Commissioning Monte Carlo algorithm for robotic radiosurgery using cylindrical 3D-array with variable density inserts

PurposeThe challenges of accurate dosimetry for stereotactic radiotherapy (SRT) with small unflattened radiation fields have been widely reported in the literature. In this case, suitable dosimeters would have to offer a submillimeter spatial resolution. The CyberKnife® (Accuray Inc., Sunnyvale, CA, USA) is an SRT‐dedicated linear accelerator (linac), which can deliver treatments with submillimeter positional accuracy using circular fields. Beams are delivered with the desired field size using fixed cones, the InCise™ multileaf collimator or a dynamic variable‐aperture Iris™ collimator. The latter, allowing for field sizes to be varied during treatment delivery, has the potential to decrease treatment time, but its reproducibility in terms of output factors (OFs) and dose profiles (DPs) needs to be verified.MethodsA 2D monolithic silicon array detector, the “Octa”, was evaluated for dosimetric quality assurance (QA) for a CyberKnife system. OFs, DPs, percentage depth‐dose (PDD) and tissue maximum ratio (TMR) were investigated, and results were benchmarked against the PTW SRS diode. Cross‐plane, in‐plane and 2 diagonal dose profiles were measured simultaneously with high spatial resolution (0.3 mm). Monte Carlo (MC) simulations with a GEANT4 (GEometry ANd Tracking 4) tool‐kit were added to the study to support the experimental characterization of the detector response.ResultsFor fixed cones and the Iris, for all field sizes investigated in the range between 5 and 60 mm diameter, OFs, PDDs, TMRs, and DPs in terms of FWHM measured by the Octa were accurate within 3% when benchmarked against the SRS diode and MC calculations.ConclusionsThe Octa was shown to be an accurate dosimeter for measurements with a 6 MV FFF beam delivered with a CyberKnife system. The detector enabled real‐time dosimetric verification for the variable aperture Iris collimator, yielding OFs and DPs consistent with those obtained with alternative methods.

Section: Discussionmentioning

confidence: 99%

CyberKnife^® fixed cone and Iris™ defined small radiation fields: Assessment with a high‐resolution solid‐state detector array

Biasi

Petasecca

Guatelli

et al. 2018

“…This material assignment method could lead to incorrect simulation of physical interactions for high‐density metal. Since different materials of similar density could introduce differences in deposited dose, we should be cautious when working at the end of a material's density range 6, 20…”

Section: Discussionmentioning

confidence: 99%

“…But this commissioning was performed for their own dual‐source model built previously 5. Dechambre et al once proposed a novel method for commissioning the MC dose calculation algorithm of Multiplan using a cylindrical 3D‐array with variable density inserts 6. However, the diode spacing of these arrays (0.5–1.0 cm) is generally too large for the small field of Cyberknife, thus may not provide sufficient information for dose verification.…”

Section: Introductionmentioning

confidence: 99%

Film‐based dose validation of Monte Carlo algorithm for Cyberknife system with a CIRS thorax phantom

Pan

Yang

et al. 2018

Monte Carlo (MC) simulation, as the most accurate dose calculation algorithm, is available in the MultiPlan treatment planning system for Cyberknife. The main purpose of this work was to perform experiments to thoroughly investigate the accuracy of the MC dose calculation algorithm. Besides the basic MC beam commissioning, two test scenarios were designed. First, single beam tests were performed with a solid water phantom to verify the MC source model in simple geometry. Then, a lung treatment plan on a CIRS thorax phantom was created to mimic the clinical patient treatment. The plan was optimized and calculated using ray tracing (RT) algorithm and then recalculated using MC algorithm. Measurements were performed in both a homogeneous phantom and a heterogeneous phantom (CIRS). Ion‐chamber and radiochromic film were used to obtain absolute point dose and dose distributions. Ion‐chamber results showed that the differences between measured and MC calculated dose were within 3% for all tests. On the film measurements, MC calculation results showed good agreements with the measured dose for all single beam tests. As for the lung case, the gamma passing rate between measured and MC calculated dose was 98.31% and 97.28% for homogeneous and heterogeneous situation, respectively, using 3%/2 mm criteria. However, RT algorithm failed with the passing rate of 79.25% (3%/2 mm) for heterogeneous situation. These results demonstrated that MC dose calculation algorithm in the Multiplan system is accurate enough for patient dose calculation. It is strongly recommended to use MC algorithm in heterogeneous media.

“…In addition to its application in dosimetric verification, its unique 3D design also makes it a potential tool for machine QA . Although the ArcCHECK has been widely used for QA of isocentric treatment machines, its applications in commissioning of Monte Carlo algorithm and patient‐specific QA for nonisocentric treatment machine such as CyberKnife were also studied by some groups . In this study, we developed a novel method for testing the constancy of beam path accuracy of our CyberKnife (model M6) system by using ArcCHECK.…”

Section: Introductionmentioning

confidence: 99%

A novel method for monitoring the constancy of beam path accuracy in CyberKnife

Yang

Wong

Lam

et al. 2019

The aim of current work was to present a novel evaluation procedure implemented for checking the constancy of beam path accuracy of a CyberKnife system based on ArcCHECK. A tailor‐made Styrofoam with four implanted fiducial markers was adopted to enable the fiducial tracking during beam deliveries. A simple two‐field plan and an isocentric plan were created for determining the density override of ArcCHECK in MultiPlan and the constancy of beam path accuracy respectively. Correlation curves for all diodes involved in the study were obtained by analyzing the dose distributions calculated by MultiPlan after introducing position shifts in anteroposterior, superoinferior, and left–right directions. The ability of detecting systematic position error was also evaluated by changing the position of alignment center intentionally. The one standard deviation (SD) result for reproducibility test showed the RMS of 0.054 mm and the maximum of 0.263 mm, which was comparable to the machine self‐test result. The mean of absolute value of position errors in the constancy test was measured to 0.091 mm with a SD of 0.035 mm, while the root‐mean‐square was 0.127 mm with a SD of 0.034 mm. All introduced systematic position errors range from 0.3 to 2 mm were detected successfully. Efficient method for evaluating the constancy of beam path accuracy of CyberKnife has been developed and proven to be sensitive enough for detecting a systematic drift of robotic manipulator. Once the workflow is streamlined, our proposed method will be an effective and easy quality assurance procedure for medical physicists.