SU-E-T-425: Impact of Model Based Dose Calculation Algorithm for Ir-192 Intracavitary Brachytherapy with Shielded...

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Dosimetry

Background:

• Intracavitary brachytherapy for cervical cancer relies on accurate dose calculation.
• Traditional methods like TG43 may not fully account for complex geometries and materials.
• Advancements in dose calculation algorithms, such as grid-based Boltzmann solvers (GBBS), offer potential improvements.

Purpose of the Study:

• To evaluate the dosimetric impact of a grid-based Boltzmann solver (GBBS) in Ir-192 intracavitary brachytherapy for cervical cancer patients.
• To compare GBBS calculations with the standard TG43 dose calculation method.
• To identify the primary factors contributing to dose differences when using GBBS with shielded applicators.

Main Methods:

• Retrospective analysis of 24 cervical cancer patients treated with Ir-192 brachytherapy.
• Dose planning using BrachyVision with GBBS Acuros, incorporating shielded colpostats and tandem applicators.
• Four GBBS calculation scenarios were performed to isolate effects of applicator modeling, tissue heterogeneity, and boundary conditions.
• Comparison of GBBS results against TG43 calculations for Point A, Point B, ICRU rectum, D2cc rectum, ICRU bladder, and D2cc bladder.

Main Results:

• GBBS calculations showed mean dose differences compared to TG43: Point A (-2.5%), Point B (-1.5%), ICRU rectum (-8.4%), D2cc rectum (-6.2%), ICRU bladder (-7.2%), D2cc bladder (-3.4%).
• Significant differences exceeding 5% were observed for rectal and bladder dose metrics.
• Analysis indicated that modeling of shielded applicators was the largest contributor to the observed dose discrepancies.

Conclusions:

• Clinically significant dose differences arise when employing model-based dose calculation algorithms like GBBS with shielded brachytherapy applicators.
• Applicator modeling is the predominant factor influencing these dose variations, outweighing contributions from tissue heterogeneity or patient boundary conditions.
• These findings highlight the importance of accurate applicator modeling in advanced dose calculation for brachytherapy.