Purpose:To quantify the dosimetric impact on patient's specific treatment plans due to set up uncertainties during LINAC commission and annual QA and to determine the maximum set up uncertainty allowance range.Methods:A 60×60×60 cm3 solid water cube was created in Varian Eclipse TPS. Beam data profiles (crossline and diagonal) and PDDs for field sizes ranging from 2×2 cm2 to 40×40 cm2 were simulated. Three main uncertainty scenarios were purposely introduced for gantry position tilts (0–5°), source axis distance changes (100–105 cm), and iso‐center position shifts (0–5 mm) during the simulation. A gamma analysis was used to compare the correct simulated profiles with the profiles for each scenario. Two static IMRT treatment plans (H&N and GYN) with tumors at 5 cm and 15 cm depths were compared using similar set up uncertainties.Results:A gamma analysis using ±3%/±3mm with 90% passing rate criteria is included to show the passing rate for each scenario. Crossline and diagonal profiles showed a gamma passing rating of ≥ 90% at depth ≤10 cm for these scenarios: gantry tilted from 0–5°, SAD changed from 100–105 cm, and iso‐center shifted ≤ 4 mm. From 10 to 20 cm depths, all three scenarios failed with gamma passing ≤ 90% excepted for diagonal profiles at Gantry =2°, SAD =1 cm, and iso‐center =1 mm off center. Diagonal profiles showed a higher gamma passing rating compared to crossline profiles for all three scenarios. PDD differences also increased as depth increased. For patient's specific treatment plans, maximum uncertainties allowed to obtain a ≥90% gamma passing rating are: gantry tilts ±1 degree, SAD shifts ±2 cm, and iso‐center moves ±3 mm.Conclusion:This study validated AAPM TG 142 recommendations on the mechanical and dosimetry uncertainties and provided proofs on maximum acceptance tolerances for LINAC annual QA and commission.