Estimation of electron source position for Electa precise digital Accelerator

In this study the electron source position data which is machine and patient specific for non-standard source to surface distance, virtual source to surface distance (VSSD) or effective source to surface distance (ESSD) or Measured source to isocentre distance (MSID) has to be determined which are to be used for correcting the output and percentage depth dose for non-standard source to surface distance (SSD).