Shall We Record and Report All X-ray Dosage in Roentgens?

THIS is not a report of physical measurement, nor a record of clinical observations. What I have to present is a proposition for discussion. It was three and a half years ago that we were given a precisely defined and internationally accepted unit of roentgen dosage. It is true that the realization of the official unit, the roentgen, and its distribution to clinical roentgen therapists have proved difficult. Clinical roentgenometers do not always agree perfectly with each other, which makes one feel uncertain as to the correctness and permanence of their calibration. One feels like sending his instrument to our U. S. Bureau of Standards for calibration. Another possibility appears in Rajewski's (1) radium standard for small ionization chambers, so arranged as to be little susceptible to small errors in the geometrical arrangement of the test. With this, one could carry the standardization (or, rather, the check on original calibration) to the instrument instead of sending the instrument to Washington. Taylor has told us that he carried a primary standard around Europe and found the national institutes in good agreement. With their service available to users of clinical roentgenometers, I think practical roentgenometry is reaching a satisfactory state of dependability. The cost of a good roentgenometer, with small chamber calibrated in r, is not too great for us to afford. Expensive ones may be had with an integrating arrangement to keep account of the total amount, but I cannot see the necessity for this as long as we have clocks. Gamma radiation has always been outside the calibrated range of our ionometers, the factor for wave length being unknown for a small chamber of any construction. Failla and Henshaw (2) have recently given us a good evaluation of the r per minute intensity of a gamma-ray beam (36 r per minute per gram of radium element at 1 cm. distance). It is interesting to note that a graphite chamber could be recalibrated for gamma rays and prove dependable, but if they had used its constant as calibrated for hard x-rays, it would have indicated nearly four times the radiation intensity actually there. These gamma-ray measurements concern the amount in a beam of radiation. Measurement of a roentgen ray can be done in the beam with good precision, within a few per cent. However, when radiation enters the body it is augmented by scattering, or, rather, its absorption is so augmented, for some elements of the tissue are irradiated twice by the same beam, once going in and once scattered back, and the tissue exacts its toll of energy absorbed at each passage. It has become a common practice to measure roentgen dosage at the patient's skin, which includes the back-scattering. The argument for this method is that this is the dosage which is really effective in the patient's tissues (skin, usually), and that it is easier to measure the total than to estimate it from the beam.