**4. Results and discussion**

The extent of coagulation necrosis is dependent on the energy deposited, local tissue interaction minus the heat lost.

Principles and Application of RF System for Hyperthermia Therapy 179

2 w atts 3 w atts 4 w atts

5 w atts 6 w atts 7 w atts

10 watts 13 watts 15 watts

**Figure 7.** Brain tissue results.

**Temperature ( oC)**

**Figure 8.** Liver tissue results.

**Temperature (oC)**

**Figure 9.** Kidney tissue results.

**Temperature (**

 **oC)**

In figure 8, the plot shows that, while 5 watts and 6 watts are within the ideal ablation zone, the 7 watts setting is too high for liver tissue as it produced carbonization resulting in temperature drop. The best result however was recorded with the 6 watts setting which

**KIDNEY**

0 2 4 6 8 10 12 14 16 **Time (min)**

0 2 4 6 8 10 12 14 16 **Time (min)**

**BRAIN TISSUE**

0 2 4 6 8 10 12 14 16 **Time (min)**

**LIVER TISSUE**

shows a steady rise in temperature without carbonization or charring.

*Coagulation necrosis energy deposited local tissue interactions heat loss* –

Heat efficacy is defined as the difference between the amount of heat produced and the amount of heat lost. Therefore, effective ablation can be achieved by optimizing heat production and minimizing heat loss within the area to be ablated. The relationship between these factors has been well characterized as the "bio-heat equation." Heat production is correlated with the intensity and duration of the radio-frequency energy deposited. Heat conduction or diffusion is usually explained as a factor of heat loss in regard to the electrode tip. Heat is lost mainly through convection by means of blood circulation. Therefore, the cooling tissue by perfusion can limit the reproducible size of the ablation lesion in vivo.

Macroscopic and microscopic examination of tissue samples tested show clear evidence of coagulation necrosis. A tissue volume of up to 20 mm diameter was necrosed with the single-tine probe developed. The plots of temperature versus time for different tissue types tested using different power settings are presented in the following figures:

**Figure 6.** Lung tissue results.

From figure 6, it is seen that, while 1 watt was inadequate for coagulation necrosis in lung tissue, 3 watts showed evidence of carbonization, leading to a drop in temperature as further conduction is inhibited. The best result was achieved with 2 watts, which showed a steady rise in temperature maintained within the ideal ablation temperature range.

The plot in figure 7 shows that, while 2 watts was below the ideal temperature range, and therefore inadequate for effective tissue necrosis, 4 watts was too high and showed evidence of carbonization, resulting in a drop in temperature due to inhibition in conduction. The best result in terms of effective tissue necrosis was achieved with the 3 watts power setting.

**Figure 7.** Brain tissue results.

**4. Results and discussion** 

interaction minus the heat lost.

the ablation lesion in vivo.

**Figure 6.** Lung tissue results.

**Temperature (oC)**

watts power setting.

The extent of coagulation necrosis is dependent on the energy deposited, local tissue

*Coagulation necrosis energy deposited local tissue interactions heat loss* –

Heat efficacy is defined as the difference between the amount of heat produced and the amount of heat lost. Therefore, effective ablation can be achieved by optimizing heat production and minimizing heat loss within the area to be ablated. The relationship between these factors has been well characterized as the "bio-heat equation." Heat production is correlated with the intensity and duration of the radio-frequency energy deposited. Heat conduction or diffusion is usually explained as a factor of heat loss in regard to the electrode tip. Heat is lost mainly through convection by means of blood circulation. Therefore, the cooling tissue by perfusion can limit the reproducible size of

Macroscopic and microscopic examination of tissue samples tested show clear evidence of coagulation necrosis. A tissue volume of up to 20 mm diameter was necrosed with the single-tine probe developed. The plots of temperature versus time for different tissue types

