Proof-of-Concept Study of Secondary PhotonDetection during VHEE Irradiation of PMMAPhantoms

Source abstract

Very high energy electrons (VHEE) generate intense secondary photon fieldsin matter through electromagnetic shower development, with bremsstrahlungrepresenting the dominant production mechanism. These secondary photonsmay provide observables for online monitoring and treatment verificationin VHEE radiotherapy. In this work, we present a proof-of-concept studyof bremsstrahlung photon detection during VHEE irradiation of a poly-methylmethacrylate (PMMA) phantom at the INFN Laboratori NazionaliFrascati (LNF) Beam Test Facility (BTF) using a LINAC electron source.Two lead-collimated LYSO scintillation detectors coupled to photomultipliertubes were positioned laterally to the beam axis and used to sample pho-tons emitted at approximately 90◦ . Longitudinal scans were performed with80 and 150 MeV electron beams. In a second experimental configuration,a 2 cm internal air gap was introduced within the phantom to investigatethe sensitivity of the detected signal to a controlled density discontinuity.The measured photon profiles exhibited a clear dependence on beam energyand showed a distinct local signal reduction at the air-gap position. MonteCarlo simulations reproduced the main features of the experimental observa-tions and supported their interpretation in terms of electromagnetic showerdevelopment. To the best of our knowledge, these results provide the firstexperimental demonstration that laterally detected bremsstrahlung photonsare sensitive to both beam energy and internal density variations duringVHEE irradiation.Keywords: Very high energy electrons, bremsstrahlung photons, onlinemonitoring, scintillation detector