This report describes the study on the optimization of the magnetic field generated by a low-field magnetic resonance imaging modality. In the optimization the Genetic Algorithm and a quasi-Newton Algorithm are used.

FLASH proton therapy is a growing field of research, especially due to its biological benefits in radiation oncology: sparing healthy tissue while delivering the treatment within a millisecond. However, instead of sparing healthy tissue, the conventional FLASH approach, using transmission beams, damages the tissue behind the distal edge of a tumour. Therefore, this approach is less attractive in some clinical applications of FLASH proton therapy. To solve this problem, the use of a ridge filter and patient-specific range compensator, to shift the spread-out Bragg peak (SOBP) of the proton beam to the tumour, is proposed. In this research, the clinical feasibility and acceptability of FLASH-compatible treatment plans, optimized with multiple, Monte Carlo-simulated ridge filter beams, is analysed. An SOBP-database is generated using energy spectrum approximations and interpolations of energy spectra retrieved from Monte Carlo simulations in TOPAS. To obtain optimized FLASH-compatible treatment plans for neuro-oncological targets, this database is implemented in the in-house treatment planning software of the Erasmus Medical Center, iCycle.  The resulting treatment plans show that it is possible to generate FLASH-compatible treatment plans using a ridge filter. A FLASH enhancement ratio between 1.4 and 2.1 would potentially give clinically acceptable plans for the three patients considered. In some optimized plans, the homogeneity of the tumour dose is also increased. A limitation of this research is that configuration of a stable ridge filter beam treatment plan optimizer appears to be challenging. Besides this, the FLASH enhancement ratio and the dose rate are not taken into account to find the regions in the patient where the FLASH conditions (dose > 8 Gy, dose rate > 40 Gy/s and treatment time < 0.1 s) are met.  Recommendations for future research include: implementing the FLASH enhancement ratio and the dose rate optimization in treatment plan optimization; investigating the influence of fractionation ofa FLASH treatment plan on the tumour control and the healthy tissue irradiated; study the relative biological effectiveness (RBE) and the biological character of FLASH radiotherapy, and investigate the clinical potential of a combination of FLASH and non-FLASH treatment.