Introducing an on-line adaptive procedure for prostate image guided intensity modulate proton therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Proton Therapy

Background:

• Image guidance (IG) in intensity-modulated proton therapy (IG-IMPT) corrects prostate shifts via patient realignment.
• Proton range sensitivity to material changes during realignment can cause significant dose variations.

Purpose of the Study:

• To investigate dose variations in IG-IMPT due to patient realignment.
• To propose and evaluate an on-line adaptive procedure to restore the planned dose distribution.

Main Methods:

• A 2D anthropomorphic phantom was used with CT-based proton therapy plans (3D-modulation and distal edge tracking/DET).
• Simulated delivery compared non-adaptive (realignment only) and on-line adaptive (realignment with re-determined proton beam energies) procedures.
• Dose distributions were re-calculated for individual fractions under different conditions.

Main Results:

• Non-adaptive procedures led to significant dose degradation (cold/hot spots) in both 3D-modulation and DET plans, with DET being more affected.
• The on-line adaptive procedure effectively restored the planned dose for DET plans, achieving excellent target coverage.
• For 3D-modulation plans, the adaptive procedure's effectiveness varied, sometimes yielding results similar to non-adaptive methods.

Conclusions:

• The on-line adaptive procedure, by updating proton beam energy post-realignment, is necessary and effective for DET-based IG-IMPT.
• This adaptive strategy can be readily integrated into clinical workflows without dose re-optimization.
• Further investigation may be needed for 3D-modulation plans to ensure consistent dose restoration.