[Determination of the field length in planning radioisotope teletherapy]

The authors present a method for the determination of irradiation field length in the planning of gamma-beam therapy based on the use of decrement lines and decrement surfaces for describing dose distributions. For a case of rotation and static multifield irradiation from open fields when central beam rays lie in the same plane and are crossed at the same point, data of the atlas of dose distributions for single fields were used to make correlation between field length and target sizes in a varied preset degree of dose distribution irregularity in the target volume and under various conditions of irradiation.