SU-E-T-430: Evaluation of Inverse Optimization in Brachytherapy for Locally Advanced Cervix Cancer

Area of Science:

• Radiation Oncology
• Medical Physics
• Gynecologic Oncology

Background:

• Brachytherapy is crucial for locally advanced cervix cancer treatment.
• Traditional 2D planning is being advanced by 3D conformal planning using CT/MRI-compatible HDR brachytherapy applicators.
• The EMBRACE protocol recommends manual optimization over inverse optimization due to concerns about high-dose uncertainties.

Purpose of the Study:

• To investigate the feasibility and benefits of inverse optimization planning in HDR brachytherapy for cervix cancer.
• To compare inverse planning with manual planning regarding planning time and dose metrics.

Main Methods:

• Eight cervix cancer cases were planned using both manual and inverse optimization techniques with Oncentra® Brachy.
• Plans were evaluated based on planning time, DVH parameters (D90, V100%, D2cc), and high-dose volumes (V100%, V200%) for targets and organs at risk.
• Dose was reported in total EQD2, assuming standard external beam and HDR treatment schedules.

Main Results:

• Inverse planning reduced average planning time by 55%.
• Target coverage (HR-CTV, IR-CTV) showed minimal differences (<2%) between inverse and manual plans.
• Inverse planning improved organ-at-risk sparing, reducing D2cc by 4.2%-5.7% and normal tissue V100%/V200% by 31%/40% respectively.
• Small bowel received significant dose in 7/8 cases, regardless of planning method.

Conclusions:

• Inverse planning is feasible and offers improved DVH parameters and reduced planning time compared to manual planning.
• Reporting normal tissue doses, including for the small bowel, is essential to address concerns about high-dose regions.
• Inverse planning represents a valuable advancement for cervix cancer brachytherapy.