It doesn't matter if you have a PhD in Spain (it is a pitty but...), if you want to work in medical physics in a Hospital you have to pass an exam to work as a medical physicist in practice during 3 years, after that you can work as a medical physicist senior.
That's right. In Germany, conditions are similar to those in Spain. But, as far as I may remember right, in Germany there are 2 different types: medical physicist, and medical physics expert (MPE). And concerning my recommendation from September 5th., this should have been understood as: I recommend this area of additional specialisation, because there is a great need of such personal (in Germany), .....(may be the same in Spain)), and it will easy to find a good Job, or to work even as a freelancer, especially if in addition you have a PhD in Science (like myself, (MPE and PhD in science)).