Evaluation of the possibility of boron neutron capture therapy with medical linear accelerators in radiotherapy

Although, Boron Neutron Capture Therapy (BNCT) is accepted as successful method in cancer treatment, current methods are based on reactor based neutrons. It has begun to use specially designed proton accelerators for BNCT in very few centers. Because the numbers of reactors and proton based BNCT centers are not enough in numbers, BNCT cannot be widely used for routine patient treatments. Medical linear accelerators used in radiotherapy today is widely available and if there is a possibility, it could be possible to do BNCT treatment in every hospital equipped with medical linac. Thus, in this thesis, possibility of BNCT with neutrons produced by medical linacs has been evaluated. Varian Clinac 2300CD linac has been simulated with GEANT4 platform which uses Monte Carlo method. Minimal scattered narrow profile, pencil beam type new beam mode with energy of 24MeV and current of 50mA without target and flattening filter (foil) has been generated with the modifications made in linac. With the simulations using this new beam mode, spectral shifting column with uranium target, primary and secondary moderators, filter and collimator has been optimized. Total dozes in Phantom calculated with GEANT4 DNA (GEANT4 version capable of micro dosimetry) With the modified beam mode, Linac get about ten times faster than any other mode. Optimized moderator results are uranium target with 5cm diameter and 5cm length, 20cm thick MgF2 as a primary moderator, 25cm thick AlF3 as a secondary moderator, 10cm bismuth as a thermal neutron and gamma filter and a collimator with thin nickel layer. Epithermal neutron flux at collimator exit is 5,048 n.cm-2s-1. Mean energy of epidermal neutrons is 10-3,559 MeV. Fast neutron versus epithermal neutron ratio is 4,4x10-13 ve gamma epithermal neutron ratio is 7,03x10-13. Mean Dose of tumor 3cm diameter and 3cm depth with 40ppm boron concentration is 3,7x10-15 Gy/n. With developed treatment time is under 10 minutes for 25Gy fraction. Both treatment time and beam characteristics specified by IAEA is met. BNCT treatment with medical accelerator is possible with modified beam and designed epithermal column.