2076 - Spatially-Fractionated Radiation Therapy on Brain Metastases Using Volumetric-Modulated Arc Therapy with Two Different Lattice Arrangements
Presenter(s)
T. Gray1, A. Hadfield2, B. Andelic3, H. Nordstroem4, B. Guo1, N. Yoon5, J. G. Scott6, J. H. Suh7, and Y. B. Cho7; 1Department of Radiation Oncology, Taussig Cancer Institute, Cleveland Clinic, Cleveland, OH, 2Cleveland Clinic, Cleveland, OH, 3Elekta, Stockholem, Sweden, 4Elekta Instrument AB, Stockholm, Sweden, 5Adelphi University, Garden City, NY, 6Department of Radiation Oncology, Taussig Cancer Center, Cleveland Clinic, Cleveland, OH, 7Department of Radiation Oncology, Cleveland Clinic Foundation, Cleveland, OH
Purpose/Objective(s): To investigate and compare the biological effect of Spatially Fractionated Radiation Therapy (SFRT) using volumetric-modulated arc therapy (VMAT) Lattice stereotactic radiosurgery (SRS) with a fixed size lattice pattern (static) vs an optimized (dynamic) lattice pattern. This retrospective study presents Equivalent Uniform Dose (EUD) and Therapeutic Ratio (TR) of VMAT SFRT plans as well as a dosimetric characterization as a function of target size and sphere diameter between 4mm vs 8mm sphere sizes.
Materials/Methods: CT images and target contours were obtained from 20 patients with the largest brain metastases and enrolled in an IRB-approved study over the past 10 years. Spherical target contours were manually placed inside of the tumor using either a static lattice or optimized lattice (dynamic as a function of target size and collimator) pattern, both in a face-centered cubic arrangement and given a dose of 18Gy in a single fraction. The sphere contours (both 4mm and 8mm sizes) were generated by using an in-house script, which was imported into the treatment planning system (TPS). Three full arcs were employed in each plan to deliver adequate sphere coverage of D50%=18Gy. The number of spheres, valley-to-peak ratio (VPR), average target dose, average sphere dose, modulation factor, TR and EUD are compared.
Results: Average number of spheres, VPR, target mean dose (Gy), sphere mean dose (Gy), and modulation factor (cGy/MU) are shown in Table 1. The difference in VPR and target mean dose were reduced for the dynamic lattice pattern as compared with the static lattice pattern. The dynamic lattice pattern produced a more consistent EUD and TR between 4 mm and 8 mm resolutions than the static pattern for radio-resistant tumors, with differences being 1.8 Gy for EUD and 10.67 for TR for radio-resistant tumors. All parameters were statistically significant, with p<0.05.
Conclusion: We conclude that the dynamic lattice pattern in VMAT SFRT planning is generally more consistent than using the static lattice pattern. SFRT, in general is beneficial for radioresistant tumors over radiosensitive tumors, and using a dynamic lattice pattern for SFRT produces better dosimetric quality plans than for the static lattice pattern.
Abstract 2076 - Table 1: Dosimetric characterization of Static vs Optimized (Dynamic) Lattice type for 4mm and 8mm lattice sizes| Metric | |||||
| Lattice Type | # spheres | VPR | Target mean dose (Gy) | Sphere mean dose (Gy) | Modulation Factor (cGy/MU) |
| Static 4 mm | 29±8.04 [17-46] | 0.50±0.05 [0.33-0.60] | 12.99±0.73 [11.72-14.66] | 18.0±0.07 [17.92-18.12] | 3.38±0.44 [2.66-4.43] |
| Static 8 mm | 4.6±1.46 [3-9] | 0.28±0.05 [0.09-0.43] | 7.27±0.09 [5.49-10.12] | 18.18±0.16 [17.92-18.62] | 3.14±0.42 [2.55-4.35] |
| Dynamic 4 mm | 18.6±2.79 [14-25] | 0.48±0.05 [0.41-0.55] | 11.18±0.68 [9.82-12.35] | 18.02±0.07 [17.87-18.14] | 3.46 ±0.41 [2.88-4.19] |
| Dynamic 8 mm | 8.1±2.02 [4-14] | 0.34±0.09 [0.13-0.49] | 8.89±1.22 [6.18-11.76] | 18.11±0.08 [17.95-18.26] | 3.21±0.37 [2.6-3.86] |