Patient neutron dosimetry in clinical proton therapy using bubble detector technology

SCK•CEN Mentor

De Saint-Hubert Marijke,, +32 (0)14 33 21 40

Expert group

Research in Dosimetric Applications

SCK•CEN Co-mentor

Van Hoey Olivier,, +32 (0)14 33 27 09


Hadron therapy (i.e. proton or heavy ion irradiation) is becoming one of the most attractive approaches in the treatment of cancer. The reduction of the dose burden is particularly important for children because long-term survivors of childhood cancer receiving RT are at a significantly increased risk of second malignant neoplasms (SMNs) [Oeffinger, et al., N Engl J Med, 2006]. Nevertheless there is a major concern related to the carcinogenic risk from secondary neutrons, which are unavoidably present with particle treatments [Newhauser, et al., Nat Rev Cancer, 2011]. In particular neutrons are believed to be the most harmful radiation for the human body because they are highly biological effective with regard to cancer induction and thus even a very small absorbed dose might cause side effects. Therefore assessment of neutron doses in clinical proton therapy requires special attention for radiation protection and prevention of SMNs.

In the coming years cancer patients will be treated with protons in Belgium. Two new proton therapy facilities will be constructed; one in UZ Leuven and one in CHU Charleroi. These facilities will operate with high-energy proton beams up to 250 MeV, meaning patients will be subjected to unwanted absorbed doses of very high-energy secondary neutrons.

To monitor neutron doses is however a big challenge because both the biological effect of neutrons and the neutron detection efficiency of most neutron detectors are largely depending on the neutron energies and to have a complete picture of the energy spectrum there is a need for a large range of equipment hampering neutron dose monitoring in a small area. Currently in vivo neutron doses in particle therapy are not performed routinely and are limited to Monte Carlo (MC) simulations. Additionally there is a lack of measured data in anthropomorphic phantoms [Sahay, et al., J Radiol Prot, 2014]. The use of bubble detectors has been proposed to estimate the patient secondary neutron doses by irradiation in anthropomorphic phantoms. In SCK•CEN we have developed superheated droplet detectors (SSDs).  The droplets undergo transition to the gas phase upon energy deposition by fast neutrons. Bubbles are formed accompanied by an acoustic shock wave which is read in an acoustic detection system.


In the current project we would like to build a neutron detector system in anthropomorphic phantoms for Proton Therapy centers such as the future Belgian PT centers in UZ Leuven and CHU Charleroi.

A first part of the project will be dedicated to the development and characterization of the bubble detector technology:

  • Stable and reproducible development of the detectors (with an existing protocol)

  • Irradiations with neutron sources in the calibration laboratory (LNK) and/or in a high-dose rate neutron field in Belgian Reactor 1 (BR1)

    • Test dose-response linearity

    • Test reproducibility of the detector

    • Test energy-response, including irradiations in accelerator (Czech Technical University (CTU) in Prague) and Proton therapy center (IFJ-PAN, Krakow).

    • Test effect of temperature and/or other climatic conditions

    • Find a technique to calibrate the detectors

In parallel, the acquisition system will be extended to allow reading several detectors simultaneously. Therefore multi-channel amplification system, multi-channel data card and mutli-channel data analysis system will be developed (together with the instrumental group in our department).

Finally we need to integrate the detector system in an anthropomorphic phantom. At SCK•CEN we have pediatric phantoms (5y-old and 10y-old phantoms from CIRS) which will be elaborated for the purpose of in vivo neutron dosimetry in proton therapy.

The minimum diploma level of the candidate needs to be

Academic bachelor , Master of industrial sciences , Master of sciences , Master of sciences in engineering

The candidate needs to have a background in

Bio-engineering , Chemistry , Physics