Hybrid inverse treatment planning optimization in gynecologic brachytherapy: Comparison with conventional method

Area of Science:

• Medical Physics
• Radiation Oncology
• Gynecological Oncology

Background:

• Brachytherapy is crucial for gynecological cancer treatment.
• Achieving optimal dose distribution, particularly the pear-shaped pattern, is essential for efficacy and minimizing toxicity.
• Current inverse planning optimization methods may deviate from desired dose distributions.

Purpose of the Study:

• To evaluate a semi-automatic hybrid inverse treatment planning optimization (HIPO) approach for gynecological brachytherapy.
• To assess HIPO's ability to preserve the conventional pear-shaped dose distribution without using dummy structures.
• To compare different HIPO configurations for their clinical plan quality and dose distribution characteristics.

Main Methods:

• Retrospective analysis of 29 gynecological cancer patients treated with combined intracavitary and interstitial (IC/IS) brachytherapy.
• Four HIPO methods (H_ovoid, H_free, H_MS, H_MS*) were applied and compared to clinical plans (CPs).
• Optimization involved dwell times for specific applicators, with varying fixation strategies and use of pre-generated organ at risk (OAR) doses.

Main Results:

• All HIPO methods achieved clinically acceptable dose-volume histogram (DVH) parameters for high-risk clinical target volume (HR-CTV) coverage and OAR sparing.
• Significant deviations from the pear-shaped dose distribution were noted, especially with the H_free method.
• The H_MS* method, with adjusted parameters, most closely matched the CP's HR-CTV D_90% while maintaining the pear-shaped dose distribution.

Conclusions:

• The modified Manchester system (H_MS) with pre-optimized OAR doses is recommended for fixation in HIPO.
• The H_MS* approach offers a balance between DVH parameter quality and preservation of the conventional pear-shaped dose distribution.
• The proposed HIPO method is clinically acceptable for gynecological brachytherapy planning.