Room: Exhibit Hall | Forum 2
Purpose: To quantitatively compare the visibility of commercially available fiducial markers for prostate MR-guided radiotherapy. Most fiducial markers appear as small signal voids in MR images. This makes them difficult to differentiate from calcifications and other small tissue heterogeneities. In this study we use a multimodality male anthropomorphic pelvis phantom to objectively assess the visibility of a variety commercially available fiducial markers using a set of standard clinical MR sequences.
Methods: Eight fiducial markers and a calcium fragment with similar dimensions to a typical prostate calcification were tested. MR and CT images were acquired on a 3T Siemens Skyra and a Siemens Somatom (Siemens, Erlangen, Germany), respectively. MR sequences included T1 and T2 weighted Turbo Spin Echo (TSE) and T1 weighted gradient-echo (GRE). Marker visibility was quantified using the contrast-to-noise-ratio (CNR) and apparent marker size (AMS). The AMS was defined as the difference between the 75th and 25th percentile iso-intensity volumes, relative to the peak marker contrast. A larger AMS represents a more easily identifiable marker. Each marker was implanted into a 3D-printed anthropomorphic male pelvis phantom before imaging.
Results: Visibility results are reported for eight fiducial markers from three vendors. For MR, the 0.4x20mm Gold Anchor (Naslund Medical Inc, Sweden) had the highest CNR (20.4) and largest AMS (65 mmÂ³). For CT images, the 0.6x5mm Civco Pointcoil (Civco Medical Systems, Iowa) had the highest peak CNR of 156.7. The 0.4x20mm Gold Anchor had the largest CT AMS of 15.8 mmÂ³. The GRE sequence resulted in the highest MR CNR and AMS for all markers.
Conclusion: The T1-weighted GRE sequence with the 0.4x20mm Gold Anchor fiducial marker yielded the best visibility on MR in terms of both CNR and AMS. All markers demonstrated good visibility on CT. Future work involves testing the most visible markers in a patient study.
Funding Support, Disclosures, and Conflict of Interest: Funded partially through a master research agreement with Varian Medical Systems.