SU-F-T-334: Has IMRT Changed the Impact of MLC Leaf Width? A Systematic Review and Meta-Analysis of TPS Studies




We have performed a systematic review and meta-analysis in order to compare MLC leaf width used for different treatment techniques such as conformal and IMRT.


Medline and Google scholar databases have been searched using the “MLC leaf width” keywords with a cut-off date of 31st December 2015, considering only peer-reviewed papers. We have defined as intervention the MLC leaf width of 5 and 2.5 mm. We used the Conformity Index (CI) as the outcome subjected to the analysis. The mean and standard deviation of each group has been either extracted or calculated. The association between MLCs and Conformity Index reduction across the selected studies was then computed as Pooled Mean Difference (PMD) with 95% CI.


From the literature search 43 studies were selected, 12 of them compared MLC 2.5 or 3 mm vs. 5 mm in terms of Conformity Index. On the whole there is a slight significant difference between MLC2.5 and MLC5.0 in favour of the former. The pooled mean difference is −0.036 with a 95% confidence interval ranging between −0.068 and −0.005 (p=0.026). The analysis highlights a very large heterogeneity (I2=87.7%) suggesting the results could be different in specific subgroups. Therefore a subgroup analysis has been performed by comparing techniques (IMRT/VMAT vs 3DCRT/DCA). In the subgroup of IMRT/VMAT the difference between MLC2.5 and MLC5.0 appears to be negligible (mean diff:-0.006; 95%CI: −0.013–0.001) and not significantly different from zero (p=0.064). On the contrary in the subgroup of studies which used the conformal 3DCRT/ DCA techniques, the MLC2.5 resulted significantly different from the MLC5.0 (mean difference: −0.054; 95% CI: −0.096–0.012; p=0.02).


A systematic review of TPS studies have been performed. In this analysis, using IMRT/VMAT shows identical capability of achieving good target coverage ability (CI) with 2.5 and 5mm MLC, differently from 3DCRT/DCA.

Marco Luzzara and Kevin Brown are Elekta employees. Luigi Santoro has a scientific collaboration with Elekta