A method for restricting intracatheter dwell time variance in high-dose-rate brachytherapy plan optimization.

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Optimization

Background:

• Inverse planning simulated annealing (IPSA) is a key optimization engine in brachytherapy.
• Controlling dwell time variance within catheters is crucial for treatment planning.
• Existing IPSA methods may not sufficiently address dwell time uniformity.

Purpose of the Study:

• To introduce a modification to the IPSA algorithm enabling restriction of intracatheter dwell time variance.
• To present the dwell time deviation constraint (DTDC) parameter for controlling dwell time uniformity.

Main Methods:

• Modified the IPSA optimization engine to incorporate the DTDC parameter.
• DTDC ranges from 0 (no restriction) to 1 (uniform dwell times within a catheter).
• Evaluated the impact of DTDC on the optimization penalty function and dwell time distribution.

Main Results:

• The modified algorithm maintains the core inverse planning and dose optimization principles of IPSA.
• Increasing DTDC reduces dwell time variance within catheters, leading to smoother dwell time changes.
• Non-zero DTDC values consistently increased the overall optimization penalty function value.

Conclusions:

• The DTDC extension to IPSA allows for controlled reduction of dwell time differences between adjacent positions.
• This can lead to clinically desirable reductions in dwell time variation.
• The clinical relevance of DTDC must be assessed case-by-case due to potential degradation of dose-volume histogram metrics at higher values.