Outcomes of Adjuvant Therapy in Stage 3 Endometrial Cancer Confined to the Pelvis

Abstract

The aim of this study was to evaluate a calcium phosphate cement (CPC) marker as an injectable nonmetallic fiducial marker. We investigated interfraction cervical motion with cone beam CT (CBCT) images using a CPC marker and marker visibility on T2-weighted MRI for cervical cancer patients. Materials/Methods: Our commercially available CPC, widely used as a bone substitute, was prepared by mixing a powder component and liquid. A volume of 0.1-0.2 cc of the paste was injected by a disposable syringe with a 19-gauge long needle. This paste was self-hardening and recrystallizes to calcium hydroxylapatite in a living body. Six patients received 3-4 injections of CPC paste placed at a depth of 10 mm into a tumor of the cervix before planning CT. Patients were first treated with external beam radiation therapy to the whole pelvis with a total prescribed dose of 48.6-50.4 Gy delivered in 27-28 fractions. Three fractionated highdose rate brachytherapy treatments were performed with a prescribed dose per fraction of 6 Gy to Point A. Concurrent chemotherapy was delivered to all except one patient. In each fraction, a CBCT scan was acquired before dose delivery. Position verification was based on registration of the bony structures in the CBCT images corresponding to planning CT images. Systematic and random displacement of the marker centroid analysis was performed in 3 directions. Visibility of the markers using T2-weighted MRI before final brachytherapy was also assessed. Results: The procedure was well-tolerated. There was no interruption of the implantation due to pain or hemorrhage. There were no other procedure-related complications during or after CPC marker injection. Comparing the initial and final CBCT images, one patient had lost all three markers and one patient lost one marker. Gross tumor volumes (GTV) before radiation therapy of these patients were 250.7 and 91.7 cc, and GTV before final brachytherapy were 7.5 and 1.1 cc, respectively. The initial GTV of patients with no marker loss ranged from 49.1-67.2 cc, and GTV before the final brachytherapy ranged from 2.4-8.4 cc. Of 15 markers in the final CBCT images, 11 markers with a size >0.15 cc on planning CT images were visible on T2-weighted MRI. For CPC marker movement with rigid bony anatomy registration, the mean-of-means /systematic variation / random variation were 0.6/2.4/0.5, 1.5/4.6/1.9, and 3.4/2.6/1.1 mm for the left-right, anterior-posterior, and cranial-caudal directions, respectively. Conclusion: The injection of CPC paste into the cervix was feasible and safe. More than 0.15 cc of CPC paste was required to be visualized with T2-weighted MRI. For patients with a large cervical tumor, technical improvements in CPC marker placement are necessary.