Modified Fletcher's 3-channel brachytherapy system with vaginal line source loading versus uterine tandem and vaginal cylinder system in Stage IIIA cervical cancer

PURPOSE The uterine tandem with open-ended vaginal cylinder is the most commonly used brachytherapy system for Federation Internationale de Gynecologie et d'Obstetrique (FIGO) Stage IIIA cervix cancer at the National Cancer Centre, Singapore. Without the 3-channel ovoid system, the dose to the parametrium is often compromised. In this study, a vaginal cylinder that could potentially be incorporated with the 3-channel system was developed, hence addressing the problem of treating both the vaginal disease extension and the parametrium. METHODS AND MATERIALS A hollow cylinder of 3 cm in diameter was incorporated with the Fletcher's 3-channel tandem and ovoid system. Treatment plans were generated with the single tandem line source with a vaginal cylinder applicator and the modified Fletcher's system using the Abacus version 3 brachytherapy treatment planning software. A nominal dose of 5 Gy was prescribed to point H for both plans. The perpendicular distance of the 5 Gy isodose line from the uterine tandem plane at the centre of the ovoid and the vaginal cylinder plane 1 cm below the os guard were then compared. RESULTS The 5 Gy isodose line was 1.7 cm from the uterine tandem source at the location lateral through the centre of the ovoids on the plan with the uterine tandem and vaginal cylinder system as compared to a distance of 3.3 cm using the modified 3-channel Fletcher system. The 5 Gy isodose line was 2 cm lateral to the central source at the vaginal cylinder plane 1 cm below the os guard on the uterine tandem and vaginal cylinder system as compared to a distance of 2.5 cm on the Modified-Fletcher system. This corresponds to an increase of 1.6 cm and 0.5 cm depth of treated parametrium on the uterine tandem plane and vaginal cylinder plane respectively with the modified Fletcher's applicator as compared with the single line source cylinder system. CONCLUSION As compared with the single uterine tandem and open-ended vaginal cylinder system, an addition of 1.6 cm of the parametrium was covered within the 5Gy isodose on the uterine tandem plane and 0.5 cm on the vaginal cylinder plane with the modified Fletcher's applicator. A feasibility study was started to address the ease of insertion of this modified Fletcher system into patients.