Analysis of prostate patient setup and tracking data: potential intervention strategies

Area of Science:

• Radiation Oncology
• Medical Physics
• Image-Guided Therapy

Background:

• Prostate radiotherapy requires precise targeting to minimize radiation dose to surrounding tissues.
• Intrafraction organ motion can lead to significant setup and treatment errors.
• Accurate assessment of motion error distributions is crucial for optimizing treatment margins.

Purpose of the Study:

• To evaluate setup, interfraction, and intrafraction organ motion error distributions in prostate radiotherapy.
• To simulate intrafraction intervention strategies for motion management.
• To quantify the impact of these strategies on planning target volume (PTV) margins.

Main Methods:

• 17 patients undergoing prostate radiotherapy were monitored using the Calypso system for intrafraction prostate motion.
• Systematic and random errors were calculated from patient couch shift and motion data.
• Two intervention strategies (deviation threshold and periodic correction) were simulated.
• PTV margins were calculated using the van Herk formula.

Main Results:

• On-line setup correction reduced PTV margins from 8.4-14.7 mm to 1.3-2.8 mm.
• Prostate motion showed significant correlation between superoinferior and anteroposterior directions.
• Threshold-based and time-based corrections further reduced PTV margins to 0.5-1.5 mm.
• Time-based corrections increased treatment time and instances of transient excursions.

Conclusions:

• On-line setup correction effectively minimizes residual systematic and random errors from intrafraction prostate motion.
• Both threshold-based and time-based intervention strategies successfully reduced PTV margins.
• Time-based strategies, while effective in margin reduction, increased treatment duration and intrafraction motion fluctuation.