Ring Versus Ovoids and Intracavitary Versus Intracavitary-Interstitial Applicators in Cervical Cancer Brachytherapy: Results From the EMBRACE I Study

Purpose: The aim of this study was to investigate the influence of brachytherapy technique and applicator type on target dose, isodose surface volumes, and organ-at-risk (OAR) dose.

Methods and materials: Nine hundred two patients treated with tandem/ovoids (T&O) (n = 299) and tandem/ring (T&R) (n = 603) applicators from 16 EMBRACE centers were analyzed. Patients received external beam radiation therapy and magnetic resonance imaging guided brachytherapy with dose prescription according to departmental practice. Centers were divided into 4 groups, according to applicator/technique: Ovoids and ring centers treating mainly with the intracavitary (IC) technique and ovoids and ring centers treating routinely with the intracavitary/interstitial (IC/IS) technique. V85Gy EQD2₁₀, CTV_HR D_90% (EQD2₁₀), and bladder, rectum, sigmoid, and vaginal 5-mm lateral-point doses (EQD2₃) were evaluated among center groups. Differences between T&O and T&R were tested with multivariable analysis.

Results: For similar point A doses, mean CTV_HR D_90% was 3.3 Gy higher and V85Gy was 23% lower for ring-IC compared with ovoids-IC centers (at median target volumes). Mean bladder/rectum doses (D_2cm3 and ICRU-point) were 3.2 to 7.7 Gy smaller and vaginal 5-mm lateral-point was 19.6 Gy higher for ring-IC centers. Routine use of IC/IS technique resulted in increased target dose, whereas V85Gy was stable (T&R) or decreased (T&O); reduced bladder and rectum D_2cm3 and bladder ICRU-point by 3.5 to 5.0 Gy for ovoids centers; and similar OAR doses for ring centers. CTV_HR D_90% was 2.8 Gy higher, bladder D_2cm3 4.3 Gy lower, rectovaginal ICRU-point 4.8 Gy lower, and vagina 5-mm lateral-point 22.4 Gy higher for ring-IC/IS versus ovoids-IC/IS centers. The P values were <.002 for all comparisons. Equivalently, significant differences were derived from the multivariable analysis.

Conclusions: T&R-IC applicators have better target dose and dose conformity than T&O-IC in this representative patient cohort. IC applicators fail to cover large target volumes, whereas routine application of IC/IS improves target and OAR dose considerably. Patients treated with T&R show a more favorable therapeutic ratio when evaluating target, bladder/rectum doses, and V85Gy. A comprehensive view on technique/applicators should furthermore include practical considerations and clinical outcome.