Prog Med Phys.  2019 Dec;30(4):120-127. 10.14316/pmp.2019.30.4.120.

Feasibility Study of Mobius3D for Patient-Specific Quality Assurance in the Volumetric Modulated Arc Therapy

• Lee CY
• Kim WC
• Kim HJ
• Lee J
• Huh HD

• KMID: 2468173
• DOI: http://doi.org/10.14316/pmp.2019.30.4.120

Abstract

PURPOSE
This study was designed to evaluate the dosimetric performance of Mobius3D by comparison with an aSi-based electronic portal imaging device (EPID) and Octavius 4D, which are conventionally used for patient-specific prescription dose verification.
METHODS
The study was conducted using nine patients who were treated by volumetric modulated arc therapy. To evaluate the feasibility of Mobius3D for prescription dose verification, we compared the QA results of Mobius3D to an aSi-based EPID and the Octavius 4D dose verification methods. The first was the comparison of the Mobius3D verification phantom dose, and the second was to gamma index analysis.
RESULTS
The percentage differences between the calculated point dose and measurements from a PTW31010 ion chamber were 1.6%±1.3%, 2.0%±0.8%, and 1.2%±1.2%, using collapsed cone convolution, an analytical anisotropic algorithm, and the AcurosXB algorithm respectively. The average difference was found to be 1.6%±0.3%. Additionally, in the case of using the PTW31014 ion chamber, the corresponding results were 2.0%±1.4%, 2.4%±2.1%, and 1.6%±2.5%, showing an average agreement within 2.0%±0.3%. Considering all the criteria, the Mobius3D result showed that the percentage dose difference from the EPID was within 0.46%±0.34% on average, and the percentage dose difference from Octavius 4D was within 3.14%±2.85% on average.
CONCLUSIONS
We conclude that Mobius3D can be used interchangeably with phantom-based dosimetry systems, which are commonly used as patient-specific prescription dose verification tools, especially under the conditions of 3%/3 mm and 95% pass rate.

Keyword

Mobius3D; Patient-specific quality assurance; Volumetric modulated arc therapy; Gamma index analysis

MeSH Terms

Feasibility Studies*
Humans
Prescriptions
Radiotherapy, Intensity-Modulated*

Figure

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  Fig. 1 Image of the mobius verification phantom with seven available ionization chamber positions.

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  Fig. 2 Percentage differences between dose calculated with (a) Eclipse AAA and Mobius3D, and dose measured with PTW 31010 in the MVP (b) Eclipse AcurosXB and Mobius3D, and dose measured with PTW 31014 in the MVP. MVP, mobius verification phantom; CC, collapsed cone; AAA, analytical anisotrophic algorithm.

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  Fig. 3 Comparison histogram for average gamma passing rates with (a) 2%/2 mm, and (b) 3%/3 mm criteria using Mobius3D, electronic portal imaging device (EPID), and Octavius 4D for head and neck, lung and prostate.

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