Pmeet,
for our daughter we have seen the doc following the rules as below...
if the Hgb before Tx is between 9 & 10, then she gets 15ml/Kg. = so, your child should get 105.
below 9, it is 20/Kg . that will be 140ml for your child.
We go for every 4 weeks Tx schedule and following the above rule, we have been able to hold our daughter's Hgb between 9 & 10 most of the times.