New possibilities for volumetric-modulated arc therapy using the Agility™ 160-leaf multileaf collimator

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT) are advanced radiation techniques.
• Multileaf collimators (MLCs) shape radiation beams, with varying leaf widths impacting plan quality.
• Complex target volumes in anal, head and neck, and prostate cancers present planning challenges.

Purpose of the Study:

• To compare the dosimetric quality of IMRT and VMAT plans generated using two different MLCs: Elekta Agility (5 mm leaf width) and Elekta MLCi2 (10 mm leaf width).
• To evaluate plan quality for complex target volumes in anal, head and neck, and prostate cancer.
• To assess the impact of MLC type on target coverage, organ at risk (OAR) sparing, and normal tissue dose.

Main Methods:

• Retrospective analysis of 15 patient plans treated with IMRT or VMAT using the MLCi2.
• Creation of new plans using both MLCi2 and Agility MLC for both IMRT and VMAT techniques.
• Comparison of dose-volume histograms (DVHs), dose conformity, homogeneity, OAR sparing, and normal tissue dose.

Main Results:

• Agility MLC plans demonstrated superior or equivalent PTV dose conformity and homogeneity compared to MLCi2 plans.
• No significant difference in compliance with OAR dose criteria between MLC types or techniques.
• VMAT optimization time increased with Agility MLC, but treatment time decreased; verification measurements met acceptance criteria.

Conclusions:

• VMAT treatment of complex target volumes with the MLCi2 required compromises in target coverage.
• The Agility MLC enables VMAT for complex targets without compromising coverage or increasing OAR/normal tissue dose.
• The 5 mm Agility MLC offers improved capabilities for advanced radiotherapy techniques on complex cases.