Can irradiated RBCs be irradiated a second time if the first irradiation dose was inadequate?

A transfusion medicine physician in Pennsylvania asks if the correct time for irradiation of units of red cells for a particular Cesium source irradiator is for example 7 minutes, but a technologist inadvertently irradiates units of red cells for only 5 minutes, can the red cells be put back in the irradiator for the remaining 2 minutes, to complete the irradiation process? The inquiring physician wonders if there might be some physics-based reason why this would not necessarily be the case. Is there regulatory reason why the red cells cannot be irradiated for an additional 2 minutes, then used?

The following comments have been received.

ADDENDA Dec. 17, 2008

1. A colleague at a blood center in the United Kingdom, who works for the National Blood Service (England & North Wales) as a Scientific Trainer, has provided the following information which is an extract taken from the British Committee for Standards in Haematology (BCSH) guidelines on gamma irradiation of blood components for the prevention of TA-GvHD, 1996.
   
   "with commercial irradiators, the dose of gamma radiation delivered can vary from the centre of the container to the periphery by up to 35%, and along the axis by up to 30%. Thus it is important to specify whether the recommended dose is an average value or the minimum dose to any point of the container. In the USA, the FDA require a central dose of 25Gy & a minimum of 15Gy to any other point in the container (J. Fratantoni, oral communication, April 1993). In the UK, a minimum of 25 Gy is recommended (NBTS/NIBSC, 1993). To ensure by dosimetry that this does distribution is achieved, consultation with supporting physicists is recommended. Recommendation. The minimum dose achieved in the irradiation field should be 25 Gy, with no part receiving >50 Gy"
   
   She concludes that a product that has been removed too early & undergone inadequate irradiation will have had it's content disturbed in the handling process. Returning to the irradiator to 'finish the job' could potentially lead to overexposure of some cells as a result of this movement. This is quite a simple & straightforward reason for the length of exposure to radiation to be completed in one sitting. In addition she would like to ask the transfusion medicine physician in Pennsylvania under what circumstances would a technologist fail to properly irradiate a product and need to do the irradiation a second time? If one has a robust standard operating procedure & training protocol to irradiate blood products, the problem shouldn't occur.

2. A respected senior Medical Director comments: "I see no reason why the remaining time (and thus dose) of irradiation could not be applied to the unit. One wants to administer the correct dose. Another label to detect irradiation should be affixed to show that it was performed. I have heard of people irradiating a second time with the full dose because they were not sure the first dose had been given. If they used 25 Gray each time, this would still only equal 50 Gy, which is the maximum before there is more damage to RBCs to warrant further shortening of the dating period."

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