Dose verification for respiratory-gated volumetric modulated arc therapy.

A novel commercial medical linac system (TrueBeam™, Varian Medical Systems, Palo Alto, CA) allows respiratory-gated volumetric modulated arc therapy (VMAT), a new modality for treating moving tumors with high precision and improved accuracy by allowing for regular motion associated with a patient's breathing during VMAT delivery. The purpose of this work is to adapt a previously-developed dose reconstruction technique to evaluate the fidelity of VMAT treatment during gated delivery under clinic-relevant periodic motion related to patient breathing. A Varian TrueBeam system was used in this study. VMAT plans were created for three patients with lung or pancreas tumors. Conventional 6 and 15 MV beams with flattening filter and high-dose-rate 10 MV beams with no flattening filter were used in these plans. Each patient plan was delivered to a phantom first without gating and then with gating for three simulated respiratory periods (3, 4.5 and 6 s). Using the adapted log-file-based dose reconstruction procedure supplemented with ion chamber array (Seven29™, PTW, Freiburg, Germany) measurements, the delivered dose was used to evaluate the fidelity of gated VMAT delivery. Comparison of Seven29 measurements with and without gating showed good agreement with gamma-index passing rates above 99% for 1%/1 mm dose accuracy/distance-to-agreement criteria. With original plans as reference, gamma-index passing rates were 100% for the reconstituted plans (1%/1 mm criteria) and 93.5-100% for gated Seven29 measurements (3%/3 mm criteria). In the presence of leaf error deliberately introduced into the gated delivery of a pancreas patient plan, both dose reconstruction and Seven29 measurement consistently indicated substantial dosimetric differences from the original plan. In summary, a dose reconstruction procedure was demonstrated for evaluating the accuracy of respiratory-gated VMAT delivery. This technique showed that under clinical operation, the TrueBeam system faithfully realized treatment plans with gated delivery. This methodology affords a useful tool for machine- and patient-specific quality assurance of the newly available respiratory-gated VMAT.

[1]  James L. Bedford,et al.  Evaluation of Respiratory-adapted Volumetric Modulated Arc Radiotherapy (VMAT) Planning for Gastro-esophageal Malignancies , 2011 .

[2]  A. L. Angelini,et al.  Characterization of a 2D ion chamber array for the verification of radiotherapy treatments , 2005, Physics in medicine and biology.

[3]  Niko Papanikolaou,et al.  Treatment planning and delivery of IMRT using 6 and 18MV photon beams without flattening filter. , 2009, Applied radiation and isotopes : including data, instrumentation and methods for use in agriculture, industry and medicine.

[4]  James L Bedford,et al.  Evaluation of the Delta4 phantom for IMRT and VMAT verification , 2009, Physics in medicine and biology.

[5]  E. Schreibmann,et al.  Patient-specific quality assurance method for VMAT treatment delivery. , 2009, Medical physics.

[6]  Parag J. Parikh,et al.  Development of the 4D Phantom for patient-specific end-to-end radiation therapy QA , 2007, SPIE Medical Imaging.

[7]  Jan-Jakob Sonke,et al.  3D Dosimetric verification of volumetric-modulated arc therapy by portal dosimetry. , 2010, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[8]  Lei Xing,et al.  Image-Guided and Adaptive Radiation Therapy , 2012 .

[9]  Tommy Knöös,et al.  Current status and future perspective of flattening filter free photon beams. , 2011, Medical physics.

[10]  S. Korreman,et al.  RapidArc treatment verification in 3D using polymer gel dosimetry and Monte Carlo simulation , 2010, Physics in medicine and biology.

[11]  L. Cozzi,et al.  Pre-clinical evaluation of respiratory-gated delivery of volumetric modulated arc therapy with RapidArc , 2010, Physics in medicine and biology.

[12]  Toshikazu Imae,et al.  Quality assurance of volumetric modulated arc therapy using Elekta Synergy , 2009, Acta oncologica.

[13]  L. Xing,et al.  Retrospective IMRT dose reconstruction based on cone-beam CT and MLC log-file. , 2008, International journal of radiation oncology, biology, physics.

[14]  Barbara Dobler,et al.  Commissioning of volumetric modulated arc therapy (VMAT) in a dual-vendor environment. , 2011, Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology.

[15]  J. Dempsey,et al.  An extensive log-file analysis of step-and-shoot intensity modulated radiation therapy segment delivery errors. , 2004, Medical physics.

[16]  J. Bedford,et al.  Commissioning of volumetric modulated arc therapy (VMAT). , 2009, International journal of radiation oncology, biology, physics.

[17]  C. Ling,et al.  Commissioning and quality assurance of RapidArc radiotherapy delivery system. , 2008, International journal of radiation oncology, biology, physics.

[18]  James F Dempsey,et al.  Validation of dynamic MLC-controller log files using a two-dimensional diode array. , 2003, Medical physics.

[19]  Tae-Suk Suh,et al.  Multisource modeling of flattening filter free (FFF) beam and the optimization of model parameters. , 2011, Medical physics.

[20]  R D Wiersma,et al.  Examination of geometric and dosimetric accuracies of gated step-and-shoot intensity modulated radiation therapy. , 2007, Medical physics.

[21]  D. Huyskens,et al.  On-line quality assurance of rotational radiotherapy treatment delivery by means of a 2D ion chamber array and the Octavius phantom. , 2007, Medical physics.

[22]  Bo Lu,et al.  Calibration of a novel four-dimensional diode array. , 2009, Medical physics.

[23]  Lei Xing,et al.  SU‐GG‐T‐271: Dosimetric Properties of Flattening Filter Free Photon Beams from a New Clinical Accelerator , 2010 .

[24]  E. Mok,et al.  Dose reconstruction for volumetric modulated arc therapy (VMAT) using cone-beam CT and dynamic log files , 2010, Physics in medicine and biology.

[25]  D. Low,et al.  A technique for the quantitative evaluation of dose distributions. , 1998, Medical physics.