Neutron Activation of Patients Following Boron Neutron Capture Therapy of Brain Tumours at the HFR Petten (EORTC Trials 11961 and 11011)

Background and purpose: At the High Flux Reactor (HFR), Petten in The Netherlands, EORTC clinical trials of Boron Neutron Capture Therapy (BNCT) have been in progress since 1997. BNCT involves the irradiation of cancer patients by a beam of neutrons, with an energy range of predominantly 1eV to 10 keV. The patient is infused with a tumour-seeking, 10B-loaded compound prior to irradiation. Neutron capture in the 10B atoms results in a high local radiation dose to the tumour cells, whilst sparing the healthy tissue. Neutron capture however also occurs in other atoms naturally present in tissue, sometimes resulting in radionuclides that will be present after treatment. The patient is therefore, following BNCT, radioactive. The importance of this induced activity with respect to the absorbed dose in the patient as well as to the radiation exposure of the staff has been investigated. Material and Methods: As a standard radiation protection procedure, the ambient dose equivalent rate was measured on all patients following BNCT using a dose ratemeter. Furthermore, some of the patients underwent measurements using a gamma-ray spectrometer to identify which elements and confirm which isotopes are activated. Results: Peak levels, i.e. at contact and directly after radiation, are of the order of 40-60 Sv/h, falling to less than 10 Sv/h 30-50 minutes after treatment. The average ambient dose equivalent in the first 2 hours at a distance of 2 m from our patients is in the order of 2.5 Sv. The ambient dose equivalent rate in 2 m distance from the patients head at the earliest time of leaving the reactor centre (20 minutes after the end of treatment) is far less than 1 µSv/h. The main radioisotopes were identified as 38Cl, 49Ca and 24Na. Furthermore, in two patients, the isotopes 198Au and 116mIn were also present. The initial activity is predominantly due to 49Ca, whilst the remaining activity is predominantly due to 24Na. Conclusions: The absorbed dose resulting from the activated isotopes in the irradiated volume is in the order of less then 1% of the prescribed dose and therefore does not add a significant contribution to the absorbed dose in the target volume. In other parts of the patient’s body, the absorbed dose by induced activity is magnitudes smaller and can be neglected. The levels of radiation received by staff members and non-radiation workers (i.e. accompanying persons) are well below the recommended limits

WITTIG Andrea;  MOSS Raymond;  STECHER-RASMUSSEN Finn;  APPELMAN Klaas;  RASSOW Juergen;  ROCA Antoanetta;  SAUERWEIN Wolfgang; 

2006-01-20

Urban & Vogel

JRC32255

https://publications.jrc.ec.europa.eu/repository/handle/JRC32255,   

10.1007/s00066-005-1433-4,