(Monday, 7/30/2018) 9:30 AM - 10:00 AM
Room: Exhibit Hall | Forum 3
Purpose: The phase III EF-14 trial demonstrated a 4.9-month median overall survival advantage in 695 glioblastoma patients using anti-mitotic TTFields therapy in combination with adjuvant TMZ. TTFields therapy requires placement of an array on the patient’s head. The purpose of this study is to examine the dosimetric compatibility of TTFields with concurrent RT/TMZ and determine whether dosimetric perturbations are affected by array placement.
Methods: Ten consecutive glioblastoma patient plans were recomputed on an anthropomorphic phantom with the TTFields array in three distinct positions. A 5 mm thick skin contour (skin5mm) was added to each plan and used as an intensity modulated RT constraint given concern for bolus-effect. Plans were optimized on a kV CT of the phantom without the ceramic array. MV CT scans of the phantom with the array in each of the three positions were then fused to the planning CT and the densities of autocontours of the array were overridden to the known density value of 5 g/cc. The following Dx and Vx levels were compared with and without the array for the planning target volume (PTV): V97%, V96%, V95%, D97%, D96%, D95%.
Results: The maximum change in PTV coverage for any analyzed Vx or Dx were within +/-3.0%. When averaged over the three positions of the array, Vx and Dx changes over all dose recalculations for each copied patient had standard deviation +/-1.0%. Changes in PTV coverage were attributable to a combination of attenuation by the ceramic discs and increased superficial dose owing to bolus effect.
Conclusion: The dosimetric impact of TTFields is within clinical tolerance for any individual array position and is further mitigated by repositioning of the arrays as will occur during chemoradiation. These dose calculations are promising but will need to be verified through clinical trials to assess patient effect and safety.
Funding Support, Disclosures, and Conflict of Interest: Research funded by a manufacturer of a TTFields device
Keywords
Brain, Dose Volume Histograms, Megavoltage Imaging
Taxonomy
TH- External beam- photons: treatment planning/virtual clinical studies
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