This article reports on gamma-ray diagnosis of ICRF-accelerated 4He-ions and fusion alpha-particles used for the first time in the JET tokamak. This diagnostic based on the analysis of gamma-rays emitted in nuclear reaction 9Be(alpha,n gamma)12C. Doppler broadening effects which could be used for the fast 4 He-ion diagnosis with high energy resolution gamma-ray detectors are discussed. Assessments of the diagnostic application of other nuclear reactions are presented. Capabilities of the gamma-ray measurements in next step D-T devices are discussed.