http://emmrem.unh.edu/papers/general/parsons.pdf
Thanks for the link; interesting.
Some comments on terminology, since the paper doesn't fully explain it.
"Deterministic effects" refers to acute radiation sickness. "Stochastic effects" refers to increasing the probability of getting cancer some time later, possibly years. The "blood forming organs", i.e., bone marrow, are an important target of radiation because they're among the most rapidly dividing cells in the body. A typical healthy adult forms about 3.5 million red blood cells/sec and 3,500 white blood cells/sec. An acute radiation dose will kill some or all of these newly forming blood cells and result in at least temporary anemia and reduced immunity to infection, which could be what actually kills you. The infection doesn't have to be from an external source; we all carry huge numbers of bacteria (e.g. in our gut) that are normally benign or even helpful.
The classic "stochastic effect" of a sublethal radiation dose also involves the blood forming organs: an increased chance of certain forms of leukemia.
Having been through a stem cell transplant (as treatment for lymphoma, a blood cancer) where this was done deliberately (though by chemicals rather than radiation) I can tell you it's not very pleasant. I survived because I received a carefully calibrated dose over 6 days, then a re-injection of my own uninjured stem cells that had been harvested and preserved, followed by constant medical care for 3 weeks to keep my blood chemistry stable and my body uninfected while those stem cells "took" and repopulated my bone marrow. An uncontrolled radiation dose to an astronaut crew far from good medical care might not do as well.
This does raise the interesting possibility of harvesting stem cells from the astronauts going on an interplanetary flight and storing them frozen (and well shielded) on the spacecraft in the event of a radiation emergency. At least they'd be completely isolated from the world and its diseases, and being in zero gravity would certainly have helped me while I was recovering from anemia. But I'm an engineer, not an oncologist or radiation specialist, and it would be interesting to hear the opinions of some professionals in those fields.
"RBE" is Radio-Biological Effectiveness, the relative amount of actual biological damage for a given amount of absorbed energy. The latter quantity is measured in grays (joules/kg) while the former is in sieverts:
RBE = sieverts / grays
The paper is saying that while they can calculate the amount of energy deposited in body tissue by solar protons, high energy protons are such an unusual radiation hazard that we don't really know how much damage that a given amount of deposited energy would cause. Most radiation exposures (intentional or accidental) are from gamma, which is much better understood. Some are from neutrons; those result from proximity to a small nuclear bomb (Hiroshima or Nagasaki) or to a nuclear criticality accident.
