RESUMEN
PURPOSE: To evaluate three-dimensional needle displacements during multifractionated interstitial brachytherapy (BT) for cervical cancers. METHODS AND MATERIALS: Patients scheduled to undergo pelvic interstitial BT for postoperative and or postradiation vault recurrences were included from November 2009 to December 2010. All procedures were performed under spinal anesthesia. Postprocedure BT planning CT scans were obtained with patients in supine position with arms on the chest (interslice thickness of 3 mm). Thereafter, verification CT was repeated at every alternate fraction. Needle displacements were measured in reference to a relocatable bony point. The mean cranial, caudal, anteroposterior, and mediolateral displacements were recorded. Statistical significance of mean interfraction displacements was evaluated with Wilcoxon Test. RESULTS: Twenty patients were included. Seventeen received boost BT (20 Gy/5 fractions/3 days) after external radiation, three received radical BT alone (36 Gy/9 fractions/5-8 days). An average of three scans (range, 2-3) were available per patient, and 357 needle displacements were analyzed. For the entire study cohort, the average of mean needle displacement was 2.5 mm (range, 0-7.4), 17.4 mm (range, 0-27.9), 1.7 mm (range, 0-6.7), 2.1 mm (range, 0-9.5), 1.7 mm (range, 0-9.3), and 0.6 mm (range, 0-7.8) in cranial, caudal, anterior, posterior, right, and left directions, respectively. The mean displacement in the caudal direction was higher between Days 1 and 2 than that between Days 2 and 3 (13.4 mm vs. 3.8 mm; p = 0.01). The average caudal displacements were no different between reirradiation and boost cohort (15.2 vs. 17.8 mm). CONCLUSIONS: Clinically significant caudal displacements occur during multifractionated pelvic brachytherapy. Optimal margins need to be incorporated while preplanning brachytherapy to account for interfraction displacements.