Stereotactic micro-IMRT for cranial tumors is now routinely utilized for cranial IMRS/IMRT. The ability of the IMRS/IMRT system to deliver the dose with stereotactic accuracy depends on the accuracy of leaf positioning, linear accelerator beam on and off characteristics and small beamlet dose modelling accuracy. This study attempts a detailed evaluation of accuracy of step and shoot versus dynamic IMRS/IMRT treatment using the BrainLAB MicroMLC system for stereotactic cranial treatments. A customized stereotactic IMRS/IMRT QA phantom was designed and built for this purpose to obtain sub-millimeter accuracy in setup and delivery required for this analysis. Calibrated EDR-2 film is used in conjunction with the IMRS QA phantom to minimize spatial effects of detector size, for absolute dosimetry. Scanned film data was analyzed with software developed in-house for this purpose. Data for planning and delivery of an acoustic Neuroma case is analyzed for verification of spatial isodose distribution and dosimetric agreement with the treatment plan, for both step and shoot and dynamic IMRS delivery. However, no attempt is made in this study to deconvolve the setup reproducibility of the BrainLAB relocatable stereotactic mask system. Fractionated IMRS patients are treated using the BrainLAB relocatable stereotactic mask system and the QA phantom is also scanned in the same stereotactic frame. Results indicate excellent agreement for spatial dose distribution (< 1mm) and absolute dosimetry (< 1.9 %) for both step and shoot and dynamic IMRS/IMRT delivery methods, when compared to calculated values.