Estimation of Complication Probability for Non-Uniform Normal Tissue Irradiation Using the Effective Volume Method and Normal Distribution

Abstract

Purpose: To estimate normal tissue complication probability (NTCP) for nonuniform irradiation. Materials and Methods: Before calculation of NTCP, dose volume histograms are calculated for the organs of interest and tolerance doses for uniform whole and partial organ irradiation are obtained from published data. The calculation of dose volume histograms is straightforward if there are an adequate number of CT scans and dose distributions for organs of interest. The effective volume method transforms the histogram into a uniform one of height (effective volume) and dose (D(subscript max))equal to the maximum dose in the histogram. NTCP can be obtained using Lyman's model and table of the normal distribution. Results: Dose volume histograms for various organs are obtained by calculation with Render-Plan treatment planning system. Effective volumes for these organs are obtained by calculation with Kutcher's effective volume method. Calculation using Lyman's model and table of the normal distribution, we obtained the NTCP values for these organs. Conclusion During radiotherapy normal tissues are irradiated along with the tumor. Radiation oncologists try to minimize the dose to normal tissues while delivering a high dose to the tumor. Often this is difficult and complications arise due to irradiation of normal tissues. Estimation of NTCP is important for evaluation of 3-dimensional treatment plans. It is preferable to use NTCP as an additional tool for plan evaluation, in conjunction with a review of graphical dose distributions and dose volume histograms.