Dosimetric evaluation of MLC-based dynamic tumor tracking radiotherapy using digital phantom: Desired setup margin...

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• Accurate tumor targeting is crucial in radiotherapy, especially for mobile tumors.
• Dynamic tumor tracking aims to improve dose delivery precision by adapting to tumor motion.
• Evaluating setup margins is essential for optimizing treatment efficacy and minimizing off-target dose.

Purpose of the Study:

• To assess the dosimetric impact of setup margins in multileaf collimator-based dynamic tumor tracking plans.
• To determine an equivalent setup margin (EM) for tracking plans comparable to gated plans.
• To establish a relationship between tumor characteristics (diameter, motion) and the required EM.

Main Methods:

• Utilized a 4-dimensional extended cardiac-torso phantom with varying tumor diameters (1-5 cm) and motion ranges (1-3 cm).
• Developed both respiratory gating and dynamic tumor tracking treatment plans using 8-field 3D conformal radiation therapy.
• Employed 4-dimensional dose calculation and evaluated lung V20 to determine dosimetric impact and estimate EMs.

Main Results:

• Equivalent setup margins (EMs) varied based on tumor diameter (TD) and motion range (MR).
• Larger MRs generally led to increased EMs (e.g., 1 cm TD, 3 cm MR had EM of 4.24 mm).
• Larger TDs generally resulted in smaller EMs (e.g., 5 cm TD, 3 cm MR had EM of 7.49 mm).

Conclusions:

• The study provides crucial data on equivalent setup margins for dynamic tumor tracking.
• Findings indicate that EM is significantly influenced by tumor motion and size.
• The established EMs support accurate treatment delivery in multileaf collimator-based dynamic tumor tracking radiotherapy.