A point for discussion: Regarding radiation risk and effect on our body. I saw in a number of threads where folks cautioned against CT and bone scan for they could increase cancer risk. I think some analysis and discussion maybe helpful.
1. Radiation Oncologist measures radiation in Gy. Most treatment now uses 70 Gy.
2. EPA measures radiation risk in Si (Sievert). Mostly limits exposure to < 20 mSi (1/1000 Si) per year. That is the limit for nuclear reactor workers.
Gy is radiation dose and Si is radiation dose absorbed by a human.
1 GY is roughly equal 1 Si (very approximate).
CT scan and bone scan are about 4 to 7 mSi each, well within the risk level of EPA. 70 Gy is a lot of radiation. No matter how sharp the radiation beam is there is spillover. If during treatment, 1% of the radiation spills over to the other organs, they would be getting 700 mSi, equivalent to taking 100 CT scan. If the spillover is minimized, then they may not be killing all the cancer cells. The damage to surrounding cells supposedly can be minimized, by splitting the radiation over 30 to 40 smaller doses. But they also argued that radiation is cumulative so splitting into smaller dose does not diminish the radiation treatment effectiveness? So, I do not know if splitting the radiation into smaller doses help reduce secondary cancer risk in the long term. Some medical books are saying radiation damage to cells is cumulative.
Therefore, I think, first, the risk of CT scan and bone scan are very small, and second, the radiation spillover during the treatment itself may be more of a risk. How much spillover vs insufficient coverage will depend on the equipment and the skill of the radiation oncologist.
In the Japanese reactor accident, I think they are talking about limiting exposure to rescuers at less than 1 Si, which is roughly equal to the spillover radiation in the above example.