During operation Barbarossa the Germans took an immense number of Sovjet POW's. The prisoners who had the 'luck' not to be executed immediately were transfered to camps. These camps were (mostly) improvised fields in Ukraine, Poland or Russia that were fenced off with barbwire.

Because of a lack of basis neccecities like food, medicine, clothing etc the mortality rate was very high. So while the conditions in these camps were brutal, they were very different from a concentration camp.

A notable difference were the 'unwanted individuals' (read: academics, sovjet party members, jews, etc.) who were transferred to concentration camps and executed immediately.

When the tide of the war turned and the sovjets liberated their own POW's they were very skeptical of them and regarded them as traitors. A small % of the freed POW's were sent to the gulags.

To my understanding the number of people who went to (and survived) a concentration camp and a gulag is very small. And even then I seriously doubt that if someone went through both a concentration camp and a gulag would be allowed by the USSR to write a book about it.

There was a woman called Margarete Buber-Neumann who was first imprisoned in a Siberian Soviet camp, and then in 1939 or 1940 the Nazi-Soviet Pact caused her to be transferred to the Germans. She survived Ravensbrück (I forgot the name of the Soviet camp she was in) and was freed in 1945.

I just finished rereading her book "Under two dictators. Prisoner of Stalin and Hitler."