Do you believe in phantoms?

“Phantoms” are tools that simulate a therapy’s response by mimicking the conditions of the human body. They are required in hadron therapy in order to optimise and verify the therapy before performing it on the patient. The better the phantom, the more accurate the treatment plan and the more effective the therapy. In the framework of the EU-funded project ENTERVISION*, a team of CERN researchers has designed an innovative piece of equipment able to evaluate radiobiology-related parameters in a very accurate way.


The ENTERVISION phantom being tested at HIT.

A key challenge in hadron therapy – i.e. the medical use of hadrons to treat cancer – is to evaluate the biological effect of the delivered radiation. This can be achieved by using accurate dosimetry techniques to study the biological response in terms of the dose deposited and other physical parameters of the beam, such as the Linear Energy Transfer (LET). The job of the “phantom” is to allow this accurate assessment of the deposited dose versus the dose response that a given cell culture shows to different types of particle beams. In this way, the oncologist can evaluate in advance the right dose to guarantee the best results of the treatment.

Thiago Viana Miranda Lima joined CERN in 2012 as a member of the ENTERVISION project team with the task of designing a new phantom in the context of improving digital medical imaging for radiotherapy. The ENTERVISION team works in close collaboration with CNAO, HIT and INFN Torino“I spent the first year of my fellowship studying the phantoms already available and, eventually, providing the first design of the new one. Thanks to the joint efforts of a multidisciplinary team, we produced the earliest prototype in the first half of 2013,” explains Thiago. The phantom is a box connected to particle detectors. It is made out of polymethyl methacrylate (PMMA), a material with a density close to that of water, the main component of the human body.

The main advantage of the ENTERVISION phantom is that it uses pre-sterilised commercial cell plates, thereby avoiding the risk of contamination. “Using commercial cell plates also enables us to perform as many tests as we want, obtaining much better statistics concerning the biological response of the tissues and reducing uncertainties that arise from delayed cell preparation,” says Thiago. The current phantom is the result of several stages of development and testing. “The box evolved from having a single-cell-flask plate to the current 12-cell-flask plate, and in the next model the number of cell flasks will be increased to 96 in order to enhance the spatial resolution and statistics of the phantom performance.

“The final goal of the project is to evaluate precisely the difference between irradiating cells with protons and with other charged particles so that we’ll be able to work out their biological effect on human tissues, which will aid radiobiologists in the development of different biological models,” concludes Thiago. The ENTERVISION team is now in the process of finalising the analysis and gathering all the results in order to study the reproducibility of the phantom so that it can be used by both radiobiologists and medical physicists.

*ENTERVISION is a Marie Curie Initial Training Network project composed of 16 researchers, three of whom are based at CERN, in the field of online medical imaging and dose delivery for hadron therapy. The project was established in response to the clinical need for further research into online imaging and to train highly skilled professionals. You can find additional information about the ENTERVISION project here.

by Rosaria Marraffino