A CONFORMATION NUMBER TO QUANTIFY THE DEGREE OF CONFORMALITY IN BRACHYTHERAPY AND EXTERNAL-BEAM IRRADIATION - APPLICATION TO THE PROSTATE

Purpose: This article presents a method of quantitative assessment of the degree of conformality and its designation by a single numerical v alue. Methods and Materials: A conformation number is introduced to ev aluate objectively the degree of conformality, A comparison is made be tween the conformation number as found for external beam treatment pla ns and ultrasonically guided I-125 Seed implants for localized prostat e cancer. Results: The conformation number in case of a planning targe t volume irradiated with two opposed open beams, three open beams, and three beams with customized blocks amounted to 0.17, 0.39, and 0.65, respectively, The conformation number as found for ultrasonically guid ed permanent prostate implants using I-125 seeds averaged 0.72. Conclu sions: The conformation number is a convenient instrument for indicati ng the degree of conformality by a single numerical value, Treatments with a conformation number greater than 0.60 might be termed conformal radiotherapy. (C) 1997 Elsevier Science Inc.