Dosimetric Impact of Tumor Treating Field Arrays on Radiation Treatment for Locally Advanced NSCLC
Abstract
Purpose
A coming phase-1 study will look at feasibility and safety of Tumor-Treating-Field(TTField) arrays on treatment of locally-advanced stage III non-small cell lung cancer(NSCLC). This array maintains low-intensity alternating electric fields around the tumor, and requires patients to wear the array during radiation treatment(while powered-off). No studies to date have analyzed the impact of TTFields on treatment for lung radiation therapy. To do this, we performed retrospective analysis of past radiation treatments as well as a phantom study to validate predictions.
Methods
We modeled TTFields in our treatment planning system(Eclipse/Acuros) with the most appropriate geometric and material representation. Next, ten previously treated patients representative of the population to be enrolled were anonymized, and array models integrated into the treatment plan to characterize impact that would have occurred if the array had been present. Finally, end-to-end analysis was performed on a RANDO phantom by scanning the thorax with the array and generating a VMAT treatment plan. This plan was delivered and dose distribution characterized with multiple measurement devices including film.
Results
Overall, dosimetric measurements show a bolus effect with a Dmax shift of ~0.5cm, increasing max skin dose within 5mm by 8.5% and 38.5% within 2mm. Attenuation by the TTField had moderate impact at depth due to the PDD shift and hardening of the beam(difference in D5cm=0.4% and in D10cm=5.6%). Retrospective analysis of clinical plans showed plan specific variability, with VMAT minimizing dosimetric impacts(skin dose increase~9-32%, and max dose difference beyond Dmax~3.8-7.0%).
Conclusion
Dosimetric analysis shows moderate impact of the TTField, particularly for skin dose. Despite these impacts, DVH analysis shows relatively negligible impact on target coverage. Basic modeling of the TTField in the treatment plan is recommended, as well as utilization of VMAT for delivery. During the upcoming study particular attention should be given to monitoring of patient skin toxicity.