The value of hybrid interstitial tandem and ring applicators for organ at risk dose reduction in small volume cervical cancer

PURPOSE: Magnetic resonance imaging (MRI)-guided adaptive brachytherapy is the standard of care for cervical cancer. Hybrid intracavitary/interstitial applicators for bulky tumor (high-risk clinical target volume [HR-CTV] > 30 cc) dose escalation is recommended in the EMBRACE II trial. The value of hybrid applicators for smaller HR-CTV (< 30 cc) in organ at risk (OAR) sparing is less certain. MATERIAL AND METHODS: Twenty-seven patients with FIGO stage I-IVA cervical cancer treated with definitive chemoradiation and MRI-based brachytherapy using conventional tandem and ring (TR) applicators were re-planned using virtual needles. They were then summed with the external beam dose to evaluate target coverage and OAR dose using EQD(2) summation. Target and OAR dose with/without hybrid applicator use were compared. RESULTS: Eighty-one percent had HR-CTV volumes < 30 cc, for which, hybrid TR applicators had significantly lower mean D(2cc) to all OARs without differences in target coverage. For HR-CTV < 30 cc, the bladder and rectal OAR goals per EMBRACE II were exceeded in significantly fewer patients with the hybrid TR applicators. No significant difference was found in the sigmoid D(2cc) dose goal. CONCLUSIONS: In small volume tumors (< 30 cc), hybrid applicators may offer improved OAR sparing compared with conventional tandem and ring applicators, and may increase the proportion of patients meeting EMBRACE II OAR goals.