A dose homogeneity index for evaluating 192Ir interstitial breast implants.

To evaluate and optimize dose homogeneity of 192Ir interstitial breast implants, we define a quantity, the dose homogeneity index (DHI), as follows: DHI = [V(TDR)--V(HDR)]/V(TDR), where V(TDR) denotes the total treatment volume enclosed by the prescribed treatment dose rate (TDR) and V(HDR) denotes the volume enclosed by high-dose rate (HDR), which is 1.5 X TDR or greater. We have used the DHI to examine and compare 192Ir double-plane implants of various sizes planned by the Memorial system or the Tufts system. Criteria have been suggested for the number of planes required for implants in a given treatment volume. Anderson's volume-dose histogram with inverse square suppression is adopted for illustration.