Abstract
In radiation therapy, a secondary independent dose verification is an important component of a quality control system. Mobius3D calculates three‐dimensional (3D) patient dose using reference beam data and a collapsed cone convolution algorithm and analyzes dose‐volume histogram automatically. There are currently no published data on commissioning and determining tolerance levels of Mobius3D for TomoTherapy. To verify the calculation accuracy and adjust the parameters of this system, we compared the measured dose using an ion chamber and film in a phantom with the dose calculated using Mobius3D for nine helical intensity‐modulated radiation therapy plans, each with three nominal field widths. We also compared 126 treatment plans used in our institution to treat prostate, head‐and‐neck, and esophagus tumors based on dose calculations by treatment planning system for given dose indices and 3D gamma passing rates with those produced by Mobius3D. On the basis of these results, we showed that the action and tolerance levels at the average dose for the planning target volume (PTV) at each treatment site are at μ ± 2σ and μ ± 3σ, respectively. After adjusting parameters, the dose difference ratio on average was −0.2 ± 0.6% using ion chamber and gamma passing rate with the criteria of 3% and 3 mm on average was 98.8 ± 1.4% using film. We also established action and tolerance levels for the PTV at the prostate, head‐and‐neck, esophagus, and for the organ at risk at all treatment sites. Mobius3D calculations thus provide an accurate secondary dose verification system that can be commissioned easily and immediately after installation. Before clinical use, the Mobius3D system needs to be commissioned using the treatment plans for patients treated in each institution to determine the calculational accuracy and establish tolerances for each treatment site and dose index.
Highlights
In radiation therapy, a secondary independent dose verification of the treatment planning system calculations is an essential part of the quality assurance (QA) process.[1]
We adjusted the calibration value, which we increased to 3% from the initial registered data, and we increased the output factor for nominal field widths (NFWs) 1.0 cm by 2.5% from initial registered data
We described our experience with commissioning Mobius3D for TomoTherapy, and it revealed that Mobius3D has enough accuracy for the independent dose calculation system in our institution
Summary
A secondary independent dose verification of the treatment planning system calculations is an essential part of the quality assurance (QA) process.[1]. A secondary independent dose verification has been performed using a monitor unit (MU).[1] This method uses data measured in a water phantom to verify the MU values calculated by the TPS. Before using this system in a clinical environment, it is necessary to spend considerable time and human resources to measure data and verify the accuracy of the dose calculations. The verification system is not completely independent from the TPS This independent verification system uses a simple dose calculation algorithm, so it can only verify single point doses, and it only works well for homogeneous conditions.[2]
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