Evaluation of a diode array for QA measurements on a helical tomotherapy unit

Area of Science:

• Medical Physics
• Radiation Oncology
• Quality Assurance in Radiotherapy

Background:

• Helical tomotherapy systems deliver intensity-modulated radiation therapy (IMRT).
• IMRT delivery eliminates traditional field flatness requirements, leading to inhomogeneous beam profiles.
• Accurate monitoring of these beam profiles is crucial for quality assurance.

Purpose of the Study:

• To investigate the utility of a commercial diode array for quality assurance of helical tomotherapy beam profiles.
• To assess the accuracy and sensitivity of the diode array compared to ion chamber measurements.
• To evaluate the diode array's ability to detect beam profile variations over time.

Main Methods:

• Acquired central axis beam profiles at various depths using solid water phantom.
• Compared diode array measurements with ion chamber scans in a water tank.
• Monitored beam profiles over seven weeks and compared trends with an on-board monitor.

Main Results:

• Diode array measurements showed excellent agreement with ion chamber scans (average ratio 1.000 +/- 0.005 in high dose regions).
• Agreement in penumbra regions met the 2 mm distance-to-agreement (DTA) requirement.
• The diode array accurately reflected trends in beam profile variations, consistent with the on-board monitor.

Conclusions:

• The commercial diode array is a valuable tool for accurate and efficient beam profile monitoring in helical tomotherapy.
• It demonstrates sufficient sensitivity to detect subtle beam profile variations.
• The diode array facilitates robust quality assurance for IMRT delivery.