SynthRAD2023 Report: A Radiant Adventure in Synthetic CT

Setting the Scene Two years ago, a team of passionate junior researchers embarked on an ambitious journey. Their mission was to organise a challenge that would enable the comparison of different methods of generating CT from other imaging modalities; democratise data access; and enable the design of fair rules for algorithm comparison. Thus, SynthRAD2023 ( was conceived.

The Grand Equation

  1. Data access: accessible data is at the core of SynthRAD2023. The dataset comprises brain and pelvis CTs from 1080 patients across three centres, scanned using different manufacturers’ equipment and various imaging protocols. This multi-centre mosaic accurately reflects reality.
  2. The challenge: consists of two tasks:
    • MRI-to-CT: generate synthetic CT (sCT) from MRI for MRI-only radiotherapy.
    • CBCT-to-CT: generate sCT from cone beam computed tomography (CBCT) for adaptive radiotherapy.
  3. The magic metrics: the quality of the submitted sCTs is evaluated based on image similarity and dose-based comparison, using over 200 photon and proton plans.

The Uncharted Territory Why explore the realm of sCT? Despite the numerous methods proposed, it remains unclear which one is the best. Additionally, the available datasets are typically single-centric, and no existing guidelines assess clinical acceptability. We hope that by opening up data access and establishing some rules, we can initiate a discussion on the best metrics for evaluating the quality of sCT for clinical use.

The Grand Finale After holding the challenge prize presentation at the Medical Image Computing and Computer-assisted Convention (MICCAI) 2023 international conference, fast forward to ESTRO 2024. Following the publication of a paper ( that describes the dataset, another paper that reports on the challenge ( has been submitted. The adventure has garnered recognition at this year’s ESTRO conference, with one of the proffered papers being named the best in physics. The legacy of SynthRAD2023 is now immortalised in pixels and ink. However, this is just the beginning. Stay tuned for our ESTRO presentation, at which we will reveal the next steps for the SynthRAD adventure.


Matteo Maspero

UMC Utrecht

The Netherlands