A Volumetric Delta TCP Tool to Quantify Treatment Outcome Effectiveness Based on Biological Parameters and Different Dose Distributions

Intra-tumor variability of oxygenation and clonogenic cell density causes tumor non-uniform spatial response to radiation. Strategies like dose redistribution/boosting, whose impact should be quantified in terms of tumor control probability (TCP), have been proposed to improve treatment outcome. In 1999, Sánchez-Nieto et al. developed a tool to evaluate the impact of dose distribution inhomogeneities, compared to a reference homogeneous dose distribution, in terms of TCP. DVH data were used to calculate the so-called ∆TCP, defined as the difference in TCP arising from dose variations in individual DVH-bins. In this work, we develop an open source tool to calculate volumetric ∆TCP and evaluate the impact on TCP of: (i) Spatial dose distribution variations with respect to a reference dose; (ii) Spatial radiosensitivity variations with respect to a reference radiosensitivity; (iii) Simultaneous variation in dose distribution and radiosensitivity. ∆TCP calculations can be evaluated voxel-by-voxel, or in a user defined subvolume basis. The tool capabilities are shown with 2 examples of H&N RT treatments and subvolume contours data providing information about tumor oxygenation status. ΔTCP values are computed for a homogeneous dose to a well oxygenated tumor volume (with a homogeneous 5% vascular fraction), as reference condition, with respect to the same dose now considering 3 oxygenation levels and 3 cell density values (10⁴, 10⁶ and 10⁷ cells/mm³, respectively). ΔTCP values are also computed for the comparison of a homogenous dose distribution vs a redistributed dose distribution delivered to the non-homogeneous tumor.