A theoretical approach to the problem of dose-volume constraint estimation and their impact on the dose-volume histogram selection

Abstract

This paper outlines a theoretical approach to the problem of estimating and choosing dose-volume constraints. Following this approach, a method of choosing dose-volume constraints based on biological criteria is proposed. This method is called "reverse normal tissue complication probability (NTCP) mapping into dose-volume space" and may be used as a general guidance to the problem of dose-volume constraint estimation. Dose-volume histograms (DVHs) are randomly simulated, and those resulting in clinically acceptable levels of complication, such as NTCP of 5 +/- 0.5%, are selected and averaged producing a mean DVH that is proven to result in the same level of NTCP. The points from the averaged DVH are proposed to serve as physical dose-volume constraints. The population-based critical volume and Lyman NTCP models with parameter sets taken from literature sources were used for the NTCP estimation. The impact of the prescribed value of the maximum dose to the organ, D(max), on the averaged DVH and the dose-volume constraint points is investigated. Constraint points for 16 organs are calculated. The impact of the number of constraints to be fulfilled based on the likelihood that a DVH satisfying them will result in an acceptable NTCP is also investigated. It is theoretically proven that the radiation treatment optimization based on physical objective functions can sufficiently well restrict the dose to the organs at risk, resulting in sufficiently low NTCP values through the employment of several appropriate dose-volume constraints. At the same time, the pure physical approach to optimization is self-restrictive due to the preassignment of acceptable NTCP levels thus excluding possible better solutions to the problem.

Sparing of the Neural Stem Cell Compartment During Whole-Brain Radiation Therapy: A Dosimetric Study Using Helical Tomotherapy

“…Additionally, for the clinically relevant endpoint of cognitive dysfunction in humans, we do not have clear evidence at this point of a causal link between loss of NSCs or the dose exposure of these cells and the subsequent development of this late effect. Thus, while NTCP models would provide a valuable tool for assessing plan quality and predicting clinical outcomes in this setting, as has been demonstrated in other intensity-modulated radiation therapy treatment settings, we do not have sufficient clinical data at this point to accurately generate these models for this clinical setting (63,(69)(70)(71). These limitations argue strongly in favor of the need for the collection of longer-term data for late neurocognitive function in patients treated with PCI or WBRT and the need for clonogenic studies for human NSCs.…”

Experience‐driven dose‐volume histogram maps of NTCP risk as an aid for radiation treatment plan selection and optimization

“…The more often navigated high-dose sections of the map that identify risk would therefore serve as a more reliable indicator. [11][12][13] Outlier DVH trajectories and their relation to NTCP distributions can be a source of misrepresentation of the "average" generated map, which presents an issue for further investigation.…”

“…A more recent study 13 has aimed at linking model-based biological response information to DVH trajectories. The purpose was to obtain dose-volume constraint points more suited to heterogeneous organ irradiations by mapping theoretical normal tissue complication probability ͑NTCP͒ values onto dose-volume space.…”

Clinical comparative study of dose–volume and equivalent uniform dose based predictions in post radiotherapy acute complications

“…The second one is that there is no information tabulated about intermediate levels of risk, especially when several DVH points are considered. Although some studies have been carried out; assuming a linear relationship such as in Linear Discriminant Analysis [2], using Principal Component Analysis [3] or neural networks [4]; conclusions highly depend on the assumptions made and are quite uneasy to use in practice. For simplicity reasons, this study is focused on defining a single DVH point, for a single tolerance dose to be found.…”