Answer to Question #6550 Submitted to "Ask the Experts"

Do radioactive source gamma irradiators differ from x-ray generating irradiators in the quality and/or quantity of radiation administered to cell samples (e.g., blood cells, tumor cells, etc.)?

I am posing this question to see if it is feasible to replace our current ¹³⁷Cs Gammacell 1000 with an x-ray-generating irradiator that could perform equally, if such an irradiator exists. There would be advantages to using a nonradioactive source x-ray-producing irradiator such as avoiding the "increased controls" as well as the potential source hazard, disposal, and replacement.

It is feasible to replace a ¹³⁷Cs irradiator with an x-ray-generating irradiator. However the two sources of radiation are different. The ¹³⁷Cs source has monoenergetic gamma ray of 661.65 keV, which is quite energetic and penetrating. Most of the x rays, produced by an x-ray machine, have much less energy than the maximum keV rating for the x-ray machine. The x rays from a machine have a broad energy range, from very low to the maximum keV rating for the machine. Most x-ray machines use a metal "filter," placed in the x-ray machine's primary beam. The filter is used to remove (absorb) the lower-energy x rays. Thicker or more dense filters remove more of the softer (lower-energy x rays) to make the x-ray beam more penetrating or harder. However, irradiating cell samples may not require such a penetrating photon, as that of the ¹³⁷Cs; so you may not need to replace the ¹³⁷Cs with an equivalent higher-energy keV x-ray machine with a dense filter.

Some of the main considerations before replacing a ¹³⁷Cs irradiator with an x-ray-generating irradiator are:

1. Carefully consider if changing the irradiation protocol will affect the continuation of research data based upon earlier irradiations using ¹³⁷Cs.
   
   
2. Consider if the cell sample irradiation "standard" is using ¹³⁷Cs.
   
   
3. The dose rate for the x-ray machine must match the dose rate of the ¹³⁷Cs, unless you can irradiate the cell samples for a longer or shorter time period.

John P. Hageman, MS, CHP