A method to enhance 2D ion chamber array patient specific quality assurance for IMRT

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Patient-specific quality assurance (QA) is crucial for intensity-modulated radiation therapy (IMRT).
• Detector arrays offer an alternative to radiographic films for 2D dose distribution measurements.
• Detector arrays have spatial resolution limitations compared to films, which can be addressed by advanced methodologies.

Purpose of the Study:

• To evaluate an enhanced methodology for patient-specific QA in IMRT using a PTW-729 detector array.
• To compare the accuracy of gamma index comparison using films versus an improved detector array method.

Main Methods:

• Delivered 35 IMRT beams on a phantom and recorded 2D dose distributions using a PTW-729 ion chamber array and radiographic films.
• Employed a multiple acquisition sequence for adjacent 2D dose distributions with the detector array.
• Convolved calculated dose distributions with the detector's spatial response.
• Performed gamma index comparisons between measured and calculated doses using RITv5.2 software.

Main Results:

• Radiographic films showed 3.7% ± 2.7% of points surpassing the accepted Gamma index.
• The PTW-729 array with multiple acquisitions showed 4.1% ± 1.3% surpassing points.
• The enhanced method (multiple acquisitions and convolved dose) reduced surpassing points to 2.7% ± 1.3%.

Conclusions:

• The combination of multiple adjacent 2D dose distributions and convolved calculated dose improves IMRT patient-specific QA accuracy.
• This enhanced methodology using the PTW-729 array offers a more precise quality assurance procedure.
• Detector arrays, when used with advanced data processing, can overcome spatial resolution limitations for IMRT QA.