Four-dimensional layer-stacking carbon-ion beam dose distribution by use of a lung numeric phantom

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Intrafractional organ motion, particularly in lung cancer, poses challenges for precise radiotherapy delivery.
• Layer-stacking irradiation techniques require optimization to account for respiratory-induced target movement.
• Accurate dose distribution is crucial for effective tumor control and minimizing dose to healthy tissues.

Purpose of the Study:

• To evaluate carbon-ion layer-stacking dose distribution in the presence of intrafractional organ motion.
• To assess the impact of various parameters on dose conformation to moving targets within a numeric lung phantom.
• To determine strategies for improving dose delivery accuracy in carbon-ion radiotherapy for mobile tumors.

Main Methods:

• Utilized a numeric lung phantom to simulate respiratory motion during carbon-ion layer-stacking irradiation.
• Designed range compensators and calculated planning target volumes based on respiratory phases.
• Accumulated dose distributions were computed by registering phase-specific dose data; evaluated six parameters including gating window and prescribed dose.

Main Results:

• Shortening the gating window (e.g., T40-T60 vs. T00-T90) significantly improved dose metrics, reducing Dmax and homogeneity index (HI).
• Dose metrics, except HI, were largely independent of the respiratory cycle length.
• Gating strategies and increased prescribed dose demonstrably improved dose conformation to the moving target.

Conclusions:

• Gating strategies and optimized prescribed doses are effective in enhancing dose conformation for moving targets in carbon-ion layer-stacking radiotherapy.
• These approaches can be integrated into existing treatment protocols without requiring major modifications.
• The findings support the clinical applicability of advanced dose calculation methods for mobile tumors.