Intracavitary brachytherapy (IBT) is the standard boost treatment for patients with locally advanced cervical cancer. Volumetric modulated arc therapy (VMAT) boost serves as an alternative to IBT boost, but it has inferior target tumour coverage and organ at risk (OAR) sparing. In this study, a pear-shaped dose distribution was generated in the applicator-guided (AG)-VMAT boost on the existing IBT boost patient by an intercomparison with the existing VMAT boost practice.

The treatment plan of eight patients treated with the VMAT boost and ten patients treated with the IBT boost was analysed. Then, the IBT boost CT images were exported from the OnCentra Brachytherapy treatment planning system (TPS) to Eclipse TPS to plan AG-VMAT boost to reproduce the pear-shaped dose distribution.

AG-VMAT boost successfully reproduced the pear-shaped outline using the 100% isodose line from the IBT boost. The IBT boost treatment planning had the best dosimetry coverage for tumours by D90 23·33 Gy and CI 1·00. The D2cc of the bladder, rectum and femoral heads in the VMAT boost were in significantly higher doses than IBT and AG-VMAT boosts (p ≤ 0·05). The cumulative EQD2 for the D90 in the IBT boost only fell within the tolerance limit. Meanwhile, the D2cc of all the OAR doses in these three techniques was within the dose constraint set by the American Brachytherapy Society (ABS).

24 Gy/3 fractions AG-VMAT boost successfully reproduced the pear-shaped dose distribution for D90 of the target, with D2cc of the OAR remaining within the ABS limit.