Post written by Jérémie Dabin, Belgian Nuclear Research Centre (SCK CEN) and leader of HARMONIC WP4, and Adelaida Sarukhan, ISGlobal and WP6 leader
Radiation may sound scary, but actually its use in medical settings has radically improved the diagnosis and treatment of many patients, including those with cancer. True, high doses of ionising radiation can damage our DNA and eventually lead to tumors later in life, so the secret to using it for medical purposes is finding the optimal doses in order to maximise the benefits while lowering as much as possible the risk of long-term toxicities, particularly in children.
This is why it is so important to correctly estimate the doses of radiation delivered to specific organs of patients who are undergoing imaging or treatment procedures that involve radiation. The challenge is that interactions between radiation and the body are complex, and doses delivered to different organs vary widely depending on their position and composition, among other things. Obviously, dose measurements are impossible to do in people, since we would need to insert a dosimeter (a small device that measures the amount of radiation) directly into the patient’s organs. Here is where our “phantoms” come in. These human-looking dummies are made of a material that interacts with ionising radiation just as human tissue would. Plus, they are composed of slices with cavities that conveniently allow to insert dosimeters at places where the organs would be located (Figure 1, left). From the outside, they certainly do not look very impressive, but if you do an X-ray, you will see they are very realistic. There are some that even have real human skeletons inside! (Figure 1, right).
The downside of dummies is that experiments are quite time-consuming: they need to be loaded – and then unloaded – with hundreds of dosimeters. In fact, they are less used nowadays with the development of computer-aided simulations (Figure 2). Nonetheless, they are still very useful, since they provide a physical validation of these simulations. In HARMONIC, we will first use mathematical models to simulate doses delivered to the organs of interest for more than 100,000 children involved in our two cohorts: cancer patients treated with radiotherapy, and cardiac patients treated through X-ray guided procedures. We will then validate these calculations using phantoms that mimic the body of young children. The phantom measurements will help us make sure that our simulations are realistic.
Now you know what phantoms are doing in our study: by helping us estimate and optimise radiation doses in human bodies, they will allow us to improve the quality of life of children that have been treated with medical radiation.
Fig 1. 5-year-old anthropomorphic phantom (left) and the image generated by tomography (right) (from Dabin et al. 2016. Physics in Medicine and Biology. 61:4168-4183)
Fig 2. 5 year-old computational phantom (from Dabin et al. 2016. Physics in Medicine and Biology. 61:4168-4183)