Author: Tirthraj Adhikari, Timothy J Allen, Abdullah A. Alshreef, Clara Ferreira 👨🔬
Affiliation: Medical School Department of Radiation Oncology University of Minnesota, University of Minnesota, Loma Linda University Medical Center 🌍
Purpose: GammaTile Brachytherapy with 131Cs is an effective treatment for glioblastomas, offering local control with minimal radiation necrosis. While the line source model is preferred for dose distribution calculation, some clinics may use the point source model. This study aimed to assess the dosimetric impact on the dose calculation when using line versus point 131Cs source models in GammaTile Brachytherapy.
Methods: This study compared dosimetric differences in high-risk clinical target volumes (HR-CVT) for 42 patients between point and line source models. Treatment plans were retrospectively recreated using the point source model in the Varian Brachytherapy Treatment Planning System (BrachyVision) and compared with the original line source model plan. DVH indices (V90, V100, V150, V200, D90, D100,) and dose statistics were recorded and compared.
Results: The comparison revealed minimal differences in dose coverage between the two models. For the line source model, average V90, V100, V150, and V200 were 87.9%, 83.6%, 57.0%, and 33.4%, respectively, while the point source model showed slightly higher values of 88.2%, 84.0%, 57.1%, and 33.1%. Differences in dose coverage were minimal, with variations of ˂ 0.4%. Average D90 and D100 values were similar for both models: 61.8 Gy and 33.1 Gy for the point source, and 61.4 Gy and 32.4 Gy for the line source (p-values > 0.05, R² ~ 1). However, 21% of patients showed >5% difference in D100 with the point source, and 2.4% showed >12% difference. The point source model overestimated HR-CVT Dmax doses by 12%, averaging 103.1 Gy, compared to 92.1 Gy for the line source model.
Conclusion:
The point versus line source models did not show significant differences in dose calculations. However, in some cases, the point source model can overestimate Dmax to HR-CVT. Despite comparable dose calculations, the point source model should be carefully reconsidered in clinical decision-making.