Computed Tomography–Guided Optimization of Needle Insertion for Combined Intracavitary/Interstitial Brachytherapy With Utrecht Applicator in Locally Advanced Cervical Cancer

Purpose: There are no international guidelines for optimal needle insertion during interstitial intracavitary brachytherapy (IS-ICBT) for cervical cancer. We aimed to investigate the clinical feasibility and added value of computed tomography (CT) guidance to optimize needle insertion in IS-ICBT using the Utrecht applicator and to evaluate needle shifts. Methods and Materials: We enrolled 24 patients who were treated with interstitial-brachytherapy. Two CT scans each were performed for every patient: (1) after applicator insertion without needles (CT_preneedle) and (2) after needle insertion (CT_postneedle). In addition to magnetic resonance imaging after external-beam radiation therapy, CT_preneedle was used to determine optimal needle locations and insertion lengths based on applicator and organs at risk positioning on the day of treatment; CT_postneedle was used for IS-ICBT planning. The needle-channel axis was used as a reference to determine needle-shift evolution. Results: A total of 266 interstitial needles were inserted in 76 of 93 BT fractions with high intra- and interpatient variations in the number of inserted needles. Based on CT_preneedle findings, needle insertion was avoided in 9, 4, 2, and 2 patients at the first, second, third, and fourth fractions, respectively. The unloaded needle frequency was 4%. Average needle contribution to total dwell time was 37.2% ± 19.2%. Shifting was observed in 68% of the needles (mean shift 2.0 ± 2.3 mm), mostly in the posterior direction, and in needles with a larger insertion length. Needle reinsertion was not needed in any patient. No complication due to needle insertion was observed, except for minor vaginal bleeding in 1 patient after needle removal. Conclusions: The adaptive CT-guided IS-ICBT application was feasible and resulted in fewer unloaded needle insertions or complications and more efficient use with higher needle contribution to the treatment. Needle shift was frequent but did not require needle reinsertion with the proposed method.