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


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


CONCLUSIONS
As the MLC speeds and accelerations increased, VMAT delivery accuracy reduced.
1 Department of Radiation Oncology, Seoul National University Hospital, Seoul, Republic of Korea.
J M
JM
Park
H-G
HG
Wu
J H
JH
Kim
J N K
JN
Carlson
K
K
Kim
D000465:Algorithms; D005720:Gamma Rays; D006258:Head and Neck Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008297:Male; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D011471:Prostatic Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D011786:Quality Control; D011829:Radiation Dosage; D011859:Radiography; D011874:Radiometry; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D056910:Republic of Korea; D012680:Sensitivity and Specificity