Author: David L. Barbee, Jose R. Teruel Antolin, Jinyu Xue 👨🔬
Affiliation: NYU Langone Health 🌍
Purpose: This work introduces a method of regional dose evaluation of normal brain tissue using local target-specific evaluation and compares to global dose evaluation for linac-based single-isocenter multi-metastases (SIMM) treatments.
Methods: Ten SIMM plans were created using an automatic treatment planning script developed in-house using the Varian Eclipse Scripting API, with each target receiving a single fraction dose between 18 and 22 Gy. All plans were created for a Varian TrueBeam using 10X-FFF energy and 4 non-coplanar arcs. We developed a technique to calculate individual V12Gy, V10Gy, V6Gy per-target using a metric-dependent search radius for each individual target. The search radius was selected as 1 cm for the CI index and 2 cm for the volumetric dose parameters.
Results: Twenty-nine metastases met inclusion criteria over the ten cases analyzed. Individual metastases had an average volume [range] of 0.71cc [0.13, 3.25]cc with an average [range] individual CI of 1.24 [1.08,1.57]. All individual metastases PTVs achieved a coverage of V100% of Rx ≥ 99%. For individual metastases, the average brain V12Gy including target was 3.04cc [0.67, 10.53]cc, the average brain V10Gy was 4.29cc [1.0, 14.91]cc, and the average brain V6Gy was 11.16cc [2.79, 38.15]cc. Out of all 29 metastases analyzed, 26 had a brain V12Gy<5cc, two had a brain V12Gy<10cc, and one had a brain V12Gy<15cc, which indicated an estimate of less than 10%, 15%, and 20% respectively, for normal brain tissue complication probability based on the HyTEC. A statistically significant correlation (p<0.001) was found between the individual target volumes and the per-metastasis brain V12Gy, V10Gy, and V6Gy of 0.92, 0.90, and 0.85, respectively.
Conclusion: Analysis of individual metastasis volume, CI, and per-metastasis brain dosimetric values V12Gy, V10Gy, and V6Gy, have the potential to inform about dose objectives feasibility and limits in the clinical setting for SIMM treatments using a linear accelerator.