1. Template Matching Can Accurately Track Tumor Evaluation of Dose Calculation of RayStation Planning System in Heterogeneous Media
Huijun Xu, Byongyong Yi, Heeteak Chung, Karl Prado, Shifeng Chen
Purpose
To investigate the clinical reliability of heterogeneity-based dose algorithm using RayStation treatment planning system v.4.0.
Methods
RayStation collapsed cone dose calculations were compared with a) ion chamber and film measurement and b) Monte Carlo dose calculation
Heterogeneous media included a multi-layer phantom (Figure 1) and 8 lung cancer patients
To measure the phantom dose corresponding 6MV beam with MLC-defined field size 5x5, 10x10, 15x15 or 20x20 cm2, farmer chamber positioned at center of central solid water layer, and the films placed at interfaces of solid water and Styrofoam. Measurement was performed by using (Figure 1)
For Monte-Carlo-based dose comparison, the absolute gamma analyses (3mm/3%) were performed for PDD in the phantom and for patient volumes receiving dose above 10% of maximum dose.
Figure 1. Schematic figure of the heterogeneous multi-layer phantom and positions of ion chamber and film
Results
Between RayStation and ion chamber measurement: <1% point dose differences for all of the field sizes (Table 1)
Between RayStation and film measurement: 5x5cm2 field had < 4mm maximum difference in penumbra <0.3mm for the field width at all phantom interfaces (Figure 2)
Between RayStation and Monte Carlo: > 95% gamma passing rate for PDD along beam axis in the phantom (Table 1) and > 95% 3D gamma passing rate for all the patients
Table 1. Comparison between RayStation and chamber measurement or Monte Carlo in terms of phantom dose for different MLC-defined fields
Field size
(cm2)
RayStation vs. chamber dose difference (%)
RayStation vs. Monte Carlo PDD gamma (%)
5x5
-0.88
95.4
10x10
-0.05
98.6
15x15
-0.69
99.6
20x20
-0.98
99.3
Figure 2. Dose profiles measured by film (blue dots) versus RayStation calculation (red solid line). Depth is at interface between central solid phantom and lower Styrofoam. Field size is 5x5cm2 at center of central solid water slab..
Table 2. Average, minimum and maximum 3D gamma passing rate (3mm/3%) between RayStation and Monte Carlo for 8 lung patient cases. A 10% dose threshold was used here.
Conclusion
RayStation provides clinically acceptable heterogeneity-based algorithm
Average (%)
Minimum
Maximum
98.0
95.1
99.8