Measurement of the dose components of fast and thermal neutrons and photons from a 0.1 mg 252Cf source in water for brachytherapy treatment planning.

The use of 252Cf in brachytherapy is expected to be more effective with the therapy of bulky tumors than the conventional therapy with photons. For treatment planning a code developed for calculation of gamma dose was used to generate the dose distributions of fast and 10B enhanced thermal neutrons and photons. Dose distributions of these components measured with ionization chambers and a GM counter were fitted to analytical functions as required by the modified treatment planning program. A comparison of these experimental results and the treatment planning output indicate good agreement. Therefore, the program may be used to optimize the brachytherapy procedure considering all three dose components. A realistic case of a patient being treated with conventional brachytherapy has been used to calculate the dose distribution that would be obtained by use of the 252Cf source.

Neutron doses in negative pion radiotherapy.

Absorbed neutron doses in regions outside the treatment volume from negative pion radiotherapy are presented, based on neutron spectral measurements for pions stopping in a tissue-equivalent target. A Monte Carlo neutron transport computer code was developed and used to calculate the absorbed dose as a function of the distance from the centre of the treatment volume. The Monte Carlo code, which is a modification of a neutron detector efficiency code, follows neutrons and gamma rays as they interact with either hydrogen or oxygen nuclei in a phantom. The code includes neutron elastic scattering on both hydrogen and oxygen as well as five inelastic nuclear reactions on oxygen. The recoil charged particles which provide the absorbed dose are considered until the neutron escapes the phantom or its kinetic energy falls below 1 ke V. Calculations of absorbed dose are compared with earlier dose calculations and measurements. Measurements of the neutron spectrum from a tissue-equivalent target indicate that the total kinetic energy carried away by neutrons is about 76 MeV, which is a significantly higher value than that used in earlier estimates of the neutron dose. The calculations presented here suggest that the neutron dose outside large treatment volumes may limit the use of negative pions for some therapeutic applications.

High resolution emission spectra of TL materials.

High resolution emission spectra of several TL materials, that are commonly used in dosimetry, were measured using a low cost fibre optic spectrometer containing a 2048 pixel CCD array. The spectra were taken from 177 to 890 nm with a wavelength resolution of 1.3 nm. This allowed for line width discrimination and the resolution of transitions that have not been seen so far. For rare earth doped materials like CaF2:Tm (TLD-300) and CaF2:Dy (TLD-200) the spectral lines were compared to the energy levels measured by Dieke and Crosswhite leading to the identification of most of the transition lines.