Application of multi-leaf collimator quality assurance phantom on Truebeam / 中华放射医学与防护杂志

Objective To perform a routine quality assurance procedure for Truebeam multi-leaf collimator (MLC) using MLC quality assurance (QA) phantom,verifying the reliability of MLC during the treatment.Methods MLC QA phantom was a specialized phantom for multi-leaf collimator QA,and contained five radio-opaque spheres that were embedded in an L-shape.The phantom was placed isocentrically on the Truebeam treatment couch for the tests.A quality assurance plan was settled up in the Eclipse v10.0 so that the fields for acquiring the necessary images could be created.The images were acquired by the electronic portal imaging device (EPID),and imported into the PIPSpro software for the analysis.The tests were delivered once a week for six weeks to verify consistency of the delivery,and the images were acquired in the same manner each time.Results For the leaf position test,the average position error was (0.21 ± 0.02) mm.The leaf width was measured at the isocenter,and the average error was (0.04±0.02) mm for the leaf width test.Multi-Port test showed the dynamic leaf shift error,the average error was (0.26 ± 0.04) mm.For the leaf transmission test,the average inter-leaf leakage value was 1.0％ ± 0.14％.Conclusions The MLC system of Truebeam could operate very well and the QA phantom is a useful test tool for the MLC QA.

Monte Carlo simulation of 6 MV flattening-filter-free beams in TrueBeam accelerator / 中华放射医学与防护杂志

Objective To find the best model parameters through Monte Carlo simulation of 6 MV flattening-filter-free (FFF) beams in TrueBeam accelerator, and establish the foundation for the further study of the clinical dosimetry on 6 MV FFF X-rays.Methods Using the BEAMnrc and DOSXYZnrc codes, the percentage depth dose (PDD) and the off-axis ratio (OAR) curves of field ranges from 4 cm ×4 cm to 40 cm × 40 cm were simulated for 6 MV FFF X-ray by adjusting the incident beam energy, radial intensity distribution and angular spread, respectively.The simulation results and measured data were compared, where the optimal Monte Carlo model input parameters were acquired.Results The simulation was most comparable to the measurement when the incident electron energy, full width at half maximum (FWHM) and the spread angle were set as 6.1 MeV, 0.75 mm and 0.9°, respectively.The deviation of 1 mm (position)/1％ (local dose) could be met by the PDD of all tested field sizes and by the OAR when the fields sizes were no larger than 30 cm ×30 cm.The OAR of 40 cm ×40 cm field sizes fulfilled criteria of 1 mm (position)/1.5％ (local dose).Conclusions Monte Carlo simulation agrees well with the measurement and the proposed model parameters, which can be used for further clinical dosimetry studies of 6 MV FFF X-rays.

Quality Assurance for Truebeam Imaging System Based on MIMI Phantom / 中国医学影像学杂志

PurposeTo perform a quality assurance program for Truebeam imaging system using MIMI phantom, and to evaluate the accuracy of the imaging system center with the radiation isocenter and the accuracy of couch shift.Materials and Methods The reference images of MIMI phantom were acquired using CT scanner. The reference images were imported into the treatment planning system and a simple plan was created. The MIMI phantom was placed on the treatment couch. The images were acquired using the MV/KV imaging system, and a match registration was performed with the reference images from the TPS.Results Measured over six months, the precision of the imager and linac's isocenter was <1 mm, and the couch shift accuracy was <1 mm. The measurements over six months demonstrate that isocenters of the MV/KV imaging systems on Truebeam system are stable.Conclusion The accuracy of the Truebeam imaging system center and couch shift is safe and reliable. The error of Truebeam imaging system center and couch shift can be tested on a monthly base.