A dosimetric comparison of various multileaf collimators

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Technology

Background:

• Multileaf collimators (MLCs) are critical components in modern radiotherapy, shaping radiation beams.
• Different MLC designs, including leaf-end shape and collimator positioning, can impact dosimetric performance.
• Understanding these differences is essential for optimizing treatment delivery and patient outcomes.

Purpose of the Study:

• To comparatively analyze the dosimetric characteristics of three distinct 10 mm leaf width multileaf collimator (MLC) systems (Elekta, Siemens, Varian).
• To evaluate parameters such as penumbra width, radiation leakage, tongue-and-groove effect, and isodose undulation.
• To assess the influence of leaf-end design (rounded vs. flat) and collimator-to-target distance on these dosimetric properties.

Main Methods:

• Utilized a 6 MV photon beam for all measurements across the three MLC systems.
• Employed film dosimetry with a scanning densitometer (Wellhöfer) for precise analysis.
• Standardized analysis techniques and measurement protocols across all systems for direct comparison.

Main Results:

• Penumbra widths (80-20%) were comparable across divergent and non-divergent leaf designs, within 2.0 mm.
• The Varian MLC, positioned closer to the patient, exhibited the smallest penumbra despite rounded leaf ends.
• Siemens MLC showed reduced tongue-and-groove effect, while Varian displayed significant isodose undulation closest to the patient.

Conclusions:

• No single MLC system is universally superior; each presents unique advantages and disadvantages.
• Factors like leaf-end shape, collimator distance, and specific dosimetric performance must be considered.
• Clinical selection should balance dosimetric accuracy with practical aspects such as comfort, ease of use, and cost-effectiveness.