Quantification of residual dose estimation error on log file-based patient dose calculation.

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Log file-based patient dose estimation in VMAT can be inaccurate due to leaf miscalibration.
• This inaccuracy, termed residual dose estimation error, is not reflected in the calculated dose.
• Accurate dose estimation is critical for effective cancer treatment and minimizing side effects.

Purpose of the Study:

• To determine the residual dose estimation error in VMAT delivery.
• To investigate the impact of multileaf collimator (MLC) calibration accuracy on dose estimation errors.
• To quantify these errors for clinical planning target volumes (PTVs) and organs at risk (OARs).

Main Methods:

• Simulated leaf miscalibration (gap errors and shifts) in head-and-neck and prostate VMAT plans using in-house software.
• Generated modified log files reflecting these errors.
• Recalculated doses in the treatment planning system and quantified generalized equivalent uniform dose (gEUD) for PTVs and OARs.

Main Results:

• Residual dose estimation errors were quantified for MLC leaves calibrated within ±0.5mm.
• For head-and-neck plans, errors were 1.32±0.27% for PTV and 0.82±0.17 Gy for spinal cord.
• For prostate plans, errors were 1.22±0.36% for PTV, 0.95±0.14 Gy for rectum, and 0.45±0.08 Gy for bladder.

Conclusions:

• Residual dose estimation errors in VMAT are dependent on MLC calibration accuracy.
• The study provides quantitative data on these errors for specific clinical scenarios.
• Findings are essential for improving the reliability of log file-based dose calculations in radiotherapy.