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

Abstract

Accurately determining the dose from low energy x rays is becoming increasingly important. This is especially so because of high doses in interventional radiology procedures and also because of the desire to model accurately the dose around low energy brachytherapy sources. Various methods to estimate the dose from specific procedures are available but they only give a general idea of the true dose to various organs. The use of sophisticated three-dimensional (3D) dose deposition algorithms designed originally for radiation therapy treatment planning can be extended to lower photon energy regions. The majority of modern 3D treatment planning systems use a variation of the convolution algorithm to calculate dose distributions. This could be extended into the diagnostic energy range with the availability of lower energy deposition kernels ( < 100 keV). We have used version four of the Electron Gamma Shower (EGS4) system of Monte Carlo codes to generate photon energy deposition kernels in the energy range of 20-110 keV and have implemented them in a commercial 3D treatment planning system (Pinnacle, ADAC Laboratories, Milpitas, CA). The kernels were generated using the "SCASPH" EGS4 user code by selecting the appropriate transport parameters suitable for the relative low energy of the incident photons. The planning system was subsequently used to model diagnostic quality beams and to calculate depth dose and cross profile curves. Comparisons of the calculated curves have been made with measurements performed in a homogeneous water phantom.

Commissioning kilovoltage cone‐beam CT beams in a radiation therapy treatment planning system

“…Although the energy range of the kernels does not cover the full spectrum of energies possible in a 100 or 120 kVp beam, modeling of a beam with beam qualities desired here is easily achievable with the available kernels. The generation, validation, and use of these low‐energy deposition kernels has been described previously 14 , 16 …”

Implementation of full/half bowtie filter models in a commercial treatment planning system for kilovoltage cone‐beam CT dose estimations

“…The low‐energy deposition kernels created by Alaei et al (4) were added to a retired Pinnacle TPS (version 9.6, Philips Healthcare, Best, Netherlands) which is currently not used for patient treatments. Detailed information about the kernels’ generation can be found in the publication of Alaei et al (4) …”

“…Detailed information about the kernels’ generation can be found in the publication of Alaei et al (4) …”

“…Alaei et al 4 , 5 , 6 explored the possible use of a commercial treatment planning system (TPS) to estimate the dose in the kilovoltage range, including that of kV CBCT. They generated kilovoltage X‐ray energy deposition kernels using Electron Gamma Shower (EGS) 4 SCASPH user code (7) and implemented them in the Pinnacle TPS (Philips Medical Systems, Andover, MA; formerly ADAC Laboratories, Milpitas, CA) in 1999 (4) .…”

“…They generated kilovoltage X‐ray energy deposition kernels using Electron Gamma Shower (EGS) 4 SCASPH user code (7) and implemented them in the Pinnacle TPS (Philips Medical Systems, Andover, MA; formerly ADAC Laboratories, Milpitas, CA) in 1999 (4) . They subsequently performed dose calculations for a 120 kV static X‐ray beam by using Pinnacle TPS in 2000 (5) .…”