The future role of particle beams in the treatment of pediatric tumours, by a medical physics point of view

Abstract

Proton therapy, as compared to standard photon radiotherapy, presents the advantage of sparing non-target tissue. This is especially important for treatments of paediatric patients, where the reduction of integral dose and dose to organs at risk can significantly improve children’s quality of life, while reducing the risk for late toxicity, not limited but including secondary malignancies. Cranio-spinal irradiation with protons represents a good example of reduced integral dose, as the dose to all anatomical structures anterior to the spinal cord (such as kidneys, heart, liver) are reduced when compared to photon treatments. Those advantages are increased by the use of proton beam scanning technique (PBS) as compared with passive scattering, due to more accurate proximal dose conformity and to the use of Intensity Modulated Proton therapy (IMPT) for OARs sparing in vicinity of the target. From medical physic’s perspective, the efforts are focused in further exploiting those advantages in different areas, such as: (i) evaluation of optimal fields’ number, as a compromise between dose conformality and plan robustness; (ii) plan evaluation considering radiobiological effects (i.e. LET) (iii) dose sparing for sensitive functional structures; (iv) reduction and optimisation of PTV margins; (v) improvement in image guidance for positioning, in order both to reduce dose and to increase positioning accuracy. This could be obtained by extensive use of MRI for daily positioning (no extra dose, high soft tissue contrast). Paediatrics proton treatments already present several advantages if compared to standard photon treatments; the medical physics role is to exploit them even further.