Benefit of replacing the Sigma-60 by the Sigma-Eye applicator : a Monte Carlo-based uncertainty analysis

BACKGROUND AND PURPOSE: To investigate the clinical benefit of replacing the BSD-2000 Sigma-60 with the Sigma-Eye applicator, taking into account effects of uncertainties in tissue and water bolus parameters.

PATIENTS AND METHODS: For 20 patients, specific absorption rate (SAR) and temperature distributions were calculated and optimized, based on computed tomography (CT) scans in treatment position. The impact of uncertainties on predicted distributions was studied using a Monte Carlo uncertainty assessment.

RESULTS: Replacing the Sigma-60 by the Sigma-Eye applicator resulted in a higher SAR in the tumor [on average a decrease of the hotspot tumor quotient (HTQ) by 24%; p < 0.001], and higher temperatures (T90: +0.4°C, p < 0.001; T50: +0.6°C, p < 0.001) using literature values and SAR optimization. When temperature optimization (T90) was used, a larger average increase was found (T90: +0.7°C, p < 0.001; T50: +0.8°C, p < 0.001). When taking into account uncertainties, a decrease of 23% in median HTQ (p < 0.001) and an increase in T50 and T90 of 0.4°C (p < 0.001) could be demonstrated.

CONCLUSION: Based on this uncertainty analysis, significant and clinically relevant improvements in HTQ and tumor temperature were achieved when replacing the Sigma-60 by the Sigma-Eye applicator.