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Br J Radiol. 2015 May;88(1049):20140698. doi: 10.1259/bjr.20140698. Epub 2015 Mar 3.

The effect of MLC speed and acceleration on the plan delivery accuracy of VMAT.

Author information

1
1 Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.

Abstract

OBJECTIVE:

To determine a new metric utilizing multileaf collimator (MLC) speeds and accelerations to predict plan delivery accuracy of volumetric modulated arc therapy (VMAT).

METHODS:

To verify VMAT delivery accuracy, gamma evaluations, analysis of mechanical parameter difference between plans and log files, and analysis of changes in dose-volumetric parameters between plans and plans reconstructed with log files were performed with 40 VMAT plans. The average proportion of leaf speeds ranging from l to h cm s(-1) (Sl-h and l-h = 0-0.4, 0.4-0.8, 0.8-1.2, 1.2-1.6 and 1.6-2.0), mean and standard deviation of MLC speeds were calculated for each VMAT plan. The same was carried out for accelerations in centimetre per second squared (Al-h and l-h = 0-4, 4-8, 8-12, 12-16 and 16-20). The correlations of those indicators to plan delivery accuracy were analysed with Spearman's correlation coefficient (rs).

RESULTS:

The S1.2-1.6 and mean acceleration of MLCs showed generally higher correlations to plan delivery accuracy than did others. The highest rs values were observed between S1.2-1.6 and global 1%/2 mm (rs = -0.698 with p < 0.001) as well as mean acceleration and global 1%/2 mm (rs = -0.650 with p < 0.001). As the proportion of MLC speeds and accelerations >0.4 and 4 cm s(-2) increased, the plan delivery accuracy of VMAT decreased.

CONCLUSION:

The variations in MLC speeds and accelerations showed considerable correlations to VMAT delivery accuracy.

ADVANCES IN KNOWLEDGE:

As the MLC speeds and accelerations increased, VMAT delivery accuracy reduced.

PMID:
25734490
PMCID:
PMC4628477
DOI:
10.1259/bjr.20140698
[Indexed for MEDLINE]
Free PMC Article

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