It is the Percentage depth dose curve that is one of important deta of deep therapy. In order to draw this curve, the accurate measurement of the depth dose is required. The authors studied theoretically as well as experimentally the two problems which must be considered in measuring the depth dose in a phantom. These two problems are : 1) When a dosimeter is inserted in a phantom, the volume of the dosimeter causes an error in the depth dose measurement. 2) X-ray spectrum changes according to the depth of a phantom, which makes an effect on the sensitivity of the dosimeter and causes an error in percentage depth dose curve. These errors mentioned above are calculated and are measured experimentally. The conclusions on these two errors are obtained as follows : 1) In the former case, the volume of the dosimeter has certein effect on the depth dose mesurement ; when the radius of the dosimeter is 1cm, an errow reaches to 6% of accurate depth dose and if that of the dosimeter is 0.5cm, an error eaaches to 3%. 2) In the latter case, an error of the depth dose measurement reaches to about 1-1.5% in the field which we usually uses.

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Relatively high voltage has been used to widen the examination area of chest photograph. In the Lysholm-Blende, which has been used for removing scattering rays, the image of the grid prevents reading and irregular image of the grid often makes density spots. The author made comperative study of density spots and made experiments of the removing the density spots. The conclusion obtained from these experiments are as follows : 1) It is necessary to make a distintion in regulation between the travelling grid and ordinary one. 2) The travelling grid is allowed to be used even though the density spots becomes tolerably dim. 3) The grid of foreign make has been said not to be good, because it makes many density spots. But it takes many advantages over the grid of home make, if the using method is distinguished from that of home-made grid. The foreign made grid is high density and it is desired that such a gird will be made also in our country as soon as possible.

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Thyroid scintigramm is the only important diagnosis method. However, thyroid scintigramm image is much influenced by such elements as the state of the diseased part, the apparatus and drawing method etc. Therefore the reappearance of the image is hardly possible and the drawing of the full-sized image is almost impossible. Different size images are got from one and the same patient, so it is questionable to use scintigramm image for comparison, tracing diseases and weighing thyroid gland etc. The standardization of thyroid scintigramm is much desired. The author studied the drawing method of full sized image as a preparation of standardization of thyroid scintigramm. He originated "The regulation of energy zone"in which the index of the drawing condition is the percentage of I^<131> taken in thyroid gland. It is concluded through the experiments that this originated method takes advantages over the usual methods : 1) The full-sized image recorded with this new method has smaller background and is more reliable. 2) The conditions of the drawing are selected easily and the reappearance of the image is more possible. 3) Moreover, it is possible to get a satisfying full-sized image, if the dose of I^<131> is adjusted according to the percentage of I^<131> intaken.

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The purpose of the experiment : Compearing with x-ray photograph taken with a diagnosic x-ray apparatus, the authors studied Coradiograph taken with Co^<60> therapy apparatus. They researched the advantages of the supper high voltage radiography and tried to make a photograph useful for diagnosis. The result of the experiment : 1) The dose of short time irradiation : If the changes of the dose caused in the make and break at the source is considered, the dose of the irradiation has a direct proportional relation with time. The numerous value valculated through this relation is correspond to the measurement value at each time. 2) Elimination of scattering x-rays : In eliminating the scattering x-rays of the sbject, the lead plate of 1mm thick has a little effect. It, however, has sufficient effect to eliminate the scattering x-rays of things at the background. 3) The effect of geometrical condition on images : When size of the source is 10mmφ, the surfacefilm distance is 300cm, and the object-film distance is 8cm, half shadow has little effect on an image. An image of Co-radiography is as sufficient for the reading as that of high voltage radiograph taken with x-ray diagnosis apparatus. 4) Developing and fixing : As for the bulr of the radiograph, which is caused by the thickness of the emulsion layer of industrial x-ray film, it dosen't appear in developing but in fixing clearly. 5) Others : The source and film were studied and it was concluded that the Co-radiograph taken with Co^<60> therapy apparatus which we generally use is very useful for diagnosis.

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