<qa>  What is the total annual dose constraint for whole body radiation exposure?There is no published data available on the intra-patient variation of bone marrow dose using either of the two proposed blood sampling methods. Without knowledge of the expected variances of the measurements in question, accurate sample size calculations are not possible prior to commencing the study. A sample size of 35 patients will be used in this pilot study - this sample size was chosen based on the number of patients seen in the department for this therapy. Recruiting a sample size of 35 patients is achievable within a 2 year time frame. However, the study will be stopped early if the total annual radiation exposure to the operators, combined with the total radiation exposure due to normal clinical workload, is likely to exceed the annual UK dose constraint of 2mSv for whole body radiation exposure The Ionising Radiations Regulations 1999, SI 19993232. 