Calculation of dose distributions for iridium-192 implants

Anisotropy function for 192Ir low-dose-rate brachytherapy sources: an EGS4 Monte Carlo study

The anisotropy function of low-dose-rate 192Ir interstitial brachytherapy sources was studied. Absolute dose rates around 192Ir seeds with stainless steel or platinum cladding and a platinum covered wire have been estimated using the EGS4 Monte Carlo simulation system with a very well tested user code. Our results were compared with available experimental data. Excellent agreement between calculated and measured anisotropy function was found for stainless steel clad 192Ir sources, except along the longitudinal axis of the sources. Dosimetry data for the platinum covered seed and 3 mm long wire with platinum cladding as well as for the stainless steel clad 192Ir source are presented in TG43 format. The influence of phantom dimensions on the anisotropy function was found to be non-negligible over 7 cm, enhancing the anisotropy function by 1-2%. Our results have estimated statistical uncertainties below 1% at 1 sigma level up to 10 cm excluding the longitudinal axis where statistical uncertainties below 3% up to 10 cm are observed.

Physical aspects of interstitial therapy using flexible iridium-192 wire

A semi-automated procedure for the calculation of point doses and isodose distributions for a curved multi-wire implant is described. A dose optimisation method has been developed for producing acceptable dose distributions from non-ideal implants and the dosimetry of such implants is discussed. Source preparation, handling and stock control methods are described which facilitate the re-use of the encapsulated wire with consequent benefits in the reduction of staff radiation exposure and the costs of treatment.

Interstitial radiotherapy in treatment of superficial tumours of the lower alveolar ridge

An adaptation of a routine afterloading implant technique for local irradiation of small tumours of the lower alveolar ridge is described. The methods the authors have used for radiation dosimetry are explained and some clinical results in 12 such lesions are presented. The technique has the advantage that the need for mandibular resection may be avoided, although this procedure is still available if the primary treatment fails.

Intercomparison of iridium-192 wire used in interstitial radiation therapy

The results of an intercomparison which took place in 1976 when 2 sets of 192Ir wire, one English, the other French, were exchanged and their activities measured by the producers, one standardizing laboratory and two radiation therapy centres. The average differences ranged from 0.7 to 3.2 per cent. The differences in the derivation of basal dose rate as defined in the Paris system, by the two radiation therapy centres, were also investigated.