Passive spectrometry of linear energy transfer: development and use.

A linear energy transfer (LET) spectrometer based on the evaluation of particle track parameters in a chemically etched polyallyldiglycolcarbonate (PADC) track detector has been developed at our laboratory. It permits us to determine LET spectra between 10 and 700 keV microm(-1) in tissues. The LET spectra obtained permit us to calculate total dose and dose equivalent corresponding to particles with etchable tracks also. We have recently been able to verify the calibration curves used by using C, Mg, Ne, Si and Fe ion beams with different energies. The calibration curves obtained are presented and compared with those originally used, and a good correlation is found. The LET spectrometer with new calibration was used to analyse the radiation quality of the radiotherapy proton beam at the Joint Institute for Nuclear Research (JINR). The radiation quality was studied along the proton's range, particular attention being devoted to the region of the Bragg peak. It was found that the biologically weighted effective dose (BWE) reaches a value of about 1.25 at the Bragg peak region. At the beam entrance this value increases to about 1.02 due to secondary particles created through primary proton nuclear reactions in tissues.