The NOVO project: NeutrOn detection for real-time range VerificatiOn in proton therapy – A Monte Carlo feasibility study

Uncertainties in the estimation of proton ranges in proton radiotherapy pose a significant challenge in the correct delivery of the prescribed radiation doses, especially when tumors are located in close proximity of the organs at risk (OARs). In order to ensure that the treatment goals are achieved, a distal margin (e.g. 3.5% of the nominal range + 1 mm or fixed 5 mm)1 is introduced in clinical protocols. Development of methods that could reduce the range uncertainties during treatment are therefore of crucial importance in proton therapy. Existing methods include positron emission tomography (PET) imaging, prompt gamma (PG) imaging and detection, imaging of large angle scattered protons and, for carbon-ion therapy, imaging of secondary ions emerging from the patient. In addition to the abovementioned secondaries, neutrons are produced in nuclear interactions of the primary beam with the target material with considerable abundance. It has recently been proposed to detect these neutrons in vivo to characterize the secondary neutron doses, but no attempt has yet been done for utilizing the neutron component of the secondary radiation field in proton therapy for range verification purposes 2,3. In this work, we propose and investigate the feasibility of a novel and previously unexplored concept for range verification in proton therapy through FLUKA Monte Carlo (MC) simulations. The NOVO (NeutrOn detection for real-time range VerificatiOn) project aims at the detection of secondary neutrons produced in nuclear interactions during proton therapy for real-time range verification purposes. We show that the proposed detector concept has potential as a real-time range verification device and is a promising alternative to PET and PG imaging systems.