Hybrid plan verification for intensity-modulated radiation therapy (IMRT) using the 2D ionization chamber array I'mRT...

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• The I'mRT MatriXX is a 2D ionization chamber array designed for intensity-modulated radiation therapy (IMRT) verification with perpendicular beam incidence.
• Its applicability for oblique beam incidence and hybrid plan verification in IMRT requires further evaluation.

Purpose of the Study:

• To assess the performance of the I'mRT MatriXX for oblique beam incidence in IMRT.
• To evaluate its suitability for hybrid plan verification of IMRT using original gantry angles.

Main Methods:

• Angular dependence was assessed using open fields at various gantry angles.
• Hybrid plan verification involved 17 clinical IMRT plans and one rotational plan.
• Calculations utilized validated pencil beam (PB), collapsed cone (CC), and Monte Carlo (MC) methods; measurements were performed on an Elekta SynergyS linear accelerator.

Main Results:

• Hybrid plan verification met gamma test criteria (4%/3 mm) in all instances.
• Success rates for 3%/3 mm and 3%/2 mm tolerances were 82-88% and 59-76%, respectively.
• The I'mRT MatriXX is suitable for IMRT hybrid plan verification within 3%/3 mm, with a relaxed 4% tolerance in low-dose regions outside the multileaf collimator (MLC).

Conclusions:

• The I'mRT MatriXX demonstrates applicability for IMRT hybrid plan verification, even with oblique beam incidence.
• The system provides reliable dosimetry for IMRT verification, with specific considerations for low-dose regions.
• These findings support the use of I'mRT MatriXX in advanced radiotherapy verification protocols.