MapCHECK used for rotational IMRT measurements: step-and-shoot, TomoTherapy, RapidArc

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Patient-specific quality assurance (QA) is crucial for ensuring accurate dose delivery in intensity-modulated radiation therapy (IMRT).
• The MapCHECK, a 2D diode array, is commonly used for IMRT QA, but its accuracy can be affected by intrinsic diode properties and setup.
• Optimizing QA tools is essential for reliable patient treatment verification.

Purpose of the Study:

• To evaluate and enhance the accuracy of the MapCHECK device for patient-specific QA of dose distributions in IMRT.
• To assess the performance of the MapCHECK with both step-and-shoot and rotational IMRT delivery techniques.

Main Methods:

• Two MapCHECK devices were tested in original and modified configurations within a solid water phantom.
• Modifications included filling air gaps with Lucite and adding copper to mitigate diode asymmetry.
• Measurements were performed using Varian linear accelerators and a TomoTherapy machine with various IMRT delivery methods (step-and-shoot, RapidArc, helical).

Main Results:

• Original MapCHECK exhibited significant angular dependence (+/- 20%), while modifications reduced it to +/- 2%.
• CT imaging revealed streak artifacts requiring correction for accurate dose calculation.
• The modified MapCHECK demonstrated reliable performance for patient-specific QA across different IMRT techniques, particularly improving measurements for high-fluence directions.

Conclusions:

• Proper modification of the MapCHECK renders its response isotropic, significantly enhancing its accuracy.
• The modified MapCHECK is a suitable tool for patient-specific QA in IMRT, including rotational techniques like helical TomoTherapy and RapidArc.