (jaws, wedges, block and multileaf collimator (MLC)) as well as for the calculation of the dose distributions within the phantom. The voxel size of the dose distributions was 2mm in all directions. The statistical uncertainty of the calculated dose distributions was below 0.4%. Simulated depth dose curves and dose profiles in terms of [Gy/MU] for static and dynamic fields were compared with the corresponding measurements using dose difference and γ analysis. For the dose difference criterion of ±1% of D(max) and the distance to agreement criterion of ±1 mm, the γ analysis showed an excellent agreement between measurements and simulations for all static open and MLC fields. The tuning of the density and the thickness for all hard wedges lead to an agreement with the corresponding measurements within 1% or 1mm. Similar results have been achieved for the block. For the validation of the tuned hard wedges, a very good agreement between calculated and measured dose distributions was achieved using a 1%/1mm criteria for the γ analysis. The calculated dose distributions of the enhanced dynamic wedges (10°, 15°, 20°, 25°, 30°, 45° and 60°) met the criteria of 1%/1mm when compared with the measurements for all situations considered. For the IMRT fields all compared measured dose values agreed with the calculated dose values within a 2% dose difference or within 1 mm distance. The SMCP has been successfully validated for a static and dynamic 6 MV photon beam, thus resulting in accurate dose calculations suitable for applications in clinical cases

Erhebung von Patienten-Lagerungsunsicherheiten in IGRT in Kombination mit einem Tisch mit sechs Freiheitsgraden

PURPOSE The range of patient setup errors in six dimensions detected in clinical routine for cranial as well as for extracranial treatments, were analyzed while performing linear accelerator based stereotactic treatments with frameless patient setup systems. Additionally, the need for re-verification of the patient setup for situations where couch rotations are involved was analyzed for patients treated in the cranial region. METHODS AND MATERIALS A total of 2185 initial (i.e. after pre-positioning the patient with the infrared system but before image guidance) patient setup errors (1705 in the cranial and 480 in the extracranial region) obtained by using ExacTrac (BrainLAB AG, Feldkirchen, Germany) were analyzed. Additionally, the patient setup errors as a function of the couch rotation angle were obtained by analyzing 242 setup errors in the cranial region. Before the couch was rotated, the patient setup error was corrected at couch rotation angle 0° with the aid of image guidance and the six degrees of freedom (6DoF) couch. For both situations attainment rates for two different tolerances (tolerance A: ± 0.5mm, ± 0.5°; tolerance B: ± 1.0 mm, ± 1.0°) were calculated. RESULTS The mean (± one standard deviation) initial patient setup errors for the cranial cases were -0.24 ± 1.21°, -0.23 ± 0.91° and -0.03 ± 1.07° for the pitch, roll and couch rotation axes and 0.10 ± 1.17 mm, 0.10 ± 1.62 mm and 0.11 ± 1.29 mm for the lateral, longitudinal and vertical axes, respectively. Attainment rate (all six axes simultaneously) for tolerance A was 0.6% and 13.1% for tolerance B, respectively. For the extracranial cases the corresponding values were -0.21 ± 0.95°, -0.05 ± 1.08° and -0.14 ± 1.02° for the pitch, roll and couch rotation axes and 0.15 ± 1.77 mm, 0.62 ± 1.94 mm and -0.40 ± 2.15 mm for the lateral, longitudinal and vertical axes. Attainment rate (all six axes simultaneously) for tolerance A was 0.0% and 3.1% for tolerance B, respectively. After initial setup correction and rotation of the couch to treatment position a re-correction has to be performed in 77.4% of all cases to fulfill tolerance A and in 15.6% of all cases to fulfill tolerance B. CONCLUSION The analysis of the data shows that all six axes of a 6DoF couch are used extensively for patient setup in clinical routine. In order to fulfill high patient setup accuracies (e.g. for stereotactic treatments), a 6DoF couch is recommended. Moreover, re-verification of the patient setup after rotating the couch is required in clinical routine.Zweck Der klinisch relevante Bereich, in welchem Unsicherheiten der Patientenlagerung in sechs Dimensionen sowohl bei kraniellen wie auch bei extrakraniellen Bestrahlungen auftreten, wurde für Linearbeschleuniger-basierte stereotaktische Bestrahlungen mit rahmenlosen Patienten-Positionierungs-Systemen untersucht. Zusätzlich wurde die Lagerungsunsicherheit für Patienten, welche im kraniellen Bereich bestrahlt wurden, als Funktion des Tischrotationswinkels ausgewertet. Methoden und Material Mit Hilfe von ExacTrac (BrainLAB AG, Feldkirchen, Deutschland) wurden insgesamt 2185 initiale (d.h. nach dem Vorpositionieren des Patienten mit dem Infrarotsystem aber vor der bildgestützten Lagerung) Lagerungsunsicherheiten gemessen (1705 im kraniellen und 480 im extrakraniellen Bereich). Die Unsicherheiten wurden zudem als Funktion des Tischrotationswinkels mit Hilfe von 242 Lagerungsunsicherheiten im kraniellen Bereich untersucht. Vor der Tischrotation wurde die Lagerungsunsicherheit der Patienten beim Tischwinkel 0° bildgestützt und mit Hilfe des Tisches mit sechs Freiheitsgraden (6D-Tisch) korrigiert. Für beide Situationen wurde die Rate, mit welcher zwei verschiedene Toleranzen (Toleranz A: ±0.5 mm, ±0.5°; Toleranz B: ±1.0 mm, ±1.0°) erfüllt waren, berechnet. Resultate Die Mittelwerte (± eine Standardabweichung) der initialen Lagerungsunsicherheiten der kraniellen Fälle waren -0.24 ± 1.21°, -0.23 ± 0.91° und -0.03 ± 1.07° für die Achsen Pitch, Roll und Tischrotationswinkel und 0.10 ± 1.17 mm, 0.10 ± 1.62 mm und 0.11 ± 1.29 mm für die laterale, longitudinale und vertikale Achse. Die Lagerungsunsicherheit war in 0.6%, resp. 13.1% aller kraniellen Fälle für alle sechs Achsen gleichzeitig innerhalb der Toleranz A, resp. der Toleranz B. Die Mittelwerte (± eine Standardabweichung) der initialen Patienten-Lagerungsunsicherheiten der extrakraniellen Fälle waren -0.21 ± 0.95°, -0.05 ± 1.08° und -0.14 ± 1.02° für die Achsen Pitch, Roll und Tischrotationswinkel und 0.15 ± 1.77 mm, 0.62 ± 1.94 mm und -0.40 ± 2.15 mm für die laterale, longitudinale und vertikale Achse. Die Patienten-Lagerungsunsicherheit war in 0.0%, resp. 3.1% aller extrakraniellen Fälle für alle sechs Achsen gleichzeitig innerhalb der Toleranz A, resp. der Toleranz B. Nach initialer Lagerungskorrektur und anschliessendem Rotieren des Tisches in die Bestrahlungsposition waren in 77.4% resp. 15.6% aller Fälle erneute Lagerungskorrekturen nötig, um die Toleranz A resp. Toleranz B zu erfüllen. Schlussfolgerung Unsere Daten zeigen, dass alle sechs Achsen eines 6D-Tisches extensiv für die Patientenlagerung in der klinischen Routine gebraucht werden. Um hohe Genauigkeiten bei der Patientenlagerung zu erreichen (z.B. für stereotaktische Bestrahlungen), ist ein 6D-Tisch empfohlen. Ausserdem zeigen die Resultate, dass nach einer Tischrotation eine erneute Verifikation der Patientenlagerung notwendig ist

