Effect of MLC leaf width on the planning and delivery of SMLC IMRT using the CORVUS inverse treatment planning system

Abstract

This study investigates the influence of multileaf collimator (MLC) leaf width on intensity modulated radiation therapy (IMRT) plans delivered via the segmented multileaf collimator (SMLC) technique. IMRT plans were calculated using the Corvus treatment planning system for three brain, three prostate, and three pancreas cases using leaf widths of 0.5 and 1 cm. Resulting differences in plan quality and complexity are presented here. Plans calculated using a 1 cm leaf width were chosen over the 0.5 cm leaf width plans in seven out of nine cases based on clinical judgment. Conversely, optimization results revealed a superior objective function result for the 0.5 cm leaf width plans in seven out of the nine comparisons. The 1 cm leaf width objective function result was superior only for very large target volumes, indicating that expanding the solution space for plan optimization by using narrower leaves may result in a decreased probability of finding the global minimum. In the remaining cases, we can conclude that we are often not utilizing the objective function as proficiently as possible to meet our clinical goals. There was often no apparent clinically significant difference between the two plans, and in such cases the issue becomes one of plan complexity. A comparison of plan complexity revealed that the average 1 cm leaf width plan required roughly 60% fewer segments and over 40% fewer monitor units than required by 0.5 cm leaf width plans. This allows a significant decrease in whole body dose and total treatment time. For very complex IMRT plans, the treatment delivery time may affect the biologically effective dose. A clinically significant improvement in plan quality from using narrower leaves was evident only in cases with very small target volumes or those with concavities that are small with respect to the MLC leaf width. For the remaining cases investigated in this study, there was no clinical advantage to reducing the MLC leaf width from 1 to 0.5 cm. In such cases, there is no justification for the increased treatment time and whole body dose associated with the narrower MLC leaf width.

A Planning Comparison of Dynamic IMRT for Different Collimator Leaf Thicknesses with Helical Tomotherapy and RapidArc for Prostate and Head and Neck Tumors

“…We have shown that for both investigated tumor sites, the dosimetric effects of leaf widths between 2.5 mm, 5 mm and 10 mm are small with regard to target coverage as already found in previously reported studies [1,4,14,18,25]. The general observation is that dIMRT has more difficulties to match the locally prescribed doses than HT.…”

Impact of the high-definition multileaf collimator on linear accelerator-based intracranial stereotactic radiosurgery

“…Jin et al [6], in an intensity-modulated radiotherapy and radiosurgery study of 54 patients, concluded that the 3 mm MLC has a better conformity index and better sparing of small organs at risk (OARs) than either the 5 mm or the 10 mm MLC with a target volume dependence. Burmeister et al [2], on the other hand, reported no apparent clinically significant difference between the 5 and 10 mm MLC systems on 3 patients treated with intensity-modulated radiotherapy except for very small target volumes or those with concavities that are small with respect to the MLC leaf width. More recently, Wu et al [11], in a preliminary evaluation of the dosimetric impact of a 2.5 mm MLC over the 5 mm MLC for various treatment techniques and for a subset of five brain tumour cases abutting the brainstem, showed that the 2.5 mm leaf width MLC in combination with the intensity-modulated radiotherapy technique can yield dosimetric benefits to the treatment of small lesions in cases involving complex target/organ-at-risk geometry.…”

“…The advantage of the smaller leaf width has been studied by several groups [1][2][3][4][5][6][7][8][9][10][11], but with mixed results. Kubo et al [7] were the first to assess the conformity of threedimensional (3D) conformal plans using 1.7, 3 and 10 mm leaf width MLC systems.…”

Impacts of Multileaf Collimators Leaf Width on Intensity-Modulated Radiotherapy Planning for Nasopharyngeal Carcinoma: Analysis of Two Commercial Elekta Devices

“…11 Conversely, Burmeister et al reported that there was no apparent clinically significant difference between the 5-and 10-mm MLCs except for very small target volumes or those with concavities that are small, with respect to the MLC leaf widths. 24 Similar to the studies mentioned before, our data indicate that in IMRT treatment for NPC, the plans with the MMLC show the more optimized dose coverage (CI: Pgtv 0.790 Ϯ 0.036 and PTV 0.858 Ϯ 0.026) and the better dose homogeneity for the targets (HI: Pgtv 1.062 Ϯ 0.011 and PTV 1.185 Ϯ 0.011) than those plans with the SMLC (CI: Pgtv 0.754 Ϯ 0.038 and PTV 0.850 Ϯ 0.021; HI: Pgtv 1.07 Ϯ 0.01 and PTV 1.195 Ϯ 0.011) (p Ͻ 0.05).…”