Planning 4D intensity-modulated arc therapy for tumor tracking with a multileaf collimator

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-Guided Therapy

Background:

• Tumor motion due to respiration complicates radiation therapy planning and delivery.
• Accurate tumor tracking requires accounting for both translational and deformable motion.
• Current 3D planning methods often use large margins, increasing dose to normal tissues.

Purpose of the Study:

• To develop and evaluate a practical four-dimensional (4D) Intensity-Modulated Arc Therapy (IMAT) planning scheme for tumor tracking.
• To compensate for respiratory-induced tumor motion using 4D computed tomography (4D CT).
• To reduce radiation dose to surrounding normal tissues compared to traditional 3D planning.

Main Methods:

• A 4D planning scheme using 4D CT and dynamic multileaf collimation was developed.
• Tumor targets were contoured at each respiratory phase without motion-induced margins.
• A direct aperture deformation method transformed 3D-IMAT segments to create 4D-IMAT plans, ensuring smooth delivery.
• The method accounts for translational and deformable tumor motion, synchronizing delivery with respiratory phase.

Main Results:

• The 4D-IMAT plans demonstrated similar dose distributions to static 3D-IMAT plans.
• The method effectively eliminated dosimetric effects of breathing-induced target motion.
• Compared to 3D-IMAT plans with large margins, 4D-IMAT plans significantly reduced radiation doses to surrounding normal organs and tissues.

Conclusions:

• The proposed 4D-IMAT planning scheme is practical and easily integrated into clinical workflows.
• This approach accurately compensates for respiratory tumor motion, improving treatment precision.
• The 4D-IMAT strategy offers dosimetric benefits by reducing radiation exposure to healthy tissues.