**LUNG TISSUE**

1 watt 2 watt 3 watts

From figure 6, it is seen that, while 1 watt was inadequate for coagulation necrosis in lung tissue, 3 watts showed evidence of carbonization, leading to a drop in temperature as further conduction is inhibited. The best result was achieved with 2 watts, which showed a

0 2 4 6 8 10 12 14 16 **Time (min)**

The plot in figure 7 shows that, while 2 watts was below the ideal temperature range, and therefore inadequate for effective tissue necrosis, 4 watts was too high and showed evidence of carbonization, resulting in a drop in temperature due to inhibition in conduction. The best result in terms of effective tissue necrosis was achieved with the 3

steady rise in temperature maintained within the ideal ablation temperature range.

tested using different power settings are presented in the following figures:

**Figure 8.** Liver tissue results.

In figure 8, the plot shows that, while 5 watts and 6 watts are within the ideal ablation zone, the 7 watts setting is too high for liver tissue as it produced carbonization resulting in temperature drop. The best result however was recorded with the 6 watts setting which shows a steady rise in temperature without carbonization or charring.

**Figure 9.** Kidney tissue results.

In figure 9, the results show that 15 watts produced temperature above the ideal ablation range, leading to carbonization and consequently a drop in temperature. Both 10 watts and 13 watts are suitable for ablating kidney tissue as seen, with 13 watts giving the best results since it allows the use of a higher temperature.

Principles and Application of RF System for Hyperthermia Therapy 181

The search for less morbid and less invasive techniques for cancer treatment has led to a strong drive within the global oncology community to develop and implement even more minimally invasive diagnostic and therapeutic procedures. The goals of these minimally invasive therapies for the treatment of cancerous tumours that have made them attractive to

They are safer, with minimal side effects, and limit postoperative morbidities and

They can be performed as an outpatient procedure, or with only a short hospital stay

Their low-cost make them cheaper and ultimately reduce the overall cost of cancer

With several ablation techniques available, the ablation characteristics and method of application will differentiate one ablation method from another. Though RF ablation is more widely used, it has its limitations. Most thermo-ablative procedures could be performed in the doctor's office as an outpatient procedure with mild or no sedation. With RF ablation, it requires an increase in temperature to induce necrosis (tissue death). The heat needed for this necrosis requires that large amount of local anaesthetic be infused around the treatment site. This excess fluid blurs the ultrasound visualization of RFA and other heat-based ablation techniques. Though all the available literature agree that thermal ablation therapy is relatively safe and much less traumatic than radical surgical procedures, some complications and side effects have been reported. Some of these complications and side effects have been associated with probe design, probe placement, or the use of multiple probes. The use of both single and multiple probe placements have been described in many studies. Both have their advantages and disadvantages. Though multiple probes appear to be more successful in destroying larger tissue volumes, their use increases the risk of complications in the procedure. Finally, the high cost of RF ablation equipment, coupled with their limited availability has placed these treatment procedures above the reach of most patients and physicians in Sub-Saharan Africa. This project work which aims to investigate the design and development of a minimally invasive thermo-active oncology probe, will narrow this price gap and make treatment more affordable, and readily available to the ordinary patient in Sub-Saharan

Viable and effective treatment options and eradicate in situ local disease

Most procedures require only local anaesthesia, and recovery time is faster

Non-surgical candidates can benefit from these treatment modalities

**6. Conclusion** 

mortality

treatment.

Africa.

both patients and physicians are summarized as:

They are minimally invasive and less traumatic

Procedure can be repeated in case of cancer recurrence

Shorten the time to return to daily function and work, and

Real-time imaging guidance is possible

Real-time imaging guidance is possible

**Figure 10.** Soft tissue test results.

In figure 10, the results show that, while 15 watts produced temperature within the ideal ablation range, the best result was obtained with the 20 watts power setting since the temperature is higher. This means that the ideal temperature range for treatment will be reached quicker with 20 watts. The 10 watts power setting produces temperature below the ideal range, and was therefore inadequate for ablating soft tissue.
