Measurement of patient setup errors using port films and a computer-aided graphical alignment tool

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Treatment Verification

Background:

• Accurate patient positioning is critical for effective radiation therapy.
• Previous studies have investigated patient setup errors, but large datasets are valuable for robust analysis.

Purpose of the Study:

• To quantify patient setup errors in radiation therapy across different anatomical regions.
• To analyze the nature (random vs. systematic) and magnitude of setup errors.
• To compare initial setup with setup at the time of treatment.

Main Methods:

• Measurement of patient orientations for 49 patients undergoing treatment in abdominal, chest, and pelvic regions over 20 months.
• Determination of setup errors using a curve-matching graphical interface comparing digitized port films to simulation films.
• Analysis of data at both population and individual patient levels, sorted by anatomical area.

Main Results:

• Setup errors were predominantly random, with population standard deviations of 5-6 mm for translations and 2-3 degrees for rotations.
• Correlations between translational and rotational errors were minimal at each treatment site.
• Data included both initial patient setup and setup at the time of treatment, showing comparable error distributions.

Conclusions:

• Patient setup errors in the studied cohort are primarily random, necessitating strategies to mitigate random variations.
• The findings are consistent with existing literature, reinforcing the understanding of setup error characteristics in radiation oncology.
• This study contributes one of the largest datasets to date on patient setup errors, enhancing the statistical power of the analysis.