The nIORT® is administered with a medical device basically composed by a CNG (Compact Neutron Generator) and a BSA (Beam Shaping Assembly), that shields and (partially) collimates neutrons towards a circular exit window for irradiation. The CNG is a compact light ion accelerator of deuterons that exploits the DD (Deuterium-Deuterium) fusion reactions to generate fast neutrons (2.45 MeV energy) into a Titanium (Ti) target under DC high electrical voltage (100 kV-10 mA power generator). The current technology is nowadays mature for industrial and medical development of this kind of CNG, having some specific advantageous features such as: to provide a high and almost mono-energetic neutron flux; to have a high/safety standards; do not produce high level wastes; can be made compact, mobile and light with a comparably lower costs compared to other IOERT mobile technologies devices. The CNG-BSA system design was addressed by a detailed study with the MCNP code in which the whole CNG-BSA system was modelled: the apparatus takes up t he volume of a cylinder with an external diameter of 30 cm and a length of about 40 cm (for a total weight lower than 100kg). The small size and weight permit the CNG-BSA remote handling by a robotic arm and its utilization in an operating room dedicated to IORT. Working at 100 kV-10 mA power, the CNG supplies a neutron yield at the Ti Target of 3.3 10⁹ [s^-1]. With the possibility to tune the exit window diameter in the 1 ÷ 6 cm range, the CNG-BSA irradiation performances (due to neutrons and secondary photons created by neutrons interactions with the BSA walls and with the tumor bed tissue in front of the irradiation window) can be summarised as it follows:

• a neutron flux at the irradiation window of 1.01 ÷ 0.51 10⁸ [cm^-2 s^-1];
• a maximum neutron flux in the tumor bed tissue of 9.1 ÷ 7.3 10⁷ [cm^-2 s^-1];
• a maximum photon flux in the tumor bed tissue of 4.9 ÷ 4.8 10⁶ [cm^-2 s^-1];
• a maximum equivalent (or biological) dose rate in the tumor bed tissue of 2.36 ÷ 2.10 [Sv min ^-1].

The equivalent dose rate profiles obtained with different window diameters differ mostly in the surface tissues: the peak values are above 2 Sv / min for all diameters in the 1 ÷ 6 cm range and decrease by a factor ≅ 4 at 3 cm depth, that should preserve the nearest organs from harmful radiations. Focusing on the superficial tissues (i.e.; open wound tumor bed), the maximum dose rates are delivered at the window centre and decreases by moving towards the window borders.

The CNG-BSA is able to operate in (at least) 3 regimes having different dose targets:

• the Boost nIORT® with the clinical end-points of about 10 Sv ;
• the Radical nIORT® with the clinical end-point of 20 Sv as peak dose in the tumor bed;
• the Ultra radical nIORT® with the clinical end-point of 20 Sv as average dose in the tumor bed over the whole irradiation window area.

The high flux and the high Relative Biological Effectiveness (RBE) of neutrons (16 in the CNG-BSA, vs. 1 for X-rays and electrons) permits to deliver the Boost, Radical and Ultra-Radical nIORT® applications in very limited treatment times of ∼ 5 ÷ 20 minutes, depending on the clinical end-point and the window diameter chosen. There is also a general consensus that the high RBE of neutrons induces bystander effects, abscopal effects and hinders Epithelial-Mesenchymal Transitions (EMT).