Session Item

This work focusses on CHU de Québec-Université Laval’s initial 6 months experience in a new state of the art brachytherapy suite optimized for gynecology patients housing an OR, a dedicated MR and a sliding gantry CT. A Kevlar CT and MR compatible tabletop is used to move the patient from the OR to the MR to the CT, making the procedure “transferless” (i.e. patient remains on the same surface). Initial results are presented and compared to a standard multiple manual transfer procedure to validate if this concept minimizes the patient’s applicator/needle displacements.

The OR houses a Getinge Magnus table and is co-located next to a MAGNETOM Aera with a Combi-Suite Docktable Table. A Transmobile stretcher is used to transfer the patient from the MR to the Getinge Pilot table and Siemens CT. The MAGNETOM Aera commissioning was performed based on AAPM recommendations. Image distortion for the Combi-Suite Dockable Table was validated and compared with the standard MR Dockable Table. MR and CT patient images were fused, based on the applicator, using landmark registration in Oncentra Brachy (Elekta, Veenendaal, The Netherlands) and a root mean square error between CT and MR registration points calculated to evaluate the fusion accuracy for 12 patients. Furthermore, the needle tip positioning difference between CT and MR was evaluated for 10 patients (cases with freehand interstitial needles in addition to the brachytherapy applicator).

Fig.1 shows that for regions of interest (spheres of radii of 10 cm approximately)  in brachy gynecology, the average and maximum MR distortion are 0.2 mm and 0.8 mm, respectively; there was no difference between the standard and the Combi-Suite table. The root-mean-squared error between applicator registration points is 0.63±0.37 and 1.10±0.51 mm in the transferless and standard procedures respectively. For interstitial gynecology cases, the needle tip deviates by 0.51±0.63 and 1.16±0.83 mm in lateral, 0.29±0.49 and 1.01±0.68 mm in vertical and 0.73±1.08 and 1.52±1.21 mm in longitudinal planes between CT and MR images for the transferless and standard procedures respectively. Fig.2 shows the needle tip position on CT and MR images (gray dot if the CT needle tip) for the transferless and standard procedures. The MR imaging time was 19 min per patient on average, somewhat comparable to the CT imaging time (15 min on average).

The transferless gynecology brachytherapy procedure results in a submillimeter MR distortion comparable to the standard MR table. The applicator fusion accuracy and interstitial needle tip displacements are improved by ~50% in the transferless procedure allowing improved registration accuracy and demonstrating reduced applicator/needles displacement. These improvements should increase the treatment delivery accuracy for gynecology cases when delineating the target on MR and planning on CT. The submillimeter MR distortion also opens the door to MR only planning for these patients in the near future.