MLC parameters from static fields to VMAT plans: an evaluation in a RT-dedicated MC environment (PRIMO)

Area of Science:

• Medical Physics
• Radiotherapy Physics
• Computational Physics

Background:

• PRIMO, a PENELOPE Monte Carlo (MC) simulation environment, calculates radiotherapy dose distributions.
• The dosimetric characteristics of a Varian HD-120 MLC were evaluated using PRIMO.
• Simulations were compared against experimental measurements and Acuros calculations.

Purpose of the Study:

• To validate the accuracy of PRIMO for simulating the Varian HD-120 MLC.
• To compare PRIMO's calculations with experimental measurements and Acuros treatment planning system (TPS) calculations.
• To assess the potential of PRIMO as an independent dose calculation check tool in clinical radiotherapy.

Main Methods:

• A 10 MV FFF beam from a Varian EDGE linac with HD-120 MLC was simulated in PRIMO.
• Static and dynamic MLC tests were performed, including output factors, transmitted dose, dosimetric leaf gap (DLG), and tongue and groove (TG) effects.
• Simulated doses were compared with EBT3 film measurements in solid water and Acuros calculations in Eclipse TPS.

Main Results:

• MC simulations in PRIMO showed excellent agreement with measurements for static output factors (0.5%) and DLG (0.033 cm).
• Dose distributions for TG tests agreed within 1-2%, with ~4-5% difference in extreme cases.
• Clinical case comparisons demonstrated a 99.5% Gamma agreement (3%/2mm) between PRIMO MC and Acuros calculations.

Conclusions:

• PRIMO Monte Carlo simulations accurately represent the dosimetric characteristics of the HD-120 MLC.
• The study confirms PRIMO's capability for consistent comparison with clinical cases.
• PRIMO is validated as a potential independent dose calculation check tool for radiotherapy.