2. TBI における Long SAD 法について(全身照射法の技術的諸問題)

抄録

We studied the physical and technical situation of total body irradiation (TBI) for long SAD and a 6MV X-rays. In principle this paper consists of the following : Physical characteristics of 6MV X-rays; Basic TBI dosimetry; Dose distribution in the phantom; Compensating method for inhomogeneity; Practical TBI technique; In vivo dosimetry of the oesophagus. For TBI, it is very important to have uniformity of the three-dimensional dose distribution in the whole body. TBI technique is performed by AP/PA opposing fields, bilateral opposing fields and four fields (combined AP/PA and bilateral opposing fields). As a result of measured dose distribution in the phantom, four fields with compensators is the best TBI technique, which indicating unaccuracy dose of ±10%. It is impossible to deliver a dose uniformity of ±10% for bilateral fields. For TBI dosimetry, it needs to measure for the phantom size needs to be measured to achieve the full scattering conditions, but the phantom size for dosimetry is practically suitable for use of a minimum dimension of 30×30×30cm^3. Compensating methods are used to give homogeneous dose to different thick bodys and inhomogenities. We use tissue-equivalent bolus and compensator such as lead or copper. For in vivo measurement, expected dose ratio in the oesophagus is 0.947±0.044 for four fields, 0.994±0.025 for AP/PA fields, and 0.987±0.077 for the bilateral fields. The unaccuracy of irradiation doses are less than 5% for various TBI. In the future, TBI technique should be established the best irradiated method that the uncertainty dose is delivred within ±5%.