The MapCHECK Measurement Uncertainty function and its effect on planar dose pass rates

Area of Science:

• Medical Physics
• Radiation Oncology
• Dosimetry

Background:

• Planar dosimetry is crucial for verifying radiation therapy treatment accuracy.
• The Sun Nuclear Corporation MapCHECK 2 system is widely used for dose verification.
• Software features like Measurement Uncertainty can influence analysis outcomes.

Purpose of the Study:

• To quantify the impact of the Measurement Uncertainty function on planar dosimetry pass rates.
• To determine how this function affects dose difference tolerances and pass/fail criteria.
• To assess the implications for reporting and inter-institutional comparisons.

Main Methods:

• Measured dose planes from 109 IMRT fields and 40 VMAT arcs using MapCHECK 2.
• Calculated dose planes were exported from a commercial treatment planning system.
• Planar dose comparison pass rates were analyzed with and without the Measurement Uncertainty function enabled.

Main Results:

• The Measurement Uncertainty function increased the effective percent difference criterion by 0.7%-1.2% on average.
• This resulted in average pass rate increases of 1.0%-8.1%, with maximums up to 14.2%.
• The function had a more significant effect on comparisons with lower initial pass rates.

Conclusions:

• The Measurement Uncertainty function can substantially inflate planar dose comparison pass rates.
• The function's uncertainty estimates may not accurately reflect real-world measurement conditions.
• Clear reporting of Measurement Uncertainty function usage is essential to avoid misinterpretation of dosimetry results.