Ablation zone considerations in cryoablation of RCC: accuracy of manufacturer provided model and change from first to second freeze cycle.

PURPOSE

To determine the accuracy of manufacturer models and difference in ice ball dimensions from the first to second freeze cycles during cryoablation of renal cell carcinoma (RCC).

METHODS

All patients who underwent cryoablation for RCC and had either a uniform type of needle placed in a pattern consistent with manufacturer provided data (n = 48) or computed tomography performed during the first and second freeze cycles (n = 28) were retrospectively reviewed. Ice ball measurements were made in relationship to the cryoablation probes. Factors which may affect the manufacturer prediction or change in the size of the ice ball from first to second freeze cycles were evaluated.

RESULTS

The visualized ice ball was significantly smaller than predicted in the long axis (LA) (Visualized: 29 mm ± 8; Predicted: 54 mm ± 7; p < 0.001), perpendicular transverse (PTR) (Visualized: 31 mm ± 7; Predicted: 52 mm ± 6; p < 0.001) and perpendicular craniocaudal (PCC) (Visualized: 30 mm ± 8; Predicted: 50 mm ± 7; p < 0.001). Furthermore, in the LA, PTR and PCC directions the achieved ice ball size was significantly closer to the predicted size as the total number of probes increased (p = 0.006, p = 0.048 and p = 0.023, respectively). The ice ball was significantly larger in the LA (3 mm (range: -7, 14 mm), p < 0.001), PTR (3 mm (range: -4, 11 mm), p < 0.001), and PCC (3 mm (range: 0, 26 mm), p < 0.001) dimensions on the second as compared to the first freeze cycle.

CONCLUSION

The manufacturer provided model overestimates the size of the visualized Ice ball and Ice balls formed on the second freeze are significantly larger (median 3 mm) than those formed on the first freeze.