SECONDARY NEUTRON DOSES IN A PROTON THERAPY CENTRE.

The formation of secondary high-energy neutrons in proton therapy can be a concern for radiation protection of staff. In this joint intercomparative study (CERN, SCK•CEN and IBA/IRISIB/ULB), secondary neutron doses were assessed with different detectors in several positions in the Proton Therapy Centre, Essen (Germany). The ambient dose equivalent H(*)(10) was assessed with Berthold LB 6411, WENDI-2, tissue-equivalent proportional counter (TEPC) and Bonner spheres (BS). The personal dose equivalent Hp(10) was measured with two types of active detectors and with bubble detectors. Using spectral and basic angular information, the reference Hp(10) was estimated. Results concerning staff exposure show H(*)(10) doses between 0.5 and 1 nSv/monitoring unit in a technical room. The LB 6411 showed an underestimation of H(*)(10), while WENDI-2 and TEPC showed good agreement with the BS data. A large overestimation for Hp(10) was observed for the active personal dosemeters, while the bubble detectors showed only a slight overestimation.

Neutron H*(10) inside a proton therapy facility: comparison between Monte Carlo simulations and WENDI-2 measurements.

Inside an IBA proton therapy centre, secondary neutrons are produced due to nuclear interactions of the proton beam with matter mainly inside the cyclotron, the beam line, the treatment nozzle and the patient. Accurate measurements of the neutron ambient dose equivalent H*(10) in such a facility require the use of a detector that has a good sensitivity for neutrons ranging from thermal energies up to 230 MeV, such as for instance the WENDI-2 detector. WENDI-2 measurements have been performed at the Westdeutsches Protonentherapiezentrum Essen, at several positions around the cyclotron room and around a gantry treatment room operated in two different beam delivery modes: Pencil Beam Scanning and Double Scattering. These measurements are compared with Monte Carlo simulation results for the neutron H*(10) obtained with MCNPX 2.5.0 and GEANT4 9.6.

A prospective, observational study comparing postoperative residual curarisation and early adverse respiratory events in patients reversed with neostigmine or sugammadex or after apparent spontaneous recovery.

Six years ago, a study performed in our department reported that the incidence of postoperative residual curarisation (PORC) was 39%. The reassessment of neuromuscular monitoring and reversal of neuromuscular block in routine anaesthetic practice is relevant now that sugammadex has become available. The incidence of PORC, defined by a train-of-four (TOF) <90%, was evaluated at post-anaesthesia care unit (PACU) arrival in patients whose neuromuscular block had been reversed with neostigmine or sugammadex and those in whom reversal was felt unnecessary (adequate spontaneous recovery). During the PACU stay we recorded the oxygen saturation (SpO(2)) at arrival, episodes of SpO(2) <90%, airway manoeuvres and/or stimulation required to maintain SpO(2) >90%, and the need for re-intubation. In total, 624 patients were studied. Fifteen percent (66/441) of the patients who were not reversed, 15% (21/139) of those who were reversed with neostigmine and 2% (1/44) of those who received sugammadex exhibited PORC (P=0.06). No patient required reintubation in the PACU. The absence of neuromuscular monitoring and pharmacological reversal before extubation were not associated with PORC. A TOF <90% at PACU arrival was not associated with SpO(2) <90% during the PACU stay. Body mass index was the only independent predictor of SpO(2) <90% during the stay in the PACU. These findings indicate that in recent years, the incidence of PORC, defined by a TOF <90%, has dramatically decreased in our institution. The differences in PORC were not statistically significant between patients who received sugammadex for reversal and patients with spontaneous recovery or neostigmine reversal.