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In a superficial X-ray therapy unit, the Dermopan, recently installed at this hospital, an unexpected relationship was observed between X-ray output and tube current when the latter was varied from the specified value at the 10 kV setting. It is thought worth while to record this observation, since failure to appreciate this behaviour could lead to serious errors in dosage. It will also be seen that, by means of a simple adjustment of the control circuit of the machine, this characteristic can be turned to good account by providing improved dose control.The equipment uses a self-rectified tube with a beryllium window. A selector switch on the control panel provides for operation at 10, 29, 43 or 50 kVp. An electrical interlock system ensures that the tube can be energised only when the filter appropriate to the selected kilovoltage is in place. A fine control of line voltage is provided. A tube current of precisely 25 mA is specified at all four X-ray qualities. Tube current control is smooth and adequately fine, but no stabiliser of cathode current is provided.Measurements of X-ray output were made using a grenz-ray ionisation chamber (Osborn and Clifton).*If the exposure rate for each kilovoltage setting at 25 mA is taken as unity, the relative outputs observed for other values of tube current are shown in Fig. 1.

Formulae derived by Rossi and Ellis (1950) for the calculation of radiation dose from distributed sources of beta-emitters have been made applicable to the case of tritium by a consideration of the appropriate value for the effective absorption coefficient employed in these expressions. An example is given of their application to the calculation of dose to a cell from tritium incorporated in the nucleus.

A description is given of a trolley incorporating a hydraulic lift, which facilitates the setting-up of radiation beam treatments in a high-pressure oxygen chamber used in conjunction with a linear accelerator of isocentric type having a fixed height of rotational centre. Use is made of a synchronised pair of hydraulic jacks acting on two independent sliding frames at the ends of the trolley. As compared with a design employing a single jack, this arrangement avoids the difficulty of constructing a parallel-motion system which would perform satisfactorily under the stresses imposed on the structure by inequalities in floor level. The design further provides ample ground clearance and so eliminates the necessity to retract the supporting ram of the normal couch during oxygen treatments.

1. Thirty-two thyrotoxic patients were treated with radioiodine by a single dose procedure after drug preparation with thiouracil and thyroxine; at a one-year follow-up, 26 had remitted, 5 had needed re-treatment and 1 had permanent myxoedema.2. This clinical response could be related to the estimated mean radiation received by the thyroid calculated in “radiation dose units”. This depended partly on the planned dose given (100, 150 or 250 μc/g thyroid at 48 hours) and partly on the effective half-life of the iodine in the thyroid.3. The thyroid glands of those patients given a routine drug preparation with thiouracil and thyroxine retained the iodine longer (biological half-life 27·8 days) than those given an atypical drug preparation (biological half-life 10·6 days).4. The clinical management of the radioiodine treatment of thyrotoxicosis has been simplified by a drug preparation. It can be so planned that a single dose will frequently suffice.

The effect of radiation on the in vivostability of 131I-labelled human serum albumin (IHSA) has been investigated, with the object of revealing whether self-irradiation is a significant factor affecting the stability of available preparations.Samples externally irradiated in doses up to 200,000 rads with X rays from a 4 MeV linear accelerator were injected intravenously into human volunteer subjects and the urinary excretion of activity was measured over a period of six to nine days. Fast (degraded) and slow (stable) components were identified by their differing rates of excretion and their proportions were determined for each sample. The effect of radiation was to increase the percentage of fast component, to an extent proportional to the dose, without materially influencing the rate of excretion of the slow component. For a given preparation a constant weight of albumin per millilitre was converted to the rapidly excreted form per unit dose of radiation, irrespective of concentration. This finding is in accord with the theory of “indirect action” of radiation on solutions and explains the protection afforded by increasing the protein concentration. The effects of self-irradiation only become significant where the specific activity exceeds about 100 microcuries 131I per milligram of albumin.

The device to be described performs graphically some of the operations involved in calculating the ?-ray dose-rate at a point near a screened linear radioactive source. It has proved useful in a hospital physics department where evaluation of the dose rates at a number of points near a group of such sources is often required, the accuracy obtainable being sufficient for this type of work.