深部線量測定に際する考察

Abstract

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.