Characterization of a 2.5 MV inline portal imaging beam

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Medical Imaging

Background:

• Varian TrueBeam linear accelerators now feature a new megavoltage (MV) energy for imaging.
• This 2.5 MV inline portal imaging beam requires thorough experimental characterization for clinical implementation.

Purpose of the Study:

• To experimentally characterize the 2.5 MV inline portal imaging beam for Varian TrueBeam accelerators.
• To assess its suitability for commissioning, routine clinical use, and quality assurance.

Main Methods:

• Beam quality was determined using percent depth dose (PDD) measurements in a water phantom with ion chambers and EBT3 film.
• Absolute dosimetry was performed following AAPM TG-51 protocol.
• Output stability, beam coincidence with 6 MV therapy beams, and image quality were evaluated using phantoms.

Main Results:

• The 2.5 MV beam's quality is comparable to 60Co, with dmax at approximately 5-6 mm and PDD(10) around 51.7-51.9%.
• Output stability was within 1% over five months.
• The 2.5 MV beam demonstrated superior image quality compared to the 6 MV beam, with excellent coincidence (within 0.2 mm).

Conclusions:

• The 2.5 MV imaging beam is well-characterized, stable, and provides superior image quality compared to 6 MV beams.
• This novel energy offers a valuable tool for imaging applications in radiotherapy.
• These findings provide essential reference data for clinics commissioning this new imaging modality.