The clinical target distribution: a probabilistic alternative to the clinical target volume

TL;DR

This paper introduces the clinical target distribution (CTD), a probabilistic approach to tumor target delineation in radiation therapy, aiming to improve flexibility, reduce variability, and better account for uncertainties in treatment planning.

Contribution

The paper presents the concept of CTD, a novel probabilistic method for tumor targeting, and demonstrates its implementation and advantages in treatment planning systems.

Findings

CTD allows flexible tradeoffs between coverage and organ sparing.

Implementation of CTD is straightforward in commercial planning systems.

CTD reduces inter-user variability in target delineation.

Abstract

Definition of the clinical target volume (CTV) is one of the weakest links in the radiation therapy chain. In particular, inability to account for uncertainties is a severe limitation in the traditional CTV delineation approach. Here, we introduce and test a new concept for tumor target definition, the clinical target distribution (CTD). The CTD is a continuous distribution of the probability of voxels to be tumorous. We describe an approach to incorporate the CTD in treatment plan optimization algorithms, and implement it in a commercial treatment planning system. We test the approach in two synthetic and two clinical cases, a sarcoma and a glioblastoma case. The CTD is straightforward to implement in treatment planning and comes with several advantages. It allows one to find the most suitable tradeoff between target coverage and sparing of surrounding healthy organs at the treatment planning stage, without having to modify or redraw a CTV. Owing to the variable probabilities afforded by the CTD, a more flexible and more clinically meaningful sparing of critical structure becomes possible. Finally, the CTD is expected to reduce the inter-user variability of defining the traditional CTV.