Out-of-field doses for paediatric and pregnant patients in radiotherapy

Even though many studies on non-target doses are available in the literature, the estimation of out-of-field doses for an individual patient remains a challenge. Since 2010 EURADOS Working Group 9 (Radiation Dosimetry in Radiotherapy) has been working to improve out-of-field dosimetry for photon and particle therapy, especially in the case of pediatric patients. Firstly, WG9 performed a detailed characterization of the out-of-field doses, associated with photon and proton radiotherapy in a simplistic set-up of a water phantom with both measurements and MC simulation. Our investigations clearly showed the complexity associated with the secondary radiation field produced in radiotherapy and allowed us to improve dosimetric methods used for out-of-field dose measurements. The next step included measurement campaigns organized by WG9 to study secondary radiation for different photon radiotherapy techniques. Those experiments were followed by a measurement campaigns dedicated to proton radiotherapy with pencil beam scanning technique (PBS). In both photon and proton therapy, out-of-field organ doses were measured inside 5- and 10-year-old anthropomorphic phantoms for the same target size and location. Our studies were performed for a realistic clinical treatment of a pediatric brain lesion, to give a fair comparison between different treatment methods. Recently, we have focused our work on the estimation of doses received by the fetus during the mother's radiotherapy. Approximately 1 in 1000 pregnancies is complicated by cancer and today around 70% of patients are being treated during their pregnancy. However, radiotherapy is only administered in 3% of these patients mostly due to the lack of accurate dose data as well as reliable information on the risk of fetal damage and the debate of what is considered acceptable. Significant technological advances in radiotherapy open up new opportunities for the treatment of cancer during pregnancy and create the need for a better understanding of out-of-field doses in radiotherapy.