Multicatheter-guided rigid registration for high-dose-rate interstitial brachytherapy for mobile tongue cancer.

PURPOSE: We aimed to develop a multicatheter-guided rigid registration (MCgRR) to assess the displacement of catheters and changes in distance between neighboring catheters of high-dose-rate (HDR) interstitial brachytherapy (ISBT) for mobile tongue cancer. METHODS: We analyzed two cases of mobile tongue cancer treated by the HDR ISBT with a two-step method, with the first plan on the initial computed tomography (CT) (P1) and the second plan created on the CT images acquired on the third day (P2). An in-house software of the MCgRR to fit P2 to P1 was developed using Python. Transverse shift (TS) to the mean catheter direction of each catheter and the change in the inter-catheter distance (DeltaICD) for neighboring catheters were analyzed. RESULTS: The TS and DeltaICD were successfully calculated as a function of Z, which is the longitudinal direction along the catheters. The maximum TS was 2.0 and 3.4 mm for Cases #1 and #2, respectively. Visualized TS was found useful for identifying the location of specific areas with large deformation. The DeltaICD was also successfully calculated as a function of Z and ranged from -1.8 to 1.3 mm for Case #1 and from -1.8 to 2.5 mm for Case #2. CONCLUSION: The MCgRR developed in this study demonstrated sufficient performance in visualization and identification of areas with large deformation of the CTV in HDR ISBT for mobile tongue cancer.