Dosimetric evaluation and clinical application of virtual mini-multileaf collimator

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Multileaf collimators (MLC) exhibit jagged field edges, leading to larger penumbras and dosimetric undulation compared to Cerrobend blocks.
• Software solutions, like virtual mini-MLC, offer a cost-effective alternative to hardware replacement for improving MLC performance.

Purpose of the Study:

• To investigate the dosimetric characteristics of a virtual mini-MLC (HD270 software) in the penumbra region for clinical radiotherapy applications.
• To compare the performance of HD270 with traditional Cerrobend blocks and standard MLC setups in terms of penumbra width, isodose line undulation, and treatment delivery time.

Main Methods:

• Film dosimetry was employed to analyze penumbra regions at various depths for 6-MV and 15-MV x-ray beams.
• HD270 software with 5 mm, 3 mm, and 2 mm resolutions was evaluated against clinical blocks and standard MLC configurations.
• Dose-volume histogram (DVH) analysis was performed for clinical cases (head and neck, prostate), and treatment delivery times were compared.

Main Results:

• HD270 significantly reduced penumbra width and isodose line undulation compared to standard MLC, particularly at 2 mm resolution, eliminating scalloping.
• While HD270 provided a smaller penumbra than MLC, it remained wider than that achieved with Cerrobend blocks.
• HD270 demonstrated significant improvements in spinal cord dose distribution and reduced irradiated rectal volume in prostate cases, with the 3 mm resolution offering the best balance of penumbra, delivery time, and dosimetric improvement.

Conclusions:

• The HD270 software is a versatile and cost-effective solution for mitigating MLC-induced isodose undulation and improving dose conformity in radiotherapy.
• Clinical implementation of HD270, especially at 3 mm resolution, enhances treatment precision for head and neck and prostate cancers, offering a favorable alternative to standard MLC.
• HD270 provides improved dose distribution and reduced irradiated volumes, contributing to better patient outcomes in radiation oncology.