Commissioning and Quality Assurance of RapidArc Radiotherapy Delivery System

For an institution that already owns the licenses, it is economically advantageous and technically feasible to use Pinnacle TPS (Philips Radiation Oncology Systems, Fitchburg, WI) with the BrainLab Novalis delivery system (BrainLAB A.G., Heimstetten, Germany). This takes advantage of the improved accuracy of the convolution algorithm in the presence of heterogeneities compared with the pencil beam calculation, which is particularly significant for lung SBRT treatments. The reference patient positioning DRRs still have to be generated by the BrainLab software from the CT images and isocenter coordinates transferred from Pinnacle. We validated this process with the end‐to‐end hidden target test, which showed an isocenter positioning error within one standard deviation from the previously established mean value. The Novalis treatment table attenuation is substantial (up to 6.2% for a beam directed straight up and up to 8.4% for oblique incidence) and has to be accounted for in calculations. A simple single‐contour treatment table model was developed, resulting in mean differences between the measured and calculated attenuation factors of 0.0%–0.2%, depending on the field size. The maximum difference for a single incidence angle is 1.1%. The BrainLab micro‐MLC (mMLC) leaf tip, although not geometrically round, can be represented in Pinnacle by an arch with satisfactory dosimetric accuracy. Subsequently, step‐and‐shoot (direct machine parameter optimization) IMRT dosimetric agreement is excellent. VMAT (called “SmartArc” in Pinnacle) treatments with constant gantry speed and dose rate are feasible without any modifications to the accelerator. Due to the 3 mm‐wide mMLC leaves, the use of a 2 mm calculation grid is recommended. When dual arcs are used for the more complex cases, the overall dosimetric agreement for the SmartArc plans compares favorably with the previously reported results for other implementations of VMAT: γ(3%,3mm) for absolute dose obtained with the biplanar diode array passing rates above 97% with the mean of 98.6%. However, a larger than expected dose error with the single‐arc plans, confined predominantly to the isocenter region, requires further investigationPACS numbers: 87.55Qr, 87.56Nk

Section: Discussionsupporting

confidence: 90%

“…( 28 , 29 ) They were recorded for a number of SmartArc plans and analyzed with Varian Argus v. 4.7 software. The available data include the average RMS deviations across all leaves, the maximum RMS deviation in that cohort, the 95% range on the error histogram, the maximum leaf deviation, and the leaf speed.…”

Section: Methodsmentioning

confidence: 99%

Validation of Pinnacle treatment planning system for use with Novalis delivery unit

Faygelman

Hunt

Walker

et al. 2010

“…It is also ideal to relate MLC positioning accuracy to the dose delivery errors in the patient, so that decisions on MLC performance can be based off metrics that are clinically relevant for the patient. This is not currently possibly using the widely accepted test MLC patterns for arc therapy MLC QA 4 , 5 . In this paper the method presented has the ability to directly measure MLC positions during clinical VMAT deliveries.…”

Section: Discussionmentioning

confidence: 99%

“…These three dynamic components (i.e., MLC, gantry angle, and dose rate) must remain synchronized throughout the treatment in order to deliver the intended dose to the planning target volume (PTV) and organs at risk (OAR). Due to this high level of complexity, there is a need for comprehensive and informative quality assurance (QA) techniques 4 , 5 …”

Section: Introductionmentioning

confidence: 99%

An EPID‐based system for gantry‐resolved MLC quality assurance for VMAT

Zwan

Barnes

Fuangord

et al. 2016

Multileaf collimator (MLC) positions should be precisely and independently measured as a function of gantry angle as part of a comprehensive quality assurance (QA) program for volumetric‐modulated arc therapy (VMAT). It is also ideal that such a QA program has the ability to relate MLC positional accuracy to patient‐specific dosimetry in order to determine the clinical significance of any detected MLC errors. In this work we propose a method to verify individual MLC trajectories during VMAT deliveries for use as a routine linear accelerator QA tool. We also extend this method to reconstruct the 3D patient dose in the treatment planning system based on the measured MLC trajectories and the original DICOM plan file. The method relies on extracting MLC positions from EPID images acquired at 8.41 fps during clinical VMAT deliveries. A gantry angle is automatically tagged to each image in order to obtain the MLC trajectories as a function of gantry angle. This analysis was performed for six clinical VMAT plans acquired at monthly intervals for three months. The measured trajectories for each delivery were compared to the MLC positions from the DICOM plan file. The maximum mean error detected was 0.07 mm and a maximum root‐mean‐square error was 0.8 mm for any leaf of any delivery. The sensitivity of this system was characterized by introducing random and systematic MLC errors into the test plans. It was demonstrated that the system is capable of detecting random and systematic errors on the range of 1–2 mm and single leaf calibration errors of 0.5 mm. The methodology developed in the work has potential to be used for efficient routine linear accelerator MLC QA and pretreatment patient‐specific QA and has the ability to relate measured MLC positional errors to 3D dosimetric errors within a patient volume.PACS number(s): 87.55.Qr

“…Commissioning and QA procedures for VMAT can be conducted using electronic portal imaging device (EPID). One of the most commonly used QA procedures for Varian linacs (Varian Medical Systems, Palo Alto, CA, USA) are the Ling tests, which rely solely on integrated EPID images 9. These tests, like most common QA methodologies, focus on the accuracy of the dose rate and MLC control systems rather than the gantry angle and gantry speed aspects of the VMAT delivery.…”

Section: Introductionmentioning

confidence: 99%

A novel and independent method for time‐resolved gantry angle quality assurance for VMAT

Fuangrod

Greer

Zwan

et al. 2017

Volumetric‐modulated arc therapy (VMAT) treatment delivery requires three key dynamic components; gantry rotation, dose rate modulation, and multi‐leaf collimator motion, which are all simultaneously varied during the delivery. Misalignment of the gantry angle can potentially affect clinical outcome due to the steep dose gradients and complex MLC shapes involved. It is essential to develop independent gantry angle quality assurance (QA) appropriate to VMAT that can be performed simultaneously with other key VMAT QA testing. In this work, a simple and inexpensive fully independent gantry angle measurement methodology was developed that allows quantitation of the gantry angle accuracy as a function of time. This method is based on the analysis of video footage of a “Double dot” pattern attached to the front cover of the linear accelerator that consists of red and green circles printed on A4 paper sheet. A standard mobile phone is placed on the couch to record the video footage during gantry rotation. The video file is subsequently analyzed and used to determine the gantry angle from each video frame using the relative position of the two dots. There were two types of validation tests performed including the static mode with manual gantry angle rotation and dynamic mode with three complex test plans. The accuracy was 0.26° ± 0.04° and 0.46° ± 0.31° (mean ± 1 SD) for the static and dynamic modes, respectively. This method is user friendly, cost effective, easy to setup, has high temporal resolution, and can be combined with existing time‐resolved method for QA of MLC and dose rate to form a comprehensive set of procedures for time‐resolved QA of VMAT delivery system.