Dear Dr. Parach, Though this is not an official response from GATE developers, this is what I know. (1) Yes, the dose output is in units of cGy. You may a take a look at file: gate_v4.0.0/source/voxel/src/GateVoxelOutput.cc (2) "Vacuum" in GATE is not really vacuum. It is defined as follows: Vacuum: d=0.000001 mg/cm3 ; n=1 +el: name=Hydrogen ; n=1 Maybe this is the reason why there is dosage in the dose output file. But logically, the dose should be very small. I hope this helps! Sincerely, Jan Mickelle V. Maratas -- #################################################### Physics Department, MSU - Iligan Institute of Technology A. Bonifacio Ave., Tibanga, 9200 Iligan City, Philippines ####################################################