Radiation Physics

PV QA 3 - Poster Viewing Q&A 3

TU_14_3250 - Power Density Loss and related measures can be used to quantify the dose of Tumor Treating Fields (TTFields)

Tuesday, October 23
1:00 PM - 2:30 PM
Location: Innovation Hub, Exhibit Hall 3

Power Density Loss and related measures can be used to quantify the dose of Tumor Treating Fields (TTFields)
H. S. Hershkovich, N. Urman, A. Naveh, S. Levi, and Z. Bomzon; Novocure, Haifa, Israel

Purpose/Objective(s): Tumor Treating Fields are alternating electric fields known to inhibit cancer cell growth. Preclinical studies have shown that TTFields inhibitory effect increases with field intensity. Hence, intensity of the electric field has historically been used as for quantifying TTFields dose. Electric field intensity quantifies the force that the field applies on intracellular objects. However, when considering the dose of a physical modality such as TTFields, it is important not only to consider the forces at work, but also the amount of energy transferred from the modality to the tissue (in other words, the work that the modality performs). This is because quantifying energy and work provides a better description of the extent to which the physical modality alters the state of the objects on which it operates. Here we show how the power density loss of the electric field can be used to quantify TTFields dose, and how using this measure sheds new light on the mechanism of action of TTFields.

Materials/Methods: The power density loss of an electric field, L is defined as L=½σ|E|² where σ is the conductivity of tissue and |E| is the intensity of the electric field. Power density loss is measured in units of mill-Watts per cubic centimeter (mW/cm3). To examine the distribution TTFields power density loss when delivering TTFields to the brain, we numerically simulated delivery of TTFields to realistic head models of Glioblastoma patients. We then calculated the field intensity distribution and the power loss density distribution with the models and visually compared the two. Finally, we calculated the total power loss within the models to gain a measure of the power delivered by TTFields to the body during treatment.

Results: The electric field intensity tends to increase in regions of low conductivity, such as white matter, and tends to be lowest in regions of high conductivity such as the ventricles and resection cavities. The power density loss tends to increase in regions of higher conductivity, and within the ventricles and resection cavity can take on values comparable to those observed in other tissue types. The average power density loss within the gross tumor volumes of all patients was 5 mW/cm³. The total power loss of TTFields within the simulated cases was between 20-40 Watts (equivalent to 412-825 Kcalories per day). Thus, the power delivered by TTFields to the brain is on-par with the resting metabolic rate of the brain (about 20% of the body’s resting metabolic rate).

Conclusion: This analysis shows that power loss density is a viable physical measurement to accurately quantify TTFields dose in treatment planning. The analysis also shows that the power delivered by TTFields to cells is comparable to the metabolic rate of the cells. This observation could lead to new hypotheses about the mechanism of action of TTFields.

Author Disclosure: H.S. Hershkovich: Stock Options; Novocure. N. Urman: Stock Options; Novocure. S. Levi: None. Z. Bomzon: Stock; Novocure. Stock Options; Novocure.

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