Experimental and Monte Carlo based dosimetric investigation of a novel 3mm radiosurgery 3MV beam using the microSilicon detector.

Abstract

The ZAP-X system is a novel gyroscopic radiosurgical system based on a 3MV linear accelerator and collimator cones with a diameter between 4 and 25mm. Advances in imaging modalities to detect small and early-stage pathologies allow for an early and less invasive treatment, where a smaller collimator matching the anatomical target could provide better sparing of surrounding healthy tissue. A novel 3mm collimator cone for the ZAP-X was developed. This study aims to investigate the usability of a commercial diode detector (microSilicon) for the dosimetric characterization of this small collimator cone; and to investigate the underlying small field perturbation effects. Profile measurements in five depths as well as PDD and output ratio measurements were performed with a microSilicon detector and radiochromic EBT3 films. In addition, comprehensive Monte Carlo simulations were performed to validate the measurement observations and to quantify the perturbation effects of the microSilicon detector in these extremely small field conditions. It is shown that the microSilicon detector enables an accurate dosimetric characterization of the 3mm beam. The profile parameters, such as the FWHM and 20%-80% penumbra width, agree within 0.1 to 0.2mm between film and detector measurements. The output ratios agree within the measurement uncertainty between microSilicon detector and films, whereas the comparisons of the PDD results show good agreement with the Monte Carlo simulations. The analysis of the perturbation factors of the microSilicon detector reveals a small field correction factor of approximately 3% for the 3mm circular beam and a correction factor smaller than 1.5% for field diameters above 3mm. It could be shown that the microSilicon detector is well-suitable for the characterization of the new 3mm circular beam of the ZAP-X system.