ABSTRACT
The aim of this study is to evaluate plan quality and dose accuracy for Volumetric Modulated Arc Therapy (VMAT) on the TG-119 and is to investigate the effects on variation of the selectable optimization parameters of VMAT. VMAT treatment planning was implemented on a Varian iX linear accelerator with ARIA record and verify system (Varian Mecical System Palo Alto, CA) and Oncentra MasterPlan treatment planning system (Nucletron BV, Veenendaal, Netherlands). Plan quality and dosimetric accuracy were evaluated by effect of varying a number of arc, gantry spacing and delivery time for the test geometries provided in TG-119. Plan quality for the target and OAR was evaluated by the mean value and the standard deviation of the Dose Volume Histograms (DVHs). The ionization chamber and Delta4PT bi-planar diode array were used for the dose evaluation. For treatment planning evaluation, all structure sets closed to the goals in the case of single arc, except for the C-shape (hard), and all structure sets achieved the goals in the case of dual arc, except for C-shape (hard). For the variation of a number of arc, the simple structure such as a prostate did not have the difference between single arc and dual arc, whereas the complex structure such as a head and neck showed a superior result in the case of dual arc. The dose distribution with gantry spacing of 4degrees was shown better plan quality than the gantry spacing of 6degrees, but was similar results compared with gantry spacing of 2degrees. For the verification of dose accuracy with single arc and dual arc, the mean value of a relative error between measured and calculated value were within 3% and 4% for point dose and confidence limit values, respectively. For the verification on dose accuracy with the gantry intervals of 2degrees, 4degrees and 6degrees, the mean values of relative error were within 3% and 5% for point dose and confidence limit values, respectively. In the verification of dose distribution with Delta4PT bi-planar diode array, gamma passing rate was 98.72+/-1.52% and 98.3+/-1.5% for single arc and dual arc, respectively. The confidence limit values were within 4%. The smaller the gantry spacing, the more accuracy results were shown. In this study, we performed the VMAT QA based on TG-119 procedure, and demonstrated that all structure sets were satisfied with acceptance criteria. And also, the results for the selective optimization variables informed the importance of selection for the suitable variables according to the clinical cases.
Subject(s)
Head , Neck , Particle Accelerators , Prostate , Radiotherapy, Intensity-ModulatedABSTRACT
PURPOSE: To study the feasibility of verifying real-time 2-D dose distribution measurement system with the scintillation screen for the quality assurance. MATERIALS AND METHODS: The water phantom consisted of a scintillation screen (LANEX fast screen, Kodak, USA) that was axially located in the middle of an acrylic cylinder with a diameter of 25 cm. The charge-coupled device (CCD) camera was attached to the phantom in order to capture the visible light from the scintillation screen. To observe the dose distribution in real time, the intensity of the light from the scintillator was converted to a dosage. The isodose contours of the calculations from RTP and those of the measurements using the scintillation screen were compared for the arc therapy and the intensity modulated radiation therapy (IMRT). RESULTS: The kernel, expressed as a multiplication of two error functions, was obtained in order to correct the sensitivity of the CCD of the camera and the scintillation screen. When comparing the calculated isodose and measured isodose, a discrepancy of less than 8 mm in the high dose region was observed. CONCLUSIONS: Using the 2-D dosimetry system, the relationship between the light and the dosage could be found, and real-time verification of the dose distribution was feasible.
Subject(s)
Feasibility Studies , Light , WaterABSTRACT
Objective The goal of this work is to evaluate the dosimetric characteristics of a new 2D diode array (Mapcheck from Sun Nuclear Corporation,Melbourne,Florida) and assess the role it can play in routine IMRT QA. Methods Fundamental properties of the Mapcheck such as reproducibility and linearity were studied for high-energy photon beams. Clinical performance of the MapCheck for relative and absolute dosimetry was demonstrated with head and neck IMRT plans,and compared with plan dose distribution. Absolute dose measured by Ion chamber and Mapcheck are compared with the one given in TPS. Results The Mapcheck offers the dosimetric characteristics required for performing both relative and absolute dose measurements. Conclusion Mapcheck can provide the verification of absolute dose and relative dose. Its use in the clinic can simplify and reduce the IMRT QA workload.