THE ROLE OF HYBRID BRACHYTHERAPY IN MANAGEMENT OF LOCALLY ADVANCED CERVICAL CANCER: DOSIMETRIC STUDY AND INITIAL RESULTS

Purpose:The aims of this study were to investigate the clinical feasibility and to report our preliminary treatment outcomes of combined intracavitary/interstitial brachytherapy (IC/IS BT), using a hybrid applicator and magnetic resonance imaging (MRI)based treatment planning in patients with locally advanced cervical cancer. Methods and Materials:Between January 2017 and December 2018, eight patients with locally advanced uterine cervical cancer were treated with primary radiation therapy including hybrid BT. Patients with distant metastasis other than para-aortic lymph node spread were excluded from this study. A hybrid applicator for guidance of parametrial needles was used to perform high-dose-rate-brachytherapy (HDR BT) with MRIbased treatment pre-planning. Parametrial extent of the disease or large residual disease in these patients was judged to exceed the coverage limit of intracavitary brachytherapy alone. The number of needles, chosen guiding holes through the ovoids, and insertion depths were based on the extent of residual disease. We investigated the dosimetric gain by comparing the clinical interstitial optimized plan (IC/IS clinical) with an additionally generated optimized plan without needle use (ICstudy). Results: The clinical use of the hybrid applicator system proved to be feasible in all 32 treatment fractions. The applicator Fletcher interstitial 6mm or Utrecht interstitial consists of the IC tandem and two ovoids that serves as a template for needle insertion. MRI preplanning was performed the week before the implant in 5 cases and the day of application with applicator in place in 3 cases. Four to eight needles were placed per fraction, and overall a total of 152 needles were used. Significant differences in IC/IS plan and IC study plan were derived for dose application to the target volume D90 high-riskclinical target volume (D90 CTV HR) was 90.1Gy (IC/ISclinical) vs 85.36 Gy(IC study)with an average gain of 4.74 Gy. Likewise, sparing of organs at risk differed significantly for bladder D2cc: 82,5 Gy(IC/ISclinical) vs 95.7 Gy (IC study) and rectum D2cc: 65,5 Gy (IC/ISclinical) vs 67.8 Gy (IC study).With an average follow-up of 27,25 months (range 18–34): no patient experienced local relapse, three patients experienced distant metastasis two of them died, no acute complications such as bleeding or organ penetration occurred due to needle placement, one patient developed recto-vaginal fistula. Conclusions: Our preliminary clinical experience indicates that combined intracavitary and interstitial MRI- based brachytherapy in patients with significant residual disease extending up to the distal third of parametriaafter external-beam therapy is feasible and allows excellent local control and a low rate of morbidity.