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Thank you for addressing all the issues pointed by the reviewers and for amending the manuscript accordingly. I am pleased to accept the revised manuscript now.
[# PeerJ Staff Note - this decision was reviewed and approved by Glynn Gould, a PeerJ Section Editor covering this Section #]
Appropriate as presented.
Acceptable.
Acceptable.
Please address the concerns of both reviewers and amend your manuscript accordingly.
[# PeerJ Staff Note: Please ensure that all review and editorial comments are addressed in a response letter and any edits or clarifications mentioned in the letter are also inserted into the revised manuscript where appropriate. #]
The article is written clearly, with the introduction providing motivation for the problem addressed. TTF is a therapeutic modality that gaining wider interest, and having a real-time reporting/monitoring system would be beneficial. The literature and background/context for the proposed solution of EIT is well motivated. The article structure, figures and tables as presented are acceptable.
The authors present an original result where the use a head phantom to test whether electrode configurations used for TTF can detect a tumor mass via impedance measurements. The results are in align with the hypothesis and demonstrates the feasibility of the approach.
The only perceivable weakness of the topic is that it reports on the feasibility of impedance measurements using TTF electrode arrays, that would be further strengthened if actual treatment vs. response were to be measured. Perhaps these experiments could be performed in a petri dish setting.
Further, the use of a potato, which is a heterogenous mass, in an otherwise homogeneous background is expected to provide distinct results as seen here. More nuanced studies or measurements where the inclusion has much less dramatic conductivity differences in comparison to the background would be of interest.
This is a fairly basic paper evaluating the potential of applying electrical impedance using tumor treating field electrodes as a means of assessing tumor response to therapy. In other words, one set of electrodes could serve as both a means for the treating the tumor and measuring the effect of treatment. The paper uses a fairly basic model of a skull, a potatoes of different sizes to mimic the tumor and a gel to mimic brain tissue. The demonstrate that impedance changes can be detected and these mirror tumor size. A sensitivity analysis is also completed.
The language is clear, the figures, sufficient, references look complete.
But the article is incredibly sparse and many details are omitted (see below).
Table 1 does not need to be a table.
The experimental design is very straightforward, but the model is a very weak approximation of human anatomy and the tumor behavior. GBMS are not simply solitary masses but rather are often deeply infiltrating tumors, with scattered neoplastic cells extending out far from any observable mass on MRI. Moreover, the brain has ventricles which can take up a substantial volume of the cranial vault. It is entirely unclear how the non-homogeneities in normal brain would impact this model as well. Thus the model is really quite unrealistic, yet there is absolutely no discussion as to these huge limitations.
Moreover there is often considerable edema associated with these tumors...again another limitation that this model does not include.
We are told very little about the impedance methods used except the frequency (200 kHz), the rationale of which is not provided. It is also unclear which electrodes were used for the impedance measurements, and were these 4-electrode measurements (I think so)? And if so, which are the voltage and which are the current electrodes.
What impedance system was used?
Only the impedance magnitude was measured. Why? They mention simulations showed that phase was less sensitive, but why not provide that information too?
The validity is limited as noted above based on the very simplistic nature of this model.
There is no inclusion of any kind of skin layer which could also impact the findings.
The conclusions are vastly overstated the limitations of this very simplistic model are not included.
See comments regarding limitations of the study design above.
Overall, the results decided unsurprising and I think this adds relatively little to the literature, although the basic idea of using electrical impedance along with TTFs is good. I really which the authors had spent more time constructing a more realistic model than that presented here. The article is also short on many details. While the results here could be useful for further developmental work, they could also be highly misleading.
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