SU-E-T-318: Source Position Localization for ICBT Tandem & Ovoid Applicators Utilizing Oncentra Brachy Applicator...

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Image artifacts in HDR cervical brachytherapy can hinder accurate dwell position localization.
• The Nucletron Oncentra Brachy Applicator Modeling plugin (AMp) offers a potential solution by using 3D CAD models for defining dwell positions.

Purpose of the Study:

• To compare the accuracy of source localization and dosimetric equivalence between clinical practice and the AMp for HDR cervical brachytherapy.
• To evaluate the impact of AMp-based localization on organs at risk (OARs) in a phantom study.

Main Methods:

• KVCT imaging of a water phantom with bladder and rectum surrogates and a Fletcher-type tandem and ovoid applicator.
• Catheter reconstruction using both clinical protocols (dwell position markers) and the AMp within Oncentra's Brachy TPS.
• Treatment planning to 600cGy at Point A, followed by spatial comparison of dwell positions and dosimetric analysis (D0.1cc, D1cc, D2cc) for surrogates.

Main Results:

• 80% of dwell positions localized by AMp agreed within 1mm of clinical protocol for a 25mm ovoid/30° tandem applicator.
• Maximum deviation between AMp and clinical protocol localization was 1.17mm.
• Dosimetric differences for OAR surrogates were minimal, with slight increases in D0.1cc, D1cc, and D2cc when using AMp.

Conclusions:

• Preliminary findings suggest that the AMp provides equivalent dosimetry compared to clinical protocols for HDR cervical brachytherapy in a simple phantom setup.
• Further investigation is ongoing with different ovoid sizes and a vaginal cylinder to validate these results.