# Cancer Treatment: An Overview of Pulsed Electric Field Utilization and Generation
## 6 Reversible and Irreversible Electroporation Parameters
### Membrane Threshold Voltage  
The optimal pulse voltage threshold value differs based on the cell type and the percentage of viability targeted by the process; therefore, the literature reports different threshold values of suitable electric fields for RE and IRE. In vitro (It describes medical procedures, tests, and experiments that researchers perform outside of a living organism) and in vivo (referring to tests, experiments, and procedures in or on whole living organisms) pulse parameters range are concluded from the literature in Table 4. For RE, reported in vitro values vary between 400 and 600 V/cm, for a total of eight repetitive pulses each having 100 \(\upmu\)s exposure duration [57]. For IRE, in vitro values vary between 1000 and 2000 V/cm and depend on the number of pulses, pulse duration, repetition frequency, and total exposure time [7]. Reported in vivo threshold values for IRE vary between 500 and 1300 V/cm [7; 58]; as with in vitro experiments, the specific values depend on the other pulse parameters. \begin{table}
\begin{tabular}{l l l l l} \hline \hline  & \multicolumn{2}{c}{**RE**} & \multicolumn{2}{c}{**IRE**} \\ \hline  & **In Vitro** & **In Vivo** & **In Vitro** & **In Vivo** \\ \hline Peak & 400\(\sim\)600 V/cm & — & 250\(\sim\)2000 V/cm & 500\(\sim\)1300 V/cm \\ \hline \# of pulses & 8 & — & 10\(\sim\)3000 & 8\(\sim\)180 \\ \hline Duration & 100 \(\upmu\)s & — & 50 \(\upmu\)s\(\sim\)300 ms & 50 \(\upmu\)s\(\sim\)20 ms \\ \hline \end{tabular}
\end{table} 
Table 4: In vivo and in vitro membrane threshold voltages. During different experiments in the literature, it has been found that the transition from non-electroporated to reversible electroporated and in turn to irreversible electroporated states is continuous. Therefore, mathematical models can be used to describe the resulting permeabilization, survival, and cell viability and display them in curves [7]. This is achieved by performing the same process a number of times, recording the results, then applying statistical analysis to filter the results and organize them in the form of a table, graph, or both. The critical cell membrane voltage varies depending on a variety of parameters, including the ambient temperature, pulse rise time, duration, and repetition frequency. The critical voltage increases with increasing temperature rise as well as with lower pulse duration, especially in nano/picosecond-range treatment pulses. To introduce pores in the cell membrane, the induced voltage should exceed at least 0.2\(\sim\)0.3 V, [59]; usually, the value needed to create primary membrane pores with a minimum radius of \(\sim\)1 nm varies between 0.5\(\sim\)1 V [60]. This is usually assumed to be 1 V, as presented in [61]. For nanosecond and shorter pulses with extremely short rise times the membrane voltage can reach 1.6 V, at which point it becomes saturated and pore formation prevents any further increase, as shown experimentally in [62]. A high voltage field value is required, leading to increased thermal effects. The temperature increase \(\Delta T\) depends on the electric field \(E\), pulse duration \(\tau\), conductivity of the cell \(\sigma\), density of the medium \(\rho\), and specific heat \(c\), and can be calculated as follows:  
\[\Delta T=\frac{\sigma E^{2}\tau}{\rho c}. \tag{7}\]  
In order to limit the damage to neighbouring tissues due to the thermal effect of the HV short pulses or LV long pulses, the temperature increase should be kept lower than \(\Delta T=1\)\({}^{\circ}\)C through proper selection of the pulse duration and field intensity. The charging time constant of the mammalian cell membrane is in the range of microseconds (the actual value varies based on parameters such as the type of cell and the concentration of other substances); in order to cause changes in the internal structure of the cell, a high-voltage nanosecond-range short electric pulse with a duration less than the membrane charging time constant should be applied.