Vilhelm Ekstrand

Influence of electrical and thermal properties on RF ablation of breast cancer: is the tumour preferentially heated?

BackgroundTechniques based on radio frequency (RF) energy have many applications in medicine, in particular tumour ablation. Today, mammography screening detects many breast cancers at an early stage, facilitating treatment by minimally invasive techniques such as radio frequency ablation (RFA). The breast cancer is mostly surrounded by fat, which during RFA-treatment could result in preferential heating of the tumour due to the substantial differences in electrical parameters. The object of this study was to investigate if this preferential heating existed during experimental in vitro protocols and during computer simulations.MethodsExcised breast material from four patients with morphologically diagnosed breast cancers were treated with our newly developed RFA equipment. Subsequently, two finite element method (FEM) models were developed; one with only fat and one with fat and an incorporated breast cancer of varying size. The FEM models were solved using temperature dependent electrical conductivity versus constant conductivity, and transient versus steady-state analyses.ResultsOur experimental study performed on excised breast tissue showed a preferential heating of the tumour, even if associated with long tumour strands. The fat between these tumour strands was surprisingly unaffected. Furthermore, the computer simulations demonstrated that the difference in electrical and thermal parameters between fat and tumour tissue can cause preferential heating of the tumour. The specific absorption rate (SAR) distribution changed significantly when a tumour was present in fatty tissue. The degree of preferential heating depended on tissue properties, tumour shape, and placement relative to the electrode. Temperature dependent electrical conductivity increased the thermal lesion volume, but did not change the preferential heating. Transient solutions decreased the thermal lesion volume but increased the preferential heating of the tumour.ConclusionBoth the computer model and the in vitro study confirmed that preferential heating of the tumour during RFA exists in breast tissue. However, the observed preferential heating in the in vitro studies were more pronounced, indicating that additional effects other than the difference in tissue parameters might be involved. The existing septa layers between the cancer tissue and the fatty tissue could have an additional electrical or thermal insulating effect, explaining the discrepancy between the in vitro study and the computer model.

A new specially designed needle significantly increases sample yield during fine needle aspiration of breast lesions.

A large and increasing number of women in the western world will at some point during their life be investigated morphologically for breast cancer. Fine needle aspiration (FNA) is one morphological method which is considered to be the fastest, cheapest and the most patient-friendly approach. Nevertheless, the technique has not gained major clinical success outside of Scandinavia, mainly because of a high frequency of insufficient samples. With this in mind it is quite peculiar that standard needles which are mainly configured for blood sampling and infusion therapy, comprising large quantities of residual spaces, are used. In this study we have developed and tested a new needle dedicated for FNA, which is intended to abate this drawback by increasing the sampling yield by changing the tip angle, the cannula wall-thickness and the storage compartment. In total, 499 consecutive aspiration procedures of palpable breast lesions were performed to compare the new needle (outer diameter 0.6mm) with standard needles (outer diameters 0.6 mm and 0.7 mm). The new needle provided three times more material than did standard needles of the same diameter. Surprisingly, the new needle also provided more material than the standard 0.7 mm needle, which increased up to almost twice the material in cases with no material in the syringe. The frequency of tests with sparse harvested material (< 4 mg) was less with the new needle (9%) compared to its standard counterpart (35%). The presented results were obtained by a very skilled sampling operator. Thus for the average sampling operator who probably obtains more samples in the spare range, the new dedicated FNA needle should have even more added value.