The Use of CT Perfusion to Monitor the Effect of Hypocapnia During Laser Thermal Therapy in a Rabbit Model

One of the limiting factors in the thermal therapy of tumours is the dissipation of heat by blood flow. The current study investigates the use of hyperventilation (hypocapnia) to decrease tumour blood flow during laser thermal therapy. Rabbits with implanted VX2 thigh tumours were treated using a diode laser (805 nm) as the heating source. One group of rabbits (n = 8) was treated with the new hypocapnia protocol and another group (n = 8) with the conventional (normocapnia) protocol. The mean tumour volume and blood flow were the same for the two groups prior to treatment. The laser power temporal profile (3.0-1.5 W) and the duration of treatment (60 min) were also the same for both treatment protocols. Blood flow maps were calculated from a series of contrast-enhanced CT images. The average change in thermal lesion area at 60 min post-laser thermal therapy from pre-treatment normalized to the pre-treatment tumour area was significantly different between the two treatment protocols: 0.52+/-0.13 (hypocapnia) vs 0.33+/-0.12 (normocapnia) (p < 0.001). Similarly, the average fractional decrease in global tumour blood flow 60 min post-treatment from pre-treatment was also significantly different between the two protocols: 0.64+/-0.10 (hypocapnia) vs 0.41+/-0.14 (normocapnia) (p < 0.001). The hypocapnia protocol produced larger thermal lesion area and greater decrease in tumour blood flow post-treatment than the normocapnia protocol. These results support the further investigation of the use of hypocapnia to increase the therapeutic effect of laser thermal therapy.