Assessment of spatial uncertainties in the radiotherapy process with the Novalis system.

Nagoya Radiosurgery Center, Nagoya Kyoritsu Hospital, Nagoya, Japan.
International journal of radiation oncology, biology, physics (Impact Factor: 4.18). 11/2009; 75(2):549-57. DOI: 10.1016/j.ijrobp.2009.02.080
Source: PubMed

ABSTRACT The purpose of this study was to evaluate the accuracy of a new version of the ExacTrac X-ray (ETX) system with statistical analysis retrospectively in order to determine the tolerance of systematic components of spatial uncertainties with the Novalis system.
Three factors of geometrical accuracy related to the ETX system were evaluated by phantom studies. First, location dependency of the detection ability of the infrared system was evaluated. Second, accuracy of the automated calculation by the image fusion algorithm in the patient registration software was evaluated. Third, deviation of the coordinate scale between the ETX isocenter and the mechanical isocenter was evaluated. From the values of these examinations and clinical experiences, the total spatial uncertainty with the Novalis system was evaluated.
As to the location dependency of the detection ability of the infrared system, the detection errors between the actual position and the detected position were 1% in translation shift and 0.1 degrees in rotational angle, respectively. As to the accuracy of patient verification software, the repeatability and the coincidence of the calculation value by image fusion were good when the contrast of the X-ray image was high. The deviation of coordinates between the ETX isocenter and the mechanical isocenter was 0.313 +/- 0.024 mm, in a suitable procedure.
The spatial uncertainty will be less than 2 mm when suitable treatment planning, optimal patient setup, and daily quality assurance for the Novalis system are achieved in the routine workload.

Download full-text


Available from: Tatsuya Kobayashi, Jul 16, 2014
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: To compare the positioning accuracy and stability of two distinct noninvasive immobilization devices, a dedicated (D-) and conventional (C-) mask, and to evaluate the applicability of a 6-degrees-of-freedom (6D) correction, especially to the C-mask, based on our initial experience with cranial stereotactic radiotherapy (SRT) using ExacTrac (ET)/Robotics integrated into the Novalis Tx platform. The D- and C-masks were the BrainLAB frameless mask system and a general thermoplastic mask used for conventional radiotherapy such as whole brain irradiation, respectively. A total of 148 fractions in 71 patients and 125 fractions in 20 patients were analyzed for the D- and C-masks, respectively. For the C-mask, 3D correction was applied to the initial 10 patients, and thereafter, 6D correction was adopted. The 6D residual errors (REs) in the initial setup, after correction (pre-treatment), and during post-treatment were measured and compared. The D-mask provided no significant benefit for initial setup. The post-treatment median 3D vector displacements (interquatile range) were 0.38 mm (0.22, 0.60) and 0.74 mm (0.49, 1.04) for the D- and C-masks, respectively (p<0.001). The post-treatment maximal translational REs were within 1 mm and 2 mm for the D- and C-masks, respectively, and notably within 1.5 mm for the C-mask with 6D correction. The pre-treatment 3D vector displacements were significantly correlated with those for post-treatment in both masks. The D-mask confers positional stability acceptable for SRT. For the C-mask, 6D correction is also recommended, and an additional setup margin of 0.5 mm to that for the D-mask would be sufficient. The tolerance levels for the pre-treatment REs should similarly be set as small as possible for both systems.
    Radiotherapy and Oncology 11/2011; 102(2):198-205. DOI:10.1016/j.radonc.2011.10.012 · 4.86 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Strereotactic body radiation therapy needs adapted or dedicated equipment to allow fulfilling the particular conditions of the stereotactic treatments: submillimetric accuracy during the treatment delivery, high doses for a reduced number of sessions. This kind of treatment can be either performed using delivery equipment conceived and dedicated to the technique, or performed on conventional machines adapted to meet the criteria. Contrary to intracranial treatments, the positioning of the target volume raises new difficulties, mainly due to the diversity of localization to treat and also due to inter- and intrafraction movements that can occur. To reduce these effects that could affect the irradiation accuracy, positioning or movement compensation, mostly due to respiration, tools have been developed.
    Cancer/Radiothérapie 07/2014; DOI:10.1016/j.canrad.2014.03.012 · 1.11 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The purpose of this study was to perform comprehensive measurements and testing of a Novalis Tx linear accelerator, and to develop technical guidelines for com-missioning from the time of acceptance testing to the first clinical treatment. The Novalis Tx (NTX) linear accelerator is equipped with, among other features, a high-definition MLC (HD120 MLC) with 2.5 mm central leaves, a 6D robotic couch, an optical guidance positioning system, as well as X-ray-based image guidance tools to provide high accuracy radiation delivery for stereotactic radiosurgery and stereotactic body radiation therapy procedures. We have performed extensive tests for each of the components, and analyzed the clinical data collected in our clinic. We present technical guidelines in this report focusing on methods for: (1) efficient and accurate beam data collection for commissioning treatment planning systems, including small field output measurements conducted using a wide range of detectors; (2) commissioning tests for the HD120 MLC; (3) data collection for the baseline characteristics of the on-board imager (OBI) and ExacTrac X-ray (ETX) image guidance systems in conjunction with the 6D robotic couch; and (4) end-to-end testing of the entire clinical process. Established from our clinical experience thus far, recommendations are provided for accurate and efficient use of the OBI and ETX localization systems for intra- and extracranial treatment sites. Four results are presented. (1) Basic beam data measurements: Our measurements confirmed the necessity of using small detectors for small fields. Total scatter factors varied significantly (30% to approximately 62%) for small field measurements among detectors. Unshielded stereotactic field diode (SFD) overestimated dose by ~ 2% for large field sizes. Ion chambers with active diameters of 6 mm suffered from significant volume averaging. The sharpest profile penumbra was observed for the SFD because of its small active diameter (0.6 mm). (2) MLC commissioning: Winston Lutz test, light/radiation field congruence, and Picket Fence tests were performed and were within criteria established by the relevant task group reports. The measured mean MLC transmission and dynamic leaf gap of 6 MV SRS beam were 1.17% and 0.36 mm, respectively. (3) Baseline characteristics of OBI and ETX: The isocenter localization errors in the left/right, posterior/anterior, and superior/inferior directions were, respectively, -0.2 ± 0.2 mm, -0.8 ± 0.2 mm, and -0.8 ± 0.4 mm for ETX, and 0.5 ± 0.7 mm, 0.6 ± 0.5 mm, and 0.0 ± 0.5 mm for OBI cone-beam computed tomography. The registration angular discrepancy was 0.1 ± 0.2°, and the maximum robotic couch error was 0.2°. (4) End-to-end tests: The measured isocenter dose differences from the planned values were 0.8% and 0.4%, measured respectively by an ion chamber and film. The gamma pass rate, measured by EBT2 film, was 95% (3% DD and 1 mm DTA). Through a systematic series of quantitative commissioning experiments and end-to-end tests and our initial clinical experience, described in this report, we demonstrate that the NTX is a robust system, with the image guidance and MLC requirements to treat a wide variety of sites - in particular for highly accurate delivery of SRS and SBRT-based treatments.
    Journal of Applied Clinical Medical Physics 05/2012; 13(3):3729. · 1.11 Impact Factor