When it comes to testing efficacy, we would like to use a treatment duration as long as possible to maximize the effect. However, this duration varies between in vitro and in vivo work. For cell cultures, the control samples continue to grow throughout the treatment duration, and so after 72 h the plates are very much confluent, and may not be left to continue and grow any further (without drastic changes in the environmental conditions, making them inadequate control cells). It is also noteworthy that such treatment periods for in vitro work are well accepted in the field of TTFields research. In vivo, prior studies also used similar time frames of 2 to 3 weeks from inoculation when working with the N1S1 model (Buijs et al., 2012 -; Ju et al., 2009; Thompson et al., 2012). Extending treatment duration was also limited by the physical status of the animals, as was explained in response 3.
N1S1 cells were treated with TTFields (1.7 V/cm RMS) across a frequency range of 100–400 kHz, and cell count were determined following 24 hours of treatment.