Impact of heterogeneity-based dose calculation using a deterministic grid-based Boltzmann equation solver for...

Area of Science:

• Medical Physics
• Radiation Oncology
• Computational Imaging

Background:

• Brachytherapy is a crucial treatment for cervical cancer, often involving complex dose calculations.
• Accurate dose calculation is essential for optimizing treatment efficacy and minimizing toxicity.
• Heterogeneity correction in dose calculation is vital for improving treatment plan accuracy.

Purpose of the Study:

• To evaluate the dosimetric impact of the Acuros grid-based Boltzmann equation solver (GBBS) for brachytherapy in cervical cancer.
• To compare GBBS calculations with established TG-43 guidelines for clinical dosimetric parameters.
• To assess the influence of tissue heterogeneities and contrast material mapping on dose calculations.

Main Methods:

• Retrospective analysis of 26 cervical cancer patients treated with (192)Ir brachytherapy.
• GBBS modeling of sources, patient boundaries, applicators, and tissue heterogeneities.
• Comparison of GBBS calculations with TG-43 guidelines for parameters like Points A/B, ICRU, and D2cm3 values for bladder, rectum, and sigmoid.

Main Results:

• Most clinical dosimetric parameters (Points A/B, bladder D2cm3, ICRU bladder, 3/9 o'clock) were within 5% of TG-43 for all GBBS calculations.
• Differences between GBBS and TG-43 were primarily attributed to source/boundary modeling and applicator representation.
• Significant deviations (>5%) were observed for rectal and sigmoid D2cm3 and ICRU rectal points in worst-case contrast mapping scenarios.

Conclusions:

• The GBBS demonstrates minimal impact on clinical parameters for patients with unshielded applicators in cervical brachytherapy.
• Incorrect mapping of rectal and balloon contrast materials showed no significant impact on clinical parameters.
• Rectal dose parameters may exhibit sensitivity to the mapping of radiopaque packing materials.