Aim

Dose distribution was compared between two alternative methods for the brachytherapy of tumours of the CNS: conventional implants which complied with the regulations of the Paris system and stereotactic implants. A biological model was analysed in stereotactic implants.

Materials/Methods

31 sequential stereotactic CNS tumour implants were analysed. The analysed implants were compared with appropriate hypothetical implants designed according to the classic standards of the Paris system. Physical parameters of Dose distribution were analysed, including: coverage index (CI), conformity factor (CF), high dosage treatment volume (V₂₀₀), and minimum dose. A value for the radiobiological parameter – Equivalent Uniform Dose (EUD) – was calculated.

Results

In comparison with classic Paris System implants, stereotactic implants affected only half the volume of healthy tissue within the area of the reference isodose, though the high dose volume was greater. EUD was sensitive to changes in minimal dose and coverage index CI.

Conclusions

This parameter may be a criterion in the optimization of dose distribution in radiotherapy.