Stem cell, high dose chemo

Hello 

I am just going to start stem cell treatment after doing a series of treatments prior that were very intense. I have germ cell cancer and have been told that I need to have a tandem of HDCT and stem cell and I am reluctant as there is no statistics to say the second does any thing other than cause organ toxicity. Has any one had 2? Or no the impact of 1? 

just any information would be great cause am thinking of saying no to the second as it also comes with higher risk of mortality having 2. 

Michelle xx