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

Soo-Min Chae,Ki Woong Lee,Seok Hyun Son

doi:10.18632/oncotarget.12974

Soo-Min Chae, Ki Woong Lee + Show 1 more

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https://doi.org/10.18632/oncotarget.12974

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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.

Highlights

Radiotherapy (RT) has been optimized to enable the delivery of a higher dose of radiation to the target volume in order to enhance the treatment results and lower the dose to the surrounding normal tissues to minimize radiationrelated complications
When using 2.5-mm multi-leaf collimator (MLC) instead of 5.0-mm MLC, target volume coverage (TVC) and conformity index (CI) improved by 1.30% ± 0.88% and 1.36% ± 0.98%, respectively
When comparing the downsizing effect of MLC leaf width in intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT), TVC improved by 1.68 ± 0.84% with IMRT and 0.54 ± 0.26% with VMAT (p < 0.001), and CI improved by 1.67 ± 1.02% with IMRT and 0.72 ± 0.45% with VMAT (p < 0.001)

Summary

Introduction

Radiotherapy (RT) has been optimized to enable the delivery of a higher dose of radiation to the target volume in order to enhance the treatment results and lower the dose to the surrounding normal tissues to minimize radiationrelated complications. Radiosurgery is a leading technique within RT, and includes procedures such as 3-dimensional conformal radiotherapy (3DCRT), dynamic conformal arc therapy (DCAT), and intensity-modulated radiotherapy (IMRT) With development of these planning techniques, the multi-leaf collimator (MLC), which make a shape of the irradiated field to deliver radiation to the target volume, was developed. The MLC leaf width can be made smaller to create a precise irradiated field acceptable for use in accurate radiosurgery This micro-MLC has reported to be suitable for radiosurgery in terms of both target volume coverage and normal tissues sparing, regardless of which of the aforementioned techniques is used [1–7]. There have been several reports indicating that the downsizing effect of MLC leaf width differs according to the complexity of the target shape [4, 8–10] To reduce this kind of bias, relatively simple shapes should be selected for evaluation with respect to the target volume

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