Neutron dose evaluation in conventional and FLASH proton therapy

Abstract

Cancer is the second leading cause of death for children and one of the treatment options for this disease is radiotherapy. Children treated with radiotherapy using photon beams are more likely to develop secondary neoplasms. Proton therapy can reduce the probability of neoplasm formation by up to 50%. Recent studies propose the use of ultra high dose rates as a treatment option. From the threshold of 40 Gy/s it is possible to reach the FLASH effect. This technique protects healthy tissue while maintaining tumor control. The effect was validated in vivo using a proton beam and, therefore, it will be available as a new treatment option. On the other hand, the proposal for FLASH treatment with a proton beam would not use the Bragg peak located in the target volume, which is the differential of proton radiotherapy. In addition, the increase in the intensity of the beam and the energy of the particles, lead to the generation of a greater amount of neutrons. The objective of this work is to evaluate the dose due to the neutrons generated in the interaction with the accelerator components in FLASH proton therapy in relation to conventional proton therapy. The dose evaluation was performed through Monte Carlo simulations, using a water phantom, with the code TOPAS MC. The results found show that the dose of neutrons in the FLASH technique would be about 100 times greater than the dose in the conventional technique. Still, it would be below 1% of the prescribed dose.