Feasibility of X-ray interstitial radiosurgery based on plasma focus device

A narrow beam of relativistic electrons (REB) generated during a pinch implosion (shot) in a Mather-like plasma focus (PF) device and impinging on a high Z target is considered as X-ray brachytherapy source. The main feature of the REB consists of a narrow back warded small divergence beam with an initial cross section of few mm. The apparatus includes a PF device of about 20 cm diameter and 30 cm length. Attached to the housing that contains the inner anode in the PF, an electron pipe is at first realised by several collimations which define a target spot of about 5 mm when the target is posed at 20 cm far from the pinch region. With the actual configuration, this means a practical length of the X-ray probe of about 10 cm. First experimental results with a tungsten target show that the energy spectra of the photons consist mainly of characteristic L-X rays of mean energy around 10 keV superimposed to a continuous low intensity Bremsstrahlung which photon energy extend up to several tens of keV. A selective K shell ionisation assessment performed by using target from Fe to Cd indicates a mean energy of the REB in the range 35-40 keV. The dose rate delivered in a LiF dosimeter at 10 mm far from the X-ray source has been estimated around 4.5 Gy/shot. The obtained dose rate greater than 10(8) Gy/s and the relatively high repetition rate of the PF devices makes this proposal suitable for interstitial radiosurgery