Nuclear interactions of new ions in cancer therapy: impact on dosimetry
Since its beginning at the Lawrence Berkeley Laboratory (LBL) in 1954, radiotherapy popularity has grown steadily and today has become a standard approach for most cases, in combination with surgery and chemotherapy. The experience gained from the pioneering work done at the Heavy-Ion Medical Accelerator (HIMAC) in Japan, the Helmholtz Center for Heavy Ion Research (GSI) in Germany and the Paul Scherrer Institute (PSI) in Switzerland established the ground for the use of protons and 12C ions, basing this choice on their advantageous physical and radiobiological properties. However, the limited success rate in treating radioresistant tumors combined with the concern of using heavy ions in pediatric cases and with the goal of extending the application of charged particles for curing non-cancer diseases, opened up the opportunity to consider other ions. The idea of finding the “optimal particle” for curing cancer has been substituted by an approach where the selection is done case-by-case out of a pool of possible candidates ions. Experimental data pointed to 4He and 16O ions as the most promising species and several heavy ions centers have been designed to offer the capability to deliver these particles. In this work, the physical processes of interest in particle therapy are presented. The review focuses on nuclear reactions and summarizes the theoretical approaches proposed for modeling them. Literature information have been screened to find available experimental data for characterizing different types of interactions and identify the “gaps” that need to be filled to extend treatment planning system (TPS) to new ions. The influence of electromagnetic and nuclear interactions on the depth dose and lateral profiles is outlined for existing (protons and Carbon) and candidate (Helium and Oxygen) ions in radiotherapy. The combination of these results with radiobiological and clinical considerations is used as a baseline for discussing advantages and disadvantages of each ion.