| Summary: | Scarce data exist on concurrent chemotherapy in locally advanced cervical cancer (LACC) patients (pts) treated with image-guided adaptive brachytherapy (IGABT). We examined the effect of a number of chemotherapy cycles and their interaction with brachytherapy dose/volume parameters. Clinical records of 209 consecutive pts treated for a LACC were reviewed. Pts received CRT concurrently with cisplatin 40 mg/m² or carboplatin AUC2. An additional cycle could have been delivered during the pulse-dose rate (PDR)-IGABT. The impact of a number of chemotherapy cycles on outcome was examined, as well as the interactions with dose volume parameters. The number of cycles was four in 55 (26.3%) pts, five in 154 (73.7%) including 101 receiving the fifth cycle during IGABT. Median follow-up was 5.5 years. Pts receiving five cycles had a better outcome on all survival endpoints, including three year local control rate (93.9% vs. 77.2%; <i>p</i> < 0.05). In the subgroup, only pts with tumor FIGO (Fédération Internationale de Gynécologie Obstétrique) stage ≤IIB or with CTV<sub>HR</sub> > 25 cm<sup>3</sup> had a better outcome. Pts receiving four cycles with D<sub>90</sub>CTV<sub>HR</sub> > 80Gy<sub>EQD2</sub> had the same locoregional control–(LRC) as those receiving five cycles and achieving D<sub>90</sub>CTV<sub>HR</sub> ≤ 80 Gy<sub>EQD2</sub> (<i>p</i> = 0.75). An optimal propensity score matching the balance for the FIGO stage, CTV<sub>HR</sub> volume and D<sub>90</sub>CTV<sub>HR</sub> confirmed the effect, with the largest life expectancy benefit for locoregional failure-free survival (absolute gain: 1.5 years; <i>p</i> = 0.017). Long-term radiation-induced toxicity was not increased. Increasing the total number of cycles from 4 to 5 improved LFS, suggesting a place for systemic strategies aimed at in-field cooperation. Delivering an additional cycle at the time of brachytherapy did not increase morbidity and there permitted an increase in chemotherapy dose intensity.
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