Generation and use of photon energy deposition kernels for diagnostic quality x rays

Accurately determining the dose from low energy x rays is becoming increasi ngly important. This is especially so because of high doses in intervention al radiology procedures and also because of the desire to model accurately the dose around low energy brachytherapy sources. Various methods to estima te the dose from specific procedures are available but they only give a gen eral idea of the true dose to various organs. The use of sophisticated thre e-dimensional (3D) dose deposition algorithms designed originally for radia tion therapy treatment planning can be extended to lower photon energy regi ons. The majority of modern 3D treatment planning systems use a variation o f the convolution algorithm to calculate dose distributions. This could be extended into the diagnostic energy range with the availability of lower en ergy deposition kernels (<100 keV). We have used version four of the Electr on Gamma Shower (EGS4) system of Monte Carlo codes to generate photon energ y deposition kernels in the energy range of 20-110 keV and have implemented them in a commercial 3D treatment planning system (Pinnacle. ADAC Laborato ries, Milpitas, CA). The kernels were generated using the "SCASPH" EGS4 use r code by selecting the appropriate transport parameters suitable for the r elative low energy of the incident photons, The planning system was subsequ ently used to model diagnostic quality beams and to calculate depth dose an d cross profile curves. Comparisons of the calculated curves have been made :with measurements performed in a homogeneous water phantom. (C) 1999 Ameri can Association of Physicists in Medicine. [S0094-2405(99)00208-4].