Dosimetric impact of multileaf collimator leaf width according to sophisticated grade of technique in the IMRT and VMAT planning for pituitary adenoma lesion

Abstract

We analyzed the difference in the dosimetric effect between 5-mm and 2.5-mm multileaf collimator (MLC) leaf width according to the sophisticated grades of intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). Nineteen patients with pituitary adenomas were selected for this study. The treatment plans were performed according to the size of the MLC (5-mm and 2.5-mm MLC), the type of technique (IMRT and VMAT), and the sophisticated grades of each technique (5-field, 9-field, 13-field, 17-field technique in IMRT and 1-arc and 2-arc techniques in VMAT). The downsizing effects of MLC leaf width were analyzed using target volume coverage (TVC), conformity index (CI), dose gradient index (GI), and normal tissue difference 70% isodose line and 50% isodose line. Upon replacing the 5-mm MLC with the 2.5-mm MLC, TVC and CI improved by 1.30% and 1.36%, respectively, in total plans. The TVC and CI improved by 1.68% and 1.67% in IMRT, respectively, and by 0.54% and 0.72% in VMAT, respectively. TVC improved by 2.53%, 1.82%, 1.34%, and 0.94%, and CI also improved by 2.70%, 1.81%, 1.24%, and 0.94%, in 5-field, 9-field, 13-field, and 17-field IMRT, respectively. TVC improved by 0.66% and 0.43%, and CI also improved by 0.93%, and 0.52% in 1-arc and 2-arc VMAT, respectively. Regarding the target coverage, there were dosimetric benefits of a smaller MLC leaf width. However, the downsizing effect of the MLC leaf width decreased with the use of a more precise RT technique and a more sophisticated grade of the same technique.

Effects of Multileaf Collimator Design and Function When Using an Optimized Dynamic Conformal Arc Approach for Stereotactic Radiosurgery Treatment of Multiple Brain Metastases With a Single Isocenter: A Planning Study

“…Historically, a smaller MLC leaf width has been associated with an improvement in dose conformity, and this benefit was associated with intensity-modulated techniques and demonstrating improvement when moving from a 5.0 mm to 2.5 mm MLC leaf width [23]. Conversely, other investigators have concluded that the improvement provided by smaller leaves can be overcome with larger leaves by the use of a more sophisticated delivery technique such as intensity-modulated radiotherapy (IMRT) or volumetric-modulated arc therapy (VMAT) [24]. Further, it has been suggested that software solutions provide comparable target conformity, regardless of MLC width [25].…”

Technological quality requirements for stereotactic radiotherapy

“…We found that the MLC leaf width may be a simple measure for assessment of the geometrical resolution of treatment platforms and hence serve as a quality requirement for stereotactic radiotherapy based on the literature [139][140][141][142][143][144][145][146][147][148]. However, looking deeper into the treatment plan quality, the MLC leaf width does not directly represent the minimal possible field size, which is, together with the beam penumbra and its origins (e.g., beam spot size), also an important parameter to define the geometrical resolution [162].…”

“…Similar to this, a study comparing three different MLCs with leaf widths of 2.5, 4, and 5 mm for IMAT of spinal targets with volumes between 24 and 220 cm 3 concluded that any of these leaf widths can be used for spinal SBRT [143]. Furthermore, a study on the difference between planning with an MLC leaf width of 2.5 vs. 5 mm with respect to different levels of plan complexity, namely 5-up to 17-field IMRT and IMAT with one or two arcs for the treatment of pituitary adenomas, demonstrated coverage and conformity improvement with the smaller leaves of about 2% for the 5-field IMRT and only about 0.5% for the two-arc IMAT technique [144].…”

“…These studies might be exemplary to show that there is a notable benefit in reducing the MLC leaf width from 10 mm, but the benefit of using leaves smaller than 5 mm seems only marginal, maybe except for small or very irregularly formed targets. However, the differences between treatment platforms can be compensated when using more complex delivery techniques (e.g., [144,145]), besides other influences on the comparison, such as calculation grid size. Part of this ambiguity is likely caused by the fact that MLC leaf width on the one hand is an easily defined quantity, but on the other hand, the mechanical size of the leaves is only one parameter among many in defining the actual geometrical resolution for an MLC.…”

The influence of radiotherapy techniques on the plan quality and on the risk of secondary tumors in patients with pituitary adenoma

“…For over one decade patients with pituitary adenoma have been treated primarily with two parallel opposed fields or a three field technique [1][2][3][4][5][6][7]. Only a few recent publications describe the application of intensity modulated radiotherapy (IMRT) or volumetric modulated arc (VMAT) technique in this region [8][9][10], none of them mentioning the flatness filter free (FFF) mode. FFF is applicable in combination with fluence modulating techniques like IMRT or VMAT.…”