Optimization of motion management parameters in a synchrotron-based spot scanning system

Area of Science:

• Medical Physics
• Radiation Oncology
• Proton Therapy

Background:

• The interplay effect in proton therapy arises from the interaction between moving targets and dynamic beam delivery.
• This effect can lead to dosimetric degradation, compromising treatment accuracy.
• Respiratory motion is a significant challenge in delivering precise proton therapy.

Purpose of the Study:

• To quantify the effectiveness of combining layer-based repainting and respiratory gating.
• To mitigate dosimetric degradation caused by the interplay effect in dynamic spot-scanning proton delivery.
• To evaluate the impact on target coverage, dose homogeneity, and delivery time.

Main Methods:

• An analytic routine modeled 3D dose distributions for pencil-beam proton plans delivered to moving targets.
• Simulated respiratory motion using patient breathing traces, investigating parallel and orthogonal motion.
• Evaluated 20 delivery schemes combining gate window amplitudes and repainting techniques.

Main Results:

• Ungated delivery showed significant plan quality degradation and variability.
• Reduced gate windows improved quality but increased delivery time; orthogonal motion showed greater dose deviations.
• Layer-based repainting with gating partially restored dosimetric coverage efficiently.

Conclusions:

• Layer-based repainting effectively suppresses interplay effects from intra-gate motion.
• The strategy offers a modest increase in delivery time.
• Patient-specific breathing patterns and tumor motion trajectories significantly influence treatment outcomes.