A dynamic compensation strategy to correct patient-positioning errors in conformal prostate radiotherapy

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Traditional patient positioning correction involves couch repositioning.
• Dynamic compensation offers an alternative by adjusting the treatment beam to the patient.

Purpose of the Study:

• To determine the geometric range of patient positioning errors addressable by dynamic compensation in prostate cancer patients undergoing 3D conformal radiotherapy.

Main Methods:

• Twenty-five prostate cancer patients were replanned with a four-field technique (72 Gy to 95% PTV).
• 5400 simulated isotropic positioning errors (1-10 cm) were introduced.
• Dynamic compensation adjusted beam apertures and monitor units, with corrections for inverse-square and off-axis factors.
• Plans were compared to original treatments using dose-volume histogram (DVH) analysis.

Main Results:

• Dynamic compensation maintained excellent PTV coverage (D95, Dmean, D5 within 5% of prescription dose).
• Minor discrepancies in isodose distributions and DVH were observed, increasing with error magnitude.
• Increased doses to organs at risk (rectum, femoral head, bladder) occurred in a small percentage of errors, varying with anatomy.

Conclusions:

• Dynamic compensation is robust for correcting patient positioning errors in four-field conformal prostate radiotherapy.
• This method minimizes deviations from original plans, even for large positioning errors.
• Remote correction capability reduces treatment time and secondary motion, with implications for patient setup accuracy and throughput.