Prog Med Phys.  2021 Dec;32(4):107-115. 10.14316/pmp.2021.32.4.107.

A Comparison between Portal Dosimetry and Mobius3D Results for Patient-Specific Quality Assurance in Radiotherapy

• Kim SY
• Park J
• Park JW
• Yea JW
• Oh SA

• KMID: 2524156
• DOI: http://doi.org/10.14316/pmp.2021.32.4.107

Abstract

Purpose
The purpose of this study was to compare the clinical quality assurance results of portal dosimetry using an electronic portal imaging device, a method that is extensively used for patientspecific quality assurance, and the newly released Mobius3D for intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT).
Methods
This retrospective study includes data from 122 patients who underwent IMRT and VMAT on the Novalis Tx and VitalBeam linear accelerators between April and June 2020. We used a paired t-test to compare portal dosimetry using an electronic portal imaging device and the average gamma passing rates of MobiusFX using log files regenerated after patient treatment.
Results
The average gamma passing rates of portal dosimetry (3%/3 mm) and MobiusFX (5%/3 mm) were 99.43%±1.02% and 99.32%±1.87% in V it alBeam and 97.53%±3.34% and 96.45%±13.94% in Novalis Tx, respectively. Comparison of the gamma passing rate results of portal dosimetry (3%/3 mm) and MobiusFX (5%/3 mm as per the manufacturer’s manual) does not show any statistically significant difference.
Conclusions
Log file-based patient-specific quality assurance, including independent dose calculation, can be appropriately used in clinical practice as a second-check dosimetry, and it is considered comparable with primary quality assurance such as portal dosimetry.

Keyword

Patient-specific quality assurance; Mobius3D; Electronic portal imaging device; Intensity-modulated radiotherapy; Volumetric modulated arc therapy

Figure

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  Fig. 1 Regression model using the MobiusFX ionization chamber measurement vs. the dosimetric leaf gap (DLG) for Novalis Tx with 6 MV (R2=0.995).

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  Fig. 2 Experimental setup with portal dosimetry using an EPID for patient-specific quality assurance on Novalis Tx.

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  Fig. 3 Gamma analysis image for the determination of the difference between the dose distribution planned by MobiusCalc and the dose distribution replanned by MobiusFX using the log files generated after clinical radiation treatment.

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  Fig. 4 Gamma analysis of the predicted dose by the treatment planning system and the portal dose measured using electronic portal imaging device.

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  Fig. 5 Correlation between MobiusFX (5%/3 mm) and portal dosimetry (3%/3 mm) for patient-specific quality assurance: (a) Novalis Tx and (b) VitalBeam.

Reference

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