Prog Med Phys.  2021 Dec;32(4):116-121. 10.14316/pmp.2021.32.4.116.

Evaluating the Effects of Dose Rate on Dynamic Intensity-Modulated Radiation Therapy Quality Assurance

• Kim KH
• Back TS
• Chung EJ
• Suh TS
• Sung W

• KMID: 2524157
• DOI: http://doi.org/10.14316/pmp.2021.32.4.116

Abstract

Purpose
To investigate the effects of dose rate on intensity-modulated radiation therapy (IMRT) quality assurance (QA).
Methods
We performed gamma tests using portal dose image prediction and log files of a multileaf collimator. Thirty treatment plans were randomly selected for the IMRT QA plan, and three verification plans for each treatment plan were generated with different dose rates (200, 400, and 600 monitor units [MU]/min). These verification plans were delivered to an electronic portal imager attached to a Varian medical linear accelerator, which recorded and compared with the planned dose. Root-mean-square (RMS) error values of the log files were also compared.
Results
With an increase in dose rate, the 2%/2-mm gamma passing rate decreased from 90.9% to 85.5%, indicating that a higher dose rate was associated with lower radiation delivery accuracy. Accordingly, the average RMS error value increased from 0.0170 to 0.0381 cm as dose rate increased. In contrast, the radiation delivery time reduced from 3.83 to 1.49 minutes as the dose rate increased from 200 to 600 MU/min.
Conclusions
Our results indicated that radiation delivery accuracy was lower at higher dose rates; however, the accuracy was still clinically acceptable at dose rates of up to 600 MU/min.

Keyword

Intensity modulated radiation therapy; Quality assurance; Dose rate; Multileaf collimator

Figure

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  Fig. 1 Quality assurance (QA) procedure for intensity-modulated radiation therapy. PDIP, portal dose image prediction; EPID, electronic portal imaging device; 2D, two-dimensional; 3D, three-dimensional.

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  Fig. 2 Gamma passing rate with the 3%/3-mm criterion as a function of dose rates for lung, prostate, and head and neck (H&N) disease sites (*P<0.05).

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  Fig. 3 Gamma passing rate with the 2%/2-mm criterion as a function of dose rates for lung, prostate, and head and neck (H&N) disease sites (**P<0.01 and ***P<0.001).

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  Fig. 4 Root-mean-square (RMS) multileaf collimator positional errors recorded in DynaLog files as a function of dose rates for lung, prostate, and head and neck (H&N) disease sites (***P<0.001).

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  Fig. 5 Beam-on time as a function of dose rates for lung, prostate, and head and neck (H&N) disease sites (*P<0.05 and ***P<0.001).

Reference

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