Intra-patient comparison between two annular phased array applicators, Sigma-60 and Sigma-Eye: Applied RF powers and...

To investigate whether one can replace the Sigma-60 with the Sigma-Eye applicator (or vice versa) during a deep hyperthermia treatment series without a loss in quality of the treatment.

Hyperthermia data of all 48 patients with locally advanced cervical cancer who were treated with both applicators were analysed. In this study no use was made of the longitudinal SAR steering option of the Sigma-Eye. Hence, the Sigma-Eye was used as a Sigma-60 with a modified shape and water bolus. Power and intraluminal temperature were analysed. Sub-group analyses were performed for six groups, categorised according to the reasons for switching between the applicators.

The 'all patient' analysis showed a significant difference for radio frequency (RF) power indices as applied to the two applicators, but for temperatures no difference between applicators was found. Sub-group analyses showed a consistent difference for RF power indices, i.e. the RF power for the Sigma-Eye was 8-29% higher than that for Sigma-60. In contrast, in about 90% of patients the number of switch-offs was 8-62% lower when the Sigma-Eye was applied. Similarly, in 73% of patients total switch-off time was 18-150% lower for the Sigma-Eye than for the Sigma-60. For the largest sub-group (n = 23), patients treated with the Sigma-Eye all had temperature indices slightly lower (ΔT = 0.2-0.5°C) than those for the Sigma-60 (p < 0.028). For the other five sub-groups no relevant difference was found between temperatures obtained by the two applicators.

In the case of severe patient discomfort with the Sigma-60 or Sigma-Eye applicator, or if achieved temperatures are not satisfactory, one can freely switch between both applicators without loss of hyperthermia treatment quality.