CLINICAL USE OF THE UTRECHT APPLICATOR FOR COMBINED INTRACAVITARY/INTERSTITIAL BRACHYTHERAPY TREATMENT IN LOCALLY ADVANCED CERVICAL CANCER

Purpose: The aims of this study were to investigate the benefit of the Utrecht interstitial CT/MR applicator for combined intracavitary/interstitial (IC/IS) approach, using magnetic resonance imaging-guided brachytherapy, over the intracavitary approach alone in patients with locally advanced cervical cancer and to analyze the clinical use of needles. Methods and Materials: This study includes the first 20 patients treated with the new applicator. Brachytherapy consisted of two pulsed dose rate applications, and the second application was performed with the IC/IS approach. The number of needles, chosen guiding holes through the ovoids, and insertion depths were based on the dose distribution and dosimetric shortcomings of the first application (IC alone). We investigated the dosimetric gain by comparing the clinical interstitial optimized plan (IC/ISclinical) with an additionally generated optimized plan without needle use (ICstudy). Furthermore, we studied the relation of the inserted needles and their source loading patterns with the high-risk clinical target volume (HR-CTV). Results: A total of 54 needles (range, 1-6 per application) were applied with an average depth of 25 mm. The chosen needle positions corresponded with the location of the HR-CTVextensions. The total and individual needle treatment times per application were on average 19% (range, 4-35%) and 7% (range, 2-14%) of the implant treatment time, respectively. The total (external-beam radiotherapy + brachytherapy) D90 HR-CTV for the ICstudy and the IC/ISclinical were on average 79.5 (SD 7.4) Gy(alpha/beta 10) and 83.9 (SD 6.7) Gy(alpha/beta 10), respectively, with an average gain of 4.4 (SD 2.3) Gy(alpha/beta 10) for the second application. Conclusions: Needle placement was feasible in all patients and resulted in a gain in dose and better coverage of HR-CTV. Defining the location of HR-CTV protrusions and analyzing the associated needles has given us deeper understanding of the possibilities in magnetic resonance imaging-guided (pre)treatment planning with the IC/IS Utrecht applicator. (C) 2012 Elsevier Inc.