Fast online replanning for interfraction rotation correction in prostate radiotherapy

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Interfraction variations, including rotations and translations, pose challenges in prostate radiotherapy.
• Accurate patient positioning is crucial for effective radiation delivery and minimizing dose to organs at risk.

Purpose of the Study:

• To develop and evaluate a fast online replanning system for prostate radiotherapy.
• To assess the system's ability to compensate for interfraction rotations and translations.
• To investigate the potential for reducing planning margins through online replanning.

Main Methods:

• Simulation of online daily replanning for 35 fractions in five prostate cancer cases.
• Two replanning strategies: (a) rotation and couch shift, (b) translation and rotation without couch shift.
• Comparison against a conventional protocol with daily couch repositioning and fixed margins (0-8 mm).

Main Results:

• Automated daily plan generation in under 2 minutes.
• Online replanning effectively compensated for rotations and translations across all margins.
• Conventional plans showed decreased target coverage with smaller margins due to rotations.
• Reduced non-tumor integral dose (NTID) observed, ranging from 12.6% to 32.9% with margin reduction.

Conclusions:

• Fast daily replanning is feasible for managing interfraction rotations and translations in prostate radiotherapy.
• Online correction for rotations can benefit even standard 8 mm margins.
• This technique supports potential margin reduction, limited by anatomical changes and intrafraction motion.
• The developed pipeline is suitable for future online MR-guided radiotherapy, enabling further safe margin reduction.