SU‐F‐T‐672: A Novel Kernel‐Based Dose Engine for KeV Photon Beams

Abstract

Purpose: Mimicking state‐of‐the‐art patient radiotherapy with high precision irradiators for small animals allows advanced dose‐effect studies and radiobiological investigations. One example is the implementation of pre‐clinical IMRT‐like irradiations, which requires the development of inverse planning for keV photon beams. As a first step, we present a novel kernel‐based dose calculation engine for keV x‐rays with explicit consideration of energy and material dependencies. Methods: We follow a superposition‐convolution approach adapted to keV x‐rays, based on previously published work on micro‐beam therapy. In small animal radiotherapy, we assume local energy deposition at the photon interaction point, since the electron ranges in tissue are of the same order of magnitude as the voxel size. This allows us to use photon‐only kernel sets generated by MC simulations, which are pre‐calculated for six energy windows and ten base materials. We validate our stand‐alone dose engine against Geant4 MC simulations for various beam configurations in water, slab phantoms with bone and lung inserts, and on a mouse CT with (0.275mm)3 voxels. Results: We observe good agreement for all cases. For field sizes of 1mm2 to 1cm2 in water, the depth dose curves agree within 1% (mean), with the largest deviations in the first voxel (4%) and at depths>5cm (<2.5%). The out‐of‐field doses at 1cm depth agree within 8% (mean) for all but the smallest field size. In slab geometries, the mean agreement was within 3%, with maximum deviations of 8% at water‐bone interfaces. The γ‐index (1mm/1%) passing rate for a single‐field mouse irradiation is 71%. Conclusion: The presented dose engine yields an accurate representation of keV‐photon doses suitable for inverse treatment planning for IMRT. It has the potential to become a significantly faster yet sufficiently accurate alternative to full MC simulations. Further investigations will focus on energy sampling as well as calculation times. Research at ICR is also supported by Cancer Research UK under Programme C33589/A19727 and NHS funding to the NIHR Biomedical Research Centre at RMH and ICR. MFF is supported by Cancer Research UK under Programme C33589/A19908.

Validation of a Novel General Cavity Theory Formalism

“…There is renewed interest in radiotherapy applications in the low photon energy range (kilovoltage) for small animal studies and kV breast and eye cancer therapy. [52][53][54][55][56] Specifically, in 2017 Oliver and Thomson investigated "Cavity Theory Applications for Kilovoltage Cellular Dosimetry." 24 This article reports a Monte Carlo investigation to compare the 'large', 'small' (Spencer-Attix), and 'intermediate' cavity theories (additionally comparing five different methods of determining the d parameter) to link model-based dose calculation algorithms with energy deposition in cellular targets.…”