The Implementation of the Gynaecological Groupe Européen de Curiethérapie - European Society for Therapeutic Radiology and Oncology Radiobiology Considerations in the Conversion of Low Dose Rate to Pulsed Dose Rate Treatment Schedules for Gynaecological Brachytherapy.

Abstract

AIMS: This paper details the considerations and calculations made by this centre for the implementation of the biologically equivalent dose in 2 Gy fractions (EQD(2)) radiobiology calculations recommended by the Gynaecological Groupe Européen de Curiethérapie - European Society for Therapeutic Radiology and Oncology, in converting our cervix, body of uterus and vaginal vault low dose rate (LDR) treatment prescription schedules for caesium-137 to equivalent pulsed dose rate (PDR) protocols using iridium-192. MATERIALS AND METHODS: The assumptions made in order to calculate the EQD(2) for both the LDR and the corresponding PDR schedules are detailed. The source geometries and prescription points are discussed for all standard treatment schedules. The prescription point for vaginal vault treatments has been altered to a 5 mm depth rather than the applicator surface, and the prescribed dose for all applicator sizes has been normalised at this depth. RESULTS: The calculated PDR schedules are presented, with corresponding target and organ at risk values given for LDR and PDR versions of standard treatment schedules. A standard 32.5 Gy point A cervix prescription used in Manchester with LDR has been converted to 2 × 19 Gy for PDR. CONCLUSIONS: PDR schedules have been calculated to correspond with our established LDR treatments in terms of EQD(2) dose to the target. There is a theoretical improvement in the therapeutic ratio due to a reduction in the calculated EQD(2) to organs at risk.