Thermal balloon endometrial ablator: a preclinical safety and effectiveness study

Conductive interstitial thermal therapy device for surgical margin ablation:In vivoverification of a theoretical model

PURPOSE

To demonstrate the efficacy and predictability of a new conductive interstitial thermal therapy (CITT) device to ablate surgical margins.

METHOD

The temperature distributions during thermal ablation of CITT were calculated with finite element modelling in a geometrical representation of perfused tissue. The depth of ablation was derived using the Arrhenius and the Sapareto and Dewey (S&D) models for the temperature range of 90 to 150 degrees C. The female pig animal model was used to test the validity of the mathematical model. Breast tissues were ablated to temperatures in the range of 79-170 degrees C, in vivo. Triphenyltetrazolium chloride viability stain was used to delineate viable tissue from ablated regions and the ablation depths were measured using digital imaging.

RESULTS

The calculations suggest that the CITT can be used to ablate perfused tissues to a 10-15 mm width within 20 minutes. The measured and calculated depths of ablation were statistically equivalent (99% confidence intervals) within +/- 1mm at 170 degrees C. At lower temperatures the equivalence between the model and the observations was within +/- 2 mm.

CONCLUSION

The CITT device can reliably and uniformly ablate a 10-15 mm wide region of soft tissue. Thus, it can be used to secure negative margins following the resection of a primary tumor, which could impede local recurrences in the treatment of local diseases such as early staged, non-metastatic, breast cancer.

Conductive interstitial thermal therapy (CITT) device evaluation in VX2 rabbit model

We have developed a conductive interstitial thermal therapy (CITT) device to precisely and reliably deliver controlled thermal doses to the surgical margins at the cavity site following tumor resection, intraoperatively. The temperature field created by CITT ablation of a perfused tissue was modeled with a finite element package Femlab. The modeling suggested that a maximum probe temperature of 120 degrees C and an ablation time of 20 minutes were required to ablate highly perfused tissue such as the VX2 carcinoma. Deployable pins enable faster and more reliable thermal ablation. The model predictions were tested by thermal ablation of VX2 carcinoma tumors implanted in adult New Zealand rabbits. The size of the ablated region was confirmed with a viability stain, triphenyltetrazolium chloride (TTC). Histopathological examination revealed 3 regions in the ablated area: a carbonized region (1-3 mm); a region that contained thermally fixed cells; and an area of coagulated necrosis cells. Cells in the thermally fixed region stained for PCNA (proliferating cell nuclear antigen) and were bounded by the carbonized layer at the cavity wall, and by necrotic cells that exhibit nuclear fragmentation and cell dissociation, 5 to 10 mm away from the CITT probe. Adjacent tissue outside the target region was spared with a clear demarcation between ablated and normal viable tissue. It is suggested that the CITT device can be used, clinically, to inhibit local recurrence by creating negative surgical margins following the resection of a primary tumor in non-metastatic early staged tumors.

Endometrial Ablation with a Thermal Balloon: The First 10 Years

Thermal balloon endometrial ablation (BEA) was introduced approximately 10 years ago as the first automated replacement for hysteroscopic endometrial ablation (HEA) in women with chronic abnormal uterine bleeding. Putative advantages included similar or improved clinical outcomes, and reduction of both adverse outcomes and the total cost of care, all with reduced requirements for operator skill. The published literature contains 1191 cases of BEA performed with instruments from 4 manufacturers, including a number of randomized clinical trials (RCTs) comparing the devices with HEA, usually performed by experts. In comparative RCTs, clinical and health-related quality of life outcomes as well as patient satisfaction and rate of subsequent uterine surgery appear similar in follow-up intervals that ranged from 1 to 5 years. There is a suggestion of reduced risk of adverse events with BEA, but the differences are small. There are no rigorous evaluations of resource use. The level of surgeon expertise in HEA arms of available RCTs potentially improves quality and decreases complications over what might be expected in the general population. Thus BEA seems equivalent to HEA when performed by expert surgeons with respect to most outcomes. Effectiveness studies of the two interventions should be conducted in community settings and should evaluate resource use.