There is a CLI tool to read&convert this kind of files, you can get it by running this in the Terminal (Ubuntu users):
sudo apt-get install dcmtk
You can then use these tools:
dcm2pnmI had to use dcmj2pnm, as dcm2pnm gave me errors (really depends on what kind of images you have).
Note* (in case of permission issues first copy the .dcm files to your disk, if they are on a CD issued by the doctor, and change permissions. A chmod 775 *.dcm run in the images dir will do the trick).
Run this command and it will convert the picture in a different format:
dcmj2pnm --all-frames input_image.dcm output_image