(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: Compare catheter reconstruction methods for the lunar ovoid channels of the Elekta Veneziaâ„¢ Advanced Gynecological Applicator.
Methods: Three available lunar ovoid sizes (22, 26, and 30 mm diameter) for the Venezia™ applicator were evaluated. CT scans (0.6 mm slice thickness) were performed with dummy markers inserted and with the Flexitron® Source Position Simulator (SPS) at step sizes of 5 mm from the distal end. Oncentra® treatment plans were generated utilizing three distinct catheter reconstruction techniques: automatic reconstruction using the built-in applicator model, manual reconstruction tracing the CT dummy marker, and manual reconstruction using the SPS. Dose from a single ovoid was calculated for all plans, and identical dwell times were used such that the 125% isodose line fell at the surface of the applicator following our clinical practice. For the comparison, the treatment plan based on the SPS scans taken as the true dose distribution.
Results: The maximum dose difference to a 0.1 cm³ volume outside the applicator was found to be 37% of the prescription dose (Dᵣₓ) for automatic catheter reconstruction and 39% for manual reconstruction using the CT dummy marker. For all three applicator sizes, the tissue volume with a dose difference exceeding +10% of Dᵣₓ ranged from 0.33-2.03 cm³ for automatic reconstruction and 0.62-1.67 cm³ for CT marker reconstruction. Similarly, tissue underdosing by at least -10% occurred for 0.71-2.50 cm³ using automatic channel reconstruction and 0.27-1.54 cm³ for CT marker reconstruction.
Conclusion: Both catheter reconstruction techniques yielded similar dose deviations compared to the ground-truth dose distribution created using the SPS to simulate the path of the real source. To limit the potential clinical significance of these dose differences, the accuracy of dose calculations with the Veneziaâ„¢ applicator could be improved by establishing a realistic source path for catheter reconstruction.
Keywords
Brachytherapy, Treatment Planning, Reconstruction
Taxonomy
TH- Brachytherapy: Virtual planning comparisons
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