Quality assurance of stereotactic treatment planning system: implementation of Monte Carlo technique on Leksell Gamma Knife

The purpose of this report is to describe the quality assurance (QA) program on the treatment planning system, Leksell GammaPlan, using the Monte Carlo (MC) technique. Routine dose distribution measurements using a spherical polystyrene phantom and GafChromic films may not give accurate results since the measurements are not performed in a water medium and the small energy dependence of GafChromic films may affect the measurement results. Comparison of the dose distributions solely from measurement results and the GammaPlan output is not sufficient, hn alternative QA program on GammaPlan using the MC technique is introduced. The results from GammaPlan showed good consistency with the MC results. Small discrepancies of the relative dose along the z axis were observed on the 8 mm collimator helmet. Such discrepancies may however be too small to give clinical significance.