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Year : 1997  |  Volume : 22  |  Issue : 1  |  Page : 1-5

Computation Of Dose volumes For Intraluminal Brachytherapy Of Oesophagus Using Caesium-137 Pellets

V.K Sathiya Narayanan

Source of Support: None, Conflict of Interest: None

The volume of tissue irradiated to a particular dose has been an interesting topic in radiation therapy. However, the shapes of the volume of the isodose surfaces in most of the situations are irregular and hence it is difficult to evaluate their volumes using geometrical methods. The intraluminal application of Ca-oesophagus using caesium-137 pellets presents an isodose surface, the volume of which can be evaluated or computed using basic geometrical principles. The shape of the volume is usually an elongated cylinder with its length larger than its radius and the tip of the cylinder convex in shape. The volume is obtained by a three-step process. In the first step, the ends or the tips of the volume are found. In the second step, the areas of the transverse sections of the slices at regular intervals are computed. In the third step, the areas of the slices are geometrically integrated and the volume enclosed by an isodose surface is obtained. The volume (cm3) of a particular dose rate (DR) evaluated for three source trains containing 7, 8 and 9 sources is given as V - a (DR) p where a and 13 are constants. The relationship obtained in the present study between volume (cm3) and K/D, where K is the total air kerma in mGy per hour at one metre and D is the dose rate in Gy/hr, is given as V - 162.758' (K/D)1.6788'.Thus, a method which gives the absolute volumes enclosed by the isodose surfaces of the intraluminal applications is developed and presented.

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