Page 263 - Computational Modeling in Biomedical Engineering and Medical Physics

252 Computational Modeling in Biomedical Engineering and Medical Physics

More recently Jain et al. (2005) and Zhang and Misra (2007) reported in vitro studies
on ion nanoparticle (iron oxide-based and others) platforms, which may convey chemo-
therapeutic for the sustained and stimuli-triggered release (by heating, electric fields, US,
UV light, and radiation). A promising avenue is the hyperthermia-enhanced radiotherapy
(Sekhar et al., 2007). In this respect, hyperthermia-mediated magnetic nanoparticle
(MNP)-delivered radionucleotides is prospectively attractive (Pankhurst et al., 2003), as
cited by Giustini et al. (2010).

Ablation
TA is a relatively new treatment, which leads to tissue necrosis through coagulation.
This minimally invasive procedure for cancer treatment is an efficient alternative to the
classical surgical resection of small, less than 3 cm, tumors. TA is produced either by

heating or by freezing the tumoral tissue either to raise its temperature [above 60 C, in

TA (Brace, 2011)] or to lower it below the tissue living threshold [below 40 C, in
cryoablation (Mayo Clinic; Lepock, 2005)] the tissue living threshold. Highly localizable
inside the tumoral tissue, TA is used in the treatment of lung, bone, renal, and liver can-
cers. Radiofrequency ablation (RFA), which is thought of as a type of interstitial hyper-
thermia, uses RF waves to heat and destroy cancer cells.
Ablation through hyperthermia or cryogenic processes occurs when the work of
the external source (EMF, US, and CS) produces excessive heat absorption or release
by the tissue that results in its permanent damage when a critical (necrotic) tempera-
ture is reached. The amount of damaged tissue by ablation may be evaluated by com-
puting the direct calculation (integration) of the change in the internal energy or by
the duration of the exposure to the necrotizing temperature.
In the energy analysis, the rate of tissue injury is given by the Arrhenius equation
E a
(Xu et al., 2008) kTðÞ 5 dΩ 5 Ae 2 RT , and it yields the amount of damaged tissue
dt
t
ð
E a
Ω 5 Ae 2 RT dt; ð8:1Þ
0
where t is the time since the procedure starts, R 5 8.314 J/mol K is the universal con-
stant of gasses, A [1/s] is a frequency parameter (the number of times two molecules
collide), a constant, tissue-dependent quantity, and E ava [J/mol] is the activation
energy needed to trigger the irreversible damage reaction, a tissue-dependent quantity
(Bhowmick et al., 2004; Hasgall et al., 2015; Jacques et al., 1996; Pop et al., 2003;
Rossmann and Haemmerich, 2016; Xu et al., 2008). Typical values for the liver are
5
39 -1
A 5 7.39 3 10 s and E a 5 2.577 3 10 J/mol (Jacques et al., 1996), and the frac-
2Ω
tion of destroyed tissue is Γ 5 1 2 e .
In the damage integral analysis (either TA or cryoablation) of the damaged tissue,
Ω, two distinct cases are identified: (1) ablation occurs immediately when the