Frameless linac-based (Novalis TX) stereotactic treatment for vestibular schwannoma that extend distally into the iac (Internal Acoustic Canal): an analysis of the dose to the cochlea

Objectives: We compare the dose parameters between 3 different radiosurgery delivery techniques which may have an impact on cochlea function. Methods: Five patients with unilateral vestibular schwannoma (VS) were selected for this study. Planning procedure was carried out using the BrainLAB® iPlan planning system v. 4.5. For each patient three different planning techniques were used: dynamic arc (DA) with 5 arcs per plan, hybrid arc (HA) with 5 arcs per plan and IMRT with 8 fields per plan. For each technique, two plans were generated with different methods: with the first method (PTV coverage) it was the goal to fully cover the PTV with at least 12 Gy (normalization: 12 Gy covered 99% of the PTV) and with the second method (cochlea sparing) it was the goal to spare the cochlea (normalization: 12 Gy covers 50% of the PTV/V4Gy of cochlea lower than 1%). Plan evaluation was done considering target volume and coverage (conformity and homogeneity) and OAR constraints (mean (Dmean) and maximum dose (Dmax) to cochlea, Dmax to brainstem and cochlea). The total number of monitor units (MU) was analyzed. Results: The median tumor volume was 0.95 cm³ (range, 0.86-3 cm³). The median PTV was 1.44 cm³ (range, 1-3.5 cm³). The median distance between the tumor and the cochlea's modiulus was 2.7 mm (range, 1.8-6.3 mm). For the PTV coverage method, when we compared the cochlear dose in VS patients planned with DA, HA and IMRT, there were no significant differences in Dmax (p = 0.872) and in Dmean (p= 0.860). We found a significant correlation (p< 0.05) between the target volume and the cochlear Dmean for all plans with Pearson's coefficient correlation of 0.90, 0.92 and 0.94 for the DA, HA and IMRT techniques, respectively. For the cochlea sparing method, when we compared the cochlear dose in VS patients planned with DA, HA and IMRT, there were no significant differences in Dmax (p = 0.310) and in Dmean (p= 0.275). However, in this group the V4Gy of the ipsilateral cochlea represents less than 1%. When using the HA or IMRT technique, the homogeneity and conformity in the PTV, but also the number of MUs were increased in comparison to the DA technique. Conclusion: VS tumors that extend distally into the IAC had an equivalent sparing of cochlea with DA approach compared with the HA and IMRT techniques. Disclosure: No significant relationships