Quality Assurance of fan-beam CT for Radiotherapy


Quality Control (QC) of simulators and CT scanners have been previously published by the NCS-committee in 1997 (Report 11). Besides these topics, the report also covered basic quality control for treatment planning systems (TPSs). Over two decades important changes in the workflow and major technological improvements on the CT imaging equipment for simulation have outdated this report. As a result, updated QC recommendations for TPSs were published in 2005 (NCS, report 15). However,  the CT simulation part with its specific QA remained unaddressed.  

CT-simulators used in Radiotherapy consist of a dedicated CT-scanner to which multiple components are added e.g. software for isocenter placement, movable external lasers, respiratory gating solutions for 4DCT or breath-hold acquisition amongst others.  Latest, Optical Surface Management Systems (OSMS) for a visually assisted patient positioning are becoming incorporated into CT-simulator setups and workflows.  The CT-scanner is dedicated on hardware and software level by means of a flat and geometrically accurate couch, a large bore, an extended Field of View (FOV), reliable conversion between Hounsfield Units and densities and the need for safe and seamless integration with the additional components. For proton therapy-planning Dual Energy CT (DECT) acquisition is needed, while for photon/electron RT and brachytherapy the clinical advantages of DECT are under investment.

As RT is evolving towards adaptive treatment, multiple scans are needed throughout the course of a patient. Exposure due to CT-simulation together with Image Guidance for patient positioning (at the level of the treatment unit) adds upon radiation dose to healthy tissue of the patient. Calls have been made to implement an equivalent concept of Diagnostic Reference Levels ‘DRL’, for medical exposure during therapy.

These factors contribute to a situation where, while focusing on CT scanners, existing recommendations on diagnostic CT-scanners, even for state-of-the art multi-energy CT-scanner are applicable to some extent on CT simulators but do not cover the entire simulation-process.

With this NCS subcommittee an opportunity can be taken to tackle these issues and formulate recommendations useful for the Radiotherapy community.


Topics to be covered

  • software for isocenter placement
  • movable external lasers
  • respiratory gating solutions for 4DCT
  • Optical Surface Management Systems
  • reliable conversion between Hounsfield Units and densities
  • Dual Energy CT


Members of this NCS Subcommittee

  • Guido Hilgers (Radiotherapiegroep, Arnhem) Secretary
  • Joke De Rouck (AZ Sint Lucas, Gent)
  • Koen Salvo (Emmaus, Mechelen)
  • Ko van Wingerden (HMC, Den Haag)
  • Esther Decabooter (Maastro, Maastricht)
  • Hilde Bosmans (UZ Leuven, Leuven)
  • Sima Qamhiyeh (UZ Leuven, Leuven)
  • Brent van der Heyden (KU Leuven, Leuven)
  • Duncan den Boer (Amsterdam UMC, Amsterdam)
  • Robert Kaatee (RIF, Leeuwarden)
  • Chrysi Papalarazou (LUMC Leiden)
  • Evelien Bogaert (UZ Gent, Gent) Chair, evelien.bogaert-at-uzgent.be
  • Geert Pittomvils (UZ Gent, Gent) representative of the NCS board