Practical experience in commissioning ring applicators using ring applicator component type with bravos control...

Area of Science:

• Medical Physics
• Radiation Oncology
• Brachytherapy Technology

Background:

• Brachytherapy treatment accuracy is influenced by source positioning.
• The Bravos v1.2 system introduced a ring applicator component type (ACT) to improve geometric accuracy.
• Geometric and dosimetric discrepancies can arise from source positioning inaccuracies.

Purpose of the Study:

• To commission the CT/MRI-compatible titanium ring applicator for Bravos v1.2.
• To evaluate the performance of the new ring ACT compared to the traditional rigid ACT.
• To investigate a novel commissioning method for accurate source positioning.

Main Methods:

• Two commissioning methods were evaluated across three Bravos afterloaders.
• Modified Varian commissioning involved smaller step sizes, alternating dwell times, and including odd/even positions.
• Film analysis was performed with varying offsets (0.0-0.2 cm) on 30-, 45-, and 60-degree rings.

Main Results:

• An optimal offset of 0.2 cm was identified, minimizing deviations between planned and delivered dwell positions for all rings and afterloaders.
• The rigid ACT exhibited larger positional discrepancies compared to the ring ACT.
• The optimal offset reduced dosimetric differences (<1%) for key clinical metrics (D95, D90, D2cc) and EQD2 values.

Conclusions:

• A novel commissioning procedure effectively determines an optimal offset for accurate source positioning with the ring ACT.
• This method significantly minimizes dosimetric discrepancies, enhancing treatment accuracy.
• The developed procedure standardizes commissioning for Bravos afterloaders with the v1.2 control system, outperforming the rigid ACT.