Initial follow-up of mechanical QC tests for RapidArc Dynamic (RAD)

Area of Science:

• Radiotherapy Physics
• Medical Physics
• Radiation Oncology

Background:

• RapidArc Dynamic (RAD) is an advanced radiotherapy technique by Varian.
• It integrates Volumetric Modulated Arc Therapy (VMAT) and Intensity-Modulated Radiation Therapy (IMRT).
• RAD introduces a dynamic collimator as an additional degree of freedom during treatment delivery.

Purpose of the Study:

• To validate the mechanical performance of the dynamic collimator in RAD.
• To implement and assess two novel quality control tests: the picket fence and Pac-Man tests.
• To evaluate the impact of the dynamic collimator on treatment delivery accuracy and stability.

Main Methods:

• The picket fence test used radiochromic film to measure MLC movement with a rotating collimator.
• The Pac-Man test utilized an Electronic Portal Imaging Device (EPID) to analyze dose rates and collimator speeds.
• Both tests were conducted over 12 weeks, with results compared against established literature thresholds (AAPM TG-142, MPPG 8.b) and stability verified using AAPM TG-218 control limits.

Main Results:

• Picket fence test showed a maximum difference of 0.45 mm (±0.05 mm) and a mean difference of 0.14 mm (±0.01 mm).
• Pac-Man test results demonstrated $\mathrm{Diff}\left(x\right)$ values between -1.31% and 1.02%, and $\mathrm{Dif}{f}_{\mathrm{Abs}}$ between 0.42% and 0.55%.
• All test outcomes were within established control limits, indicating stable performance.

Conclusions:

• The study confirms the mechanical feasibility of RAD plan delivery.
• The implemented picket fence and Pac-Man tests are effective for routine quality control.
• These validated tests will be integrated into the standard mechanical quality assurance procedures at UZ Leuven.