Dosimetric effect of multileaf collimator leaf width in intensity-modulated radiotherapy delivery techniques for small- and large-volume targets

Abstract

The purpose of this study was to evaluate the dosimetric effect of the leaf width of a multileaf collimator (MLC) in intensity-modulated radiotherapy (IMRT) delivery techniques for small- and large-volume targets. We retrospectively selected previously treated 5 intracranial and 5 head-neck patients for this study to represent small- (range, 18.37-72.75 cc; mean, 42.99 cc) and large-volume (range, 312.31-472.84 cc; mean, 361.14 cc) targets. A 6-MV photon beam data was configured for Brianlab m3 (3 mm), Varian Millennium 120 (5 mm) and Millennium 80 (10 mm) MLCs in the Eclipse treatment-planning system. Sliding window and step-shoot IMRT plans were generated for intracranial patients using all the above-mentioned MLCs; but due to the field size limitation of Brainlab MLC, we used only 5-mm and 10-mm MLCs in the head-and-neck patients. Target conformity, dose to the critical organs and dose to normal tissues were recorded and evaluated. Although the 3-mm MLC resulted in better target conformity (mean difference of 7.7% over 5-mm MLC and 12.7% over 10-mm MLC) over other MLCs for small-volume targets, it increased the total monitor units of the plans. No appreciable differences in terms of target conformity, organ at risk and normal-tissue sparing were observed between the 5-mm and 10-mm MLCs for large-volume targets. The effect of MLC leaf width was not quantifiably different in sliding window and step and shoot techniques. In addition, we observed that there was no additional benefit to the sliding-window (SW) technique when compared to the step-shoot (SS) technique as a result of reduction of MLC leaf width.

Dosimetric effects of multileaf collimator leaf width on intensity‐modulated radiotherapy for head and neck cancer

“…Many previous studies have investigated the dosimetric benefits of thin-leaf MLCs in IMRT and stereotactic radiosurgery for small-volume targets. 22,38 The results of the present study are consistent with the results of these previous studies. In particular, we have confirmed that 2.5-mm MLC can provide better a CI for PTV when treating a C-shape lesion with S&S_IMRT or VMAT.…”

“…25 In a study that compared 5-and 10-mm MLCs in both S&S_IMRT and sliding-window IMRT of the head and neck, the authors concluded that leaf width did not substantially affect target conformity or normal-tissue sparing. 22 In the present study, we observed similar results; dosimetric parameters did not differ significantly between 2.5-and 5-mm MLCs in either S&S_IMRT or VMAT for LH&N. Consequently, MLC leaf width could have fairly minimal effects on the dosimetric characteristics of S&S_IMRT and VMAT for LH&N, even though substantial differences were observed for C-shape targets.…”

“…[16][17][18][19][20] However, MLC with finer leaf width was not always effective in IMRT for head and neck cancers when the target sizes were relatively large. 21,22 Because the exact findings varied across these previous studies, it has been difficult to clearly identify the effects. [23][24][25] Moreover, there has been little research on the effects of MLC leaf width on volumetric-modulated arc therapy (VMAT), an increasingly common approach to treatment.…”

Dosimetric impact of the 160 MLC on head and neck IMRT treatments

“…They also reported reduced dose to the spinal cord, brainstem, and parotid glands, which is consistent with our findings. Yoganathan et al, (11) however, compared the Varian 120 leaf MLC and the Varian 80 leaf MLC for five head and neck patients and reported no appreciable difference in terms of target coverage or OARs (parotids) sparing.…”

Capability of leaf interdigitation with different inverse planning strategies in Monaco: an investigation of representative tumour sites

“…However, leaf interdigitation has a limitation, in that it may cause a leaf collision and increase the wear of MLCs. In fact, several researchers with different views have published regarding this topic [ 4 , 17 – 19 ]. However, currently, experimental investigations of the ability of MLC leaf interdigitation with inverse planning techniques for different types of tumour sites are scarce, although interdigitation is widely applied in 3D-CRT techniques.…”