Figure 3.

Multi-slice axial CT images (A) of implanted needles and a sagittal CT image (B) of the right internal iliac node (cyan dashed line), bowel (green dashed line), common/internal iliac vessels (yellow dashed line), and bladder (purple dashed line) receiving 50% (blue lines), 100% (red lines), and 150% (white lines) of the prescription dose (6 Gy) in a representative post-operative patient. Pre-treatment CT/¹⁸F-FDG-PET/CT images (C) and post-treatment CT/¹⁸F-FDG-PET/CT images (D). Both insertion points and directions were decided using pre-treatment CT. Two flexible interstitial needles (white arrows) were obliquely implanted in the prone position, passing from under the right sacroiliac joint through the front of the piriformis muscle up to the front of the second sacral vertebrae under CT guidance (no contrast medium) in the HDR room with dedicated CT. Implantation was performed under local anesthesia alone, with care taken not to damage the bowel or common/internal iliac vessels. The catheter was inserted into the central part of the node using an iterative approach of catheter implantation and adjustment with serial CT image acquisition. MPR CT was used to reconstruct the axial images into oblique anatomical planes. The patient was irradiated in the prone position in the HDR room with dedicated CT.